Implement initial negotiation of EtM
Not implemented yet:
- actually using EtM
- conditions on renegotiation
diff --git a/include/polarssl/check_config.h b/include/polarssl/check_config.h
index b4ae541..80b037e 100644
--- a/include/polarssl/check_config.h
+++ b/include/polarssl/check_config.h
@@ -257,6 +257,13 @@
#error "Illegal protocol selection"
#endif
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC) && \
+ !defined(POLARSSL_SSL_PROTO_TLS1) && \
+ !defined(POLARSSL_SSL_PROTO_TLS1_1) && \
+ !defined(POLARSSL_SSL_PROTO_TLS1_2)
+#error "POLARSSL_SSL_ENCRYPT_THEN_MAC defined, but not all prerequsites"
+#endif
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET) && \
!defined(POLARSSL_SSL_PROTO_TLS1) && \
!defined(POLARSSL_SSL_PROTO_TLS1_1) && \
diff --git a/include/polarssl/config.h b/include/polarssl/config.h
index dfe2764..6e736e2 100644
--- a/include/polarssl/config.h
+++ b/include/polarssl/config.h
@@ -811,6 +811,24 @@
*/
//#define POLARSSL_SSL_DEBUG_ALL
+/** \def POLARSSL_SSL_ENCRYPT_THEN_MAC
+ *
+ * Enable support for Encrypt-then-MAC, RFC 7366.
+ *
+ * This allows peers that both support it to use a more robust protection for
+ * ciphersuites using CBC, providing deep resistance against timing attacks
+ * on the padding or underlying cipher.
+ *
+ * This only affects CBC ciphersuites, and is useless if none is defined.
+ *
+ * Requires: POLARSSL_SSL_PROTO_TLS1 or
+ * POLARSSL_SSL_PROTO_TLS1_1 or
+ * POLARSSL_SSL_PROTO_TLS1_2
+ *
+ * Comment this macro to disable support for Encrypt-then-MAC
+ */
+#define POLARSSL_SSL_ENCRYPT_THEN_MAC
+
/** \def POLARSSL_SSL_EXTENDED_MASTER_SECRET
*
* Enable support for Extended Master Secret, aka Session Hash
diff --git a/include/polarssl/ssl.h b/include/polarssl/ssl.h
index 7b5ec8e..82ed04e 100644
--- a/include/polarssl/ssl.h
+++ b/include/polarssl/ssl.h
@@ -212,6 +212,9 @@
#define SSL_EXTENDED_MS_DISABLED 0
#define SSL_EXTENDED_MS_ENABLED 1
+#define SSL_ETM_DISABLED 0
+#define SSL_ETM_ENABLED 1
+
#define SSL_COMPRESS_NULL 0
#define SSL_COMPRESS_DEFLATE 1
@@ -409,6 +412,7 @@
#define TLS_EXT_ALPN 16
+#define TLS_EXT_ENCRYPT_THEN_MAC 22 /* 0x16 */
#define TLS_EXT_EXTENDED_MASTER_SECRET 0x0017 /* 23 */
#define TLS_EXT_SESSION_TICKET 35
@@ -548,6 +552,10 @@
#if defined(POLARSSL_SSL_TRUNCATED_HMAC)
int trunc_hmac; /*!< flag for truncated hmac activation */
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ int encrypt_then_mac; /*!< flag for EtM activation */
+#endif
};
/*
@@ -713,6 +721,9 @@
#if defined(POLARSSL_SSL_FALLBACK_SCSV) && defined(POLARSSL_SSL_CLI_C)
char fallback; /*!< flag for fallback connections */
#endif
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ char encrypt_then_mac; /*!< flag for encrypt-then-mac */
+#endif
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
char extended_ms; /*!< flag for extended master secret */
#endif
@@ -1425,6 +1436,21 @@
void ssl_set_fallback( ssl_context *ssl, char fallback );
#endif /* POLARSSL_SSL_FALLBACK_SCSV && POLARSSL_SSL_CLI_C */
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+/**
+ * \brief Enable or disable Encrypt-then-MAC
+ * (Default: SSL_ETM_ENABLED)
+ *
+ * \note This should always be enabled, it is a security
+ * improvement, and should not cause any interoperability
+ * issue (used only if the peer supports it too).
+ *
+ * \param ssl SSL context
+ * \param etm SSL_ETM_ENABLED or SSL_ETM_DISABLED
+ */
+void ssl_set_encrypt_then_mac( ssl_context *ssl, char etm );
+#endif /* POLARSSL_SSL_ENCRYPT_THEN_MAC */
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
/**
* \brief Enable or disable Extended Master Secret negotiation.
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index c40d62e..fd0a811 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -359,6 +359,32 @@
}
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+static void ssl_write_encrypt_then_mac_ext( ssl_context *ssl,
+ unsigned char *buf, size_t *olen )
+{
+ unsigned char *p = buf;
+
+ if( ssl->encrypt_then_mac == SSL_ETM_DISABLED ||
+ ssl->max_minor_ver == SSL_MINOR_VERSION_0 )
+ {
+ *olen = 0;
+ return;
+ }
+
+ SSL_DEBUG_MSG( 3, ( "client hello, adding encrypt_then_mac "
+ "extension" ) );
+
+ *p++ = (unsigned char)( ( TLS_EXT_ENCRYPT_THEN_MAC >> 8 ) & 0xFF );
+ *p++ = (unsigned char)( ( TLS_EXT_ENCRYPT_THEN_MAC ) & 0xFF );
+
+ *p++ = 0x00;
+ *p++ = 0x00;
+
+ *olen = 4;
+}
+#endif /* POLARSSL_SSL_ENCRYPT_THEN_MAC */
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
static void ssl_write_extended_ms_ext( ssl_context *ssl,
unsigned char *buf, size_t *olen )
@@ -688,6 +714,11 @@
ext_len += olen;
#endif
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ ssl_write_encrypt_then_mac_ext( ssl, p + 2 + ext_len, &olen );
+ 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;
@@ -811,6 +842,26 @@
}
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+static int ssl_parse_encrypt_then_mac_ext( ssl_context *ssl,
+ const unsigned char *buf,
+ size_t len )
+{
+ if( ssl->encrypt_then_mac == SSL_ETM_DISABLED ||
+ ssl->minor_ver == SSL_MINOR_VERSION_0 ||
+ len != 0 )
+ {
+ return( POLARSSL_ERR_SSL_BAD_HS_SERVER_HELLO );
+ }
+
+ ((void) buf);
+
+ ssl->session_negotiate->encrypt_then_mac = SSL_ETM_ENABLED;
+
+ return( 0 );
+}
+#endif /* POLARSSL_SSL_ENCRYPT_THEN_MAC */
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
static int ssl_parse_extended_ms_ext( ssl_context *ssl,
const unsigned char *buf,
@@ -1203,6 +1254,19 @@
break;
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ case TLS_EXT_ENCRYPT_THEN_MAC:
+ SSL_DEBUG_MSG( 3, ( "found encrypt_then_mac extension" ) );
+
+ if( ( ret = ssl_parse_encrypt_then_mac_ext( ssl,
+ ext + 4, ext_size ) ) != 0 )
+ {
+ return( ret );
+ }
+
+ break;
+#endif /* POLARSSL_SSL_ENCRYPT_THEN_MAC */
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
case TLS_EXT_EXTENDED_MASTER_SECRET:
SSL_DEBUG_MSG( 3, ( "found extended_master_secret extension" ) );
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index ad67c22..c884e7c 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -635,6 +635,29 @@
}
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+static int ssl_parse_encrypt_then_mac_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->encrypt_then_mac == SSL_ETM_ENABLED &&
+ ssl->minor_ver != SSL_MINOR_VERSION_0 )
+ {
+ ssl->session_negotiate->encrypt_then_mac = SSL_ETM_ENABLED;
+ }
+
+ return( 0 );
+}
+#endif /* POLARSSL_SSL_ENCRYPT_THEN_MAC */
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
static int ssl_parse_extended_ms_ext( ssl_context *ssl,
const unsigned char *buf,
@@ -1523,6 +1546,16 @@
break;
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ case TLS_EXT_ENCRYPT_THEN_MAC:
+ SSL_DEBUG_MSG( 3, ( "found encrypt then mac extension" ) );
+
+ ret = ssl_parse_encrypt_then_mac_ext( ssl, ext + 4, ext_size );
+ if( ret != 0 )
+ return( ret );
+ break;
+#endif /* POLARSSL_SSL_ENCRYPT_THEN_MAC */
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
case TLS_EXT_EXTENDED_MASTER_SECRET:
SSL_DEBUG_MSG( 3, ( "found extended master secret extension" ) );
@@ -1682,6 +1715,32 @@
}
#endif /* POLARSSL_SSL_TRUNCATED_HMAC */
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+static void ssl_write_encrypt_then_mac_ext( ssl_context *ssl,
+ unsigned char *buf,
+ size_t *olen )
+{
+ unsigned char *p = buf;
+
+ if( ssl->session_negotiate->encrypt_then_mac == SSL_EXTENDED_MS_DISABLED ||
+ ssl->minor_ver == SSL_MINOR_VERSION_0 )
+ {
+ *olen = 0;
+ return;
+ }
+
+ SSL_DEBUG_MSG( 3, ( "server hello, adding encrypt then mac extension" ) );
+
+ *p++ = (unsigned char)( ( TLS_EXT_ENCRYPT_THEN_MAC >> 8 ) & 0xFF );
+ *p++ = (unsigned char)( ( TLS_EXT_ENCRYPT_THEN_MAC ) & 0xFF );
+
+ *p++ = 0x00;
+ *p++ = 0x00;
+
+ *olen = 4;
+}
+#endif /* POLARSSL_SSL_ENCRYPT_THEN_MAC */
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
static void ssl_write_extended_ms_ext( ssl_context *ssl,
unsigned char *buf,
@@ -2012,6 +2071,11 @@
ext_len += olen;
#endif
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ ssl_write_encrypt_then_mac_ext( ssl, p + 2 + ext_len, &olen );
+ 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;
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index c8b7fa2..e8f2b7f 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1071,6 +1071,15 @@
SSL_DEBUG_MSG( 2, ( "=> encrypt buf" ) );
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ if( ssl->session_out != NULL &&
+ ssl->session_out->encrypt_then_mac == SSL_ETM_ENABLED )
+ {
+ // WIP
+ SSL_DEBUG_MSG( 3, ( "using encrypt then mac" ) );
+ }
+#endif
+
/*
* Add MAC before encrypt, except for AEAD modes
*/
@@ -3474,6 +3483,10 @@
memset( ssl-> in_ctr, 0, SSL_BUFFER_LEN );
memset( ssl->out_ctr, 0, SSL_BUFFER_LEN );
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ ssl->encrypt_then_mac = SSL_ETM_ENABLED;
+#endif
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
ssl->extended_ms = SSL_EXTENDED_MS_ENABLED;
#endif
@@ -4025,6 +4038,13 @@
}
#endif
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+void ssl_set_encrypt_then_mac( ssl_context *ssl, char etm )
+{
+ ssl->encrypt_then_mac = etm;
+}
+#endif
+
#if defined(POLARSSL_SSL_EXTENDED_MASTER_SECRET)
void ssl_set_extended_master_secret( ssl_context *ssl, char ems )
{
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index d4cde0f..444322b 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -97,6 +97,7 @@
#define DFL_ALPN_STRING NULL
#define DFL_FALLBACK -1
#define DFL_EXTENDED_MS -1
+#define DFL_ETM -1
#define GET_REQUEST "GET %s HTTP/1.0\r\nExtra-header: "
#define GET_REQUEST_END "\r\n\r\n"
@@ -136,6 +137,7 @@
const char *alpn_string; /* ALPN supported protocols */
int fallback; /* is this a fallback connection? */
char extended_ms; /* negotiate extended master secret? */
+ char etm; ; /* negotiate encrypt then mac? ? */
} opt;
static void my_debug( void *ctx, int level, const char *str )
@@ -302,6 +304,13 @@
#define USAGE_EMS ""
#endif
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+#define USAGE_ETM \
+ " etm=0/1 default: (library default: on)\n"
+#else
+#define USAGE_ETM ""
+#endif
+
#define USAGE \
"\n usage: ssl_client2 param=<>...\n" \
"\n acceptable parameters:\n" \
@@ -333,6 +342,7 @@
USAGE_ALPN \
USAGE_FALLBACK \
USAGE_EMS \
+ USAGE_ETM \
"\n" \
" min_version=%%s default: \"\" (ssl3)\n" \
" max_version=%%s default: \"\" (tls1_2)\n" \
@@ -435,6 +445,7 @@
opt.alpn_string = DFL_ALPN_STRING;
opt.fallback = DFL_FALLBACK;
opt.extended_ms = DFL_EXTENDED_MS;
+ opt.etm = DFL_ETM;
for( i = 1; i < argc; i++ )
{
@@ -559,6 +570,15 @@
default: goto usage;
}
}
+ else if( strcmp( p, "etm" ) == 0 )
+ {
+ switch( atoi( q ) )
+ {
+ case 0: opt.etm = SSL_ETM_DISABLED; break;
+ case 1: opt.etm = SSL_ETM_ENABLED; break;
+ default: goto usage;
+ }
+ }
else if( strcmp( p, "min_version" ) == 0 )
{
if( strcmp( q, "ssl3" ) == 0 )
@@ -927,6 +947,11 @@
ssl_set_extended_master_secret( &ssl, opt.extended_ms );
#endif
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ if( opt.etm != DFL_ETM )
+ ssl_set_encrypt_then_mac( &ssl, opt.etm );
+#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 35a156b..08f2ff8 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -117,6 +117,7 @@
#define DFL_ALPN_STRING NULL
#define DFL_DHM_FILE NULL
#define DFL_EXTENDED_MS -1
+#define DFL_ETM -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" \
@@ -178,6 +179,7 @@
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? */
+ char etm; /* allow negotiation of encrypt-then-MAC? */
} opt;
static void my_debug( void *ctx, int level, const char *str )
@@ -308,6 +310,13 @@
#define USAGE_EMS ""
#endif
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+#define USAGE_ETM \
+ " etm=0/1 default: (library default: on)\n"
+#else
+#define USAGE_ETM ""
+#endif
+
#define USAGE \
"\n usage: ssl_server2 param=<>...\n" \
"\n acceptable parameters:\n" \
@@ -334,6 +343,7 @@
USAGE_MAX_FRAG_LEN \
USAGE_ALPN \
USAGE_EMS \
+ USAGE_ETM \
"\n" \
" min_version=%%s default: \"ssl3\"\n" \
" max_version=%%s default: \"tls1_2\"\n" \
@@ -724,6 +734,7 @@
opt.alpn_string = DFL_ALPN_STRING;
opt.dhm_file = DFL_DHM_FILE;
opt.extended_ms = DFL_EXTENDED_MS;
+ opt.etm = DFL_ETM;
for( i = 1; i < argc; i++ )
{
@@ -900,6 +911,15 @@
default: goto usage;
}
}
+ else if( strcmp( p, "etm" ) == 0 )
+ {
+ switch( atoi( q ) )
+ {
+ case 0: opt.etm = SSL_ETM_DISABLED; break;
+ case 1: opt.etm = SSL_ETM_ENABLED; break;
+ default: goto usage;
+ }
+ }
else if( strcmp( p, "tickets" ) == 0 )
{
opt.tickets = atoi( q );
@@ -1282,6 +1302,11 @@
ssl_set_extended_master_secret( &ssl, opt.extended_ms );
#endif
+#if defined(POLARSSL_SSL_ENCRYPT_THEN_MAC)
+ if( opt.etm != DFL_ETM )
+ ssl_set_encrypt_then_mac( &ssl, opt.etm );
+#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 38bc89b..6db8571 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -247,14 +247,14 @@
if is_polar "$SRV_CMD"; then
if grep "Performing the SSL/TLS handshake" $SRV_OUT >/dev/null; then :;
else
- fail "server failed to start"
+ fail "server or client failed to reach handshake stage"
return
fi
fi
if is_polar "$CLI_CMD"; then
if grep "Performing the SSL/TLS handshake" $CLI_OUT >/dev/null; then :;
else
- fail "client failed to start"
+ fail "server or client failed to reach handshake stage"
return
fi
fi
@@ -440,6 +440,63 @@
0 \
-s "dumping 'computed mac' (10 bytes)"
+# Tests for Encrypt-then-MAC extension
+
+run_test "Encrypt then MAC: default" \
+ "$P_SRV debug_level=3" \
+ "$P_CLI debug_level=3" \
+ 0 \
+ -c "client hello, adding encrypt_then_mac extension" \
+ -s "found encrypt then mac extension" \
+ -s "server hello, adding encrypt then mac extension" \
+ -c "found encrypt_then_mac extension" \
+ -c "using encrypt then mac" \
+ -s "using encrypt then mac"
+
+run_test "Encrypt then MAC: client enabled, server disabled" \
+ "$P_SRV debug_level=3 etm=0" \
+ "$P_CLI debug_level=3 etm=1" \
+ 0 \
+ -c "client hello, adding encrypt_then_mac extension" \
+ -s "found encrypt then mac extension" \
+ -S "server hello, adding encrypt then mac extension" \
+ -C "found encrypt_then_mac extension" \
+ -C "using encrypt then mac" \
+ -S "using encrypt then mac"
+
+run_test "Encrypt then MAC: client disabled, server enabled" \
+ "$P_SRV debug_level=3 etm=1" \
+ "$P_CLI debug_level=3 etm=0" \
+ 0 \
+ -C "client hello, adding encrypt_then_mac extension" \
+ -S "found encrypt then mac extension" \
+ -S "server hello, adding encrypt then mac extension" \
+ -C "found encrypt_then_mac extension" \
+ -C "using encrypt then mac" \
+ -S "using encrypt then mac"
+
+run_test "Encrypt then MAC: client SSLv3, server enabled" \
+ "$P_SRV debug_level=3" \
+ "$P_CLI debug_level=3 force_version=ssl3" \
+ 0 \
+ -C "client hello, adding encrypt_then_mac extension" \
+ -S "found encrypt then mac extension" \
+ -S "server hello, adding encrypt then mac extension" \
+ -C "found encrypt_then_mac extension" \
+ -C "using encrypt then mac" \
+ -S "using encrypt then mac"
+
+run_test "Encrypt then MAC: client enabled, server SSLv3" \
+ "$P_SRV debug_level=3 force_version=ssl3" \
+ "$P_CLI debug_level=3" \
+ 0 \
+ -c "client hello, adding encrypt_then_mac extension" \
+ -s "found encrypt then mac extension" \
+ -S "server hello, adding encrypt then mac extension" \
+ -C "found encrypt_then_mac extension" \
+ -C "using encrypt then mac" \
+ -S "using encrypt then mac"
+
# Tests for Extended Master Secret extension
run_test "Extended Master Secret: default" \