diff --git a/include/polarssl/ssl.h b/include/polarssl/ssl.h
index 1403ab331..c7d7b12e3 100644
--- a/include/polarssl/ssl.h
+++ b/include/polarssl/ssl.h
@@ -254,6 +254,8 @@
 
 #define TLS_EXT_MAX_FRAGMENT_LENGTH          1
 
+#define TLS_EXT_TRUNCATED_HMAC               4
+
 #define TLS_EXT_SUPPORTED_ELLIPTIC_CURVES   10
 #define TLS_EXT_SUPPORTED_POINT_FORMATS     11
 
@@ -336,6 +338,7 @@ struct _ssl_session
 #endif /* POLARSSL_X509_PARSE_C */
 
     unsigned char mfl_code;     /*!< MaxFragmentLength negotiated by peer */
+    int trunc_hmac;             /*!< flag for truncated hmac activation   */
 };
 
 /*
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index c89bf0cb0..877d6cddd 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -293,6 +293,28 @@ static void ssl_write_max_fragment_length_ext( ssl_context *ssl,
     *olen = 5;
 }
 
+static void ssl_write_truncated_hmac_ext( ssl_context *ssl,
+                                          unsigned char *buf, size_t *olen )
+{
+    unsigned char *p = buf;
+
+    if( ssl->trunc_hmac == SSL_TRUNC_HMAC_DISABLED )
+    {
+        *olen = 0;
+        return;
+    }
+
+    SSL_DEBUG_MSG( 3, ( "client hello, adding truncated_hmac extension" ) );
+
+    *p++ = (unsigned char)( ( TLS_EXT_TRUNCATED_HMAC >> 8 ) & 0xFF );
+    *p++ = (unsigned char)( ( TLS_EXT_TRUNCATED_HMAC      ) & 0xFF );
+
+    *p++ = 0x00;
+    *p++ = 0x00;
+
+    *olen = 4;
+}
+
 static int ssl_write_client_hello( ssl_context *ssl )
 {
     int ret;
@@ -463,6 +485,9 @@ static int ssl_write_client_hello( ssl_context *ssl )
     ssl_write_max_fragment_length_ext( ssl, p + 2 + ext_len, &olen );
     ext_len += olen;
 
+    ssl_write_truncated_hmac_ext( ssl, p + 2 + ext_len, &olen );
+    ext_len += olen;
+
     SSL_DEBUG_MSG( 3, ( "client hello, total extension length: %d",
                    ext_len ) );
 
@@ -526,6 +551,7 @@ static int ssl_parse_renegotiation_info( ssl_context *ssl,
 
     return( 0 );
 }
+
 static int ssl_parse_max_fragment_length_ext( ssl_context *ssl,
                                               const unsigned char *buf,
                                               size_t len )
@@ -544,6 +570,23 @@ static int ssl_parse_max_fragment_length_ext( ssl_context *ssl,
     return( 0 );
 }
 
+static int ssl_parse_truncated_hmac_ext( ssl_context *ssl,
+                                         const unsigned char *buf,
+                                         size_t len )
+{
+    if( ssl->trunc_hmac == SSL_TRUNC_HMAC_DISABLED ||
+        len != 0 )
+    {
+        return( POLARSSL_ERR_SSL_BAD_HS_SERVER_HELLO );
+    }
+
+    ((void) buf);
+
+    ssl->session_negotiate->trunc_hmac = SSL_TRUNC_HMAC_ENABLED;
+
+    return( 0 );
+}
+
 static int ssl_parse_server_hello( ssl_context *ssl )
 {
     uint32_t t;
@@ -771,6 +814,17 @@ static int ssl_parse_server_hello( ssl_context *ssl )
 
             break;
 
+        case TLS_EXT_TRUNCATED_HMAC:
+            SSL_DEBUG_MSG( 3, ( "found truncated_hmac extension" ) );
+
+            if( ( ret = ssl_parse_truncated_hmac_ext( ssl,
+                            ext + 4, ext_size ) ) != 0 )
+            {
+                return( ret );
+            }
+
+            break;
+
         default:
             SSL_DEBUG_MSG( 3, ( "unknown extension found: %d (ignoring)",
                            ext_id ) );
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 3e1838667..6cbc5f406 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -306,6 +306,23 @@ static int ssl_parse_max_fragment_length_ext( ssl_context *ssl,
     return( 0 );
 }
 
+static int ssl_parse_truncated_hmac_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);
+
+    ssl->session_negotiate->trunc_hmac = SSL_TRUNC_HMAC_ENABLED;
+
+    return( 0 );
+}
+
 #if defined(POLARSSL_SSL_SRV_SUPPORT_SSLV2_CLIENT_HELLO)
 static int ssl_parse_client_hello_v2( ssl_context *ssl )
 {
@@ -848,6 +865,14 @@ static int ssl_parse_client_hello( ssl_context *ssl )
                 return( ret );
             break;
 
+        case TLS_EXT_TRUNCATED_HMAC:
+            SSL_DEBUG_MSG( 3, ( "found truncated hmac extension" ) );
+
+            ret = ssl_parse_truncated_hmac_ext( ssl, ext + 4, ext_size );
+            if( ret != 0 )
+                return( ret );
+            break;
+
         default:
             SSL_DEBUG_MSG( 3, ( "unknown extension found: %d (ignoring)",
                            ext_id ) );
@@ -957,6 +982,29 @@ have_ciphersuite:
     return( 0 );
 }
 
+static void ssl_write_truncated_hmac_ext( ssl_context *ssl,
+                                          unsigned char *buf,
+                                          size_t *olen )
+{
+    unsigned char *p = buf;
+
+    if( ssl->session_negotiate->trunc_hmac == SSL_TRUNC_HMAC_DISABLED )
+    {
+        *olen = 0;
+        return;
+    }
+
+    SSL_DEBUG_MSG( 3, ( "server hello, adding truncated hmac extension" ) );
+
+    *p++ = (unsigned char)( ( TLS_EXT_TRUNCATED_HMAC >> 8 ) & 0xFF );
+    *p++ = (unsigned char)( ( TLS_EXT_TRUNCATED_HMAC      ) & 0xFF );
+
+    *p++ = 0x00;
+    *p++ = 0x00;
+
+    *olen = 4;
+}
+
 static void ssl_write_renegotiation_ext( ssl_context *ssl,
                                          unsigned char *buf,
                                          size_t *olen )
@@ -1128,6 +1176,9 @@ static int ssl_write_server_hello( ssl_context *ssl )
     ssl_write_max_fragment_length_ext( ssl, p + 2 + ext_len, &olen );
     ext_len += olen;
 
+    ssl_write_truncated_hmac_ext( ssl, p + 2 + ext_len, &olen );
+    ext_len += olen;
+
     SSL_DEBUG_MSG( 3, ( "server hello, total extension length: %d", ext_len ) );
 
     *p++ = (unsigned char)( ( ext_len >> 8 ) & 0xFF );