Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2818 insertions, 0 deletions

diff --git a/security/nss/lib/ssl/tls13ech.c b/security/nss/lib/ssl/tls13ech.c
new file mode 100644
index 0000000000..9808a9fe2d
--- /dev/null
+++ b/security/nss/lib/ssl/tls13ech.c
@@ -0,0 +1,2818 @@
+/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nss.h"
+#include "pk11func.h"
+#include "pk11hpke.h"
+#include "ssl.h"
+#include "sslproto.h"
+#include "sslimpl.h"
+#include "selfencrypt.h"
+#include "ssl3exthandle.h"
+#include "tls13ech.h"
+#include "tls13exthandle.h"
+#include "tls13hashstate.h"
+#include "tls13hkdf.h"
+
+extern SECStatus
+ssl3_UpdateHandshakeHashesInt(sslSocket *ss, const unsigned char *b,
+                              unsigned int l, sslBuffer *transcriptBuf);
+extern SECStatus
+ssl3_HandleClientHelloPreamble(sslSocket *ss, PRUint8 **b, PRUint32 *length, SECItem *sidBytes,
+                               SECItem *cookieBytes, SECItem *suites, SECItem *comps);
+extern SECStatus
+tls13_DeriveSecret(sslSocket *ss, PK11SymKey *key,
+                   const char *label,
+                   unsigned int labelLen,
+                   const SSL3Hashes *hashes,
+                   PK11SymKey **dest,
+                   SSLHashType hash);
+
+PRBool
+tls13_Debug_CheckXtnBegins(const PRUint8 *start, const PRUint16 xtnType)
+{
+#ifdef DEBUG
+    SECStatus rv;
+    sslReader ext_reader = SSL_READER(start, 2);
+    PRUint64 extension_number;
+    rv = sslRead_ReadNumber(&ext_reader, 2, &extension_number);
+    return ((rv == SECSuccess) && (extension_number == xtnType));
+#else
+    return PR_TRUE;
+#endif
+}
+
+void
+tls13_DestroyEchConfig(sslEchConfig *config)
+{
+    if (!config) {
+        return;
+    }
+    SECITEM_FreeItem(&config->contents.publicKey, PR_FALSE);
+    SECITEM_FreeItem(&config->contents.suites, PR_FALSE);
+    SECITEM_FreeItem(&config->raw, PR_FALSE);
+    PORT_Free(config->contents.publicName);
+    config->contents.publicName = NULL;
+    PORT_ZFree(config, sizeof(*config));
+}
+
+void
+tls13_DestroyEchConfigs(PRCList *list)
+{
+    PRCList *cur_p;
+    while (!PR_CLIST_IS_EMPTY(list)) {
+        cur_p = PR_LIST_TAIL(list);
+        PR_REMOVE_LINK(cur_p);
+        tls13_DestroyEchConfig((sslEchConfig *)cur_p);
+    }
+}
+
+void
+tls13_DestroyEchXtnState(sslEchXtnState *state)
+{
+    if (!state) {
+        return;
+    }
+    SECITEM_FreeItem(&state->innerCh, PR_FALSE);
+    SECITEM_FreeItem(&state->senderPubKey, PR_FALSE);
+    SECITEM_FreeItem(&state->retryConfigs, PR_FALSE);
+    PORT_ZFree(state, sizeof(*state));
+}
+
+SECStatus
+tls13_CopyEchConfigs(PRCList *oConfigs, PRCList *configs)
+{
+    SECStatus rv;
+    sslEchConfig *config;
+    sslEchConfig *newConfig = NULL;
+
+    for (PRCList *cur_p = PR_LIST_HEAD(oConfigs);
+         cur_p != oConfigs;
+         cur_p = PR_NEXT_LINK(cur_p)) {
+        config = (sslEchConfig *)PR_LIST_TAIL(oConfigs);
+        newConfig = PORT_ZNew(sslEchConfig);
+        if (!newConfig) {
+            goto loser;
+        }
+
+        rv = SECITEM_CopyItem(NULL, &newConfig->raw, &config->raw);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        newConfig->contents.publicName = PORT_Strdup(config->contents.publicName);
+        if (!newConfig->contents.publicName) {
+            goto loser;
+        }
+        rv = SECITEM_CopyItem(NULL, &newConfig->contents.publicKey,
+                              &config->contents.publicKey);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        rv = SECITEM_CopyItem(NULL, &newConfig->contents.suites,
+                              &config->contents.suites);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        newConfig->contents.configId = config->contents.configId;
+        newConfig->contents.kemId = config->contents.kemId;
+        newConfig->contents.kdfId = config->contents.kdfId;
+        newConfig->contents.aeadId = config->contents.aeadId;
+        newConfig->contents.maxNameLen = config->contents.maxNameLen;
+        newConfig->version = config->version;
+        PR_APPEND_LINK(&newConfig->link, configs);
+    }
+    return SECSuccess;
+
+loser:
+    tls13_DestroyEchConfig(newConfig);
+    tls13_DestroyEchConfigs(configs);
+    return SECFailure;
+}
+
+/*
+ * struct {
+ *     HpkeKdfId kdf_id;
+ *     HpkeAeadId aead_id;
+ * } HpkeSymmetricCipherSuite;
+ *
+ * struct {
+ *     uint8 config_id;
+ *     HpkeKemId kem_id;
+ *     HpkePublicKey public_key;
+ *     HpkeSymmetricCipherSuite cipher_suites<4..2^16-4>;
+ * } HpkeKeyConfig;
+ *
+ * struct {
+ *     HpkeKeyConfig key_config;
+ *     uint16 maximum_name_length;
+ *     opaque public_name<1..2^16-1>;
+ *     Extension extensions<0..2^16-1>;
+ * } ECHConfigContents;
+ *
+ * struct {
+ *     uint16 version;
+ *     uint16 length;
+ *     select (ECHConfig.version) {
+ *       case 0xfe0d: ECHConfigContents contents;
+ *     }
+ * } ECHConfig;
+ */
+static SECStatus
+tls13_DecodeEchConfigContents(const sslReadBuffer *rawConfig,
+                              sslEchConfig **outConfig)
+{
+    SECStatus rv;
+    sslEchConfigContents contents = { 0 };
+    sslEchConfig *decodedConfig;
+    PRUint64 tmpn;
+    PRUint64 tmpn2;
+    sslReadBuffer tmpBuf;
+    PRUint16 *extensionTypes = NULL;
+    unsigned int extensionIndex = 0;
+    sslReader configReader = SSL_READER(rawConfig->buf, rawConfig->len);
+    sslReader suiteReader;
+    sslReader extensionReader;
+    PRBool hasValidSuite = PR_FALSE;
+    PRBool unsupportedMandatoryXtn = PR_FALSE;
+
+    /* HpkeKeyConfig key_config */
+    /* uint8 config_id */
+    rv = sslRead_ReadNumber(&configReader, 1, &tmpn);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    contents.configId = tmpn;
+
+    /* HpkeKemId kem_id */
+    rv = sslRead_ReadNumber(&configReader, 2, &tmpn);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    contents.kemId = tmpn;
+
+    /* HpkePublicKey public_key */
+    rv = sslRead_ReadVariable(&configReader, 2, &tmpBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = SECITEM_MakeItem(NULL, &contents.publicKey, (PRUint8 *)tmpBuf.buf, tmpBuf.len);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* HpkeSymmetricCipherSuite cipher_suites<4..2^16-4> */
+    rv = sslRead_ReadVariable(&configReader, 2, &tmpBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    if (tmpBuf.len & 1) {
+        PORT_SetError(SSL_ERROR_RX_MALFORMED_ECH_CONFIG);
+        goto loser;
+    }
+    suiteReader = (sslReader)SSL_READER(tmpBuf.buf, tmpBuf.len);
+    while (SSL_READER_REMAINING(&suiteReader)) {
+        /* HpkeKdfId kdf_id */
+        rv = sslRead_ReadNumber(&suiteReader, 2, &tmpn);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        /* HpkeAeadId aead_id */
+        rv = sslRead_ReadNumber(&suiteReader, 2, &tmpn2);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        if (!hasValidSuite) {
+            /* Use the first compatible ciphersuite. */
+            rv = PK11_HPKE_ValidateParameters(contents.kemId, tmpn, tmpn2);
+            if (rv == SECSuccess) {
+                hasValidSuite = PR_TRUE;
+                contents.kdfId = tmpn;
+                contents.aeadId = tmpn2;
+                break;
+            }
+        }
+    }
+
+    rv = SECITEM_MakeItem(NULL, &contents.suites, (PRUint8 *)tmpBuf.buf, tmpBuf.len);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* uint8 maximum_name_length */
+    rv = sslRead_ReadNumber(&configReader, 1, &tmpn);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    contents.maxNameLen = (PRUint8)tmpn;
+
+    /* opaque public_name<1..2^16-1> */
+    rv = sslRead_ReadVariable(&configReader, 1, &tmpBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    if (tmpBuf.len == 0) {
+        PORT_SetError(SSL_ERROR_RX_MALFORMED_ECH_CONFIG);
+        goto loser;
+    }
+    if (!tls13_IsLDH(tmpBuf.buf, tmpBuf.len) ||
+        tls13_IsIp(tmpBuf.buf, tmpBuf.len)) {
+        PORT_SetError(SSL_ERROR_RX_MALFORMED_ECH_CONFIG);
+        goto loser;
+    }
+
+    contents.publicName = PORT_ZAlloc(tmpBuf.len + 1);
+    if (!contents.publicName) {
+        goto loser;
+    }
+    PORT_Memcpy(contents.publicName, (PRUint8 *)tmpBuf.buf, tmpBuf.len);
+
+    /* Extensions. We don't support any, but must
+     * check for any that are marked critical. */
+    rv = sslRead_ReadVariable(&configReader, 2, &tmpBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    extensionReader = (sslReader)SSL_READER(tmpBuf.buf, tmpBuf.len);
+    extensionTypes = PORT_NewArray(PRUint16, tmpBuf.len / 2 * sizeof(PRUint16));
+    if (!extensionTypes) {
+        goto loser;
+    }
+
+    while (SSL_READER_REMAINING(&extensionReader)) {
+        /* Get the extension's type field */
+        rv = sslRead_ReadNumber(&extensionReader, 2, &tmpn);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+
+        for (unsigned int i = 0; i < extensionIndex; i++) {
+            if (extensionTypes[i] == tmpn) {
+                PORT_SetError(SEC_ERROR_EXTENSION_VALUE_INVALID);
+                goto loser;
+            }
+        }
+        extensionTypes[extensionIndex++] = (PRUint16)tmpn;
+
+        /* Clients MUST parse the extension list and check for unsupported
+         * mandatory extensions.  If an unsupported mandatory extension is
+         * present, clients MUST ignore the ECHConfig
+         * [draft-ietf-tls-esni, Section 4.2]. */
+        if (tmpn & (1 << 15)) {
+            unsupportedMandatoryXtn = PR_TRUE;
+        }
+
+        /* Skip. */
+        rv = sslRead_ReadVariable(&extensionReader, 2, &tmpBuf);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+    }
+
+    /* Check that we consumed the entire ECHConfig */
+    if (SSL_READER_REMAINING(&configReader)) {
+        PORT_SetError(SSL_ERROR_RX_MALFORMED_ECH_CONFIG);
+        goto loser;
+    }
+
+    /* If the ciphersuites were compatible AND if NO unsupported mandatory
+     * extensions were found set the outparam. Return success either way if the
+     * config was well-formed. */
+    if (hasValidSuite && !unsupportedMandatoryXtn) {
+        decodedConfig = PORT_ZNew(sslEchConfig);
+        if (!decodedConfig) {
+            goto loser;
+        }
+        decodedConfig->contents = contents;
+        *outConfig = decodedConfig;
+    } else {
+        PORT_Free(contents.publicName);
+        SECITEM_FreeItem(&contents.publicKey, PR_FALSE);
+        SECITEM_FreeItem(&contents.suites, PR_FALSE);
+    }
+    PORT_Free(extensionTypes);
+    return SECSuccess;
+
+loser:
+    PORT_Free(extensionTypes);
+    PORT_Free(contents.publicName);
+    SECITEM_FreeItem(&contents.publicKey, PR_FALSE);
+    SECITEM_FreeItem(&contents.suites, PR_FALSE);
+    return SECFailure;
+}
+
+/* Decode an ECHConfigList struct and store each ECHConfig
+ * into |configs|.  */
+SECStatus
+tls13_DecodeEchConfigs(const SECItem *data, PRCList *configs)
+{
+    SECStatus rv;
+    sslEchConfig *decodedConfig = NULL;
+    sslReader rdr = SSL_READER(data->data, data->len);
+    sslReadBuffer tmp;
+    sslReadBuffer singleConfig;
+    PRUint64 version;
+    PRUint64 length;
+    PORT_Assert(PR_CLIST_IS_EMPTY(configs));
+
+    rv = sslRead_ReadVariable(&rdr, 2, &tmp);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    SSL_TRC(100, ("Read EchConfig list of size %u", SSL_READER_REMAINING(&rdr)));
+    if (SSL_READER_REMAINING(&rdr)) {
+        PORT_SetError(SEC_ERROR_BAD_DATA);
+        return SECFailure;
+    }
+
+    sslReader configsReader = SSL_READER(tmp.buf, tmp.len);
+
+    if (!SSL_READER_REMAINING(&configsReader)) {
+        PORT_SetError(SEC_ERROR_BAD_DATA);
+        return SECFailure;
+    }
+
+    /* Handle each ECHConfig. */
+    while (SSL_READER_REMAINING(&configsReader)) {
+        singleConfig.buf = SSL_READER_CURRENT(&configsReader);
+        /* uint16 version */
+        rv = sslRead_ReadNumber(&configsReader, 2, &version);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        /* uint16 length */
+        rv = sslRead_ReadNumber(&configsReader, 2, &length);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        singleConfig.len = 4 + length;
+
+        rv = sslRead_Read(&configsReader, length, &tmp);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+
+        if (version == TLS13_ECH_VERSION) {
+            rv = tls13_DecodeEchConfigContents(&tmp, &decodedConfig);
+            if (rv != SECSuccess) {
+                goto loser; /* code set */
+            }
+
+            if (decodedConfig) {
+                decodedConfig->version = version;
+                rv = SECITEM_MakeItem(NULL, &decodedConfig->raw, singleConfig.buf,
+                                      singleConfig.len);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+
+                PR_APPEND_LINK(&decodedConfig->link, configs);
+                decodedConfig = NULL;
+            }
+        }
+    }
+    return SECSuccess;
+
+loser:
+    tls13_DestroyEchConfigs(configs);
+    return SECFailure;
+}
+
+/* Encode an ECHConfigList structure. We only create one config, and as the
+ * primary use for this function is to generate test inputs, we don't
+ * validate against what HPKE and libssl can actually support. */
+SECStatus
+SSLExp_EncodeEchConfigId(PRUint8 configId, const char *publicName, unsigned int maxNameLen,
+                         HpkeKemId kemId, const SECKEYPublicKey *pubKey,
+                         const HpkeSymmetricSuite *hpkeSuites, unsigned int hpkeSuiteCount,
+                         PRUint8 *out, unsigned int *outlen, unsigned int maxlen)
+{
+    SECStatus rv;
+    unsigned int savedOffset;
+    unsigned int len;
+    sslBuffer b = SSL_BUFFER_EMPTY;
+    PRUint8 tmpBuf[66]; // Large enough for an EC public key, currently only X25519.
+    unsigned int tmpLen;
+
+    if (!publicName || !hpkeSuites || hpkeSuiteCount == 0 ||
+        !pubKey || maxNameLen == 0 || !out || !outlen) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    /* ECHConfig ECHConfigList<1..2^16-1>; */
+    rv = sslBuffer_Skip(&b, 2, NULL);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /*
+     * struct {
+     *     uint16 version;
+     *     uint16 length;
+     *     select (ECHConfig.version) {
+     *       case 0xfe0d: ECHConfigContents contents;
+     *     }
+     * } ECHConfig;
+    */
+    rv = sslBuffer_AppendNumber(&b, TLS13_ECH_VERSION, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = sslBuffer_Skip(&b, 2, &savedOffset);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /*
+     * struct {
+     *     uint8 config_id;
+     *     HpkeKemId kem_id;
+     *     HpkePublicKey public_key;
+     *     HpkeSymmetricCipherSuite cipher_suites<4..2^16-4>;
+     * } HpkeKeyConfig;
+     */
+    rv = sslBuffer_AppendNumber(&b, configId, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = sslBuffer_AppendNumber(&b, kemId, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = PK11_HPKE_Serialize(pubKey, tmpBuf, &tmpLen, sizeof(tmpBuf));
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_AppendVariable(&b, tmpBuf, tmpLen, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = sslBuffer_AppendNumber(&b, hpkeSuiteCount * 4, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    for (unsigned int i = 0; i < hpkeSuiteCount; i++) {
+        rv = sslBuffer_AppendNumber(&b, hpkeSuites[i].kdfId, 2);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        rv = sslBuffer_AppendNumber(&b, hpkeSuites[i].aeadId, 2);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+    }
+
+    /*
+     * struct {
+     *     HpkeKeyConfig key_config;
+     *     uint8 maximum_name_length;
+     *     opaque public_name<1..255>;
+     *     Extension extensions<0..2^16-1>;
+     * } ECHConfigContents;
+     */
+    rv = sslBuffer_AppendNumber(&b, maxNameLen, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    len = PORT_Strlen(publicName);
+    if (len > 0xff) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        goto loser;
+    }
+    rv = sslBuffer_AppendVariable(&b, (const PRUint8 *)publicName, len, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* extensions */
+    rv = sslBuffer_AppendNumber(&b, 0, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Write the length now that we know it. */
+    rv = sslBuffer_InsertLength(&b, 0, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_InsertLength(&b, savedOffset, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    if (SSL_BUFFER_LEN(&b) > maxlen) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        goto loser;
+    }
+    PORT_Memcpy(out, SSL_BUFFER_BASE(&b), SSL_BUFFER_LEN(&b));
+    *outlen = SSL_BUFFER_LEN(&b);
+    sslBuffer_Clear(&b);
+    return SECSuccess;
+
+loser:
+    sslBuffer_Clear(&b);
+    return SECFailure;
+}
+
+SECStatus
+SSLExp_GetEchRetryConfigs(PRFileDesc *fd, SECItem *retryConfigs)
+{
+    SECStatus rv;
+    sslSocket *ss;
+    SECItem out = { siBuffer, NULL, 0 };
+
+    if (!fd || !retryConfigs) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+    ss = ssl_FindSocket(fd);
+    if (!ss) {
+        SSL_DBG(("%d: SSL[%d]: bad socket in %s",
+                 SSL_GETPID(), fd, __FUNCTION__));
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    /* We don't distinguish between "handshake completed
+     * without retry configs", and "handshake not completed".
+     * An application should only call this after receiving a
+     * RETRY_WITH_ECH error code, which implies retry_configs. */
+    if (!ss->xtnData.ech || !ss->xtnData.ech->retryConfigsValid) {
+        PORT_SetError(SSL_ERROR_HANDSHAKE_NOT_COMPLETED);
+        return SECFailure;
+    }
+
+    /* May be empty. */
+    rv = SECITEM_CopyItem(NULL, &out, &ss->xtnData.ech->retryConfigs);
+    if (rv == SECFailure) {
+        return SECFailure;
+    }
+    *retryConfigs = out;
+    return SECSuccess;
+}
+
+SECStatus
+SSLExp_RemoveEchConfigs(PRFileDesc *fd)
+{
+    sslSocket *ss;
+
+    if (!fd) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    ss = ssl_FindSocket(fd);
+    if (!ss) {
+        SSL_DBG(("%d: SSL[%d]: bad socket in %s",
+                 SSL_GETPID(), fd, __FUNCTION__));
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    SECKEY_DestroyPrivateKey(ss->echPrivKey);
+    ss->echPrivKey = NULL;
+    SECKEY_DestroyPublicKey(ss->echPubKey);
+    ss->echPubKey = NULL;
+    tls13_DestroyEchConfigs(&ss->echConfigs);
+
+    /* Also remove any retry_configs and handshake context. */
+    if (ss->xtnData.ech && ss->xtnData.ech->retryConfigs.len) {
+        SECITEM_FreeItem(&ss->xtnData.ech->retryConfigs, PR_FALSE);
+    }
+
+    if (ss->ssl3.hs.echHpkeCtx) {
+        PK11_HPKE_DestroyContext(ss->ssl3.hs.echHpkeCtx, PR_TRUE);
+        ss->ssl3.hs.echHpkeCtx = NULL;
+    }
+    PORT_Free(CONST_CAST(char, ss->ssl3.hs.echPublicName));
+    ss->ssl3.hs.echPublicName = NULL;
+
+    return SECSuccess;
+}
+
+/* Import one or more ECHConfigs for the given keypair. The AEAD/KDF
+ * may differ , but only X25519 is supported for the KEM.*/
+SECStatus
+SSLExp_SetServerEchConfigs(PRFileDesc *fd,
+                           const SECKEYPublicKey *pubKey, const SECKEYPrivateKey *privKey,
+                           const PRUint8 *echConfigs, unsigned int echConfigsLen)
+{
+    sslSocket *ss;
+    SECStatus rv;
+    SECItem data = { siBuffer, CONST_CAST(PRUint8, echConfigs), echConfigsLen };
+
+    if (!fd || !pubKey || !privKey || !echConfigs || echConfigsLen == 0) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    ss = ssl_FindSocket(fd);
+    if (!ss) {
+        SSL_DBG(("%d: SSL[%d]: bad socket in %s",
+                 SSL_GETPID(), fd, __FUNCTION__));
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    /* Overwrite if we're already configured. */
+    rv = SSLExp_RemoveEchConfigs(fd);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+
+    rv = tls13_DecodeEchConfigs(&data, &ss->echConfigs);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    if (PR_CLIST_IS_EMPTY(&ss->echConfigs)) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        goto loser;
+    }
+
+    ss->echPubKey = SECKEY_CopyPublicKey(pubKey);
+    if (!ss->echPubKey) {
+        goto loser;
+    }
+    ss->echPrivKey = SECKEY_CopyPrivateKey(privKey);
+    if (!ss->echPrivKey) {
+        goto loser;
+    }
+    return SECSuccess;
+
+loser:
+    tls13_DestroyEchConfigs(&ss->echConfigs);
+    SECKEY_DestroyPrivateKey(ss->echPrivKey);
+    SECKEY_DestroyPublicKey(ss->echPubKey);
+    ss->echPubKey = NULL;
+    ss->echPrivKey = NULL;
+    return SECFailure;
+}
+
+/* Client enable. For now, we'll use the first
+ * compatible config (server preference). */
+SECStatus
+SSLExp_SetClientEchConfigs(PRFileDesc *fd,
+                           const PRUint8 *echConfigs,
+                           unsigned int echConfigsLen)
+{
+    SECStatus rv;
+    sslSocket *ss;
+    SECItem data = { siBuffer, CONST_CAST(PRUint8, echConfigs), echConfigsLen };
+
+    if (!fd || !echConfigs || echConfigsLen == 0) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    ss = ssl_FindSocket(fd);
+    if (!ss) {
+        SSL_DBG(("%d: SSL[%d]: bad socket in %s",
+                 SSL_GETPID(), fd, __FUNCTION__));
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    /* Overwrite if we're already configured. */
+    rv = SSLExp_RemoveEchConfigs(fd);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+
+    rv = tls13_DecodeEchConfigs(&data, &ss->echConfigs);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    if (PR_CLIST_IS_EMPTY(&ss->echConfigs)) {
+        PORT_SetError(SEC_ERROR_INVALID_ARGS);
+        return SECFailure;
+    }
+
+    return SECSuccess;
+}
+
+/* Set up ECH. This generates an ephemeral sender
+ * keypair and the HPKE context */
+SECStatus
+tls13_ClientSetupEch(sslSocket *ss, sslClientHelloType type)
+{
+    SECStatus rv;
+    HpkeContext *cx = NULL;
+    SECKEYPublicKey *pkR = NULL;
+    SECItem hpkeInfo = { siBuffer, NULL, 0 };
+    sslEchConfig *cfg = NULL;
+
+    if (PR_CLIST_IS_EMPTY(&ss->echConfigs) ||
+        !ssl_ShouldSendSNIExtension(ss, ss->url) ||
+        IS_DTLS(ss)) {
+        return SECSuccess;
+    }
+
+    /* Maybe apply our own priority if >1. For now, we only support
+     * one version and one KEM. Each ECHConfig can specify multiple
+     * KDF/AEADs, so just use the first. */
+    cfg = (sslEchConfig *)PR_LIST_HEAD(&ss->echConfigs);
+
+    SSL_TRC(50, ("%d: TLS13[%d]: Setup client ECH",
+                 SSL_GETPID(), ss->fd));
+
+    switch (type) {
+        case client_hello_initial:
+            PORT_Assert(!ss->ssl3.hs.echHpkeCtx && !ss->ssl3.hs.echPublicName);
+            cx = PK11_HPKE_NewContext(cfg->contents.kemId, cfg->contents.kdfId,
+                                      cfg->contents.aeadId, NULL, NULL);
+            break;
+        case client_hello_retry:
+            if (!ss->ssl3.hs.echHpkeCtx || !ss->ssl3.hs.echPublicName) {
+                FATAL_ERROR(ss, SEC_ERROR_LIBRARY_FAILURE, internal_error);
+                return SECFailure;
+            }
+            /* Nothing else to do. */
+            return SECSuccess;
+        default:
+            PORT_Assert(0);
+            goto loser;
+    }
+    if (!cx) {
+        goto loser;
+    }
+
+    rv = PK11_HPKE_Deserialize(cx, cfg->contents.publicKey.data, cfg->contents.publicKey.len, &pkR);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    if (!SECITEM_AllocItem(NULL, &hpkeInfo, strlen(kHpkeInfoEch) + 1 + cfg->raw.len)) {
+        goto loser;
+    }
+    PORT_Memcpy(&hpkeInfo.data[0], kHpkeInfoEch, strlen(kHpkeInfoEch));
+    PORT_Memset(&hpkeInfo.data[strlen(kHpkeInfoEch)], 0, 1);
+    PORT_Memcpy(&hpkeInfo.data[strlen(kHpkeInfoEch) + 1], cfg->raw.data, cfg->raw.len);
+
+    PRINT_BUF(50, (ss, "Info", hpkeInfo.data, hpkeInfo.len));
+
+    /* Setup with an ephemeral sender keypair. */
+    rv = PK11_HPKE_SetupS(cx, NULL, NULL, pkR, &hpkeInfo);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = ssl3_GetNewRandom(ss->ssl3.hs.client_inner_random);
+    if (rv != SECSuccess) {
+        goto loser; /* code set */
+    }
+
+    /* If ECH is rejected, the application will use SSLChannelInfo
+     * to fetch this field and perform cert chain verification. */
+    ss->ssl3.hs.echPublicName = PORT_Strdup(cfg->contents.publicName);
+    if (!ss->ssl3.hs.echPublicName) {
+        goto loser;
+    }
+
+    ss->ssl3.hs.echHpkeCtx = cx;
+    SECKEY_DestroyPublicKey(pkR);
+    SECITEM_FreeItem(&hpkeInfo, PR_FALSE);
+    return SECSuccess;
+
+loser:
+    PK11_HPKE_DestroyContext(cx, PR_TRUE);
+    SECKEY_DestroyPublicKey(pkR);
+    SECITEM_FreeItem(&hpkeInfo, PR_FALSE);
+    PORT_Assert(PORT_GetError() != 0);
+    return SECFailure;
+}
+
+/*
+ * outerAAD - The associated data for the AEAD (the entire client hello with the ECH payload zeroed)
+ * chInner - The plaintext which will be encrypted (the ClientHelloInner plus padding)
+ * echPayload - Output location. A buffer containing all-zeroes of at least chInner->len + TLS13_ECH_AEAD_TAG_LEN bytes.
+ *
+ * echPayload may point into outerAAD to avoid the need to duplicate the ClientHelloOuter buffer.
+ */
+static SECStatus
+tls13_EncryptClientHello(sslSocket *ss, SECItem *aadItem, const sslBuffer *chInner, PRUint8 *echPayload)
+{
+    SECStatus rv;
+    SECItem chPt = { siBuffer, chInner->buf, chInner->len };
+    SECItem *chCt = NULL;
+
+    PRINT_BUF(50, (ss, "aad for ECH Encrypt", aadItem->data, aadItem->len));
+    PRINT_BUF(50, (ss, "plaintext for ECH Encrypt", chInner->buf, chInner->len));
+
+#ifndef UNSAFE_FUZZER_MODE
+    rv = PK11_HPKE_Seal(ss->ssl3.hs.echHpkeCtx, aadItem, &chPt, &chCt);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    PRINT_BUF(50, (ss, "ciphertext from ECH Encrypt", chCt->data, chCt->len));
+#else
+    /* Fake a tag. */
+    SECITEM_AllocItem(NULL, chCt, chPt.len + TLS13_ECH_AEAD_TAG_LEN);
+    if (!chCt) {
+        goto loser;
+    }
+    PORT_Memcpy(chCt->data, chPt.data, chPt.len);
+#endif
+
+#ifdef DEBUG
+    /* When encrypting in-place, the payload is part of the AAD and must be zeroed. */
+    PRUint8 val = 0;
+    for (int i = 0; i < chCt->len; i++) {
+        val |= *(echPayload + i);
+    }
+    PRINT_BUF(100, (ss, "Empty Placeholder for output of ECH Encryption", echPayload, chCt->len));
+    PR_ASSERT(val == 0);
+#endif
+
+    PORT_Memcpy(echPayload, chCt->data, chCt->len);
+    SECITEM_FreeItem(chCt, PR_TRUE);
+    return SECSuccess;
+
+loser:
+    SECITEM_FreeItem(chCt, PR_TRUE);
+    return SECFailure;
+}
+
+SECStatus
+tls13_GetMatchingEchConfigs(const sslSocket *ss, HpkeKdfId kdf, HpkeAeadId aead,
+                            const PRUint8 configId, const sslEchConfig *cur, sslEchConfig **next)
+{
+    SSL_TRC(50, ("%d: TLS13[%d]: GetMatchingEchConfig %d",
+                 SSL_GETPID(), ss->fd, configId));
+
+    /* If |cur|, resume the search at that node, else the list head. */
+    for (PRCList *cur_p = cur ? ((PRCList *)cur)->next : PR_LIST_HEAD(&ss->echConfigs);
+         cur_p != &ss->echConfigs;
+         cur_p = PR_NEXT_LINK(cur_p)) {
+        sslEchConfig *echConfig = (sslEchConfig *)cur_p;
+        if (echConfig->contents.configId == configId &&
+            echConfig->contents.aeadId == aead &&
+            echConfig->contents.kdfId == kdf) {
+            *next = echConfig;
+            return SECSuccess;
+        }
+    }
+
+    *next = NULL;
+    return SECSuccess;
+}
+
+/* Given a CH with extensions, copy from the start up to the extensions
+ * into |writer| and return the extensions themselves in |extensions|.
+ * If |explicitSid|, place this value into |writer| as the SID. Else,
+ * the sid is copied from |reader| to |writer|. */
+static SECStatus
+tls13_CopyChPreamble(sslSocket *ss, sslReader *reader, const SECItem *explicitSid, sslBuffer *writer, sslReadBuffer *extensions)
+{
+    SECStatus rv;
+    sslReadBuffer tmpReadBuf;
+
+    /* Locate the extensions. */
+    rv = sslRead_Read(reader, 2 + SSL3_RANDOM_LENGTH, &tmpReadBuf);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    rv = sslBuffer_Append(writer, tmpReadBuf.buf, tmpReadBuf.len);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+
+    /* legacy_session_id */
+    rv = sslRead_ReadVariable(reader, 1, &tmpReadBuf);
+    if (explicitSid) {
+        /* Encoded SID should be empty when copying from CHOuter. */
+        if (tmpReadBuf.len > 0) {
+            PORT_SetError(SSL_ERROR_RX_MALFORMED_ECH_EXTENSION);
+            return SECFailure;
+        }
+        rv = sslBuffer_AppendVariable(writer, explicitSid->data, explicitSid->len, 1);
+    } else {
+        rv = sslBuffer_AppendVariable(writer, tmpReadBuf.buf, tmpReadBuf.len, 1);
+    }
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+
+    /* cipher suites */
+    rv = sslRead_ReadVariable(reader, 2, &tmpReadBuf);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    rv = sslBuffer_AppendVariable(writer, tmpReadBuf.buf, tmpReadBuf.len, 2);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+
+    /* compression */
+    rv = sslRead_ReadVariable(reader, 1, &tmpReadBuf);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    rv = sslBuffer_AppendVariable(writer, tmpReadBuf.buf, tmpReadBuf.len, 1);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+
+    /* extensions */
+    rv = sslRead_ReadVariable(reader, 2, extensions);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+
+    /* padding (optional) */
+    sslReadBuffer padding;
+    rv = sslRead_Read(reader, SSL_READER_REMAINING(reader), &padding);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    PRUint8 result = 0;
+    for (int i = 0; i < padding.len; i++) {
+        result |= padding.buf[i];
+    }
+    if (result) {
+        SSL_TRC(50, ("%d: TLS13: Invalid ECH ClientHelloInner padding decoded", SSL_GETPID()));
+        FATAL_ERROR(ss, SSL_ERROR_RX_MALFORMED_ECH_EXTENSION, illegal_parameter);
+        return SECFailure;
+    }
+    return SECSuccess;
+}
+
+/*
+ * The ClientHelloOuterAAD is a serialized ClientHello structure, defined in
+ * Section 4.1.2 of [RFC8446], which matches the ClientHelloOuter except the
+ * payload field of the "encrypted_client_hello" is replaced with a byte
+ * string of the same length but whose contents are zeros. This value does
+ * not include the four-byte header from the Handshake structure.
+ */
+static SECStatus
+tls13_ServerMakeChOuterAAD(sslSocket *ss, const PRUint8 *outerCh, unsigned int outerChLen, SECItem *outerAAD)
+{
+    SECStatus rv;
+    sslBuffer aad = SSL_BUFFER_EMPTY;
+    const unsigned int echPayloadLen = ss->xtnData.ech->innerCh.len;               /* Length of incoming payload */
+    const unsigned int echPayloadOffset = ss->xtnData.ech->payloadStart - outerCh; /* Offset from start of CHO */
+
+    PORT_Assert(outerChLen > echPayloadLen);
+    PORT_Assert(echPayloadOffset + echPayloadLen <= outerChLen);
+    PORT_Assert(ss->sec.isServer);
+    PORT_Assert(ss->xtnData.ech);
+
+#ifdef DEBUG
+    /* Safety check that payload length pointed to by offset matches expected length */
+    sslReader echXtnReader = SSL_READER(outerCh + echPayloadOffset - 2, 2);
+    PRUint64 parsedXtnSize;
+    rv = sslRead_ReadNumber(&echXtnReader, 2, &parsedXtnSize);
+    PR_ASSERT(rv == SECSuccess);
+    PR_ASSERT(parsedXtnSize == echPayloadLen);
+#endif
+
+    rv = sslBuffer_Append(&aad, outerCh, outerChLen);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    PORT_Memset(aad.buf + echPayloadOffset, 0, echPayloadLen);
+
+    PRINT_BUF(50, (ss, "AAD for ECH Decryption", aad.buf, aad.len));
+
+    outerAAD->data = aad.buf;
+    outerAAD->len = aad.len;
+    return SECSuccess;
+
+loser:
+    sslBuffer_Clear(&aad);
+    return SECFailure;
+}
+
+SECStatus
+tls13_OpenClientHelloInner(sslSocket *ss, const SECItem *outer, const SECItem *outerAAD, sslEchConfig *cfg, SECItem **chInner)
+{
+    SECStatus rv;
+    HpkeContext *cx = NULL;
+    SECItem *decryptedChInner = NULL;
+    SECItem hpkeInfo = { siBuffer, NULL, 0 };
+    SSL_TRC(50, ("%d: TLS13[%d]: Server opening ECH Inner%s", SSL_GETPID(),
+                 ss->fd, ss->ssl3.hs.helloRetry ? " after HRR" : ""));
+
+    if (!ss->ssl3.hs.helloRetry) {
+        PORT_Assert(!ss->ssl3.hs.echHpkeCtx);
+        cx = PK11_HPKE_NewContext(cfg->contents.kemId, cfg->contents.kdfId,
+                                  cfg->contents.aeadId, NULL, NULL);
+        if (!cx) {
+            goto loser;
+        }
+
+        if (!SECITEM_AllocItem(NULL, &hpkeInfo, strlen(kHpkeInfoEch) + 1 + cfg->raw.len)) {
+            goto loser;
+        }
+        PORT_Memcpy(&hpkeInfo.data[0], kHpkeInfoEch, strlen(kHpkeInfoEch));
+        PORT_Memset(&hpkeInfo.data[strlen(kHpkeInfoEch)], 0, 1);
+        PORT_Memcpy(&hpkeInfo.data[strlen(kHpkeInfoEch) + 1], cfg->raw.data, cfg->raw.len);
+
+        rv = PK11_HPKE_SetupR(cx, ss->echPubKey, ss->echPrivKey,
+                              &ss->xtnData.ech->senderPubKey, &hpkeInfo);
+        if (rv != SECSuccess) {
+            goto loser; /* code set */
+        }
+    } else {
+        PORT_Assert(ss->ssl3.hs.echHpkeCtx);
+        cx = ss->ssl3.hs.echHpkeCtx;
+    }
+
+#ifndef UNSAFE_FUZZER_MODE
+    rv = PK11_HPKE_Open(cx, outerAAD, &ss->xtnData.ech->innerCh, &decryptedChInner);
+    if (rv != SECSuccess) {
+        SSL_TRC(10, ("%d: SSL3[%d]: Failed to decrypt inner CH with this candidate",
+                     SSL_GETPID(), ss->fd));
+        goto loser; /* code set */
+    }
+#else
+    rv = SECITEM_CopyItem(NULL, decryptedChInner, &ss->xtnData.ech->innerCh);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    decryptedChInner->len -= TLS13_ECH_AEAD_TAG_LEN; /* Fake tag */
+#endif
+
+    /* Stash the context, we may need it for HRR. */
+    ss->ssl3.hs.echHpkeCtx = cx;
+    *chInner = decryptedChInner;
+    PRINT_BUF(100, (ss, "Decrypted ECH Inner", decryptedChInner->data, decryptedChInner->len));
+    SECITEM_FreeItem(&hpkeInfo, PR_FALSE);
+    return SECSuccess;
+
+loser:
+    SECITEM_FreeItem(decryptedChInner, PR_TRUE);
+    SECITEM_FreeItem(&hpkeInfo, PR_FALSE);
+    if (cx != ss->ssl3.hs.echHpkeCtx) {
+        /* Don't double-free if it's already global. */
+        PK11_HPKE_DestroyContext(cx, PR_TRUE);
+    }
+    return SECFailure;
+}
+
+/* This is the maximum number of extension hooks that the following functions can handle. */
+#define MAX_EXTENSION_WRITERS 32
+
+static SECStatus
+tls13_WriteDupXtnsToChInner(PRBool compressing, sslBuffer *dupXtns, sslBuffer *chInnerXtns)
+{
+    SECStatus rv;
+    if (compressing && SSL_BUFFER_LEN(dupXtns) > 0) {
+        rv = sslBuffer_AppendNumber(chInnerXtns, ssl_tls13_outer_extensions_xtn, 2);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+        rv = sslBuffer_AppendNumber(chInnerXtns, dupXtns->len + 1, 2);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+        rv = sslBuffer_AppendBufferVariable(chInnerXtns, dupXtns, 1);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+    } else {
+        /* dupXtns carries whole extensions with lengths on each. */
+        rv = sslBuffer_AppendBuffer(chInnerXtns, dupXtns);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+    }
+    sslBuffer_Clear(dupXtns);
+    return SECSuccess;
+}
+
+/* Add ordinary extensions to CHInner.
+ * The value of the extension from CHOuter is in |extensionData|.
+ *
+ * If the value is to be compressed, it is written to |dupXtns|.
+ * Otherwise, a full extension is written to |chInnerXtns|.
+ *
+ * This function is always called twice:
+ * once without compression and once with compression if possible.
+ *
+ * Because we want to allow extensions that did not appear in CHOuter
+ * to be included in CHInner, we also need to track which extensions
+ * have been included.  This is what |called| and |nCalled| track.
+ */
+static SECStatus
+tls13_ChInnerAppendExtension(sslSocket *ss, PRUint16 extensionType,
+                             const sslReadBuffer *extensionData,
+                             sslBuffer *dupXtns, sslBuffer *chInnerXtns,
+                             PRBool compressing,
+                             PRUint16 *called, unsigned int *nCalled)
+{
+    PRUint8 buf[1024] = { 0 };
+    const PRUint8 *p;
+    unsigned int len = 0;
+    PRBool willCompress;
+
+    PORT_Assert(extensionType != ssl_tls13_encrypted_client_hello_xtn);
+    sslCustomExtensionHooks *hook = ss->opt.callExtensionWriterOnEchInner
+                                        ? ssl_FindCustomExtensionHooks(ss, extensionType)
+                                        : NULL;
+    if (hook && hook->writer) {
+        if (*nCalled >= MAX_EXTENSION_WRITERS) {
+            PORT_SetError(SEC_ERROR_LIBRARY_FAILURE); /* TODO new code? */
+            return SECFailure;
+        }
+
+        PRBool append = (*hook->writer)(ss->fd, ssl_hs_client_hello,
+                                        buf, &len, sizeof(buf), hook->writerArg);
+        called[(*nCalled)++] = extensionType;
+        if (!append) {
+            /* This extension is not going to appear in CHInner. */
+            /* TODO: consider removing this extension from ss->xtnData.advertised.
+             * The consequence of not removing it is that we won't complain
+             * if the server accepts ECH and then includes this extension.
+             * The cost is a complete reworking of ss->xtnData.advertised.
+             */
+            return SECSuccess;
+        }
+        /* It can be compressed if it is the same as the outer value. */
+        willCompress = (len == extensionData->len &&
+                        NSS_SecureMemcmp(buf, extensionData->buf, len) == 0);
+        p = buf;
+    } else {
+        /* Non-custom extensions are duplicated when compressing. */
+        willCompress = PR_TRUE;
+        p = extensionData->buf;
+        len = extensionData->len;
+    }
+
+    /* Duplicated extensions all need to go together. */
+    sslBuffer *dst = willCompress ? dupXtns : chInnerXtns;
+    SECStatus rv = sslBuffer_AppendNumber(dst, extensionType, 2);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    if (!willCompress || !compressing) {
+        rv = sslBuffer_AppendVariable(dst, p, len, 2);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+    }
+    /* As this function is called twice, we only want to update our state the second time. */
+    if (compressing) {
+        ss->xtnData.echAdvertised[ss->xtnData.echNumAdvertised++] = extensionType;
+        SSL_TRC(50, ("Appending extension=%d to the Client Hello Inner. Compressed?=%d", extensionType, willCompress));
+    }
+    return SECSuccess;
+}
+
+/* Call any custom extension handlers that didn't want to be added to CHOuter. */
+static SECStatus
+tls13_ChInnerAdditionalExtensionWriters(sslSocket *ss, const PRUint16 *called,
+                                        unsigned int nCalled, sslBuffer *chInnerXtns)
+{
+    if (!ss->opt.callExtensionWriterOnEchInner) {
+        return SECSuccess;
+    }
+
+    for (PRCList *cursor = PR_NEXT_LINK(&ss->extensionHooks);
+         cursor != &ss->extensionHooks;
+         cursor = PR_NEXT_LINK(cursor)) {
+        sslCustomExtensionHooks *hook = (sslCustomExtensionHooks *)cursor;
+
+        /* Skip if this hook was already called. */
+        PRBool hookCalled = PR_FALSE;
+        for (unsigned int i = 0; i < nCalled; ++i) {
+            if (called[i] == hook->type) {
+                hookCalled = PR_TRUE;
+                break;
+            }
+        }
+        if (hookCalled) {
+            continue;
+        }
+
+        /* This is a cut-down version of ssl_CallCustomExtensionSenders(). */
+        PRUint8 buf[1024];
+        unsigned int len = 0;
+        PRBool append = (*hook->writer)(ss->fd, ssl_hs_client_hello,
+                                        buf, &len, sizeof(buf), hook->writerArg);
+        if (!append) {
+            continue;
+        }
+
+        SECStatus rv = sslBuffer_AppendNumber(chInnerXtns, hook->type, 2);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+        rv = sslBuffer_AppendVariable(chInnerXtns, buf, len, 2);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+        ss->xtnData.echAdvertised[ss->xtnData.echNumAdvertised++] = hook->type;
+    }
+    return SECSuccess;
+}
+
+/* Take the PSK extension CHOuter and fill it with junk. */
+static SECStatus
+tls13_RandomizePsk(PRUint8 *buf, unsigned int len)
+{
+    sslReader rdr = SSL_READER(buf, len);
+
+    /* Read the length of identities. */
+    PRUint64 outerLen = 0;
+    SECStatus rv = sslRead_ReadNumber(&rdr, 2, &outerLen);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    PORT_Assert(outerLen < len + 2);
+
+    /* Read the length of PskIdentity.identity */
+    PRUint64 innerLen = 0;
+    rv = sslRead_ReadNumber(&rdr, 2, &innerLen);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    /* identities should contain just one identity. */
+    PORT_Assert(outerLen == innerLen + 6);
+
+    /* Randomize PskIdentity.{identity,obfuscated_ticket_age}. */
+    rv = PK11_GenerateRandom(buf + rdr.offset, innerLen + 4);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    rdr.offset += innerLen + 4;
+
+    /* Read the length of binders. */
+    rv = sslRead_ReadNumber(&rdr, 2, &outerLen);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    PORT_Assert(outerLen + rdr.offset == len);
+
+    /* Read the length of the binder. */
+    rv = sslRead_ReadNumber(&rdr, 1, &innerLen);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    /* binders should contain just one binder. */
+    PORT_Assert(outerLen == innerLen + 1);
+
+    /* Randomize the binder. */
+    rv = PK11_GenerateRandom(buf + rdr.offset, innerLen);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+
+    return SECSuccess;
+}
+
+/* Given a buffer of extensions prepared for CHOuter, translate those extensions to a
+ * buffer suitable for CHInner. This is intended to be called twice: once without
+ * compression for the transcript hash and binders, and once with compression for
+ * encoding the actual CHInner value.
+ *
+ * Compressed extensions are moved in both runs.  When compressing, they are moved
+ * to a single outer_extensions extension, which lists extensions from CHOuter.
+ * When not compressing, this produces the ClientHello that will be reconstructed
+ * from the compressed ClientHello (that is, what goes into the handshake transcript),
+ * so all the compressed extensions need to appear in the same place that the
+ * outer_extensions extension appears.
+ *
+ * On the first run, if |inOutPskXtn| and OuterXtnsBuf contains a PSK extension,
+ * remove it and return in the outparam.he caller will compute the binder value
+ * based on the uncompressed output. Next, if |compress|, consolidate duplicated
+ * extensions (that would otherwise be copied) into a single outer_extensions
+ * extension. If |inOutPskXtn|, the extension contains a binder, it is appended
+ * after the deduplicated outer_extensions. In the case of GREASE ECH, one call
+ * is made to estimate size (wiith compression, null inOutPskXtn).
+ */
+SECStatus
+tls13_ConstructInnerExtensionsFromOuter(sslSocket *ss, sslBuffer *chOuterXtnsBuf,
+                                        sslBuffer *chInnerXtns, sslBuffer *inOutPskXtn,
+                                        PRBool shouldCompress)
+{
+    SECStatus rv;
+    PRUint64 extensionType;
+    sslReadBuffer extensionData;
+    sslBuffer pskXtn = SSL_BUFFER_EMPTY;
+    sslBuffer dupXtns = SSL_BUFFER_EMPTY; /* Duplicated extensions, types-only if |compress|. */
+    unsigned int tmpOffset;
+    unsigned int tmpLen;
+    unsigned int srcXtnBase; /* To truncate CHOuter and remove the PSK extension. */
+
+    PRUint16 called[MAX_EXTENSION_WRITERS] = { 0 }; /* For tracking which has been called. */
+    unsigned int nCalled = 0;
+
+    SSL_TRC(50, ("%d: TLS13[%d]: Constructing ECH inner extensions %s compression",
+                 SSL_GETPID(), ss->fd, shouldCompress ? "with" : "without"));
+
+    /* When offering the "encrypted_client_hello" extension in its
+     * ClientHelloOuter, the client MUST also offer an empty
+     * "encrypted_client_hello" extension in its ClientHelloInner. */
+    rv = sslBuffer_AppendNumber(chInnerXtns, ssl_tls13_encrypted_client_hello_xtn, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_AppendNumber(chInnerXtns, 1, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_AppendNumber(chInnerXtns, ech_xtn_type_inner, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    sslReader rdr = SSL_READER(chOuterXtnsBuf->buf, chOuterXtnsBuf->len);
+    while (SSL_READER_REMAINING(&rdr)) {
+        srcXtnBase = rdr.offset;
+        rv = sslRead_ReadNumber(&rdr, 2, &extensionType);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+
+        /* Get the extension data. */
+        rv = sslRead_ReadVariable(&rdr, 2, &extensionData);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+
+        /* Skip extensions that are TLS < 1.3 only, since CHInner MUST
+         * negotiate TLS 1.3 or above.
+         * If the extension is supported by default (sslSupported) but unknown
+         * to TLS 1.3 it must be a TLS < 1.3 only extension. */
+        SSLExtensionSupport sslSupported;
+        (void)SSLExp_GetExtensionSupport(extensionType, &sslSupported);
+        if (sslSupported != ssl_ext_none &&
+            tls13_ExtensionStatus(extensionType, ssl_hs_client_hello) == tls13_extension_unknown) {
+            continue;
+        }
+
+        switch (extensionType) {
+            case ssl_server_name_xtn:
+                /* Write the real (private) SNI value. */
+                rv = sslBuffer_AppendNumber(chInnerXtns, extensionType, 2);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+                rv = sslBuffer_Skip(chInnerXtns, 2, &tmpOffset);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+                tmpLen = SSL_BUFFER_LEN(chInnerXtns);
+                rv = ssl3_ClientFormatServerNameXtn(ss, ss->url,
+                                                    strlen(ss->url),
+                                                    NULL, chInnerXtns);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+                tmpLen = SSL_BUFFER_LEN(chInnerXtns) - tmpLen;
+                rv = sslBuffer_InsertNumber(chInnerXtns, tmpOffset, tmpLen, 2);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+                /* Only update state on second invocation of this function */
+                if (shouldCompress) {
+                    ss->xtnData.echAdvertised[ss->xtnData.echNumAdvertised++] = extensionType;
+                }
+                break;
+            case ssl_tls13_supported_versions_xtn:
+                /* Only TLS 1.3 and GREASE on CHInner. */
+                rv = sslBuffer_AppendNumber(chInnerXtns, extensionType, 2);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+                /* Extension length. */
+                tmpLen = (ss->opt.enableGrease) ? 5 : 3;
+                rv = sslBuffer_AppendNumber(chInnerXtns, tmpLen, 2);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+                /* ProtocolVersion length */
+                rv = sslBuffer_AppendNumber(chInnerXtns, tmpLen - 1, 1);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+                /* ProtocolVersion TLS 1.3 */
+                rv = sslBuffer_AppendNumber(chInnerXtns, SSL_LIBRARY_VERSION_TLS_1_3, 2);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+                /* ProtocolVersion GREASE */
+                if (ss->opt.enableGrease) {
+                    rv = sslBuffer_AppendNumber(chInnerXtns, ss->ssl3.hs.grease->idx[grease_version], 2);
+                    if (rv != SECSuccess) {
+                        goto loser;
+                    }
+                }
+                /* Only update state on second invocation of this function */
+                if (shouldCompress) {
+                    ss->xtnData.echAdvertised[ss->xtnData.echNumAdvertised++] = extensionType;
+                }
+                break;
+            case ssl_tls13_pre_shared_key_xtn:
+                if (inOutPskXtn && !shouldCompress) {
+                    rv = sslBuffer_AppendNumber(&pskXtn, extensionType, 2);
+                    if (rv != SECSuccess) {
+                        goto loser;
+                    }
+                    rv = sslBuffer_AppendVariable(&pskXtn, extensionData.buf,
+                                                  extensionData.len, 2);
+                    if (rv != SECSuccess) {
+                        goto loser;
+                    }
+                    /* This should be the last extension. */
+                    PORT_Assert(srcXtnBase == ss->xtnData.lastXtnOffset);
+                    PORT_Assert(chOuterXtnsBuf->len - srcXtnBase == extensionData.len + 4);
+                    rv = tls13_RandomizePsk(chOuterXtnsBuf->buf + srcXtnBase + 4,
+                                            chOuterXtnsBuf->len - srcXtnBase - 4);
+                    if (rv != SECSuccess) {
+                        goto loser;
+                    }
+                } else if (!inOutPskXtn) {
+                    /* When GREASEing, only the length is used.
+                     * Order doesn't matter, so just copy the extension. */
+                    rv = sslBuffer_AppendNumber(chInnerXtns, extensionType, 2);
+                    if (rv != SECSuccess) {
+                        goto loser;
+                    }
+                    rv = sslBuffer_AppendVariable(chInnerXtns, extensionData.buf,
+                                                  extensionData.len, 2);
+                    if (rv != SECSuccess) {
+                        goto loser;
+                    }
+                }
+                /* Only update state on second invocation of this function */
+                if (shouldCompress) {
+                    ss->xtnData.echAdvertised[ss->xtnData.echNumAdvertised++] = extensionType;
+                }
+                break;
+            default: {
+                /* This is a regular extension.  We can maybe compress these. */
+                rv = tls13_ChInnerAppendExtension(ss, extensionType,
+                                                  &extensionData,
+                                                  &dupXtns, chInnerXtns,
+                                                  shouldCompress,
+                                                  called, &nCalled);
+                if (rv != SECSuccess) {
+                    goto loser;
+                }
+                break;
+            }
+        }
+    }
+
+    rv = tls13_WriteDupXtnsToChInner(shouldCompress, &dupXtns, chInnerXtns);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Now call custom extension handlers that didn't choose to append anything to
+     * the outer ClientHello. */
+    rv = tls13_ChInnerAdditionalExtensionWriters(ss, called, nCalled, chInnerXtns);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    if (inOutPskXtn) {
+        /* On the first, non-compress run, append the (bad) PSK binder.
+         * On the second compression run, the caller is responsible for
+         * providing an extension with a valid binder, so append that. */
+        if (shouldCompress) {
+            rv = sslBuffer_AppendBuffer(chInnerXtns, inOutPskXtn);
+        } else {
+            rv = sslBuffer_AppendBuffer(chInnerXtns, &pskXtn);
+            *inOutPskXtn = pskXtn;
+        }
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+    }
+
+    return SECSuccess;
+
+loser:
+    sslBuffer_Clear(&pskXtn);
+    sslBuffer_Clear(&dupXtns);
+    return SECFailure;
+}
+
+static SECStatus
+tls13_EncodeClientHelloInner(sslSocket *ss, const sslBuffer *chInner, const sslBuffer *chInnerXtns, sslBuffer *out)
+{
+    PORT_Assert(ss && chInner && chInnerXtns && out);
+    SECStatus rv;
+    sslReadBuffer tmpReadBuf;
+    sslReader chReader = SSL_READER(chInner->buf, chInner->len);
+
+    rv = sslRead_Read(&chReader, 4, &tmpReadBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = sslRead_Read(&chReader, 2 + SSL3_RANDOM_LENGTH, &tmpReadBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_Append(out, tmpReadBuf.buf, tmpReadBuf.len);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Skip the legacy_session_id */
+    rv = sslRead_ReadVariable(&chReader, 1, &tmpReadBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_AppendNumber(out, 0, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* cipher suites */
+    rv = sslRead_ReadVariable(&chReader, 2, &tmpReadBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_AppendVariable(out, tmpReadBuf.buf, tmpReadBuf.len, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* compression methods */
+    rv = sslRead_ReadVariable(&chReader, 1, &tmpReadBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_AppendVariable(out, tmpReadBuf.buf, tmpReadBuf.len, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Append the extensions. */
+    rv = sslBuffer_AppendBufferVariable(out, chInnerXtns, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    return SECSuccess;
+
+loser:
+    sslBuffer_Clear(out);
+    return SECFailure;
+}
+
+SECStatus
+tls13_PadChInner(sslBuffer *chInner, uint8_t maxNameLen, uint8_t serverNameLen)
+{
+    SECStatus rv;
+    PORT_Assert(chInner);
+    PORT_Assert(serverNameLen > 0);
+    static unsigned char padding[256 + 32] = { 0 };
+    int16_t name_padding = (int16_t)maxNameLen - (int16_t)serverNameLen;
+    if (name_padding < 0) {
+        name_padding = 0;
+    }
+    unsigned int rounding_padding = 31 - ((SSL_BUFFER_LEN(chInner) + name_padding) % 32);
+    unsigned int total_padding = name_padding + rounding_padding;
+    PORT_Assert(total_padding < sizeof(padding));
+    SSL_TRC(100, ("computed ECH Inner Client Hello padding of size %u", total_padding));
+    rv = sslBuffer_Append(chInner, padding, total_padding);
+    if (rv != SECSuccess) {
+        sslBuffer_Clear(chInner);
+        return SECFailure;
+    }
+    return SECSuccess;
+}
+
+/* Build an ECH Xtn body with a zeroed payload for the client hello inner
+ *
+ *   enum { outer(0), inner(1) } ECHClientHelloType;
+ *
+ *   struct {
+ *      ECHClientHelloType type;
+ *      select (ECHClientHello.type) {
+ *          case outer:
+ *              HpkeSymmetricCipherSuite cipher_suite;
+ *              uint8 config_id;
+ *              opaque enc<0..2^16-1>;
+ *              opaque payload<1..2^16-1>;
+ *          case inner:
+ *              Empty;
+ *      };
+ *  } ECHClientHello;
+ *
+ * payloadLen = Size of zeroed placeholder field for payload.
+ * payloadOffset = Out parameter, start of payload field
+ * echXtn = Out parameter, constructed ECH Xtn with zeroed placeholder field.
+*/
+SECStatus
+tls13_BuildEchXtn(sslEchConfig *cfg, const SECItem *hpkeEnc, unsigned int payloadLen, PRUint16 *payloadOffset, sslBuffer *echXtn)
+{
+    SECStatus rv;
+    /* Format the encrypted_client_hello extension. */
+    rv = sslBuffer_AppendNumber(echXtn, ech_xtn_type_outer, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_AppendNumber(echXtn, cfg->contents.kdfId, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_AppendNumber(echXtn, cfg->contents.aeadId, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = sslBuffer_AppendNumber(echXtn, cfg->contents.configId, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    if (hpkeEnc) {
+        /* Public Key */
+        rv = sslBuffer_AppendVariable(echXtn, hpkeEnc->data, hpkeEnc->len, 2);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+    } else {
+        /* |enc| is empty. */
+        rv = sslBuffer_AppendNumber(echXtn, 0, 2);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+    }
+    payloadLen += TLS13_ECH_AEAD_TAG_LEN;
+    rv = sslBuffer_AppendNumber(echXtn, payloadLen, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    *payloadOffset = echXtn->len;
+    rv = sslBuffer_Fill(echXtn, 0, payloadLen);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    PRINT_BUF(100, (NULL, "ECH Xtn with Placeholder:", echXtn->buf, echXtn->len));
+    return SECSuccess;
+loser:
+    sslBuffer_Clear(echXtn);
+    return SECFailure;
+}
+
+SECStatus
+tls13_ConstructClientHelloWithEch(sslSocket *ss, const sslSessionID *sid, PRBool freshSid,
+                                  sslBuffer *chOuter, sslBuffer *chOuterXtnsBuf)
+{
+    SECStatus rv;
+    sslBuffer chInner = SSL_BUFFER_EMPTY;
+    sslBuffer encodedChInner = SSL_BUFFER_EMPTY;
+    sslBuffer paddingChInner = SSL_BUFFER_EMPTY;
+    sslBuffer chInnerXtns = SSL_BUFFER_EMPTY;
+    sslBuffer pskXtn = SSL_BUFFER_EMPTY;
+    unsigned int preambleLen;
+
+    SSL_TRC(50, ("%d: TLS13[%d]: Constructing ECH inner", SSL_GETPID(), ss->fd));
+
+    /* Create the full (uncompressed) inner extensions and steal any PSK extension.
+     * NB: Neither chOuterXtnsBuf nor chInnerXtns are length-prefixed. */
+    rv = tls13_ConstructInnerExtensionsFromOuter(ss, chOuterXtnsBuf, &chInnerXtns,
+                                                 &pskXtn, PR_FALSE);
+    if (rv != SECSuccess) {
+        goto loser; /* code set */
+    }
+
+    rv = ssl3_CreateClientHelloPreamble(ss, sid, PR_FALSE, SSL_LIBRARY_VERSION_TLS_1_3,
+                                        PR_TRUE, &chInnerXtns, &chInner);
+    if (rv != SECSuccess) {
+        goto loser; /* code set */
+    }
+    preambleLen = SSL_BUFFER_LEN(&chInner);
+
+    /* Write handshake header length. tls13_EncryptClientHello will
+     * remove this upon encoding, but the transcript needs it. This assumes
+     * the 4B stream-variant header. */
+    PORT_Assert(!IS_DTLS(ss));
+    rv = sslBuffer_InsertNumber(&chInner, 1,
+                                chInner.len + 2 + chInnerXtns.len - 4, 3);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    if (pskXtn.len) {
+        PORT_Assert(ssl3_ExtensionAdvertised(ss, ssl_tls13_pre_shared_key_xtn));
+        rv = tls13_WriteExtensionsWithBinder(ss, &chInnerXtns, &chInner);
+        /* Update the stolen PSK extension with the binder value. */
+        PORT_Memcpy(pskXtn.buf, &chInnerXtns.buf[chInnerXtns.len - pskXtn.len], pskXtn.len);
+    } else {
+        rv = sslBuffer_AppendBufferVariable(&chInner, &chInnerXtns, 2);
+    }
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    PRINT_BUF(50, (ss, "Uncompressed CHInner", chInner.buf, chInner.len));
+    rv = ssl3_UpdateHandshakeHashesInt(ss, chInner.buf, chInner.len,
+                                       &ss->ssl3.hs.echInnerMessages);
+    if (rv != SECSuccess) {
+        goto loser; /* code set */
+    }
+
+    /* Un-append the extensions, then append compressed via Encoded. */
+    SSL_BUFFER_LEN(&chInner) = preambleLen;
+    sslBuffer_Clear(&chInnerXtns);
+    rv = tls13_ConstructInnerExtensionsFromOuter(ss, chOuterXtnsBuf,
+                                                 &chInnerXtns, &pskXtn, PR_TRUE);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = tls13_EncodeClientHelloInner(ss, &chInner, &chInnerXtns, &encodedChInner);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    PRINT_BUF(50, (ss, "Compressed CHInner", encodedChInner.buf, encodedChInner.len));
+
+    PORT_Assert(!PR_CLIST_IS_EMPTY(&ss->echConfigs));
+    sslEchConfig *cfg = (sslEchConfig *)PR_LIST_HEAD(&ss->echConfigs);
+
+    /* We are using ECH so SNI must have been included */
+    rv = tls13_PadChInner(&encodedChInner, cfg->contents.maxNameLen, strlen(ss->url));
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Build the ECH Xtn with placeholder and put it in chOuterXtnsBuf */
+    sslBuffer echXtn = SSL_BUFFER_EMPTY;
+    const SECItem *hpkeEnc = NULL;
+    if (!ss->ssl3.hs.helloRetry) {
+        hpkeEnc = PK11_HPKE_GetEncapPubKey(ss->ssl3.hs.echHpkeCtx);
+        if (!hpkeEnc) {
+            FATAL_ERROR(ss, SEC_ERROR_LIBRARY_FAILURE, internal_error);
+            goto loser;
+        }
+    }
+    PRUint16 echXtnPayloadOffset; /* Offset from start of ECH Xtn to ECH Payload */
+    rv = tls13_BuildEchXtn(cfg, hpkeEnc, encodedChInner.len, &echXtnPayloadOffset, &echXtn);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    ss->xtnData.echAdvertised[ss->xtnData.echNumAdvertised++] = ssl_tls13_encrypted_client_hello_xtn;
+    rv = ssl3_EmplaceExtension(ss, chOuterXtnsBuf, ssl_tls13_encrypted_client_hello_xtn,
+                               echXtn.buf, echXtn.len, PR_TRUE);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Add the padding */
+    rv = ssl_InsertPaddingExtension(ss, chOuter->len, chOuterXtnsBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Finish the CHO with the ECH Xtn payload zeroed */
+    rv = ssl3_InsertChHeaderSize(ss, chOuter, chOuterXtnsBuf);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    unsigned int chOuterXtnsOffset = chOuter->len + 2; /* From Start of CHO to Extensions list */
+    rv = sslBuffer_AppendBufferVariable(chOuter, chOuterXtnsBuf, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* AAD consists of entire CHO, minus the 4 byte handshake header */
+    SECItem aadItem = { siBuffer, chOuter->buf + 4, chOuter->len - 4 };
+    /* ECH Payload begins after CHO Header, after ECH Xtn start, after ECH Xtn header */
+    PRUint8 *echPayload = chOuter->buf + chOuterXtnsOffset + ss->xtnData.echXtnOffset + 4 + echXtnPayloadOffset;
+    /* Insert the encrypted_client_hello xtn and coalesce. */
+    rv = tls13_EncryptClientHello(ss, &aadItem, &encodedChInner, echPayload);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    sslBuffer_Clear(&echXtn);
+    sslBuffer_Clear(&chInner);
+    sslBuffer_Clear(&encodedChInner);
+    sslBuffer_Clear(&paddingChInner);
+    sslBuffer_Clear(&chInnerXtns);
+    sslBuffer_Clear(&pskXtn);
+    return SECSuccess;
+
+loser:
+    sslBuffer_Clear(&chInner);
+    sslBuffer_Clear(&encodedChInner);
+    sslBuffer_Clear(&paddingChInner);
+    sslBuffer_Clear(&chInnerXtns);
+    sslBuffer_Clear(&pskXtn);
+    PORT_Assert(PORT_GetError() != 0);
+    return SECFailure;
+}
+
+static SECStatus
+tls13_ComputeEchHelloRetryTranscript(sslSocket *ss, const PRUint8 *sh, unsigned int shLen, sslBuffer *out)
+{
+    SECStatus rv;
+    PRUint8 zeroedEchSignal[TLS13_ECH_SIGNAL_LEN] = { 0 };
+    sslBuffer *previousTranscript;
+
+    if (ss->sec.isServer) {
+        previousTranscript = &(ss->ssl3.hs.messages);
+    } else {
+        previousTranscript = &(ss->ssl3.hs.echInnerMessages);
+    }
+    /*
+     *  This segment calculates the hash of the Client Hello
+     *  TODO(djackson@mozilla.com) - Replace with existing function?
+     *  e.g. tls13_ReinjectHandshakeTranscript
+     *  TODO(djackson@mozilla.com) - Replace with streaming version
+     */
+    if (!ss->ssl3.hs.helloRetry || !ss->sec.isServer) {
+        /*
+        * This function can be called in three situations:
+        *    - By the server, prior to sending the HRR, when ECH was accepted
+        *    - By the client, after receiving the HRR, but before it knows whether ECH was accepted
+        *    - By the server, after accepting ECH and receiving CH2 when it needs to reconstruct the HRR
+        * In the first two situations, we need to include the message hash of inner ClientHello1 but don't
+        * want to alter the buffer containing the current transcript.
+        * In the last, the buffer already contains the message hash of inner ClientHello1.
+        */
+        SSL3Hashes hashes;
+        rv = tls13_ComputeHash(ss, &hashes, previousTranscript->buf, previousTranscript->len, tls13_GetHash(ss));
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        rv = sslBuffer_AppendNumber(out, ssl_hs_message_hash, 1);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        rv = sslBuffer_AppendNumber(out, hashes.len, 3);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        rv = sslBuffer_Append(out, hashes.u.raw, hashes.len);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+    } else {
+        rv = sslBuffer_AppendBuffer(out, previousTranscript);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+    }
+    /* Ensure the first ClientHello has been hashed. */
+    PR_ASSERT(out->len == tls13_GetHashSize(ss) + 4);
+    PRINT_BUF(100, (ss, "ECH Client Hello Message Hash", out->buf, out->len));
+    /* Message Header */
+    rv = sslBuffer_AppendNumber(out, ssl_hs_server_hello, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    /* Message Size */
+    rv = sslBuffer_AppendNumber(out, shLen, 3);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    /* Calculate where the HRR ECH Xtn Signal begins */
+    unsigned int absEchOffset;
+    if (ss->sec.isServer) {
+        /* We know the ECH HRR Xtn is last */
+        PORT_Assert(shLen >= TLS13_ECH_SIGNAL_LEN);
+        absEchOffset = shLen - TLS13_ECH_SIGNAL_LEN;
+    } else {
+        /* We parsed the offset earlier */
+        /* The result of pointer comparision is unspecified
+         * (and pointer arithemtic is undefined) if the pointers
+         * do not point to the same array or struct. That means these
+         * asserts cannot be relied on for correctness in compiled code,
+         * but may help the reader understand the requirements.
+         */
+        PORT_Assert(ss->xtnData.ech->hrrConfirmation > sh);
+        PORT_Assert(ss->xtnData.ech->hrrConfirmation < sh + shLen);
+        absEchOffset = ss->xtnData.ech->hrrConfirmation - sh;
+    }
+    PR_ASSERT(tls13_Debug_CheckXtnBegins(sh + absEchOffset - 4, ssl_tls13_encrypted_client_hello_xtn));
+    /* The HRR up to the ECH Xtn signal */
+    rv = sslBuffer_Append(out, sh, absEchOffset);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    rv = sslBuffer_Append(out, zeroedEchSignal, sizeof(zeroedEchSignal));
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    PR_ASSERT(absEchOffset + TLS13_ECH_SIGNAL_LEN <= shLen);
+    /* The remainder of the HRR */
+    rv = sslBuffer_Append(out, sh + absEchOffset + TLS13_ECH_SIGNAL_LEN, shLen - absEchOffset - TLS13_ECH_SIGNAL_LEN);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    PR_ASSERT(out->len == tls13_GetHashSize(ss) + 4 + shLen + 4);
+    return SECSuccess;
+loser:
+    sslBuffer_Clear(out);
+    return SECFailure;
+}
+
+static SECStatus
+tls13_ComputeEchServerHelloTranscript(sslSocket *ss, const PRUint8 *sh, unsigned int shLen, sslBuffer *out)
+{
+    SECStatus rv;
+    sslBuffer *chSource = ss->sec.isServer ? &ss->ssl3.hs.messages : &ss->ssl3.hs.echInnerMessages;
+    unsigned int offset = sizeof(SSL3ProtocolVersion) +
+                          SSL3_RANDOM_LENGTH - TLS13_ECH_SIGNAL_LEN;
+    PORT_Assert(sh && shLen > offset);
+    PORT_Assert(TLS13_ECH_SIGNAL_LEN <= SSL3_RANDOM_LENGTH);
+
+    /* TODO(djackson@mozilla.com) - Replace with streaming version */
+
+    rv = sslBuffer_AppendBuffer(out, chSource);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Re-create the message header. */
+    rv = sslBuffer_AppendNumber(out, ssl_hs_server_hello, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = sslBuffer_AppendNumber(out, shLen, 3);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Copy the version and 24B of server_random. */
+    rv = sslBuffer_Append(out, sh, offset);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Zero the signal placeholder. */
+    rv = sslBuffer_AppendNumber(out, 0, TLS13_ECH_SIGNAL_LEN);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    offset += TLS13_ECH_SIGNAL_LEN;
+
+    /* Use the remainder of SH. */
+    rv = sslBuffer_Append(out, &sh[offset], shLen - offset);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    sslBuffer_Clear(&ss->ssl3.hs.messages);
+    sslBuffer_Clear(&ss->ssl3.hs.echInnerMessages);
+    return SECSuccess;
+loser:
+    sslBuffer_Clear(&ss->ssl3.hs.messages);
+    sslBuffer_Clear(&ss->ssl3.hs.echInnerMessages);
+    sslBuffer_Clear(out);
+    return SECFailure;
+}
+
+/* Compute the ECH signal using the transcript (up to, including)
+ * ServerHello. The server sources this transcript prefix from
+ * ss->ssl3.hs.messages, as it never uses ss->ssl3.hs.echInnerMessages.
+ * The client uses the inner transcript, echInnerMessages. */
+SECStatus
+tls13_ComputeEchSignal(sslSocket *ss, PRBool isHrr, const PRUint8 *sh, unsigned int shLen, PRUint8 *out)
+{
+    SECStatus rv;
+    sslBuffer confMsgs = SSL_BUFFER_EMPTY;
+    SSL3Hashes hashes;
+    PK11SymKey *echSecret = NULL;
+
+    const char *hkdfInfo = isHrr ? kHkdfInfoEchHrrConfirm : kHkdfInfoEchConfirm;
+    const size_t hkdfInfoLen = strlen(hkdfInfo);
+
+    PRINT_BUF(100, (ss, "ECH Server Hello", sh, shLen));
+
+    if (isHrr) {
+        rv = tls13_ComputeEchHelloRetryTranscript(ss, sh, shLen, &confMsgs);
+    } else {
+        rv = tls13_ComputeEchServerHelloTranscript(ss, sh, shLen, &confMsgs);
+    }
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    PRINT_BUF(100, (ss, "ECH Transcript", confMsgs.buf, confMsgs.len));
+    rv = tls13_ComputeHash(ss, &hashes, confMsgs.buf, confMsgs.len,
+                           tls13_GetHash(ss));
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    PRINT_BUF(100, (ss, "ECH Transcript Hash", &hashes.u, hashes.len));
+    rv = tls13_DeriveEchSecret(ss, &echSecret);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    rv = tls13_HkdfExpandLabelRaw(echSecret, tls13_GetHash(ss), hashes.u.raw,
+                                  hashes.len, hkdfInfo, hkdfInfoLen, ss->protocolVariant,
+                                  out, TLS13_ECH_SIGNAL_LEN);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    SSL_TRC(50, ("%d: TLS13[%d]: %s computed ECH signal", SSL_GETPID(), ss->fd, SSL_ROLE(ss)));
+    PRINT_BUF(50, (ss, "Computed ECH Signal", out, TLS13_ECH_SIGNAL_LEN));
+    PK11_FreeSymKey(echSecret);
+    sslBuffer_Clear(&confMsgs);
+    return SECSuccess;
+
+loser:
+    PK11_FreeSymKey(echSecret);
+    sslBuffer_Clear(&confMsgs);
+    return SECFailure;
+}
+
+/* Ech Secret is HKDF-Extract(0, ClientHelloInner.random) where 
+   "0" is a string of Hash.len bytes of value 0. */
+SECStatus
+tls13_DeriveEchSecret(const sslSocket *ss, PK11SymKey **output)
+{
+    SECStatus rv;
+    PK11SlotInfo *slot = NULL;
+    PK11SymKey *crKey = NULL;
+    SECItem rawKey;
+    const unsigned char *client_random = ss->sec.isServer ? ss->ssl3.hs.client_random : ss->ssl3.hs.client_inner_random;
+    PRINT_BUF(50, (ss, "Client Random for ECH", client_random, SSL3_RANDOM_LENGTH));
+    /* We need a SECItem */
+    rv = SECITEM_MakeItem(NULL, &rawKey, client_random, SSL3_RANDOM_LENGTH);
+    if (rv != SECSuccess) {
+        goto cleanup;
+    }
+    /* We need a slot*/
+    slot = PK11_GetBestSlot(CKM_HKDF_DERIVE, NULL);
+    if (!slot) {
+        rv = SECFailure;
+        goto cleanup;
+    }
+    /* We import the key */
+    crKey = PK11_ImportDataKey(slot, CKM_HKDF_DERIVE, PK11_OriginUnwrap,
+                               CKA_DERIVE, &rawKey, NULL);
+    if (crKey == NULL) {
+        rv = SECFailure;
+        goto cleanup;
+    }
+    /* NULL will be expanded to 0s of hash length */
+    rv = tls13_HkdfExtract(NULL, crKey, tls13_GetHash(ss), output);
+    if (rv != SECSuccess) {
+        goto cleanup;
+    }
+    SSL_TRC(50, ("%d: TLS13[%d]: ECH Confirmation Key Derived.",
+                 SSL_GETPID(), ss->fd));
+    PRINT_KEY(50, (NULL, "ECH Confirmation Key", *output));
+cleanup:
+    SECITEM_ZfreeItem(&rawKey, PR_FALSE);
+    if (slot) {
+        PK11_FreeSlot(slot);
+    }
+    if (crKey) {
+        PK11_FreeSymKey(crKey);
+    }
+    if (rv != SECSuccess && *output) {
+        PK11_FreeSymKey(*output);
+        *output = NULL;
+    }
+    return rv;
+}
+
+/* Called just prior to padding the CH. Use the size of the CH to estimate
+ * the size of a corresponding ECH extension, then add it to the buffer. */
+SECStatus
+tls13_MaybeGreaseEch(sslSocket *ss, const sslBuffer *preamble, sslBuffer *buf)
+{
+    SECStatus rv;
+    sslBuffer chInnerXtns = SSL_BUFFER_EMPTY;
+    sslBuffer encodedCh = SSL_BUFFER_EMPTY;
+    sslBuffer greaseBuf = SSL_BUFFER_EMPTY;
+    unsigned int payloadLen;
+    HpkeAeadId aead;
+    PK11SlotInfo *slot = NULL;
+    PK11SymKey *hmacPrk = NULL;
+    PK11SymKey *derivedData = NULL;
+    SECItem *rawData;
+    CK_HKDF_PARAMS params;
+    SECItem paramsi;
+    /* 1B aead determinant (don't send), 1B config_id, 32B enc, payload */
+    PR_ASSERT(!ss->sec.isServer);
+    const int kNonPayloadLen = 34;
+
+    if (!ss->opt.enableTls13GreaseEch || ss->ssl3.hs.echHpkeCtx) {
+        return SECSuccess;
+    }
+
+    if (ss->vrange.max < SSL_LIBRARY_VERSION_TLS_1_3 ||
+        IS_DTLS(ss)) {
+        return SECSuccess;
+    }
+
+    /* In draft-09, CH2 sends exactly the same GREASE ECH extension. */
+    if (ss->ssl3.hs.helloRetry) {
+        return ssl3_EmplaceExtension(ss, buf, ssl_tls13_encrypted_client_hello_xtn,
+                                     ss->ssl3.hs.greaseEchBuf.buf,
+                                     ss->ssl3.hs.greaseEchBuf.len, PR_TRUE);
+    }
+
+    /* Compress the extensions for payload length. */
+    rv = tls13_ConstructInnerExtensionsFromOuter(ss, buf, &chInnerXtns,
+                                                 NULL, PR_TRUE);
+    if (rv != SECSuccess) {
+        goto loser; /* Code set */
+    }
+    rv = tls13_EncodeClientHelloInner(ss, preamble, &chInnerXtns, &encodedCh);
+    if (rv != SECSuccess) {
+        goto loser; /* Code set */
+    }
+    rv = tls13_PadChInner(&encodedCh, ss->ssl3.hs.greaseEchSize, strlen(ss->url));
+
+    payloadLen = encodedCh.len;
+    payloadLen += TLS13_ECH_AEAD_TAG_LEN; /* Aead tag */
+
+    /* HMAC-Expand to get something that will pass for ciphertext. */
+    slot = PK11_GetBestSlot(CKM_HKDF_DERIVE, NULL);
+    if (!slot) {
+        goto loser;
+    }
+
+    hmacPrk = PK11_KeyGen(slot, CKM_HKDF_DATA, NULL, SHA256_LENGTH, NULL);
+    if (!hmacPrk) {
+        goto loser;
+    }
+
+    params.bExtract = CK_FALSE;
+    params.bExpand = CK_TRUE;
+    params.prfHashMechanism = CKM_SHA256;
+    params.pInfo = NULL;
+    params.ulInfoLen = 0;
+    paramsi.data = (unsigned char *)&params;
+    paramsi.len = sizeof(params);
+    derivedData = PK11_DeriveWithFlags(hmacPrk, CKM_HKDF_DATA,
+                                       &paramsi, CKM_HKDF_DATA,
+                                       CKA_DERIVE, kNonPayloadLen + payloadLen,
+                                       CKF_VERIFY);
+    if (!derivedData) {
+        goto loser;
+    }
+
+    rv = PK11_ExtractKeyValue(derivedData);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rawData = PK11_GetKeyData(derivedData);
+    if (!rawData) {
+        goto loser;
+    }
+    PORT_Assert(rawData->len == kNonPayloadLen + payloadLen);
+
+    /* struct {
+       HpkeSymmetricCipherSuite cipher_suite; // kdf_id, aead_id
+       PRUint8 config_id;
+       opaque enc<1..2^16-1>;
+       opaque payload<1..2^16-1>;
+    } ClientECH; */
+
+    rv = sslBuffer_AppendNumber(&greaseBuf, ech_xtn_type_outer, 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+    /* Only support SHA256. */
+    rv = sslBuffer_AppendNumber(&greaseBuf, HpkeKdfHkdfSha256, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* HpkeAeadAes128Gcm = 1, HpkeAeadChaCha20Poly1305 = 3, */
+    aead = (rawData->data[0] & 1) ? HpkeAeadAes128Gcm : HpkeAeadChaCha20Poly1305;
+    rv = sslBuffer_AppendNumber(&greaseBuf, aead, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* config_id */
+    rv = sslBuffer_AppendNumber(&greaseBuf, rawData->data[1], 1);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* enc len is fixed 32B for X25519. */
+    rv = sslBuffer_AppendVariable(&greaseBuf, &rawData->data[2], 32, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    rv = sslBuffer_AppendVariable(&greaseBuf, &rawData->data[kNonPayloadLen], payloadLen, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Mark ECH as advertised so that we can validate any response.
+     * We'll use echHpkeCtx to determine if we sent real or GREASE ECH. */
+    rv = ssl3_EmplaceExtension(ss, buf, ssl_tls13_encrypted_client_hello_xtn,
+                               greaseBuf.buf, greaseBuf.len, PR_TRUE);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* Stash the GREASE ECH extension - in the case of HRR, CH2 must echo it. */
+    ss->ssl3.hs.greaseEchBuf = greaseBuf;
+
+    sslBuffer_Clear(&chInnerXtns);
+    sslBuffer_Clear(&encodedCh);
+    PK11_FreeSymKey(hmacPrk);
+    PK11_FreeSymKey(derivedData);
+    PK11_FreeSlot(slot);
+    return SECSuccess;
+
+loser:
+    sslBuffer_Clear(&chInnerXtns);
+    sslBuffer_Clear(&encodedCh);
+    PK11_FreeSymKey(hmacPrk);
+    PK11_FreeSymKey(derivedData);
+    if (slot) {
+        PK11_FreeSlot(slot);
+    }
+    return SECFailure;
+}
+
+SECStatus
+tls13_MaybeHandleEch(sslSocket *ss, const PRUint8 *msg, PRUint32 msgLen, SECItem *sidBytes,
+                     SECItem *comps, SECItem *cookieBytes, SECItem *suites, SECItem **echInner)
+{
+    SECStatus rv;
+    SECItem *tmpEchInner = NULL;
+    PRUint8 *b;
+    PRUint32 length;
+    TLSExtension *echExtension;
+    TLSExtension *versionExtension;
+    PORT_Assert(!ss->ssl3.hs.echAccepted);
+    SECItem tmpSid = { siBuffer, NULL, 0 };
+    SECItem tmpCookie = { siBuffer, NULL, 0 };
+    SECItem tmpSuites = { siBuffer, NULL, 0 };
+    SECItem tmpComps = { siBuffer, NULL, 0 };
+
+    echExtension = ssl3_FindExtension(ss, ssl_tls13_encrypted_client_hello_xtn);
+    if (echExtension) {
+        rv = tls13_ServerHandleOuterEchXtn(ss, &ss->xtnData, &echExtension->data);
+        if (rv != SECSuccess) {
+            goto loser; /* code set, alert sent. */
+        }
+        rv = tls13_MaybeAcceptEch(ss, sidBytes, msg, msgLen, &tmpEchInner);
+        if (rv != SECSuccess) {
+            goto loser; /* code set, alert sent. */
+        }
+    }
+    ss->ssl3.hs.preliminaryInfo |= ssl_preinfo_ech;
+
+    if (ss->ssl3.hs.echAccepted) {
+        PORT_Assert(tmpEchInner);
+        PORT_Assert(!PR_CLIST_IS_EMPTY(&ss->ssl3.hs.remoteExtensions));
+
+        /* Start over on ECHInner */
+        b = tmpEchInner->data;
+        length = tmpEchInner->len;
+        rv = ssl3_HandleClientHelloPreamble(ss, &b, &length, &tmpSid,
+                                            &tmpCookie, &tmpSuites, &tmpComps);
+        if (rv != SECSuccess) {
+            goto loser; /* code set, alert sent. */
+        }
+
+        versionExtension = ssl3_FindExtension(ss, ssl_tls13_supported_versions_xtn);
+        if (!versionExtension) {
+            FATAL_ERROR(ss, SSL_ERROR_UNSUPPORTED_VERSION, illegal_parameter);
+            goto loser;
+        }
+        rv = tls13_NegotiateVersion(ss, versionExtension);
+        if (rv != SECSuccess) {
+            /* code and alert set by tls13_NegotiateVersion */
+            goto loser;
+        }
+
+        *comps = tmpComps;
+        *cookieBytes = tmpCookie;
+        *sidBytes = tmpSid;
+        *suites = tmpSuites;
+        *echInner = tmpEchInner;
+    }
+    return SECSuccess;
+
+loser:
+    SECITEM_FreeItem(tmpEchInner, PR_TRUE);
+    PORT_Assert(PORT_GetError() != 0);
+    return SECFailure;
+}
+
+SECStatus
+tls13_MaybeHandleEchSignal(sslSocket *ss, const PRUint8 *sh, PRUint32 shLen, PRBool isHrr)
+{
+    SECStatus rv;
+    PRUint8 computed[TLS13_ECH_SIGNAL_LEN];
+    const PRUint8 *signal;
+    PORT_Assert(!ss->sec.isServer);
+
+    /* If !echHpkeCtx, we either didn't advertise or sent GREASE ECH. */
+    if (!ss->ssl3.hs.echHpkeCtx) {
+        SSL_TRC(50, ("%d: TLS13[%d]: client only sent GREASE ECH",
+                     SSL_GETPID(), ss->fd));
+        ss->ssl3.hs.preliminaryInfo |= ssl_preinfo_ech;
+        return SECSuccess;
+    }
+
+    if (isHrr) {
+        if (ss->xtnData.ech) {
+            signal = ss->xtnData.ech->hrrConfirmation;
+        } else {
+            SSL_TRC(50, ("%d: TLS13[%d]: client did not receive ECH Xtn from Server HRR",
+                         SSL_GETPID(), ss->fd));
+            signal = NULL;
+            ss->ssl3.hs.echAccepted = PR_FALSE;
+            ss->ssl3.hs.echDecided = PR_TRUE;
+        }
+    } else {
+        signal = &ss->ssl3.hs.server_random[SSL3_RANDOM_LENGTH - TLS13_ECH_SIGNAL_LEN];
+    }
+
+    PORT_Assert(ssl3_ExtensionAdvertised(ss, ssl_tls13_encrypted_client_hello_xtn));
+
+    /* Check ECH Confirmation for HRR ECH Xtn or ServerHello Random */
+    if (signal) {
+        rv = tls13_ComputeEchSignal(ss, isHrr, sh, shLen, computed);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+        PRINT_BUF(100, (ss, "Server Signal", signal, TLS13_ECH_SIGNAL_LEN));
+        PRBool new_decision = !NSS_SecureMemcmp(computed, signal, TLS13_ECH_SIGNAL_LEN);
+        /* Server can't change its mind on whether to accept ECH */
+        if (ss->ssl3.hs.echDecided && new_decision != ss->ssl3.hs.echAccepted) {
+            FATAL_ERROR(ss, SSL_ERROR_RX_MALFORMED_SERVER_HELLO, illegal_parameter);
+            return SECFailure;
+        }
+        ss->ssl3.hs.echAccepted = new_decision;
+        ss->ssl3.hs.echDecided = PR_TRUE;
+    }
+
+    ss->ssl3.hs.preliminaryInfo |= ssl_preinfo_ech;
+    if (ss->ssl3.hs.echAccepted) {
+        if (ss->version < SSL_LIBRARY_VERSION_TLS_1_3) {
+            FATAL_ERROR(ss, SSL_ERROR_RX_MALFORMED_SERVER_HELLO, illegal_parameter);
+            return SECFailure;
+        }
+        /* Server accepted, but sent an extension which was only advertised in the ClientHelloOuter */
+        if (ss->ssl3.hs.echInvalidExtension) {
+            (void)SSL3_SendAlert(ss, alert_fatal, unsupported_extension);
+            PORT_SetError(SSL_ERROR_RX_UNEXPECTED_EXTENSION);
+            return SECFailure;
+        }
+
+        /* Swap the advertised lists as we've accepted ECH. */
+        PRUint16 *tempArray = ss->xtnData.advertised;
+        PRUint16 tempNum = ss->xtnData.numAdvertised;
+
+        ss->xtnData.advertised = ss->xtnData.echAdvertised;
+        ss->xtnData.numAdvertised = ss->xtnData.echNumAdvertised;
+
+        ss->xtnData.echAdvertised = tempArray;
+        ss->xtnData.echNumAdvertised = tempNum;
+
+        /* |enc| must not be included in CH2.ClientECH. */
+        if (ss->ssl3.hs.helloRetry && ss->sec.isServer &&
+            ss->xtnData.ech->senderPubKey.len) {
+            ssl3_ExtSendAlert(ss, alert_fatal, illegal_parameter);
+            PORT_SetError(SSL_ERROR_BAD_2ND_CLIENT_HELLO);
+            return SECFailure;
+        }
+        ss->xtnData.negotiated[ss->xtnData.numNegotiated++] = ssl_tls13_encrypted_client_hello_xtn;
+
+        /* Only overwrite client_random with client_inner_random if CHInner was
+         *  succesfully used for handshake (NOT if HRR is received). */
+        if (!isHrr) {
+            PORT_Memcpy(ss->ssl3.hs.client_random, ss->ssl3.hs.client_inner_random, SSL3_RANDOM_LENGTH);
+        }
+    }
+    /* If rejected, leave echHpkeCtx and echPublicName for rejection paths. */
+    ssl3_CoalesceEchHandshakeHashes(ss);
+    SSL_TRC(3, ("%d: TLS13[%d]: ECH %s accepted by server",
+                SSL_GETPID(), ss->fd, ss->ssl3.hs.echAccepted ? "is" : "is not"));
+    return SECSuccess;
+}
+
+static SECStatus
+tls13_UnencodeChInner(sslSocket *ss, const SECItem *sidBytes, SECItem **echInner)
+{
+    SECStatus rv;
+    sslReadBuffer outerExtensionsList;
+    sslReadBuffer tmpReadBuf;
+    sslBuffer unencodedChInner = SSL_BUFFER_EMPTY;
+    PRCList *outerCursor;
+    PRCList *innerCursor;
+    PRBool outerFound;
+    PRUint32 xtnsOffset;
+    PRUint64 tmp;
+    PRUint8 *tmpB;
+    PRUint32 tmpLength;
+    sslReader chReader = SSL_READER((*echInner)->data, (*echInner)->len);
+    PORT_Assert(!PR_CLIST_IS_EMPTY(&ss->ssl3.hs.echOuterExtensions));
+    PORT_Assert(PR_CLIST_IS_EMPTY(&ss->ssl3.hs.remoteExtensions));
+    TLSExtension *echExtension;
+    int error = SSL_ERROR_INTERNAL_ERROR_ALERT;
+    int errDesc = internal_error;
+
+    PRINT_BUF(100, (ss, "ECH Inner", chReader.buf.buf, chReader.buf.len));
+
+    /* unencodedChInner := preamble, tmpReadBuf := encoded extensions. */
+    rv = tls13_CopyChPreamble(ss, &chReader, sidBytes, &unencodedChInner, &tmpReadBuf);
+    if (rv != SECSuccess) {
+        goto loser; /* code set */
+    }
+
+    /* Parse inner extensions into ss->ssl3.hs.remoteExtensions. */
+    tmpB = CONST_CAST(PRUint8, tmpReadBuf.buf);
+    rv = ssl3_ParseExtensions(ss, &tmpB, &tmpReadBuf.len);
+    if (rv != SECSuccess) {
+        goto loser; /* malformed, alert sent. */
+    }
+
+    echExtension = ssl3_FindExtension(ss, ssl_tls13_encrypted_client_hello_xtn);
+    if (!echExtension) {
+        error = SSL_ERROR_MISSING_ECH_EXTENSION;
+        errDesc = illegal_parameter;
+        goto alert_loser; /* Must have an inner Extension */
+    }
+    rv = tls13_ServerHandleInnerEchXtn(ss, &ss->xtnData, &echExtension->data);
+    if (rv != SECSuccess) {
+        goto loser; /* code set, alert sent. */
+    }
+
+    /* Exit early if there are no outer_extensions to decompress. */
+    if (!ssl3_FindExtension(ss, ssl_tls13_outer_extensions_xtn)) {
+        rv = sslBuffer_AppendVariable(&unencodedChInner, tmpReadBuf.buf, tmpReadBuf.len, 2);
+        if (rv != SECSuccess) {
+            goto loser;
+        }
+        sslBuffer_Clear(&unencodedChInner);
+        return SECSuccess;
+    }
+
+    /* Save room for uncompressed length. */
+    rv = sslBuffer_Skip(&unencodedChInner, 2, &xtnsOffset);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    /* For each inner extension: If not outer_extensions, copy it to the output.
+     * Else if outer_extensions, iterate the compressed extension list and append
+     * each full extension as contained in CHOuter. Compressed extensions must be
+     * contiguous, so decompress at the point at which outer_extensions appears. */
+    for (innerCursor = PR_NEXT_LINK(&ss->ssl3.hs.remoteExtensions);
+         innerCursor != &ss->ssl3.hs.remoteExtensions;
+         innerCursor = PR_NEXT_LINK(innerCursor)) {
+        TLSExtension *innerExtension = (TLSExtension *)innerCursor;
+        if (innerExtension->type != ssl_tls13_outer_extensions_xtn) {
+            SSL_TRC(10, ("%d: SSL3[%d]: copying inner extension of type %d and size %d directly", SSL_GETPID(),
+                         ss->fd, innerExtension->type, innerExtension->data.len));
+            rv = sslBuffer_AppendNumber(&unencodedChInner,
+                                        innerExtension->type, 2);
+            if (rv != SECSuccess) {
+                goto loser;
+            }
+            rv = sslBuffer_AppendVariable(&unencodedChInner,
+                                          innerExtension->data.data,
+                                          innerExtension->data.len, 2);
+            if (rv != SECSuccess) {
+                goto loser;
+            }
+            continue;
+        }
+
+        /* Decompress */
+        sslReader extensionRdr = SSL_READER(innerExtension->data.data,
+                                            innerExtension->data.len);
+        rv = sslRead_ReadVariable(&extensionRdr, 1, &outerExtensionsList);
+        if (rv != SECSuccess) {
+            SSL_TRC(10, ("%d: SSL3[%d]: ECH Outer Extensions has invalid size.",
+                         SSL_GETPID(), ss->fd));
+            error = SSL_ERROR_RX_MALFORMED_ECH_EXTENSION;
+            errDesc = illegal_parameter;
+            goto alert_loser;
+        }
+        if (SSL_READER_REMAINING(&extensionRdr) || (outerExtensionsList.len % 2) != 0 || !outerExtensionsList.len) {
+            SSL_TRC(10, ("%d: SSL3[%d]: ECH Outer Extensions has invalid size.",
+                         SSL_GETPID(), ss->fd));
+            error = SSL_ERROR_RX_MALFORMED_ECH_EXTENSION;
+            errDesc = illegal_parameter;
+            goto alert_loser;
+        }
+
+        outerCursor = &ss->ssl3.hs.echOuterExtensions;
+        sslReader compressedTypes = SSL_READER(outerExtensionsList.buf, outerExtensionsList.len);
+        while (SSL_READER_REMAINING(&compressedTypes)) {
+            outerFound = PR_FALSE;
+            rv = sslRead_ReadNumber(&compressedTypes, 2, &tmp);
+            if (rv != SECSuccess) {
+                SSL_TRC(10, ("%d: SSL3[%d]: ECH Outer Extensions has invalid contents.",
+                             SSL_GETPID(), ss->fd));
+                error = SSL_ERROR_RX_MALFORMED_ECH_EXTENSION;
+                errDesc = illegal_parameter;
+                goto alert_loser;
+            }
+            if (tmp == ssl_tls13_encrypted_client_hello_xtn ||
+                tmp == ssl_tls13_outer_extensions_xtn) {
+                SSL_TRC(10, ("%d: SSL3[%d]: ECH Outer Extensions contains an invalid reference.",
+                             SSL_GETPID(), ss->fd));
+                error = SSL_ERROR_RX_MALFORMED_ECH_EXTENSION;
+                errDesc = illegal_parameter;
+                goto alert_loser;
+            }
+            do {
+                const TLSExtension *candidate = (TLSExtension *)outerCursor;
+                /* Advance the outerCursor, we never consider the same xtn twice. */
+                outerCursor = PR_NEXT_LINK(outerCursor);
+                if (candidate->type == tmp) {
+                    outerFound = PR_TRUE;
+                    SSL_TRC(100, ("%d: SSL3[%d]: Decompressing ECH Inner Extension of type %d",
+                                  SSL_GETPID(), ss->fd, tmp));
+                    rv = sslBuffer_AppendNumber(&unencodedChInner,
+                                                candidate->type, 2);
+                    if (rv != SECSuccess) {
+                        goto loser;
+                    }
+                    rv = sslBuffer_AppendVariable(&unencodedChInner,
+                                                  candidate->data.data,
+                                                  candidate->data.len, 2);
+                    if (rv != SECSuccess) {
+                        goto loser;
+                    }
+                    break;
+                }
+            } while (outerCursor != &ss->ssl3.hs.echOuterExtensions);
+            if (!outerFound) {
+                SSL_TRC(10, ("%d: SSL3[%d]: ECH Outer Extensions has missing,"
+                             " out of order or duplicate references.",
+                             SSL_GETPID(), ss->fd));
+                error = SSL_ERROR_RX_MALFORMED_ECH_EXTENSION;
+                errDesc = illegal_parameter;
+                goto alert_loser;
+            }
+        }
+    }
+    ssl3_DestroyRemoteExtensions(&ss->ssl3.hs.echOuterExtensions);
+    ssl3_DestroyRemoteExtensions(&ss->ssl3.hs.remoteExtensions);
+
+    /* Correct the message and extensions sizes. */
+    rv = sslBuffer_InsertNumber(&unencodedChInner, xtnsOffset,
+                                unencodedChInner.len - xtnsOffset - 2, 2);
+    if (rv != SECSuccess) {
+        goto loser;
+    }
+
+    tmpB = &unencodedChInner.buf[xtnsOffset];
+    tmpLength = unencodedChInner.len - xtnsOffset;
+    rv = ssl3_ConsumeHandshakeNumber64(ss, &tmp, 2, &tmpB, &tmpLength);
+    if (rv != SECSuccess || tmpLength != tmp) {
+        error = SSL_ERROR_RX_MALFORMED_CLIENT_HELLO;
+        errDesc = internal_error;
+        goto alert_loser;
+    }
+
+    rv = ssl3_ParseExtensions(ss, &tmpB, &tmpLength);
+    if (rv != SECSuccess) {
+        goto loser; /* Error set and alert already sent */
+    }
+
+    SECITEM_FreeItem(*echInner, PR_FALSE);
+    (*echInner)->data = unencodedChInner.buf;
+    (*echInner)->len = unencodedChInner.len;
+    return SECSuccess;
+alert_loser:
+    FATAL_ERROR(ss, error, errDesc);
+loser:
+    sslBuffer_Clear(&unencodedChInner);
+    return SECFailure;
+}
+
+SECStatus
+tls13_MaybeAcceptEch(sslSocket *ss, const SECItem *sidBytes, const PRUint8 *chOuter,
+                     unsigned int chOuterLen, SECItem **chInner)
+{
+    SECStatus rv;
+    SECItem outer = { siBuffer, CONST_CAST(PRUint8, chOuter), chOuterLen };
+    SECItem *decryptedChInner = NULL;
+    SECItem outerAAD = { siBuffer, NULL, 0 };
+    SECItem cookieData = { siBuffer, NULL, 0 };
+    sslEchCookieData echData;
+    sslEchConfig *candidate = NULL; /* non-owning */
+    TLSExtension *hrrXtn;
+    PRBool previouslyOfferedEch;
+
+    if (!ss->xtnData.ech || ss->xtnData.ech->receivedInnerXtn) {
+        ss->ssl3.hs.echDecided = PR_TRUE;
+        return SECSuccess;
+    }
+
+    PORT_Assert(ss->xtnData.ech->innerCh.data);
+
+    if (ss->ssl3.hs.helloRetry) {
+        ss->ssl3.hs.echDecided = PR_TRUE;
+        PORT_Assert(!ss->ssl3.hs.echHpkeCtx);
+        hrrXtn = ssl3_FindExtension(ss, ssl_tls13_cookie_xtn);
+        if (!hrrXtn) {
+            /* If the client doesn't echo cookie, we can't decrypt. */
+            return SECSuccess;
+        }
+
+        PORT_Assert(!ss->ssl3.hs.echHpkeCtx);
+
+        PRUint8 *tmp = hrrXtn->data.data;
+        PRUint32 len = hrrXtn->data.len;
+        rv = ssl3_ExtConsumeHandshakeVariable(ss, &cookieData, 2,
+                                              &tmp, &len);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+
+        /* Extract ECH info without restoring hash state. If there's
+         * something wrong with the cookie, continue without ECH
+         * and let HRR code handle the problem. */
+        rv = tls13_HandleHrrCookie(ss, cookieData.data, cookieData.len,
+                                   NULL, NULL, &previouslyOfferedEch, &echData, PR_FALSE);
+        if (rv != SECSuccess) {
+            return SECSuccess;
+        }
+
+        ss->ssl3.hs.echHpkeCtx = echData.hpkeCtx;
+
+        const PRUint8 greaseConstant[TLS13_ECH_SIGNAL_LEN] = { 0 };
+        ss->ssl3.hs.echAccepted = previouslyOfferedEch &&
+                                  !NSS_SecureMemcmp(greaseConstant, echData.signal, TLS13_ECH_SIGNAL_LEN);
+
+        if (echData.configId != ss->xtnData.ech->configId ||
+            echData.kdfId != ss->xtnData.ech->kdfId ||
+            echData.aeadId != ss->xtnData.ech->aeadId) {
+            FATAL_ERROR(ss, SSL_ERROR_BAD_2ND_CLIENT_HELLO,
+                        illegal_parameter);
+            return SECFailure;
+        }
+
+        if (!ss->ssl3.hs.echHpkeCtx) {
+            return SECSuccess;
+        }
+    }
+
+    if (ss->ssl3.hs.echDecided && !ss->ssl3.hs.echAccepted) {
+        /* We don't change our mind */
+        return SECSuccess;
+    }
+    /* Regardless of where we return, the outcome is decided */
+    ss->ssl3.hs.echDecided = PR_TRUE;
+
+    /* Cookie data was good, proceed with ECH. */
+    rv = tls13_GetMatchingEchConfigs(ss, ss->xtnData.ech->kdfId, ss->xtnData.ech->aeadId,
+                                     ss->xtnData.ech->configId, candidate, &candidate);
+    if (rv != SECSuccess) {
+        FATAL_ERROR(ss, SEC_ERROR_LIBRARY_FAILURE, internal_error);
+        return SECFailure;
+    }
+
+    if (candidate) {
+        rv = tls13_ServerMakeChOuterAAD(ss, chOuter, chOuterLen, &outerAAD);
+        if (rv != SECSuccess) {
+            return SECFailure;
+        }
+    }
+
+    while (candidate) {
+        rv = tls13_OpenClientHelloInner(ss, &outer, &outerAAD, candidate, &decryptedChInner);
+        if (rv != SECSuccess) {
+            /* Get the next matching config */
+            rv = tls13_GetMatchingEchConfigs(ss, ss->xtnData.ech->kdfId, ss->xtnData.ech->aeadId,
+                                             ss->xtnData.ech->configId, candidate, &candidate);
+            if (rv != SECSuccess) {
+                FATAL_ERROR(ss, SEC_ERROR_LIBRARY_FAILURE, internal_error);
+                SECITEM_FreeItem(&outerAAD, PR_FALSE);
+                return SECFailure;
+            }
+            continue;
+        }
+        break;
+    }
+    SECITEM_FreeItem(&outerAAD, PR_FALSE);
+
+    if (rv != SECSuccess || !decryptedChInner) {
+        if (ss->ssl3.hs.helloRetry) {
+            FATAL_ERROR(ss, SSL_ERROR_RX_MALFORMED_ECH_EXTENSION, decrypt_error);
+            return SECFailure;
+        } else {
+            /* Send retry_configs (if we have any) when we fail to decrypt or
+            * found no candidates. This does *not* count as negotiating ECH. */
+            return ssl3_RegisterExtensionSender(ss, &ss->xtnData,
+                                                ssl_tls13_encrypted_client_hello_xtn,
+                                                tls13_ServerSendEchXtn);
+        }
+    }
+
+    SSL_TRC(20, ("%d: TLS13[%d]: Successfully opened ECH inner CH",
+                 SSL_GETPID(), ss->fd));
+    PRINT_BUF(50, (ss, "Compressed CHInner", decryptedChInner->data,
+                   decryptedChInner->len));
+
+    ss->ssl3.hs.echAccepted = PR_TRUE;
+
+    /* Stash the CHOuter extensions. They're not yet handled (only parsed). If
+     * the CHInner contains outer_extensions_xtn, we'll need to reference them. */
+    ssl3_MoveRemoteExtensions(&ss->ssl3.hs.echOuterExtensions, &ss->ssl3.hs.remoteExtensions);
+
+    rv = tls13_UnencodeChInner(ss, sidBytes, &decryptedChInner);
+    if (rv != SECSuccess) {
+        SECITEM_FreeItem(decryptedChInner, PR_TRUE);
+        return SECFailure; /* code set */
+    }
+    PRINT_BUF(50, (ss, "Uncompressed CHInner", decryptedChInner->data,
+                   decryptedChInner->len));
+    *chInner = decryptedChInner;
+    return SECSuccess;
+}
+
+SECStatus
+tls13_WriteServerEchSignal(sslSocket *ss, PRUint8 *sh, unsigned int shLen)
+{
+    SECStatus rv;
+    PRUint8 signal[TLS13_ECH_SIGNAL_LEN];
+    PRUint8 *msg_random = &sh[sizeof(SSL3ProtocolVersion)];
+
+    PORT_Assert(shLen > sizeof(SSL3ProtocolVersion) + SSL3_RANDOM_LENGTH);
+    PORT_Assert(ss->version >= SSL_LIBRARY_VERSION_TLS_1_3);
+
+    rv = tls13_ComputeEchSignal(ss, PR_FALSE, sh, shLen, signal);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    PRUint8 *dest = &msg_random[SSL3_RANDOM_LENGTH - TLS13_ECH_SIGNAL_LEN];
+    PORT_Memcpy(dest, signal, TLS13_ECH_SIGNAL_LEN);
+
+    /* Keep the socket copy consistent. */
+    PORT_Assert(0 == memcmp(msg_random, &ss->ssl3.hs.server_random, SSL3_RANDOM_LENGTH - TLS13_ECH_SIGNAL_LEN));
+    dest = &ss->ssl3.hs.server_random[SSL3_RANDOM_LENGTH - TLS13_ECH_SIGNAL_LEN];
+    PORT_Memcpy(dest, signal, TLS13_ECH_SIGNAL_LEN);
+
+    return SECSuccess;
+}
+
+SECStatus
+tls13_WriteServerEchHrrSignal(sslSocket *ss, PRUint8 *sh, unsigned int shLen)
+{
+    SECStatus rv;
+    PR_ASSERT(shLen >= 4 + TLS13_ECH_SIGNAL_LEN);
+    /* We put the HRR ECH extension last. */
+    PRUint8 *placeholder_location = sh + shLen - TLS13_ECH_SIGNAL_LEN;
+    /* Defensive check that we are overwriting the contents of the right extension */
+    PR_ASSERT(tls13_Debug_CheckXtnBegins(placeholder_location - 4, ssl_tls13_encrypted_client_hello_xtn));
+    /* Calculate signal and overwrite */
+    rv = tls13_ComputeEchSignal(ss, PR_TRUE, sh, shLen, placeholder_location);
+    if (rv != SECSuccess) {
+        return SECFailure;
+    }
+    /* Free HRR GREASE/accept_confirmation value, it MUST be restored from
+     * cookie when handling CH2 after HRR. */
+    sslBuffer_Clear(&ss->ssl3.hs.greaseEchBuf);
+    return SECSuccess;
+}
\ No newline at end of file