Add negotiation of Extended Master Secret
(But not the actual thing yet.)
diff --git a/include/polarssl/config.h b/include/polarssl/config.h
index ff0ccec..9ca39e7 100644
--- a/include/polarssl/config.h
+++ b/include/polarssl/config.h
@@ -811,6 +811,20 @@
*/
//#define POLARSSL_SSL_DEBUG_ALL
+/** \def POLARSSL_SSL_EXTENDED_MASTER_SECRET
+ *
+ * Enable support for Extended Master Secret, aka Session Hash
+ * (draft-ietf-tls-session-hash-02).
+ *
+ * This was introduced as "the proper fix" to the Triple Handshake familiy of
+ * attacks, but it is recommended to always use it (even if you disable
+ * renegotiation), since it actually fixes a more fundamental issue in the
+ * original SSL/TLS design, and has implications beyond Triple Handshake.
+ *
+ * Comment this macro to disable support for Extended Master Secret.
+ */
+#define POLARSSL_SSL_EXTENDED_MASTER_SECRET
+
/**
* \def POLARSSL_SSL_FALLBACK_SCSV
*
diff --git a/include/polarssl/ssl.h b/include/polarssl/ssl.h
index 875709c..7b5ec8e 100644
--- a/include/polarssl/ssl.h
+++ b/include/polarssl/ssl.h
@@ -209,6 +209,9 @@
#define SSL_IS_NOT_FALLBACK 0
#define SSL_IS_FALLBACK 1
+#define SSL_EXTENDED_MS_DISABLED 0
+#define SSL_EXTENDED_MS_ENABLED 1
+
#define SSL_COMPRESS_NULL 0
#define SSL_COMPRESS_DEFLATE 1
@@ -406,6 +409,8 @@
#define TLS_EXT_ALPN 16
+#define TLS_EXT_EXTENDED_MASTER_SECRET 0x0017 /* 23 */
+
#define TLS_EXT_SESSION_TICKET 35
#define TLS_EXT_RENEGOTIATION_INFO 0xFF01
@@ -657,6 +662,9 @@
#if defined(POLARSSL_SSL_SESSION_TICKETS)
int new_session_ticket; /*!< use NewSessionTicket? */
#endif /* POLARSSL_SSL_SESSION_TICKETS */
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ int extended_ms; /*!< use Extended Master Secret? */
+#endif
};
#if defined(POLARSSL_SSL_SESSION_TICKETS)
@@ -705,6 +713,9 @@
#if defined(POLARSSL_SSL_FALLBACK_SCSV) && defined(POLARSSL_SSL_CLI_C)
char fallback; /*!< flag for fallback connections */
#endif
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ char extended_ms; /*!< flag for extended master secret */
+#endif
/*
* Callbacks (RNG, debug, I/O, verification)
@@ -1414,6 +1425,21 @@
void ssl_set_fallback( ssl_context *ssl, char fallback );
#endif /* POLARSSL_SSL_FALLBACK_SCSV && POLARSSL_SSL_CLI_C */
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+/**
+ * \brief Enable or disable Extended Master Secret negotiation.
+ * (Default: SSL_EXTENDED_MS_ENABLED)
+ *
+ * \note This should always be enabled, it is a security fix to the
+ * protocol, and should not cause any interoperability issue
+ * (used only if the peer supports it too).
+ *
+ * \param ssl SSL context
+ * \param ems SSL_EXTENDED_MS_ENABLED or SSL_EXTENDED_MS_DISABLED
+ */
+void ssl_set_extended_master_secret( ssl_context *ssl, char ems );
+#endif /* POLARSSL_SSL_EXTENDED_MASTER_SECRET */
+
#if defined(POLARSSL_SSL_MAX_FRAGMENT_LENGTH)
/**
* \brief Set the maximum fragment length to emit and/or negotiate
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 50ab05f..065f3a8 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -359,6 +359,31 @@
}
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+static void ssl_write_extended_ms_ext( ssl_context *ssl,
+ unsigned char *buf, size_t *olen )
+{
+ unsigned char *p = buf;
+
+ if( ssl->extended_ms == SSL_EXTENDED_MS_DISABLED )
+ {
+ *olen = 0;
+ return;
+ }
+
+ SSL_DEBUG_MSG( 3, ( "client hello, adding extended_master_secret "
+ "extension" ) );
+
+ *p++ = (unsigned char)( ( TLS_EXT_EXTENDED_MASTER_SECRET >> 8 ) & 0xFF );
+ *p++ = (unsigned char)( ( TLS_EXT_EXTENDED_MASTER_SECRET ) & 0xFF );
+
+ *p++ = 0x00;
+ *p++ = 0x00;
+
+ *olen = 4;
+}
+#endif /* POLARSSL_SSL_EXTENDED_MASTER_SECRET */
+
#if defined(POLARSSL_SSL_SESSION_TICKETS)
static void ssl_write_session_ticket_ext( ssl_context *ssl,
unsigned char *buf, size_t *olen )
@@ -662,6 +687,11 @@
ext_len += olen;
#endif
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ ssl_write_extended_ms_ext( ssl, p + 2 + ext_len, &olen );
+ ext_len += olen;
+#endif
+
#if defined(POLARSSL_SSL_SESSION_TICKETS)
ssl_write_session_ticket_ext( ssl, p + 2 + ext_len, &olen );
ext_len += olen;
@@ -780,6 +810,25 @@
}
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+static int ssl_parse_extended_ms_ext( ssl_context *ssl,
+ const unsigned char *buf,
+ size_t len )
+{
+ if( ssl->extended_ms == SSL_EXTENDED_MS_DISABLED ||
+ len != 0 )
+ {
+ return( POLARSSL_ERR_SSL_BAD_HS_SERVER_HELLO );
+ }
+
+ ((void) buf);
+
+ ssl->handshake->extended_ms = SSL_EXTENDED_MS_ENABLED;
+
+ return( 0 );
+}
+#endif /* POLARSSL_SSL_EXTENDED_MASTER_SECRET */
+
#if defined(POLARSSL_SSL_SESSION_TICKETS)
static int ssl_parse_session_ticket_ext( ssl_context *ssl,
const unsigned char *buf,
@@ -1152,6 +1201,19 @@
break;
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ case TLS_EXT_EXTENDED_MASTER_SECRET:
+ SSL_DEBUG_MSG( 3, ( "found extended_master_secret extension" ) );
+
+ if( ( ret = ssl_parse_extended_ms_ext( ssl,
+ ext + 4, ext_size ) ) != 0 )
+ {
+ return( ret );
+ }
+
+ break;
+#endif /* POLARSSL_SSL_EXTENDED_MASTER_SECRET */
+
#if defined(POLARSSL_SSL_SESSION_TICKETS)
case TLS_EXT_SESSION_TICKET:
SSL_DEBUG_MSG( 3, ( "found session_ticket extension" ) );
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 57b0ecf..f65338e 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -635,6 +635,26 @@
}
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+static int ssl_parse_extended_ms_ext( ssl_context *ssl,
+ const unsigned char *buf,
+ size_t len )
+{
+ if( len != 0 )
+ {
+ SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
+ return( POLARSSL_ERR_SSL_BAD_HS_CLIENT_HELLO );
+ }
+
+ ((void) buf);
+
+ if( ssl->extended_ms == SSL_EXTENDED_MS_ENABLED )
+ ssl->handshake->extended_ms = SSL_EXTENDED_MS_ENABLED;
+
+ return( 0 );
+}
+#endif /* POLARSSL_SSL_EXTENDED_MASTER_SECRET */
+
#if defined(POLARSSL_SSL_SESSION_TICKETS)
static int ssl_parse_session_ticket_ext( ssl_context *ssl,
unsigned char *buf,
@@ -1500,6 +1520,16 @@
break;
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ case TLS_EXT_EXTENDED_MASTER_SECRET:
+ SSL_DEBUG_MSG( 3, ( "found extended master secret extension" ) );
+
+ ret = ssl_parse_extended_ms_ext( ssl, ext + 4, ext_size );
+ if( ret != 0 )
+ return( ret );
+ break;
+#endif /* POLARSSL_SSL_EXTENDED_MASTER_SECRET */
+
#if defined(POLARSSL_SSL_SESSION_TICKETS)
case TLS_EXT_SESSION_TICKET:
SSL_DEBUG_MSG( 3, ( "found session ticket extension" ) );
@@ -1649,6 +1679,32 @@
}
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+static void ssl_write_extended_ms_ext( ssl_context *ssl,
+ unsigned char *buf,
+ size_t *olen )
+{
+ unsigned char *p = buf;
+
+ if( ssl->handshake->extended_ms == SSL_EXTENDED_MS_DISABLED )
+ {
+ *olen = 0;
+ return;
+ }
+
+ SSL_DEBUG_MSG( 3, ( "server hello, adding extended master secret "
+ "extension" ) );
+
+ *p++ = (unsigned char)( ( TLS_EXT_EXTENDED_MASTER_SECRET >> 8 ) & 0xFF );
+ *p++ = (unsigned char)( ( TLS_EXT_EXTENDED_MASTER_SECRET ) & 0xFF );
+
+ *p++ = 0x00;
+ *p++ = 0x00;
+
+ *olen = 4;
+}
+#endif /* POLARSSL_SSL_EXTENDED_MASTER_SECRET */
+
#if defined(POLARSSL_SSL_SESSION_TICKETS)
static void ssl_write_session_ticket_ext( ssl_context *ssl,
unsigned char *buf,
@@ -1952,6 +2008,11 @@
ext_len += olen;
#endif
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ ssl_write_extended_ms_ext( ssl, p + 2 + ext_len, &olen );
+ ext_len += olen;
+#endif
+
#if defined(POLARSSL_SSL_SESSION_TICKETS)
ssl_write_session_ticket_ext( ssl, p + 2 + ext_len, &olen );
ext_len += olen;
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index bd4494f..1fe3a95 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -470,6 +470,11 @@
SSL_DEBUG_BUF( 3, "premaster secret", handshake->premaster,
handshake->pmslen );
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ if( ssl->handshake->extended_ms == SSL_EXTENDED_MS_ENABLED )
+ SSL_DEBUG_MSG( 3, ( "using extended master secret" ) );
+ // XXX to be continued, WIP
+#endif
handshake->tls_prf( handshake->premaster, handshake->pmslen,
"master secret",
handshake->randbytes, 64, session->master, 48 );
@@ -3437,6 +3442,10 @@
memset( ssl-> in_ctr, 0, SSL_BUFFER_LEN );
memset( ssl->out_ctr, 0, SSL_BUFFER_LEN );
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ ssl->extended_ms = SSL_EXTENDED_MS_ENABLED;
+#endif
+
#if defined(POLARSSL_SSL_SESSION_TICKETS)
ssl->ticket_lifetime = SSL_DEFAULT_TICKET_LIFETIME;
#endif
@@ -3984,6 +3993,13 @@
}
#endif
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+void ssl_set_extended_master_secret( ssl_context *ssl, char ems )
+{
+ ssl->extended_ms = ems;
+}
+#endif
+
#if defined(POLARSSL_SSL_MAX_FRAGMENT_LENGTH)
int ssl_set_max_frag_len( ssl_context *ssl, unsigned char mfl_code )
{
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index 8ca83eb..d4cde0f 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -96,6 +96,7 @@
#define DFL_TICKETS SSL_SESSION_TICKETS_ENABLED
#define DFL_ALPN_STRING NULL
#define DFL_FALLBACK -1
+#define DFL_EXTENDED_MS -1
#define GET_REQUEST "GET %s HTTP/1.0\r\nExtra-header: "
#define GET_REQUEST_END "\r\n\r\n"
@@ -134,6 +135,7 @@
int tickets; /* enable / disable session tickets */
const char *alpn_string; /* ALPN supported protocols */
int fallback; /* is this a fallback connection? */
+ char extended_ms; /* negotiate extended master secret? */
} opt;
static void my_debug( void *ctx, int level, const char *str )
@@ -293,6 +295,13 @@
#define USAGE_FALLBACK ""
#endif
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+#define USAGE_EMS \
+ " extended_ms=0/1 default: (library default: on)\n"
+#else
+#define USAGE_EMS ""
+#endif
+
#define USAGE \
"\n usage: ssl_client2 param=<>...\n" \
"\n acceptable parameters:\n" \
@@ -323,6 +332,7 @@
USAGE_TRUNC_HMAC \
USAGE_ALPN \
USAGE_FALLBACK \
+ USAGE_EMS \
"\n" \
" min_version=%%s default: \"\" (ssl3)\n" \
" max_version=%%s default: \"\" (tls1_2)\n" \
@@ -424,6 +434,7 @@
opt.tickets = DFL_TICKETS;
opt.alpn_string = DFL_ALPN_STRING;
opt.fallback = DFL_FALLBACK;
+ opt.extended_ms = DFL_EXTENDED_MS;
for( i = 1; i < argc; i++ )
{
@@ -539,6 +550,15 @@
default: goto usage;
}
}
+ else if( strcmp( p, "extended_ms" ) == 0 )
+ {
+ switch( atoi( q ) )
+ {
+ case 0: opt.extended_ms = SSL_EXTENDED_MS_DISABLED; break;
+ case 1: opt.extended_ms = SSL_EXTENDED_MS_ENABLED; break;
+ default: goto usage;
+ }
+ }
else if( strcmp( p, "min_version" ) == 0 )
{
if( strcmp( q, "ssl3" ) == 0 )
@@ -902,6 +922,11 @@
}
#endif
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ if( opt.extended_ms != DFL_EXTENDED_MS )
+ ssl_set_extended_master_secret( &ssl, opt.extended_ms );
+#endif
+
#if defined(POLARSSL_SSL_ALPN)
if( opt.alpn_string != NULL )
if( ( ret = ssl_set_alpn_protocols( &ssl, alpn_list ) ) != 0 )
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index 721dab4..35a156b 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -116,6 +116,7 @@
#define DFL_SNI NULL
#define DFL_ALPN_STRING NULL
#define DFL_DHM_FILE NULL
+#define DFL_EXTENDED_MS -1
#define LONG_RESPONSE "<p>01-blah-blah-blah-blah-blah-blah-blah-blah-blah\r\n" \
"02-blah-blah-blah-blah-blah-blah-blah-blah-blah-blah-blah-blah-blah\r\n" \
@@ -176,6 +177,7 @@
char *sni; /* string describing sni information */
const char *alpn_string; /* ALPN supported protocols */
const char *dhm_file; /* the file with the DH parameters */
+ char extended_ms; /* allow negotiation of extended MS? */
} opt;
static void my_debug( void *ctx, int level, const char *str )
@@ -299,6 +301,13 @@
#define USAGE_ALPN ""
#endif /* POLARSSL_SSL_ALPN */
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+#define USAGE_EMS \
+ " extended_ms=0/1 default: (library default: on)\n"
+#else
+#define USAGE_EMS ""
+#endif
+
#define USAGE \
"\n usage: ssl_server2 param=<>...\n" \
"\n acceptable parameters:\n" \
@@ -324,6 +333,7 @@
USAGE_CACHE \
USAGE_MAX_FRAG_LEN \
USAGE_ALPN \
+ USAGE_EMS \
"\n" \
" min_version=%%s default: \"ssl3\"\n" \
" max_version=%%s default: \"tls1_2\"\n" \
@@ -713,6 +723,7 @@
opt.sni = DFL_SNI;
opt.alpn_string = DFL_ALPN_STRING;
opt.dhm_file = DFL_DHM_FILE;
+ opt.extended_ms = DFL_EXTENDED_MS;
for( i = 1; i < argc; i++ )
{
@@ -880,6 +891,15 @@
{
opt.alpn_string = q;
}
+ else if( strcmp( p, "extended_ms" ) == 0 )
+ {
+ switch( atoi( q ) )
+ {
+ case 0: opt.extended_ms = SSL_EXTENDED_MS_DISABLED; break;
+ case 1: opt.extended_ms = SSL_EXTENDED_MS_ENABLED; break;
+ default: goto usage;
+ }
+ }
else if( strcmp( p, "tickets" ) == 0 )
{
opt.tickets = atoi( q );
@@ -1257,6 +1277,11 @@
};
#endif
+#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
+ if( opt.extended_ms != DFL_EXTENDED_MS )
+ ssl_set_extended_master_secret( &ssl, opt.extended_ms );
+#endif
+
#if defined(POLARSSL_SSL_ALPN)
if( opt.alpn_string != NULL )
if( ( ret = ssl_set_alpn_protocols( &ssl, alpn_list ) ) != 0 )
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index b0dcad9..eeac11b 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -440,6 +440,41 @@
0 \
-s "dumping 'computed mac' (10 bytes)"
+# Tests for Extended Master Secret extension
+
+run_test "Extended Master Secret: default" \
+ "$P_SRV debug_level=3" \
+ "$P_CLI debug_level=3" \
+ 0 \
+ -c "client hello, adding extended_master_secret extension" \
+ -s "found extended master secret extension" \
+ -s "server hello, adding extended master secret extension" \
+ -c "found extended_master_secret extension" \
+ -c "using extended master secret" \
+ -s "using extended master secret"
+
+run_test "Extended Master Secret: client enabled, server disabled" \
+ "$P_SRV debug_level=3 extended_ms=0" \
+ "$P_CLI debug_level=3 extended_ms=1" \
+ 0 \
+ -c "client hello, adding extended_master_secret extension" \
+ -s "found extended master secret extension" \
+ -S "server hello, adding extended master secret extension" \
+ -C "found extended_master_secret extension" \
+ -C "using extended master secret" \
+ -S "using extended master secret"
+
+run_test "Extended Master Secret: client disabled, server enabled" \
+ "$P_SRV debug_level=3 extended_ms=1" \
+ "$P_CLI debug_level=3 extended_ms=0" \
+ 0 \
+ -C "client hello, adding extended_master_secret extension" \
+ -S "found extended master secret extension" \
+ -S "server hello, adding extended master secret extension" \
+ -C "found extended_master_secret extension" \
+ -C "using extended master secret" \
+ -S "using extended master secret"
+
# Tests for FALLBACK_SCSV
run_test "Fallback SCSV: default" \