TLS: allow cipher information to be retrieved

In preparation for QUIC packet decryption, add a method to retrieve the
cipher used in a TLS session. (QUIC embeds the TLS handshake.)

Change-Id: If58e16bd0a01808dafa455ddc6c67ad23f33d7da
Reviewed-on: https://code.wireshark.org/review/26558
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot
Reviewed-by: Peter Wu <peter@lekensteyn.nl>

4 files changed, 86 insertions, 0 deletions

diff --git a/epan/dissectors/packet-ssl-utils.c b/epan/dissectors/packet-ssl-utils.c
index b75c55b2b5..fe7f255e41 100644
--- a/epan/dissectors/packet-ssl-utils.c
+++ b/epan/dissectors/packet-ssl-utils.c
@@ -2405,6 +2405,12 @@ ssl_find_cipher(int num)
     return NULL;
 }
 
+int
+ssl_get_cipher_algo(const SslCipherSuite *cipher_suite)
+{
+    return gcry_cipher_map_name(ciphers[cipher_suite->enc - 0x30]);
+}
+
 guint
 ssl_get_cipher_blocksize(const SslCipherSuite *cipher_suite)
 {
diff --git a/epan/dissectors/packet-ssl-utils.h b/epan/dissectors/packet-ssl-utils.h
index 6df90e1563..d861370d7a 100644
--- a/epan/dissectors/packet-ssl-utils.h
+++ b/epan/dissectors/packet-ssl-utils.h
@@ -591,6 +591,11 @@ ssl_cipher_setiv(SSL_CIPHER_CTX *cipher, guchar* iv, gint iv_len);
 extern const SslCipherSuite *
 ssl_find_cipher(int num);
 
+
+/** Returns the Libgcrypt cipher identifier or 0 if unavailable. */
+int
+ssl_get_cipher_algo(const SslCipherSuite *cipher_suite);
+
 /** Obtains the block size for a CBC block cipher.
  * @param cipher_suite a cipher suite as returned by ssl_find_cipher().
  * @return the block size of a cipher or 0 if unavailable.
diff --git a/epan/dissectors/packet-ssl.c b/epan/dissectors/packet-ssl.c
index fcedd8517c..5b2785472e 100644
--- a/epan/dissectors/packet-ssl.c
+++ b/epan/dissectors/packet-ssl.c
@@ -95,6 +95,10 @@
 /* Whether to provide support for authentication in addition to decryption. */
 #define HAVE_LIBGCRYPT_AEAD
 #endif
+#if GCRYPT_VERSION_NUMBER >= 0x010700 /* 1.7.0 */
+/* Whether AEAD_CHACHA20_POLY1305 can be supported. */
+#define HAVE_LIBGCRYPT_CHACHA20_POLY1305
+#endif
 
 void proto_register_ssl(void);
 
@@ -3846,6 +3850,71 @@ ssl_looks_like_valid_pct_handshake(tvbuff_t *tvb, const guint32 offset,
     return ret;
 }
 
+gboolean
+tls_get_cipher_info(packet_info *pinfo, int *cipher_algo, int *cipher_mode, int *hash_algo)
+{
+    conversation_t *conv = find_conversation_pinfo(pinfo, 0);
+    if (!conv) {
+        return FALSE;
+    }
+
+    void *conv_data = conversation_get_proto_data(conv, proto_ssl);
+    if (conv_data == NULL) {
+        return FALSE;
+    }
+
+    SslDecryptSession *ssl_session = (SslDecryptSession *)conv_data;
+    const SslCipherSuite *suite = ssl_find_cipher(ssl_session->session.cipher);
+    if (!suite) {
+        return FALSE;
+    }
+
+    /* adapted from ssl_cipher_init in packet-ssl-utils.c */
+    static const gint gcry_modes[] = {
+        GCRY_CIPHER_MODE_STREAM,
+        GCRY_CIPHER_MODE_CBC,
+#ifdef HAVE_LIBGCRYPT_AEAD
+        GCRY_CIPHER_MODE_GCM,
+        GCRY_CIPHER_MODE_CCM,
+        GCRY_CIPHER_MODE_CCM,
+#else
+        -1,                         /* Do not bother with fallback support. */
+        -1,
+        -1,
+#endif
+#ifdef HAVE_LIBGCRYPT_CHACHA20_POLY1305
+        GCRY_CIPHER_MODE_POLY1305,
+#else
+        -1,                         /* AEAD_CHACHA20_POLY1305 is unsupported. */
+#endif
+    };
+    static const int gcry_mds[] = {
+        GCRY_MD_MD5,
+        GCRY_MD_SHA1,
+        GCRY_MD_SHA256,
+        GCRY_MD_SHA384,
+        -1,
+    };
+    int mode = gcry_modes[suite->mode];
+    int cipher_algo_id = ssl_get_cipher_algo(suite);
+    int hash_algo_id = gcry_mds[suite->dig-DIG_MD5];
+    if (mode == -1 || cipher_algo_id == 0 || hash_algo_id == -1) {
+        /* Identifiers are unusable, fail. */
+        return FALSE;
+    }
+    if (cipher_algo) {
+        *cipher_algo = cipher_algo_id;
+    }
+    if (cipher_mode) {
+        *cipher_mode = mode;
+    }
+    if (hash_algo) {
+        *hash_algo = hash_algo_id;
+    }
+
+    return TRUE;
+}
+
 /* TLS Exporters {{{ */
 #if GCRYPT_VERSION_NUMBER >= 0x010600 /* 1.6.0 */
 /**
diff --git a/epan/dissectors/packet-ssl.h b/epan/dissectors/packet-ssl.h
index 71e365f1d1..02334cff55 100644
--- a/epan/dissectors/packet-ssl.h
+++ b/epan/dissectors/packet-ssl.h
@@ -27,6 +27,12 @@ WS_DLL_PUBLIC void ssl_set_master_secret(guint32 frame_num, address *addr_srv, a
                                   guint32 version, gint cipher, const guchar *_master_secret,
                                   const guchar *_client_random, const guchar *_server_random,
                                   guint32 client_seq, guint32 server_seq);
+/**
+ * Retrieves Libgcrypt identifiers for the current TLS cipher. Only valid after
+ * the Server Hello has been processed and if the current conversation has TLS.
+ */
+extern gboolean
+tls_get_cipher_info(packet_info *pinfo, int *cipher_algo, int *cipher_mode, int *hash_algo);
 
 /**
  * Computes the TLS 1.3 "TLS-Exporter(label, context_value, key_length)" value.