Merge pull request #4664 from tom-daubney-arm/rm_truncated_HMAC_ext

Remove truncated HMAC extension
diff --git a/ChangeLog b/ChangeLog
index ddaf3fd..565ce1c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -32,8 +32,6 @@
    * Drop support for parsing SSLv2 ClientHello
      (MBEDTLS_SSL_SRV_SUPPORT_SSLV2_CLIENT_HELLO).
    * Drop support for SSLv3 (MBEDTLS_SSL_PROTO_SSL3).
-   * Drop support for compatibility with our own previous buggy
-     implementation of truncated HMAC (MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT).
    * Drop support for TLS record-level compression (MBEDTLS_ZLIB_SUPPORT).
    * Drop support for RC4 TLS ciphersuites.
    * Drop support for single-DES ciphersuites.
diff --git a/ChangeLog.d/rm-truncated-hmac-ext.txt b/ChangeLog.d/rm-truncated-hmac-ext.txt
new file mode 100644
index 0000000..3739256
--- /dev/null
+++ b/ChangeLog.d/rm-truncated-hmac-ext.txt
@@ -0,0 +1,5 @@
+Removals
+   * Remove MBEDTLS_SSL_TRUNCATED_HMAC and also remove
+     MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT config option. Users are better served by
+     using a CCM-8 ciphersuite than a CBC ciphersuite with truncated HMAC.
+     See issue #4341 for more details.
diff --git a/docs/3.0-migration-guide.md b/docs/3.0-migration-guide.md
index d0ba43d..d76cc17 100644
--- a/docs/3.0-migration-guide.md
+++ b/docs/3.0-migration-guide.md
@@ -137,17 +137,16 @@
 to date. If one of your peers is in that case, please try contacting them and
 encouraging them to upgrade their software.
 
-Remove support for compatibility with old Mbed TLS's truncated HMAC
--------------------------------------------------------------------
+Remove support for truncated HMAC
+---------------------------------
 
-This doesn't affect people using the default configuration as it was already
-disabled by default.
+This affects users of truncated HMAC, that is, users who called
+`mbedtls_ssl_conf_truncated_hmac( ..., MBEDTLS_SSL_TRUNC_HMAC_ENABLED)`,
+regardless of whether the standard version was used or compatibility version
+(`MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT`).
 
-This only affects TLS users who enabled `MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT` and
-used the Truncated HMAC extension to communicate with peers using old version
-of Mbed TLS. Please consider using a CCM-8 ciphersuite instead of the
-Truncated HMAC extension, or convincing your peer to upgrade their version of
-Mbed TLS.
+The recommended migration path for people who want minimal overhead is to use a
+CCM-8 ciphersuite.
 
 Remove support for TLS record-level compression
 -----------------------------------------------
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 85f7efd..36959ed 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -829,6 +829,10 @@
 #error "MBEDTLS_SSL_TLS1_3_PADDING_GRANULARITY was removed in Mbed TLS 3.0. See https://github.com/ARMmbed/mbedtls/issues/4335"
 #endif
 
+#if defined(MBEDTLS_SSL_TRUNCATED_HMAC) //no-check-names
+#error "MBEDTLS_SSL_TRUNCATED_HMAC was removed in Mbed TLS 3.0. See https://github.com/ARMmbed/mbedtls/issues/4341"
+#endif
+
 /*
  * Avoid warning from -pedantic. This is a convenient place for this
  * workaround since this is included by every single file before the
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 16f93f9..1a9c924 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1618,15 +1618,6 @@
 #define MBEDTLS_SSL_SERVER_NAME_INDICATION
 
 /**
- * \def MBEDTLS_SSL_TRUNCATED_HMAC
- *
- * Enable support for RFC 6066 truncated HMAC in SSL.
- *
- * Comment this macro to disable support for truncated HMAC in SSL
- */
-#define MBEDTLS_SSL_TRUNCATED_HMAC
-
-/**
  * \def MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
  *
  * When this option is enabled, the SSL buffer will be resized automatically
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 603615b..1a963c5 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -958,10 +958,6 @@
     unsigned char MBEDTLS_PRIVATE(mfl_code);     /*!< MaxFragmentLength negotiated by peer */
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    int MBEDTLS_PRIVATE(trunc_hmac);             /*!< flag for truncated hmac activation   */
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
     int MBEDTLS_PRIVATE(encrypt_then_mac);       /*!< flag for EtM activation                */
 #endif
@@ -1182,9 +1178,6 @@
 #if defined(MBEDTLS_SSL_RENEGOTIATION)
     unsigned int MBEDTLS_PRIVATE(disable_renegotiation) : 1; /*!< disable renegotiation?     */
 #endif
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    unsigned int MBEDTLS_PRIVATE(trunc_hmac) : 1;    /*!< negotiate truncated hmac?          */
-#endif
 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
     unsigned int MBEDTLS_PRIVATE(session_tickets) : 1;   /*!< use session tickets?           */
 #endif
@@ -3330,18 +3323,6 @@
 void mbedtls_ssl_conf_preference_order( mbedtls_ssl_config *conf, int order );
 #endif /* MBEDTLS_SSL_SRV_C */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-/**
- * \brief          Activate negotiation of truncated HMAC
- *                 (Default: MBEDTLS_SSL_TRUNC_HMAC_DISABLED)
- *
- * \param conf     SSL configuration
- * \param truncate Enable or disable (MBEDTLS_SSL_TRUNC_HMAC_ENABLED or
- *                                    MBEDTLS_SSL_TRUNC_HMAC_DISABLED)
- */
-void mbedtls_ssl_conf_truncated_hmac( mbedtls_ssl_config *conf, int truncate );
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 #if defined(MBEDTLS_SSL_SESSION_TICKETS) && defined(MBEDTLS_SSL_CLI_C)
 /**
  * \brief          Enable / Disable session tickets (client only).
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 9a44138..30e64c4 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -559,36 +559,6 @@
 }
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-static int ssl_write_truncated_hmac_ext( mbedtls_ssl_context *ssl,
-                                         unsigned char *buf,
-                                         const unsigned char *end,
-                                         size_t *olen )
-{
-    unsigned char *p = buf;
-
-    *olen = 0;
-
-    if( ssl->conf->trunc_hmac == MBEDTLS_SSL_TRUNC_HMAC_DISABLED )
-        return( 0 );
-
-    MBEDTLS_SSL_DEBUG_MSG( 3,
-        ( "client hello, adding truncated_hmac extension" ) );
-
-    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 4 );
-
-    *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_TRUNCATED_HMAC >> 8 ) & 0xFF );
-    *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_TRUNCATED_HMAC      ) & 0xFF );
-
-    *p++ = 0x00;
-    *p++ = 0x00;
-
-    *olen = 4;
-
-    return( 0 );
-}
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
 static int ssl_write_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
                                            unsigned char *buf,
@@ -1304,16 +1274,6 @@
     ext_len += olen;
 #endif
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    if( ( ret = ssl_write_truncated_hmac_ext( ssl, p + 2 + ext_len,
-                                              end, &olen ) ) != 0 )
-    {
-        MBEDTLS_SSL_DEBUG_RET( 1, "ssl_write_truncated_hmac_ext", ret );
-        return( ret );
-    }
-    ext_len += olen;
-#endif
-
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
     if( ( ret = ssl_write_encrypt_then_mac_ext( ssl, p + 2 + ext_len,
                                                 end, &olen ) ) != 0 )
@@ -1479,31 +1439,6 @@
 }
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-static int ssl_parse_truncated_hmac_ext( mbedtls_ssl_context *ssl,
-                                         const unsigned char *buf,
-                                         size_t len )
-{
-    if( ssl->conf->trunc_hmac == MBEDTLS_SSL_TRUNC_HMAC_DISABLED ||
-        len != 0 )
-    {
-        MBEDTLS_SSL_DEBUG_MSG( 1,
-            ( "non-matching truncated HMAC extension" ) );
-        mbedtls_ssl_send_alert_message(
-            ssl,
-            MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
-        return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
-    }
-
-    ((void) buf);
-
-    ssl->session_negotiate->trunc_hmac = MBEDTLS_SSL_TRUNC_HMAC_ENABLED;
-
-    return( 0 );
-}
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
 static int ssl_parse_cid_ext( mbedtls_ssl_context *ssl,
                               const unsigned char *buf,
@@ -2346,19 +2281,6 @@
             break;
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-        case MBEDTLS_TLS_EXT_TRUNCATED_HMAC:
-            MBEDTLS_SSL_DEBUG_MSG( 3, ( "found truncated_hmac extension" ) );
-
-            if( ( ret = ssl_parse_truncated_hmac_ext( ssl,
-                            ext + 4, ext_size ) ) != 0 )
-            {
-                return( ret );
-            }
-
-            break;
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
         case MBEDTLS_TLS_EXT_CID:
             MBEDTLS_SSL_DEBUG_MSG( 3, ( "found CID extension" ) );
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 29569d1..4715129 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -543,28 +543,6 @@
 }
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-static int ssl_parse_truncated_hmac_ext( mbedtls_ssl_context *ssl,
-                                         const unsigned char *buf,
-                                         size_t len )
-{
-    if( len != 0 )
-    {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
-        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-                                        MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
-        return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_HELLO );
-    }
-
-    ((void) buf);
-
-    if( ssl->conf->trunc_hmac == MBEDTLS_SSL_TRUNC_HMAC_ENABLED )
-        ssl->session_negotiate->trunc_hmac = MBEDTLS_SSL_TRUNC_HMAC_ENABLED;
-
-    return( 0 );
-}
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
 static int ssl_parse_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
                                       const unsigned char *buf,
@@ -1703,16 +1681,6 @@
                 break;
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-            case MBEDTLS_TLS_EXT_TRUNCATED_HMAC:
-                MBEDTLS_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;
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
             case MBEDTLS_TLS_EXT_CID:
                 MBEDTLS_SSL_DEBUG_MSG( 3, ( "found CID extension" ) );
@@ -1721,7 +1689,7 @@
                 if( ret != 0 )
                     return( ret );
                 break;
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
             case MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC:
@@ -1967,31 +1935,6 @@
     return( 0 );
 }
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-static void ssl_write_truncated_hmac_ext( mbedtls_ssl_context *ssl,
-                                          unsigned char *buf,
-                                          size_t *olen )
-{
-    unsigned char *p = buf;
-
-    if( ssl->session_negotiate->trunc_hmac == MBEDTLS_SSL_TRUNC_HMAC_DISABLED )
-    {
-        *olen = 0;
-        return;
-    }
-
-    MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, adding truncated hmac extension" ) );
-
-    *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_TRUNCATED_HMAC >> 8 ) & 0xFF );
-    *p++ = (unsigned char)( ( MBEDTLS_TLS_EXT_TRUNCATED_HMAC      ) & 0xFF );
-
-    *p++ = 0x00;
-    *p++ = 0x00;
-
-    *olen = 4;
-}
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
 static void ssl_write_cid_ext( mbedtls_ssl_context *ssl,
                                unsigned char *buf,
@@ -2654,11 +2597,6 @@
     ext_len += olen;
 #endif
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    ssl_write_truncated_hmac_ext( ssl, p + 2 + ext_len, &olen );
-    ext_len += olen;
-#endif
-
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
     ssl_write_cid_ext( ssl, p + 2 + ext_len, &olen );
     ext_len += olen;
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 2961637..1bfbc84 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -672,9 +672,6 @@
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                                    int encrypt_then_mac,
 #endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-                                   int trunc_hmac,
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
 #endif /* MBEDTLS_SSL_SOME_SUITES_USE_MAC */
                                    ssl_tls_prf_t tls_prf,
                                    const unsigned char randbytes[64],
@@ -845,18 +842,6 @@
         mac_key_len = mbedtls_md_get_size( md_info );
         transform->maclen = mac_key_len;
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-        /*
-         * If HMAC is to be truncated, we shall keep the leftmost bytes,
-         * (rfc 6066 page 13 or rfc 2104 section 4),
-         * so we only need to adjust the length here.
-         */
-        if( trunc_hmac == MBEDTLS_SSL_TRUNC_HMAC_ENABLED )
-        {
-            transform->maclen = MBEDTLS_SSL_TRUNCATED_HMAC_LEN;
-        }
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
         /* IV length */
         transform->ivlen = cipher_info->iv_size;
 
@@ -1368,9 +1353,6 @@
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                                   ssl->session_negotiate->encrypt_then_mac,
 #endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-                                  ssl->session_negotiate->trunc_hmac,
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
 #endif /* MBEDTLS_SSL_SOME_SUITES_USE_MAC */
                                   ssl->handshake->tls_prf,
                                   ssl->handshake->randbytes,
@@ -4141,13 +4123,6 @@
 }
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-void mbedtls_ssl_conf_truncated_hmac( mbedtls_ssl_config *conf, int truncate )
-{
-    conf->trunc_hmac = truncate;
-}
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 void mbedtls_ssl_conf_legacy_renegotiation( mbedtls_ssl_config *conf, int allow_legacy )
 {
     conf->allow_legacy_renegotiation = allow_legacy;
@@ -4536,11 +4511,7 @@
 #define SSL_SERIALIZED_SESSION_CONFIG_MFL 0
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-#define SSL_SERIALIZED_SESSION_CONFIG_TRUNC_HMAC 1
-#else
 #define SSL_SERIALIZED_SESSION_CONFIG_TRUNC_HMAC 0
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
 
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
 #define SSL_SERIALIZED_SESSION_CONFIG_ETM 1
@@ -4783,13 +4754,6 @@
         *p++ = session->mfl_code;
 #endif
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    used += 1;
-
-    if( used <= buf_len )
-        *p++ = (unsigned char)( ( session->trunc_hmac ) & 0xFF );
-#endif
-
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
     used += 1;
 
@@ -5025,13 +4989,6 @@
     session->mfl_code = *p++;
 #endif
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    if( 1 > (size_t)( end - p ) )
-        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
-
-    session->trunc_hmac = *p++;
-#endif
-
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
     if( 1 > (size_t)( end - p ) )
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
@@ -5848,9 +5805,6 @@
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                   ssl->session->encrypt_then_mac,
 #endif
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-                  ssl->session->trunc_hmac,
-#endif
 #endif /* MBEDTLS_SSL_SOME_SUITES_USE_MAC */
                   ssl_tls12prf_from_cs( ssl->session->ciphersuite ),
                   p, /* currently pointing to randbytes */
diff --git a/programs/fuzz/fuzz_client.c b/programs/fuzz/fuzz_client.c
index cbd9483..ab2d134 100644
--- a/programs/fuzz/fuzz_client.c
+++ b/programs/fuzz/fuzz_client.c
@@ -102,9 +102,6 @@
     {
         mbedtls_ssl_conf_authmode( &conf, MBEDTLS_SSL_VERIFY_NONE );
     }
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    mbedtls_ssl_conf_truncated_hmac( &conf, (options & 8) ? MBEDTLS_SSL_TRUNC_HMAC_ENABLED : MBEDTLS_SSL_TRUNC_HMAC_DISABLED);
-#endif
 #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
     mbedtls_ssl_conf_extended_master_secret( &conf, (options & 0x10) ? MBEDTLS_SSL_EXTENDED_MS_DISABLED : MBEDTLS_SSL_EXTENDED_MS_ENABLED);
 #endif
diff --git a/programs/fuzz/fuzz_server.c b/programs/fuzz/fuzz_server.c
index c35b425..e6eb5a7 100644
--- a/programs/fuzz/fuzz_server.c
+++ b/programs/fuzz/fuzz_server.c
@@ -128,9 +128,6 @@
                                             &ticket_ctx );
     }
 #endif
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    mbedtls_ssl_conf_truncated_hmac( &conf, (options & 0x8) ? MBEDTLS_SSL_TRUNC_HMAC_ENABLED : MBEDTLS_SSL_TRUNC_HMAC_DISABLED);
-#endif
 #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
     mbedtls_ssl_conf_extended_master_secret( &conf, (options & 0x10) ? MBEDTLS_SSL_EXTENDED_MS_DISABLED : MBEDTLS_SSL_EXTENDED_MS_ENABLED);
 #endif
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index 322cef8..dad65e3 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -235,13 +235,6 @@
 #define USAGE_SRTP ""
 #endif /* MBEDTLS_SSL_EXPORT_KEYS */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-#define USAGE_TRUNC_HMAC                                    \
-    "    trunc_hmac=%%d       default: library default\n"
-#else
-#define USAGE_TRUNC_HMAC ""
-#endif /* MBEDTLS_SSL_TRUNCATED_HMAC */
-
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
 #define USAGE_MAX_FRAG_LEN                                      \
     "    max_frag_len=%%d     default: 16384 (tls default)\n"   \
@@ -394,7 +387,6 @@
     USAGE_TICKETS                                           \
     USAGE_EAP_TLS                                           \
     USAGE_MAX_FRAG_LEN                                      \
-    USAGE_TRUNC_HMAC                                        \
     USAGE_CONTEXT_CRT_CB                                    \
     USAGE_ALPN                                              \
     USAGE_EMS                                               \
@@ -1721,11 +1713,6 @@
     }
 #endif /* MBEDTLS_SSL_DTLS_SRTP */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    if( opt.trunc_hmac != DFL_TRUNC_HMAC )
-        mbedtls_ssl_conf_truncated_hmac( &conf, opt.trunc_hmac );
-#endif
-
 #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
     if( opt.extended_ms != DFL_EXTENDED_MS )
         mbedtls_ssl_conf_extended_master_secret( &conf, opt.extended_ms );
diff --git a/programs/ssl/ssl_context_info.c b/programs/ssl/ssl_context_info.c
index 1c506b7..b04d4b5 100644
--- a/programs/ssl/ssl_context_info.c
+++ b/programs/ssl/ssl_context_info.c
@@ -862,7 +862,6 @@
     print_if_bit( "MBEDTLS_HAVE_TIME", SESSION_CONFIG_TIME_BIT, session_cfg_flag );
     print_if_bit( "MBEDTLS_X509_CRT_PARSE_C", SESSION_CONFIG_CRT_BIT, session_cfg_flag );
     print_if_bit( "MBEDTLS_SSL_MAX_FRAGMENT_LENGTH", SESSION_CONFIG_MFL_BIT, session_cfg_flag );
-    print_if_bit( "MBEDTLS_SSL_TRUNCATED_HMAC", SESSION_CONFIG_TRUNC_HMAC_BIT, session_cfg_flag );
     print_if_bit( "MBEDTLS_SSL_ENCRYPT_THEN_MAC", SESSION_CONFIG_ETM_BIT, session_cfg_flag );
     print_if_bit( "MBEDTLS_SSL_SESSION_TICKETS", SESSION_CONFIG_TICKET_BIT, session_cfg_flag );
     print_if_bit( "MBEDTLS_SSL_SESSION_TICKETS and client", SESSION_CONFIG_CLIENT_TICKET_BIT, session_cfg_flag );
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index 51125bd..0e242a5 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -334,13 +334,6 @@
 #define USAGE_MAX_FRAG_LEN ""
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-#define USAGE_TRUNC_HMAC \
-    "    trunc_hmac=%%d       default: library default\n"
-#else
-#define USAGE_TRUNC_HMAC ""
-#endif
-
 #if defined(MBEDTLS_SSL_ALPN)
 #define USAGE_ALPN \
     "    alpn=%%s             default: \"\" (disabled)\n"   \
@@ -487,7 +480,6 @@
     USAGE_NSS_KEYLOG_FILE                                   \
     USAGE_CACHE                                             \
     USAGE_MAX_FRAG_LEN                                      \
-    USAGE_TRUNC_HMAC                                        \
     USAGE_ALPN                                              \
     USAGE_EMS                                               \
     USAGE_ETM                                               \
@@ -2510,11 +2502,6 @@
     }
 #endif /* MBEDTLS_SSL_DTLS_SRTP */
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    if( opt.trunc_hmac != DFL_TRUNC_HMAC )
-        mbedtls_ssl_conf_truncated_hmac( &conf, opt.trunc_hmac );
-#endif
-
 #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
     if( opt.extended_ms != DFL_EXTENDED_MS )
         mbedtls_ssl_conf_extended_master_secret( &conf, opt.extended_ms );
diff --git a/tests/context-info.sh b/tests/context-info.sh
index e02d330..88dfcaa 100755
--- a/tests/context-info.sh
+++ b/tests/context-info.sh
@@ -210,7 +210,6 @@
          -u "MBEDTLS_HAVE_TIME$" \
          -u "MBEDTLS_X509_CRT_PARSE_C$" \
          -u "MBEDTLS_SSL_MAX_FRAGMENT_LENGTH$" \
-         -u "MBEDTLS_SSL_TRUNCATED_HMAC$" \
          -u "MBEDTLS_SSL_ENCRYPT_THEN_MAC$" \
          -u "MBEDTLS_SSL_SESSION_TICKETS$" \
          -u "MBEDTLS_SSL_SESSION_TICKETS and client$" \
@@ -233,7 +232,6 @@
          -u "MBEDTLS_HAVE_TIME$" \
          -u "MBEDTLS_X509_CRT_PARSE_C$" \
          -u "MBEDTLS_SSL_MAX_FRAGMENT_LENGTH$" \
-         -u "MBEDTLS_SSL_TRUNCATED_HMAC$" \
          -u "MBEDTLS_SSL_ENCRYPT_THEN_MAC$" \
          -u "MBEDTLS_SSL_SESSION_TICKETS$" \
          -u "MBEDTLS_SSL_SESSION_TICKETS and client$" \
@@ -339,7 +337,6 @@
          "srv_min_cfg.txt" \
          -n "ERROR" \
          -n "MBEDTLS_SSL_MAX_FRAGMENT_LENGTH$" \
-         -n "MBEDTLS_SSL_TRUNCATED_HMAC$" \
          -n "MBEDTLS_SSL_ENCRYPT_THEN_MAC$" \
          -n "MBEDTLS_SSL_SESSION_TICKETS$" \
          -n "MBEDTLS_SSL_SESSION_TICKETS and client$" \
@@ -350,7 +347,6 @@
          "cli_min_cfg.txt" \
          -n "ERROR" \
          -n "MBEDTLS_SSL_MAX_FRAGMENT_LENGTH$" \
-         -n "MBEDTLS_SSL_TRUNCATED_HMAC$" \
          -n "MBEDTLS_SSL_ENCRYPT_THEN_MAC$" \
          -n "MBEDTLS_SSL_SESSION_TICKETS$" \
          -n "MBEDTLS_SSL_SESSION_TICKETS and client$" \
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index d122111..89eece6 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -1464,102 +1464,6 @@
             -S "next record in same datagram" \
             -C "next record in same datagram"
 
-# Tests for Truncated HMAC extension
-
-run_test    "Truncated HMAC: client default, server default" \
-            "$P_SRV debug_level=4" \
-            "$P_CLI force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC: client disabled, server default" \
-            "$P_SRV debug_level=4" \
-            "$P_CLI force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=0" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC: client enabled, server default" \
-            "$P_SRV debug_level=4" \
-            "$P_CLI force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=1" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC: client enabled, server disabled" \
-            "$P_SRV debug_level=4 trunc_hmac=0" \
-            "$P_CLI force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=1" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC: client disabled, server enabled" \
-            "$P_SRV debug_level=4 trunc_hmac=1" \
-            "$P_CLI force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=0" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC: client enabled, server enabled" \
-            "$P_SRV debug_level=4 trunc_hmac=1" \
-            "$P_CLI force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=1" \
-            0 \
-            -S "dumping 'expected mac' (20 bytes)" \
-            -s "dumping 'expected mac' (10 bytes)"
-
-run_test    "Truncated HMAC, DTLS: client default, server default" \
-            "$P_SRV dtls=1 debug_level=4" \
-            "$P_CLI dtls=1 force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC, DTLS: client disabled, server default" \
-            "$P_SRV dtls=1 debug_level=4" \
-            "$P_CLI dtls=1 force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=0" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC, DTLS: client enabled, server default" \
-            "$P_SRV dtls=1 debug_level=4" \
-            "$P_CLI dtls=1 force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=1" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC, DTLS: client enabled, server disabled" \
-            "$P_SRV dtls=1 debug_level=4 trunc_hmac=0" \
-            "$P_CLI dtls=1 force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=1" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC, DTLS: client disabled, server enabled" \
-            "$P_SRV dtls=1 debug_level=4 trunc_hmac=1" \
-            "$P_CLI dtls=1 force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=0" \
-            0 \
-            -s "dumping 'expected mac' (20 bytes)" \
-            -S "dumping 'expected mac' (10 bytes)"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Truncated HMAC, DTLS: client enabled, server enabled" \
-            "$P_SRV dtls=1 debug_level=4 trunc_hmac=1" \
-            "$P_CLI dtls=1 force_ciphersuite=TLS-RSA-WITH-AES-128-CBC-SHA trunc_hmac=1" \
-            0 \
-            -S "dumping 'expected mac' (20 bytes)" \
-            -s "dumping 'expected mac' (10 bytes)"
-
 # Tests for Context serialization
 
 requires_config_enabled MBEDTLS_SSL_CONTEXT_SERIALIZATION
@@ -5660,22 +5564,6 @@
             0 \
             -s "Read from client: 1 bytes read"
 
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Small client packet TLS 1.2 BlockCipher, truncated MAC" \
-            "$P_SRV trunc_hmac=1" \
-            "$P_CLI request_size=1 force_version=tls1_2 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1" \
-            0 \
-            -s "Read from client: 1 bytes read"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Small client packet TLS 1.2 BlockCipher, without EtM, truncated MAC" \
-            "$P_SRV trunc_hmac=1" \
-            "$P_CLI request_size=1 force_version=tls1_2 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1 etm=0" \
-            0 \
-            -s "Read from client: 1 bytes read"
-
 run_test    "Small client packet TLS 1.2 AEAD" \
             "$P_SRV" \
             "$P_CLI request_size=1 force_version=tls1_2 \
@@ -5708,24 +5596,6 @@
             0 \
             -s "Read from client: 1 bytes read"
 
-requires_config_enabled MBEDTLS_SSL_PROTO_DTLS
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Small client packet DTLS 1.2, truncated hmac" \
-            "$P_SRV dtls=1 force_version=dtls1_2 trunc_hmac=1" \
-            "$P_CLI dtls=1 request_size=1 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1" \
-            0 \
-            -s "Read from client: 1 bytes read"
-
-requires_config_enabled MBEDTLS_SSL_PROTO_DTLS
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Small client packet DTLS 1.2, without EtM, truncated MAC" \
-            "$P_SRV dtls=1 force_version=dtls1_2 trunc_hmac=1 etm=0" \
-            "$P_CLI dtls=1 request_size=1 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1"\
-            0 \
-            -s "Read from client: 1 bytes read"
-
 # Tests for small server packets
 
 run_test    "Small server packet TLS 1.2 BlockCipher" \
@@ -5749,22 +5619,6 @@
             0 \
             -c "Read from server: 1 bytes read"
 
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Small server packet TLS 1.2 BlockCipher, truncated MAC" \
-            "$P_SRV response_size=1 trunc_hmac=1" \
-            "$P_CLI force_version=tls1_2 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1" \
-            0 \
-            -c "Read from server: 1 bytes read"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Small server packet TLS 1.2 BlockCipher, without EtM, truncated MAC" \
-            "$P_SRV response_size=1 trunc_hmac=1" \
-            "$P_CLI force_version=tls1_2 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1 etm=0" \
-            0 \
-            -c "Read from server: 1 bytes read"
-
 run_test    "Small server packet TLS 1.2 AEAD" \
             "$P_SRV response_size=1" \
             "$P_CLI force_version=tls1_2 \
@@ -5797,24 +5651,6 @@
             0 \
             -c "Read from server: 1 bytes read"
 
-requires_config_enabled MBEDTLS_SSL_PROTO_DTLS
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Small server packet DTLS 1.2, truncated hmac" \
-            "$P_SRV dtls=1 response_size=1 force_version=dtls1_2 trunc_hmac=1" \
-            "$P_CLI dtls=1 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1" \
-            0 \
-            -c "Read from server: 1 bytes read"
-
-requires_config_enabled MBEDTLS_SSL_PROTO_DTLS
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Small server packet DTLS 1.2, without EtM, truncated MAC" \
-            "$P_SRV dtls=1 response_size=1 force_version=dtls1_2 trunc_hmac=1 etm=0" \
-            "$P_CLI dtls=1 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1"\
-            0 \
-            -c "Read from server: 1 bytes read"
-
 # Test for large client packets
 
 # How many fragments do we expect to write $1 bytes?
@@ -5845,23 +5681,6 @@
             -c "16384 bytes written in $(fragments_for_write 16384) fragments" \
             -s "Read from client: $MAX_CONTENT_LEN bytes read"
 
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Large client packet TLS 1.2 BlockCipher, truncated MAC" \
-            "$P_SRV trunc_hmac=1" \
-            "$P_CLI request_size=16384 force_version=tls1_2 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1" \
-            0 \
-            -s "Read from client: $MAX_CONTENT_LEN bytes read"
-
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Large client packet TLS 1.2 BlockCipher, without EtM, truncated MAC" \
-            "$P_SRV trunc_hmac=1" \
-            "$P_CLI request_size=16384 force_version=tls1_2 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA trunc_hmac=1 etm=0" \
-            0 \
-            -c "16384 bytes written in $(fragments_for_write 16384) fragments" \
-            -s "Read from client: $MAX_CONTENT_LEN bytes read"
-
 run_test    "Large client packet TLS 1.2 AEAD" \
             "$P_SRV" \
             "$P_CLI request_size=16384 force_version=tls1_2 \
@@ -5900,15 +5719,6 @@
             0 \
             -c "Read from server: 16384 bytes read"
 
-requires_config_enabled MBEDTLS_SSL_TRUNCATED_HMAC
-run_test    "Large server packet TLS 1.2 BlockCipher truncated MAC" \
-            "$P_SRV response_size=16384" \
-            "$P_CLI force_version=tls1_2 \
-             force_ciphersuite=TLS-RSA-WITH-AES-256-CBC-SHA \
-             trunc_hmac=1" \
-            0 \
-            -c "Read from server: 16384 bytes read"
-
 run_test    "Large server packet TLS 1.2 BlockCipher, without EtM, truncated MAC" \
             "$P_SRV response_size=16384 trunc_hmac=1" \
             "$P_CLI force_version=tls1_2 \
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index d4aad60..d5123fa 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -1508,9 +1508,6 @@
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
     session->mfl_code = 1;
 #endif
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    session->trunc_hmac = 1;
-#endif
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
     session->encrypt_then_mac = 1;
 #endif
@@ -4082,10 +4079,6 @@
     TEST_ASSERT( original.mfl_code == restored.mfl_code );
 #endif
 
-#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
-    TEST_ASSERT( original.trunc_hmac == restored.trunc_hmac );
-#endif
-
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
     TEST_ASSERT( original.encrypt_then_mac == restored.encrypt_then_mac );
 #endif