1 files changed, 363 insertions, 0 deletions

diff --git a/src/tls/tls_fprint.c b/src/tls/tls_fprint.c
new file mode 100644
index 0000000..2bb7e21
--- /dev/null
+++ b/src/tls/tls_fprint.c
@@ -0,0 +1,363 @@
+/*++
+/* NAME
+/*	tls_fprint 3
+/* SUMMARY
+/*	Digests fingerprints and all that.
+/* SYNOPSIS
+/*	#include <tls.h>
+/*
+/*	char	*tls_serverid_digest(props, protomask, ciphers)
+/*	const TLS_CLIENT_START_PROPS *props;
+/*	long	protomask;
+/*	const char *ciphers;
+/*
+/*	char	*tls_digest_encode(md_buf, md_len)
+/*	const unsigned char *md_buf;
+/*	const char *md_len;
+/*
+/*	char	*tls_data_fprint(buf, len, mdalg)
+/*	const char *buf;
+/*	int	len;
+/*	const char *mdalg;
+/*
+/*	char	*tls_cert_fprint(peercert, mdalg)
+/*	X509	*peercert;
+/*	const char *mdalg;
+/*
+/*	char	*tls_pkey_fprint(peercert, mdalg)
+/*	X509	*peercert;
+/*	const char *mdalg;
+/* DESCRIPTION
+/*	tls_digest_encode() converts a binary message digest to a hex ASCII
+/*	format with ':' separators between each pair of hex digits.
+/*	The return value is dynamically allocated with mymalloc(),
+/*	and the caller must eventually free it with myfree().
+/*
+/*	tls_data_fprint() digests unstructured data, and encodes the digested
+/*	result via tls_digest_encode().  The return value is dynamically
+/*	allocated with mymalloc(), and the caller must eventually free it
+/*	with myfree().
+/*
+/*	tls_cert_fprint() returns a fingerprint of the the given
+/*	certificate using the requested message digest, formatted
+/*	with tls_digest_encode(). Panics if the
+/*	(previously verified) digest algorithm is not found. The return
+/*	value is dynamically allocated with mymalloc(), and the caller
+/*	must eventually free it with myfree().
+/*
+/*	tls_pkey_fprint() returns a public-key fingerprint; in all
+/*	other respects the function behaves as tls_cert_fprint().
+/*	The var_tls_bc_pkey_fprint variable enables an incorrect
+/*	algorithm that was used in Postfix versions 2.9.[0-5].
+/*	The return value is dynamically allocated with mymalloc(),
+/*	and the caller must eventually free it with myfree().
+/*
+/*	tls_serverid_digest() suffixes props->serverid computed by the SMTP
+/*	client with "&" plus a digest of additional parameters
+/*	needed to ensure that re-used sessions are more likely to
+/*	be reused and that they will satisfy all protocol and
+/*	security requirements.
+/*	The return value is dynamically allocated with mymalloc(),
+/*	and the caller must eventually free it with myfree().
+/*
+/*	Arguments:
+/* .IP peercert
+/*	Server or client X.509 certificate.
+/* .IP md_buf
+/*	The raw binary digest.
+/* .IP md_len
+/*	The digest length in bytes.
+/* .IP mdalg
+/*	Name of a message digest algorithm suitable for computing secure
+/*	(1st pre-image resistant) message digests of certificates. For now,
+/*	md5, sha1, or member of SHA-2 family if supported by OpenSSL.
+/* .IP buf
+/*	Input data for the message digest algorithm mdalg.
+/* .IP len
+/*	The length of the input data.
+/* .IP props
+/*	The client start properties for the session, which contains the
+/*	initial serverid from the SMTP client and the DANE verification
+/*	parameters.
+/* .IP protomask
+/*	The mask of protocol exclusions.
+/* .IP ciphers
+/*	The SSL client cipherlist.
+/* LICENSE
+/* .ad
+/* .fi
+/*	This software is free. You can do with it whatever you want.
+/*	The original author kindly requests that you acknowledge
+/*	the use of his software.
+/* AUTHOR(S)
+/*	Wietse Venema
+/*	IBM T.J. Watson Research
+/*	P.O. Box 704
+/*	Yorktown Heights, NY 10598, USA
+/*
+/*	Viktor Dukhovni
+/*--*/
+
+/* System library. */
+
+#include <sys_defs.h>
+#include <ctype.h>
+
+#ifdef USE_TLS
+#include <string.h>
+
+/* Utility library. */
+
+#include <msg.h>
+#include <mymalloc.h>
+#include <stringops.h>
+
+/* Global library. */
+
+#include <mail_params.h>
+
+/* TLS library. */
+
+#define TLS_INTERNAL
+#include <tls.h>
+
+/* Application-specific. */
+
+static const char hexcodes[] = "0123456789ABCDEF";
+
+#define checkok(ret)	(ok &= ((ret) ? 1 : 0))
+#define digest_data(p, l) checkok(EVP_DigestUpdate(mdctx, (char *)(p), (l)))
+#define digest_object(p) digest_data((p), sizeof(*(p)))
+#define digest_string(s) digest_data((s), strlen(s)+1)
+
+#define digest_dane(dane, memb) do { \
+	if ((dane)->memb != 0) \
+	    checkok(digest_tlsa_usage(mdctx, (dane)->memb, #memb)); \
+    } while (0)
+
+#define digest_tlsa_argv(tlsa, memb) do { \
+	if ((tlsa)->memb) { \
+	    digest_string(#memb); \
+	    for (dgst = (tlsa)->memb->argv; *dgst; ++dgst) \
+		digest_string(*dgst); \
+	} \
+    } while (0)
+
+/* digest_tlsa_usage - digest TA or EE match list sorted by alg and value */
+
+static int digest_tlsa_usage(EVP_MD_CTX * mdctx, TLS_TLSA *tlsa,
+			             const char *usage)
+{
+    char  **dgst;
+    int     ok = 1;
+
+    for (digest_string(usage); tlsa; tlsa = tlsa->next) {
+	digest_string(tlsa->mdalg);
+	digest_tlsa_argv(tlsa, pkeys);
+	digest_tlsa_argv(tlsa, certs);
+    }
+    return (ok);
+}
+
+/* tls_serverid_digest - suffix props->serverid with parameter digest */
+
+char   *tls_serverid_digest(const TLS_CLIENT_START_PROPS *props, long protomask,
+			            const char *ciphers)
+{
+    EVP_MD_CTX *mdctx;
+    const EVP_MD *md;
+    const char *mdalg;
+    unsigned char md_buf[EVP_MAX_MD_SIZE];
+    unsigned int md_len;
+    int     ok = 1;
+    int     i;
+    long    sslversion;
+    VSTRING *result;
+
+    /*
+     * Try to use sha256: our serverid choice should be strong enough to
+     * resist 2nd-preimage attacks with a difficulty comparable to that of
+     * DANE TLSA digests.  Failing that, we compute serverid digests with the
+     * default digest, but DANE requires sha256 and sha512, so if we must
+     * fall back to our default digest, DANE support won't be available.  We
+     * panic if the fallback algorithm is not available, as it was verified
+     * available in tls_client_init() and must not simply vanish.
+     */
+    if ((md = EVP_get_digestbyname(mdalg = "sha256")) == 0
+	&& (md = EVP_get_digestbyname(mdalg = props->mdalg)) == 0)
+	msg_panic("digest algorithm \"%s\" not found", mdalg);
+
+    /* Salt the session lookup key with the OpenSSL runtime version. */
+    sslversion = OpenSSL_version_num();
+
+    mdctx = EVP_MD_CTX_create();
+    checkok(EVP_DigestInit_ex(mdctx, md, NULL));
+    digest_string(props->helo ? props->helo : "");
+    digest_object(&sslversion);
+    digest_object(&protomask);
+    digest_string(ciphers);
+
+    /*
+     * All we get from the session cache is a single bit telling us whether
+     * the certificate is trusted or not, but we need to know whether the
+     * trust is CA-based (in that case we must do name checks) or whether it
+     * is a direct end-point match.  We mustn't confuse the two, so it is
+     * best to process only TA trust in the verify callback and check the EE
+     * trust after. This works since re-used sessions always have access to
+     * the leaf certificate, while only the original session has the leaf and
+     * the full trust chain.
+     * 
+     * Only the trust anchor matchlist is hashed into the session key. The end
+     * entity certs are not used to determine whether a certificate is
+     * trusted or not, rather these are rechecked against the leaf cert
+     * outside the verification callback, each time a session is created or
+     * reused.
+     * 
+     * Therefore, the security context of the session does not depend on the EE
+     * matching data, which is checked separately each time.  So we exclude
+     * the EE part of the DANE structure from the serverid digest.
+     * 
+     * If the security level is "dane", we send SNI information to the peer.
+     * This may cause it to respond with a non-default certificate.  Since
+     * certificates for sessions with no or different SNI data may not match,
+     * we must include the SNI name in the session id.
+     */
+    if (props->dane) {
+	digest_dane(props->dane, ta);
+#if 0
+	digest_dane(props->dane, ee);		/* See above */
+#endif
+	digest_string(TLS_DANE_BASED(props->tls_level) ? props->host : "");
+    }
+    checkok(EVP_DigestFinal_ex(mdctx, md_buf, &md_len));
+    EVP_MD_CTX_destroy(mdctx);
+    if (!ok)
+	msg_fatal("error computing %s message digest", mdalg);
+
+    /* Check for OpenSSL contract violation */
+    if (md_len > EVP_MAX_MD_SIZE)
+	msg_panic("unexpectedly large %s digest size: %u", mdalg, md_len);
+
+    /*
+     * Append the digest to the serverid.  We don't compare this digest to
+     * any user-specified fingerprints.  Therefore, we don't need to use a
+     * colon-separated format, which saves space in the TLS session cache and
+     * makes logging of session cache lookup keys more readable.
+     * 
+     * This does however duplicate a few lines of code from the digest encoder
+     * for colon-separated cert and pkey fingerprints. If that is a
+     * compelling reason to consolidate, we could use that and append the
+     * result.
+     */
+    result = vstring_alloc(strlen(props->serverid) + 1 + 2 * md_len);
+    vstring_strcpy(result, props->serverid);
+    VSTRING_ADDCH(result, '&');
+    for (i = 0; i < md_len; i++) {
+	VSTRING_ADDCH(result, hexcodes[(md_buf[i] & 0xf0) >> 4U]);
+	VSTRING_ADDCH(result, hexcodes[(md_buf[i] & 0x0f)]);
+    }
+    VSTRING_TERMINATE(result);
+    return (vstring_export(result));
+}
+
+/* tls_digest_encode - encode message digest binary blob as xx:xx:... */
+
+char   *tls_digest_encode(const unsigned char *md_buf, int md_len)
+{
+    int     i;
+    char   *result = mymalloc(md_len * 3);
+
+    /* Check for contract violation */
+    if (md_len > EVP_MAX_MD_SIZE || md_len >= INT_MAX / 3)
+	msg_panic("unexpectedly large message digest size: %u", md_len);
+
+    /* No risk of overrunes, len is bounded by OpenSSL digest length */
+    for (i = 0; i < md_len; i++) {
+	result[i * 3] = hexcodes[(md_buf[i] & 0xf0) >> 4U];
+	result[(i * 3) + 1] = hexcodes[(md_buf[i] & 0x0f)];
+	result[(i * 3) + 2] = (i + 1 != md_len) ? ':' : '\0';
+    }
+    return (result);
+}
+
+/* tls_data_fprint - compute and encode digest of binary object */
+
+char   *tls_data_fprint(const char *buf, int len, const char *mdalg)
+{
+    EVP_MD_CTX *mdctx;
+    const EVP_MD *md;
+    unsigned char md_buf[EVP_MAX_MD_SIZE];
+    unsigned int md_len;
+    int     ok = 1;
+
+    /* Previously available in "init" routine. */
+    if ((md = EVP_get_digestbyname(mdalg)) == 0)
+	msg_panic("digest algorithm \"%s\" not found", mdalg);
+
+    mdctx = EVP_MD_CTX_create();
+    checkok(EVP_DigestInit_ex(mdctx, md, NULL));
+    digest_data(buf, len);
+    checkok(EVP_DigestFinal_ex(mdctx, md_buf, &md_len));
+    EVP_MD_CTX_destroy(mdctx);
+    if (!ok)
+	msg_fatal("error computing %s message digest", mdalg);
+
+    return (tls_digest_encode(md_buf, md_len));
+}
+
+/* tls_cert_fprint - extract certificate fingerprint */
+
+char   *tls_cert_fprint(X509 *peercert, const char *mdalg)
+{
+    int     len;
+    char   *buf;
+    char   *buf2;
+    char   *result;
+
+    len = i2d_X509(peercert, NULL);
+    buf2 = buf = mymalloc(len);
+    i2d_X509(peercert, (unsigned char **) &buf2);
+    if (buf2 - buf != len)
+	msg_panic("i2d_X509 invalid result length");
+
+    result = tls_data_fprint(buf, len, mdalg);
+    myfree(buf);
+
+    return (result);
+}
+
+/* tls_pkey_fprint - extract public key fingerprint from certificate */
+
+char   *tls_pkey_fprint(X509 *peercert, const char *mdalg)
+{
+    if (var_tls_bc_pkey_fprint) {
+	const char *myname = "tls_pkey_fprint";
+	ASN1_BIT_STRING *key;
+	char   *result;
+
+	key = X509_get0_pubkey_bitstr(peercert);
+	if (key == 0)
+	    msg_fatal("%s: error extracting legacy public-key fingerprint: %m",
+		      myname);
+
+	result = tls_data_fprint((char *) key->data, key->length, mdalg);
+	return (result);
+    } else {
+	int     len;
+	char   *buf;
+	char   *buf2;
+	char   *result;
+
+	len = i2d_X509_PUBKEY(X509_get_X509_PUBKEY(peercert), NULL);
+	buf2 = buf = mymalloc(len);
+	i2d_X509_PUBKEY(X509_get_X509_PUBKEY(peercert), (unsigned char **) &buf2);
+	if (buf2 - buf != len)
+	    msg_panic("i2d_X509_PUBKEY invalid result length");
+
+	result = tls_data_fprint(buf, len, mdalg);
+	myfree(buf);
+	return (result);
+    }
+}
+
+#endif