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-rw-r--r--ssh-ecdsa-sk.c468
1 files changed, 468 insertions, 0 deletions
diff --git a/ssh-ecdsa-sk.c b/ssh-ecdsa-sk.c
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+++ b/ssh-ecdsa-sk.c
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+/* $OpenBSD: ssh-ecdsa-sk.c,v 1.17 2022/10/28 00:44:44 djm Exp $ */
+/*
+ * Copyright (c) 2000 Markus Friedl. All rights reserved.
+ * Copyright (c) 2010 Damien Miller. All rights reserved.
+ * Copyright (c) 2019 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/* #define DEBUG_SK 1 */
+
+#include "includes.h"
+
+#include <sys/types.h>
+
+#ifdef WITH_OPENSSL
+#include <openssl/bn.h>
+#include <openssl/ec.h>
+#include <openssl/ecdsa.h>
+#include <openssl/evp.h>
+#endif
+
+#include <string.h>
+#include <stdio.h> /* needed for DEBUG_SK only */
+
+#include "openbsd-compat/openssl-compat.h"
+
+#include "sshbuf.h"
+#include "ssherr.h"
+#include "digest.h"
+#define SSHKEY_INTERNAL
+#include "sshkey.h"
+
+#ifndef OPENSSL_HAS_ECC
+/* ARGSUSED */
+int
+ssh_ecdsa_sk_verify(const struct sshkey *key,
+ const u_char *signature, size_t signaturelen,
+ const u_char *data, size_t datalen, u_int compat,
+ struct sshkey_sig_details **detailsp)
+{
+ return SSH_ERR_FEATURE_UNSUPPORTED;
+}
+#else /* OPENSSL_HAS_ECC */
+
+/* Reuse some ECDSA internals */
+extern struct sshkey_impl_funcs sshkey_ecdsa_funcs;
+
+static void
+ssh_ecdsa_sk_cleanup(struct sshkey *k)
+{
+ sshkey_sk_cleanup(k);
+ sshkey_ecdsa_funcs.cleanup(k);
+}
+
+static int
+ssh_ecdsa_sk_equal(const struct sshkey *a, const struct sshkey *b)
+{
+ if (!sshkey_sk_fields_equal(a, b))
+ return 0;
+ if (!sshkey_ecdsa_funcs.equal(a, b))
+ return 0;
+ return 1;
+}
+
+static int
+ssh_ecdsa_sk_serialize_public(const struct sshkey *key, struct sshbuf *b,
+ enum sshkey_serialize_rep opts)
+{
+ int r;
+
+ if ((r = sshkey_ecdsa_funcs.serialize_public(key, b, opts)) != 0)
+ return r;
+ if ((r = sshkey_serialize_sk(key, b)) != 0)
+ return r;
+
+ return 0;
+}
+
+static int
+ssh_ecdsa_sk_serialize_private(const struct sshkey *key, struct sshbuf *b,
+ enum sshkey_serialize_rep opts)
+{
+ int r;
+
+ if (!sshkey_is_cert(key)) {
+ if ((r = sshkey_ecdsa_funcs.serialize_public(key,
+ b, opts)) != 0)
+ return r;
+ }
+ if ((r = sshkey_serialize_private_sk(key, b)) != 0)
+ return r;
+
+ return 0;
+}
+
+static int
+ssh_ecdsa_sk_copy_public(const struct sshkey *from, struct sshkey *to)
+{
+ int r;
+
+ if ((r = sshkey_ecdsa_funcs.copy_public(from, to)) != 0)
+ return r;
+ if ((r = sshkey_copy_public_sk(from, to)) != 0)
+ return r;
+ return 0;
+}
+
+static int
+ssh_ecdsa_sk_deserialize_public(const char *ktype, struct sshbuf *b,
+ struct sshkey *key)
+{
+ int r;
+
+ if ((r = sshkey_ecdsa_funcs.deserialize_public(ktype, b, key)) != 0)
+ return r;
+ if ((r = sshkey_deserialize_sk(b, key)) != 0)
+ return r;
+ return 0;
+}
+
+static int
+ssh_ecdsa_sk_deserialize_private(const char *ktype, struct sshbuf *b,
+ struct sshkey *key)
+{
+ int r;
+
+ if (!sshkey_is_cert(key)) {
+ if ((r = sshkey_ecdsa_funcs.deserialize_public(ktype,
+ b, key)) != 0)
+ return r;
+ }
+ if ((r = sshkey_private_deserialize_sk(b, key)) != 0)
+ return r;
+
+ return 0;
+}
+
+/*
+ * Check FIDO/W3C webauthn signatures clientData field against the expected
+ * format and prepare a hash of it for use in signature verification.
+ *
+ * webauthn signatures do not sign the hash of the message directly, but
+ * instead sign a JSON-like "clientData" wrapper structure that contains the
+ * message hash along with a other information.
+ *
+ * Fortunately this structure has a fixed format so it is possible to verify
+ * that the hash of the signed message is present within the clientData
+ * structure without needing to implement any JSON parsing.
+ */
+static int
+webauthn_check_prepare_hash(const u_char *data, size_t datalen,
+ const char *origin, const struct sshbuf *wrapper,
+ uint8_t flags, const struct sshbuf *extensions,
+ u_char *msghash, size_t msghashlen)
+{
+ int r = SSH_ERR_INTERNAL_ERROR;
+ struct sshbuf *chall = NULL, *m = NULL;
+
+ if ((m = sshbuf_new()) == NULL ||
+ (chall = sshbuf_from(data, datalen)) == NULL) {
+ r = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ /*
+ * Ensure origin contains no quote character and that the flags are
+ * consistent with what we received
+ */
+ if (strchr(origin, '\"') != NULL ||
+ (flags & 0x40) != 0 /* AD */ ||
+ ((flags & 0x80) == 0 /* ED */) != (sshbuf_len(extensions) == 0)) {
+ r = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+
+ /*
+ * Prepare the preamble to clientData that we expect, poking the
+ * challenge and origin into their canonical positions in the
+ * structure. The crossOrigin flag and any additional extension
+ * fields present are ignored.
+ */
+#define WEBAUTHN_0 "{\"type\":\"webauthn.get\",\"challenge\":\""
+#define WEBAUTHN_1 "\",\"origin\":\""
+#define WEBAUTHN_2 "\""
+ if ((r = sshbuf_put(m, WEBAUTHN_0, sizeof(WEBAUTHN_0) - 1)) != 0 ||
+ (r = sshbuf_dtourlb64(chall, m, 0)) != 0 ||
+ (r = sshbuf_put(m, WEBAUTHN_1, sizeof(WEBAUTHN_1) - 1)) != 0 ||
+ (r = sshbuf_put(m, origin, strlen(origin))) != 0 ||
+ (r = sshbuf_put(m, WEBAUTHN_2, sizeof(WEBAUTHN_2) - 1)) != 0)
+ goto out;
+#ifdef DEBUG_SK
+ fprintf(stderr, "%s: received origin: %s\n", __func__, origin);
+ fprintf(stderr, "%s: received clientData:\n", __func__);
+ sshbuf_dump(wrapper, stderr);
+ fprintf(stderr, "%s: expected clientData premable:\n", __func__);
+ sshbuf_dump(m, stderr);
+#endif
+ /* Check that the supplied clientData has the preamble we expect */
+ if ((r = sshbuf_cmp(wrapper, 0, sshbuf_ptr(m), sshbuf_len(m))) != 0)
+ goto out;
+
+ /* Prepare hash of clientData */
+ if ((r = ssh_digest_buffer(SSH_DIGEST_SHA256, wrapper,
+ msghash, msghashlen)) != 0)
+ goto out;
+
+ /* success */
+ r = 0;
+ out:
+ sshbuf_free(chall);
+ sshbuf_free(m);
+ return r;
+}
+
+/* ARGSUSED */
+static int
+ssh_ecdsa_sk_verify(const struct sshkey *key,
+ const u_char *sig, size_t siglen,
+ const u_char *data, size_t dlen, const char *alg, u_int compat,
+ struct sshkey_sig_details **detailsp)
+{
+ ECDSA_SIG *esig = NULL;
+ BIGNUM *sig_r = NULL, *sig_s = NULL;
+ u_char sig_flags;
+ u_char msghash[32], apphash[32], sighash[32];
+ u_int sig_counter;
+ int is_webauthn = 0, ret = SSH_ERR_INTERNAL_ERROR;
+ struct sshbuf *b = NULL, *sigbuf = NULL, *original_signed = NULL;
+ struct sshbuf *webauthn_wrapper = NULL, *webauthn_exts = NULL;
+ char *ktype = NULL, *webauthn_origin = NULL;
+ struct sshkey_sig_details *details = NULL;
+#ifdef DEBUG_SK
+ char *tmp = NULL;
+#endif
+
+ if (detailsp != NULL)
+ *detailsp = NULL;
+ if (key == NULL || key->ecdsa == NULL ||
+ sshkey_type_plain(key->type) != KEY_ECDSA_SK ||
+ sig == NULL || siglen == 0)
+ return SSH_ERR_INVALID_ARGUMENT;
+
+ if (key->ecdsa_nid != NID_X9_62_prime256v1)
+ return SSH_ERR_INTERNAL_ERROR;
+
+ /* fetch signature */
+ if ((b = sshbuf_from(sig, siglen)) == NULL)
+ return SSH_ERR_ALLOC_FAIL;
+ if ((details = calloc(1, sizeof(*details))) == NULL) {
+ ret = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if (sshbuf_get_cstring(b, &ktype, NULL) != 0) {
+ ret = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ if (strcmp(ktype, "webauthn-sk-ecdsa-sha2-nistp256@openssh.com") == 0)
+ is_webauthn = 1;
+ else if (strcmp(ktype, "sk-ecdsa-sha2-nistp256@openssh.com") != 0) {
+ ret = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ if (sshbuf_froms(b, &sigbuf) != 0 ||
+ sshbuf_get_u8(b, &sig_flags) != 0 ||
+ sshbuf_get_u32(b, &sig_counter) != 0) {
+ ret = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ if (is_webauthn) {
+ if (sshbuf_get_cstring(b, &webauthn_origin, NULL) != 0 ||
+ sshbuf_froms(b, &webauthn_wrapper) != 0 ||
+ sshbuf_froms(b, &webauthn_exts) != 0) {
+ ret = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ }
+ if (sshbuf_len(b) != 0) {
+ ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
+ goto out;
+ }
+
+ /* parse signature */
+ if (sshbuf_get_bignum2(sigbuf, &sig_r) != 0 ||
+ sshbuf_get_bignum2(sigbuf, &sig_s) != 0) {
+ ret = SSH_ERR_INVALID_FORMAT;
+ goto out;
+ }
+ if (sshbuf_len(sigbuf) != 0) {
+ ret = SSH_ERR_UNEXPECTED_TRAILING_DATA;
+ goto out;
+ }
+
+#ifdef DEBUG_SK
+ fprintf(stderr, "%s: data: (len %zu)\n", __func__, datalen);
+ /* sshbuf_dump_data(data, datalen, stderr); */
+ fprintf(stderr, "%s: sig_r: %s\n", __func__, (tmp = BN_bn2hex(sig_r)));
+ free(tmp);
+ fprintf(stderr, "%s: sig_s: %s\n", __func__, (tmp = BN_bn2hex(sig_s)));
+ free(tmp);
+ fprintf(stderr, "%s: sig_flags = 0x%02x, sig_counter = %u\n",
+ __func__, sig_flags, sig_counter);
+ if (is_webauthn) {
+ fprintf(stderr, "%s: webauthn origin: %s\n", __func__,
+ webauthn_origin);
+ fprintf(stderr, "%s: webauthn_wrapper:\n", __func__);
+ sshbuf_dump(webauthn_wrapper, stderr);
+ }
+#endif
+ if ((esig = ECDSA_SIG_new()) == NULL) {
+ ret = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if (!ECDSA_SIG_set0(esig, sig_r, sig_s)) {
+ ret = SSH_ERR_LIBCRYPTO_ERROR;
+ goto out;
+ }
+ sig_r = sig_s = NULL; /* transferred */
+
+ /* Reconstruct data that was supposedly signed */
+ if ((original_signed = sshbuf_new()) == NULL) {
+ ret = SSH_ERR_ALLOC_FAIL;
+ goto out;
+ }
+ if (is_webauthn) {
+ if ((ret = webauthn_check_prepare_hash(data, dlen,
+ webauthn_origin, webauthn_wrapper, sig_flags, webauthn_exts,
+ msghash, sizeof(msghash))) != 0)
+ goto out;
+ } else if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, data, dlen,
+ msghash, sizeof(msghash))) != 0)
+ goto out;
+ /* Application value is hashed before signature */
+ if ((ret = ssh_digest_memory(SSH_DIGEST_SHA256, key->sk_application,
+ strlen(key->sk_application), apphash, sizeof(apphash))) != 0)
+ goto out;
+#ifdef DEBUG_SK
+ fprintf(stderr, "%s: hashed application:\n", __func__);
+ sshbuf_dump_data(apphash, sizeof(apphash), stderr);
+ fprintf(stderr, "%s: hashed message:\n", __func__);
+ sshbuf_dump_data(msghash, sizeof(msghash), stderr);
+#endif
+ if ((ret = sshbuf_put(original_signed,
+ apphash, sizeof(apphash))) != 0 ||
+ (ret = sshbuf_put_u8(original_signed, sig_flags)) != 0 ||
+ (ret = sshbuf_put_u32(original_signed, sig_counter)) != 0 ||
+ (ret = sshbuf_putb(original_signed, webauthn_exts)) != 0 ||
+ (ret = sshbuf_put(original_signed, msghash, sizeof(msghash))) != 0)
+ goto out;
+ /* Signature is over H(original_signed) */
+ if ((ret = ssh_digest_buffer(SSH_DIGEST_SHA256, original_signed,
+ sighash, sizeof(sighash))) != 0)
+ goto out;
+ details->sk_counter = sig_counter;
+ details->sk_flags = sig_flags;
+#ifdef DEBUG_SK
+ fprintf(stderr, "%s: signed buf:\n", __func__);
+ sshbuf_dump(original_signed, stderr);
+ fprintf(stderr, "%s: signed hash:\n", __func__);
+ sshbuf_dump_data(sighash, sizeof(sighash), stderr);
+#endif
+
+ /* Verify it */
+ switch (ECDSA_do_verify(sighash, sizeof(sighash), esig, key->ecdsa)) {
+ case 1:
+ ret = 0;
+ break;
+ case 0:
+ ret = SSH_ERR_SIGNATURE_INVALID;
+ goto out;
+ default:
+ ret = SSH_ERR_LIBCRYPTO_ERROR;
+ goto out;
+ }
+ /* success */
+ if (detailsp != NULL) {
+ *detailsp = details;
+ details = NULL;
+ }
+ out:
+ explicit_bzero(&sig_flags, sizeof(sig_flags));
+ explicit_bzero(&sig_counter, sizeof(sig_counter));
+ explicit_bzero(msghash, sizeof(msghash));
+ explicit_bzero(sighash, sizeof(msghash));
+ explicit_bzero(apphash, sizeof(apphash));
+ sshkey_sig_details_free(details);
+ sshbuf_free(webauthn_wrapper);
+ sshbuf_free(webauthn_exts);
+ free(webauthn_origin);
+ sshbuf_free(original_signed);
+ sshbuf_free(sigbuf);
+ sshbuf_free(b);
+ ECDSA_SIG_free(esig);
+ BN_clear_free(sig_r);
+ BN_clear_free(sig_s);
+ free(ktype);
+ return ret;
+}
+
+static const struct sshkey_impl_funcs sshkey_ecdsa_sk_funcs = {
+ /* .size = */ NULL,
+ /* .alloc = */ NULL,
+ /* .cleanup = */ ssh_ecdsa_sk_cleanup,
+ /* .equal = */ ssh_ecdsa_sk_equal,
+ /* .ssh_serialize_public = */ ssh_ecdsa_sk_serialize_public,
+ /* .ssh_deserialize_public = */ ssh_ecdsa_sk_deserialize_public,
+ /* .ssh_serialize_private = */ ssh_ecdsa_sk_serialize_private,
+ /* .ssh_deserialize_private = */ ssh_ecdsa_sk_deserialize_private,
+ /* .generate = */ NULL,
+ /* .copy_public = */ ssh_ecdsa_sk_copy_public,
+ /* .sign = */ NULL,
+ /* .verify = */ ssh_ecdsa_sk_verify,
+};
+
+const struct sshkey_impl sshkey_ecdsa_sk_impl = {
+ /* .name = */ "sk-ecdsa-sha2-nistp256@openssh.com",
+ /* .shortname = */ "ECDSA-SK",
+ /* .sigalg = */ NULL,
+ /* .type = */ KEY_ECDSA_SK,
+ /* .nid = */ NID_X9_62_prime256v1,
+ /* .cert = */ 0,
+ /* .sigonly = */ 0,
+ /* .keybits = */ 256,
+ /* .funcs = */ &sshkey_ecdsa_sk_funcs,
+};
+
+const struct sshkey_impl sshkey_ecdsa_sk_cert_impl = {
+ /* .name = */ "sk-ecdsa-sha2-nistp256-cert-v01@openssh.com",
+ /* .shortname = */ "ECDSA-SK-CERT",
+ /* .sigalg = */ NULL,
+ /* .type = */ KEY_ECDSA_SK_CERT,
+ /* .nid = */ NID_X9_62_prime256v1,
+ /* .cert = */ 1,
+ /* .sigonly = */ 0,
+ /* .keybits = */ 256,
+ /* .funcs = */ &sshkey_ecdsa_sk_funcs,
+};
+
+const struct sshkey_impl sshkey_ecdsa_sk_webauthn_impl = {
+ /* .name = */ "webauthn-sk-ecdsa-sha2-nistp256@openssh.com",
+ /* .shortname = */ "ECDSA-SK",
+ /* .sigalg = */ NULL,
+ /* .type = */ KEY_ECDSA_SK,
+ /* .nid = */ NID_X9_62_prime256v1,
+ /* .cert = */ 0,
+ /* .sigonly = */ 1,
+ /* .keybits = */ 256,
+ /* .funcs = */ &sshkey_ecdsa_sk_funcs,
+};
+
+#endif /* OPENSSL_HAS_ECC */
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-04 12:47:54 +0000