/* * TLS 1.3 server-side functions * * Copyright The Mbed TLS Contributors * SPDX-License-Identifier: Apache-2.0 * * Licensed under the Apache License, Version 2.0 (the "License"); you may * not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include "common.h" #if defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_SSL_PROTO_TLS1_3) #include "mbedtls/debug.h" #include "ssl_misc.h" #include "ssl_tls13_keys.h" #include "ssl_debug_helpers.h" #if defined(MBEDTLS_ECP_C) #include "mbedtls/ecp.h" #endif /* MBEDTLS_ECP_C */ #if defined(MBEDTLS_PLATFORM_C) #include "mbedtls/platform.h" #else #include #define mbedtls_calloc calloc #define mbedtls_free free #endif /* MBEDTLS_PLATFORM_C */ /* From RFC 8446: * struct { * ProtocolVersion versions<2..254>; * } SupportedVersions; */ static int ssl_tls13_parse_supported_versions_ext( mbedtls_ssl_context *ssl, const unsigned char *buf, const unsigned char *end ) { const unsigned char *p = buf; size_t versions_len; const unsigned char *versions_end; uint16_t tls_version; int tls13_supported = 0; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, 1 ); versions_len = p[0]; p += 1; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, versions_len ); versions_end = p + versions_len; while( p < versions_end ) { MBEDTLS_SSL_CHK_BUF_READ_PTR( p, versions_end, 2 ); tls_version = mbedtls_ssl_read_version( p, ssl->conf->transport ); p += 2; /* In this implementation we only support TLS 1.3 and DTLS 1.3. */ if( tls_version == MBEDTLS_SSL_VERSION_TLS1_3 ) { tls13_supported = 1; break; } } if( !tls13_supported ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "TLS 1.3 is not supported by the client" ) ); MBEDTLS_SSL_PEND_FATAL_ALERT( MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION, MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION ); return( MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION ); } MBEDTLS_SSL_DEBUG_MSG( 1, ( "Negotiated version. Supported is [%04x]", (unsigned int)tls_version ) ); return( 0 ); } #if defined(MBEDTLS_ECDH_C) /* * * From RFC 8446: * enum { * ... (0xFFFF) * } NamedGroup; * struct { * NamedGroup named_group_list<2..2^16-1>; * } NamedGroupList; */ static int ssl_tls13_parse_supported_groups_ext( mbedtls_ssl_context *ssl, const unsigned char *buf, const unsigned char *end ) { const unsigned char *p = buf; size_t named_group_list_len; const unsigned char *named_group_list_end; MBEDTLS_SSL_DEBUG_BUF( 3, "supported_groups extension", p, end - buf ); MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, 2 ); named_group_list_len = MBEDTLS_GET_UINT16_BE( p, 0 ); p += 2; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, named_group_list_len ); named_group_list_end = p + named_group_list_len; ssl->handshake->hrr_selected_group = 0; while( p < named_group_list_end ) { uint16_t named_group; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, named_group_list_end, 2 ); named_group = MBEDTLS_GET_UINT16_BE( p, 0 ); p += 2; MBEDTLS_SSL_DEBUG_MSG( 2, ( "got named group: %d", named_group ) ); if( ! mbedtls_ssl_named_group_is_offered( ssl, named_group ) || ! mbedtls_ssl_named_group_is_supported( named_group ) || ssl->handshake->hrr_selected_group != 0 ) { continue; } MBEDTLS_SSL_DEBUG_MSG( 2, ( "add named group (%04x) into received list.", named_group ) ); ssl->handshake->hrr_selected_group = named_group; } return( 0 ); } #endif /* MBEDTLS_ECDH_C */ #define SSL_TLS1_3_PARSE_KEY_SHARES_EXT_NO_MATCH 1 #if defined(MBEDTLS_ECDH_C) /* * ssl_tls13_parse_key_shares_ext() verifies whether the information in the * extension is correct and stores the first acceptable key share and its associated group. * * Possible return values are: * - 0: Successful processing of the client provided key share extension. * - SSL_TLS1_3_PARSE_KEY_SHARES_EXT_NO_MATCH: The key shares provided by the client * does not match a group supported by the server. A HelloRetryRequest will * be needed. * - A negative value for fatal errors. */ static int ssl_tls13_parse_key_shares_ext( mbedtls_ssl_context *ssl, const unsigned char *buf, const unsigned char *end ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; unsigned char const *p = buf; unsigned char const *client_shares_end; size_t client_shares_len, key_exchange_len; int match_found = 0; /* From RFC 8446: * * struct { * KeyShareEntry client_shares<0..2^16-1>; * } KeyShareClientHello; * */ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, 2 ); client_shares_len = MBEDTLS_GET_UINT16_BE( p, 0 ); p += 2; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, client_shares_len ); ssl->handshake->offered_group_id = 0; client_shares_end = p + client_shares_len; /* We try to find a suitable key share entry and copy it to the * handshake context. Later, we have to find out whether we can do * something with the provided key share or whether we have to * dismiss it and send a HelloRetryRequest message. */ for( ; p < client_shares_end; p += key_exchange_len ) { uint16_t group; /* * struct { * NamedGroup group; * opaque key_exchange<1..2^16-1>; * } KeyShareEntry; */ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, client_shares_end, 4 ); group = MBEDTLS_GET_UINT16_BE( p, 0 ); p += 2; key_exchange_len = MBEDTLS_GET_UINT16_BE( p, 0 ); p += 2; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, client_shares_end, key_exchange_len ); /* Continue parsing even if we have already found a match, * for input validation purposes. */ if( match_found == 1 ) continue; if( ! mbedtls_ssl_named_group_is_offered( ssl, group ) || ! mbedtls_ssl_named_group_is_supported( group ) ) { continue; } /* * For now, we only support ECDHE groups. */ if( mbedtls_ssl_tls13_named_group_is_ecdhe( group ) ) { const mbedtls_ecp_curve_info *curve_info = mbedtls_ecp_curve_info_from_tls_id( group ); ((void) curve_info); MBEDTLS_SSL_DEBUG_MSG( 2, ( "ECDH curve: %s", curve_info->name ) ); ret = mbedtls_ssl_tls13_read_public_ecdhe_share( ssl, p - 2, key_exchange_len + 2 ); if( ret != 0 ) return( ret ); match_found = 1; } else { MBEDTLS_SSL_DEBUG_MSG( 4, ( "Unrecognized NamedGroup %u", (unsigned) group ) ); continue; } ssl->handshake->offered_group_id = group; } if( match_found == 0 ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "no matching key share" ) ); return( SSL_TLS1_3_PARSE_KEY_SHARES_EXT_NO_MATCH ); } return( 0 ); } #endif /* MBEDTLS_ECDH_C */ #if defined(MBEDTLS_DEBUG_C) static void ssl_tls13_debug_print_client_hello_exts( mbedtls_ssl_context *ssl ) { ((void) ssl); MBEDTLS_SSL_DEBUG_MSG( 3, ( "Supported Extensions:" ) ); MBEDTLS_SSL_DEBUG_MSG( 3, ( "- KEY_SHARE_EXTENSION ( %s )", ( ( ssl->handshake->extensions_present & MBEDTLS_SSL_EXT_KEY_SHARE ) > 0 ) ? "TRUE" : "FALSE" ) ); MBEDTLS_SSL_DEBUG_MSG( 3, ( "- PSK_KEY_EXCHANGE_MODES_EXTENSION ( %s )", ( ( ssl->handshake->extensions_present & MBEDTLS_SSL_EXT_PSK_KEY_EXCHANGE_MODES ) > 0 ) ? "TRUE" : "FALSE" ) ); MBEDTLS_SSL_DEBUG_MSG( 3, ( "- PRE_SHARED_KEY_EXTENSION ( %s )", ( ( ssl->handshake->extensions_present & MBEDTLS_SSL_EXT_PRE_SHARED_KEY ) > 0 ) ? "TRUE" : "FALSE" ) ); MBEDTLS_SSL_DEBUG_MSG( 3, ( "- SIGNATURE_ALGORITHM_EXTENSION ( %s )", ( ( ssl->handshake->extensions_present & MBEDTLS_SSL_EXT_SIG_ALG ) > 0 ) ? "TRUE" : "FALSE" ) ); MBEDTLS_SSL_DEBUG_MSG( 3, ( "- SUPPORTED_GROUPS_EXTENSION ( %s )", ( ( ssl->handshake->extensions_present & MBEDTLS_SSL_EXT_SUPPORTED_GROUPS ) >0 ) ? "TRUE" : "FALSE" ) ); MBEDTLS_SSL_DEBUG_MSG( 3, ( "- SUPPORTED_VERSION_EXTENSION ( %s )", ( ( ssl->handshake->extensions_present & MBEDTLS_SSL_EXT_SUPPORTED_VERSIONS ) > 0 ) ? "TRUE" : "FALSE" ) ); #if defined ( MBEDTLS_SSL_SERVER_NAME_INDICATION ) MBEDTLS_SSL_DEBUG_MSG( 3, ( "- SERVERNAME_EXTENSION ( %s )", ( ( ssl->handshake->extensions_present & MBEDTLS_SSL_EXT_SERVERNAME ) > 0 ) ? "TRUE" : "FALSE" ) ); #endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */ } #endif /* MBEDTLS_DEBUG_C */ static int ssl_tls13_client_hello_has_exts( mbedtls_ssl_context *ssl, int exts_mask ) { int masked = ssl->handshake->extensions_present & exts_mask; return( masked == exts_mask ); } static int ssl_tls13_client_hello_has_exts_for_ephemeral_key_exchange( mbedtls_ssl_context *ssl ) { return( ssl_tls13_client_hello_has_exts( ssl, MBEDTLS_SSL_EXT_SUPPORTED_GROUPS | MBEDTLS_SSL_EXT_KEY_SHARE | MBEDTLS_SSL_EXT_SIG_ALG ) ); } static int ssl_tls13_check_ephemeral_key_exchange( mbedtls_ssl_context *ssl ) { if( !mbedtls_ssl_conf_tls13_ephemeral_enabled( ssl ) ) return( 0 ); if( !ssl_tls13_client_hello_has_exts_for_ephemeral_key_exchange( ssl ) ) return( 0 ); ssl->handshake->tls13_kex_modes = MBEDTLS_SSL_TLS1_3_KEY_EXCHANGE_MODE_EPHEMERAL; return( 1 ); } /* * * STATE HANDLING: ClientHello * * There are three possible classes of outcomes when parsing the ClientHello: * * 1) The ClientHello was well-formed and matched the server's configuration. * * In this case, the server progresses to sending its ServerHello. * * 2) The ClientHello was well-formed but didn't match the server's * configuration. * * For example, the client might not have offered a key share which * the server supports, or the server might require a cookie. * * In this case, the server sends a HelloRetryRequest. * * 3) The ClientHello was ill-formed * * In this case, we abort the handshake. * */ /* * Structure of this message: * * uint16 ProtocolVersion; * opaque Random[32]; * uint8 CipherSuite[2]; // Cryptographic suite selector * * struct { * ProtocolVersion legacy_version = 0x0303; // TLS v1.2 * Random random; * opaque legacy_session_id<0..32>; * CipherSuite cipher_suites<2..2^16-2>; * opaque legacy_compression_methods<1..2^8-1>; * Extension extensions<8..2^16-1>; * } ClientHello; */ #define SSL_CLIENT_HELLO_OK 0 #define SSL_CLIENT_HELLO_HRR_REQUIRED 1 static int ssl_tls13_parse_client_hello( mbedtls_ssl_context *ssl, const unsigned char *buf, const unsigned char *end ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; const unsigned char *p = buf; size_t legacy_session_id_len; const unsigned char *cipher_suites; size_t cipher_suites_len; const unsigned char *cipher_suites_end; size_t extensions_len; const unsigned char *extensions_end; const mbedtls_ssl_ciphersuite_t* ciphersuite_info; ssl->handshake->extensions_present = MBEDTLS_SSL_EXT_NONE; /* * ClientHello layout: * 0 . 1 protocol version * 2 . 33 random bytes * 34 . 34 session id length ( 1 byte ) * 35 . 34+x session id * .. . .. ciphersuite list length ( 2 bytes ) * .. . .. ciphersuite list * .. . .. compression alg. list length ( 1 byte ) * .. . .. compression alg. list * .. . .. extensions length ( 2 bytes, optional ) * .. . .. extensions ( optional ) */ /* * Minimal length ( with everything empty and extensions ommitted ) is * 2 + 32 + 1 + 2 + 1 = 38 bytes. Check that first, so that we can * read at least up to session id length without worrying. */ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, 38 ); /* ... * ProtocolVersion legacy_version = 0x0303; // TLS 1.2 * ... * with ProtocolVersion defined as: * uint16 ProtocolVersion; */ if( mbedtls_ssl_read_version( p, ssl->conf->transport ) != MBEDTLS_SSL_VERSION_TLS1_2 ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "Unsupported version of TLS." ) ); MBEDTLS_SSL_PEND_FATAL_ALERT( MBEDTLS_SSL_ALERT_MSG_PROTOCOL_VERSION, MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION ); return ( MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION ); } p += 2; /* * Only support TLS 1.3 currently, temporarily set the version. */ ssl->tls_version = MBEDTLS_SSL_VERSION_TLS1_3; /* --- * Random random; * --- * with Random defined as: * opaque Random[32]; */ MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, random bytes", p, MBEDTLS_CLIENT_HELLO_RANDOM_LEN ); memcpy( &ssl->handshake->randbytes[0], p, MBEDTLS_CLIENT_HELLO_RANDOM_LEN ); p += MBEDTLS_CLIENT_HELLO_RANDOM_LEN; /* --- * opaque legacy_session_id<0..32>; * --- */ legacy_session_id_len = p[0]; p++; if( legacy_session_id_len > sizeof( ssl->session_negotiate->id ) ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) ); return( MBEDTLS_ERR_SSL_DECODE_ERROR ); } ssl->session_negotiate->id_len = legacy_session_id_len; MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, session id", p, legacy_session_id_len ); /* * Check we have enough data for the legacy session identifier * and the ciphersuite list length. */ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, legacy_session_id_len + 2 ); memcpy( &ssl->session_negotiate->id[0], p, legacy_session_id_len ); p += legacy_session_id_len; cipher_suites_len = MBEDTLS_GET_UINT16_BE( p, 0 ); p += 2; /* Check we have enough data for the ciphersuite list, the legacy * compression methods and the length of the extensions. */ MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, cipher_suites_len + 2 + 2 ); /* --- * CipherSuite cipher_suites<2..2^16-2>; * --- * with CipherSuite defined as: * uint8 CipherSuite[2]; */ cipher_suites = p; cipher_suites_end = p + cipher_suites_len; MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, ciphersuitelist", p, cipher_suites_len ); /* * Search for a matching ciphersuite */ int ciphersuite_match = 0; for ( ; p < cipher_suites_end; p += 2 ) { uint16_t cipher_suite; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, cipher_suites_end, 2 ); cipher_suite = MBEDTLS_GET_UINT16_BE( p, 0 ); ciphersuite_info = mbedtls_ssl_ciphersuite_from_id( cipher_suite ); /* * Check whether this ciphersuite is valid and offered. */ if( ( mbedtls_ssl_validate_ciphersuite( ssl, ciphersuite_info, ssl->tls_version, ssl->tls_version ) != 0 ) || !mbedtls_ssl_tls13_cipher_suite_is_offered( ssl, cipher_suite ) ) continue; ssl->session_negotiate->ciphersuite = cipher_suite; ssl->handshake->ciphersuite_info = ciphersuite_info; ciphersuite_match = 1; break; } if( !ciphersuite_match ) { MBEDTLS_SSL_PEND_FATAL_ALERT( MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE, MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE ); return ( MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE ); } MBEDTLS_SSL_DEBUG_MSG( 2, ( "selected ciphersuite: %s", ciphersuite_info->name ) ); p = cipher_suites + cipher_suites_len; /* ... * opaque legacy_compression_methods<1..2^8-1>; * ... */ if( p[0] != 1 || p[1] != MBEDTLS_SSL_COMPRESS_NULL ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad legacy compression method" ) ); MBEDTLS_SSL_PEND_FATAL_ALERT( MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER, MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER ); return ( MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER ); } p += 2; /* --- * Extension extensions<8..2^16-1>; * --- * with Extension defined as: * struct { * ExtensionType extension_type; * opaque extension_data<0..2^16-1>; * } Extension; */ extensions_len = MBEDTLS_GET_UINT16_BE( p, 0 ); p += 2; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, extensions_len ); extensions_end = p + extensions_len; MBEDTLS_SSL_DEBUG_BUF( 3, "client hello extensions", p, extensions_len ); while( p < extensions_end ) { unsigned int extension_type; size_t extension_data_len; const unsigned char *extension_data_end; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, extensions_end, 4 ); extension_type = MBEDTLS_GET_UINT16_BE( p, 0 ); extension_data_len = MBEDTLS_GET_UINT16_BE( p, 2 ); p += 4; MBEDTLS_SSL_CHK_BUF_READ_PTR( p, extensions_end, extension_data_len ); extension_data_end = p + extension_data_len; switch( extension_type ) { #if defined(MBEDTLS_ECDH_C) case MBEDTLS_TLS_EXT_SUPPORTED_GROUPS: MBEDTLS_SSL_DEBUG_MSG( 3, ( "found supported group extension" ) ); /* Supported Groups Extension * * When sent by the client, the "supported_groups" extension * indicates the named groups which the client supports, * ordered from most preferred to least preferred. */ ret = ssl_tls13_parse_supported_groups_ext( ssl, p, extension_data_end ); if( ret != 0 ) { MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_parse_supported_groups_ext", ret ); return( ret ); } ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_SUPPORTED_GROUPS; break; #endif /* MBEDTLS_ECDH_C */ #if defined(MBEDTLS_ECDH_C) case MBEDTLS_TLS_EXT_KEY_SHARE: MBEDTLS_SSL_DEBUG_MSG( 3, ( "found key share extension" ) ); /* * Key Share Extension * * When sent by the client, the "key_share" extension * contains the endpoint's cryptographic parameters for * ECDHE/DHE key establishment methods. */ ret = ssl_tls13_parse_key_shares_ext( ssl, p, extension_data_end ); if( ret == SSL_TLS1_3_PARSE_KEY_SHARES_EXT_NO_MATCH ) { MBEDTLS_SSL_DEBUG_MSG( 2, ( "HRR needed " ) ); ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE; } if( ret != 0 ) return( ret ); ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_KEY_SHARE; break; #endif /* MBEDTLS_ECDH_C */ case MBEDTLS_TLS_EXT_SUPPORTED_VERSIONS: MBEDTLS_SSL_DEBUG_MSG( 3, ( "found supported versions extension" ) ); ret = ssl_tls13_parse_supported_versions_ext( ssl, p, extension_data_end ); if( ret != 0 ) { MBEDTLS_SSL_DEBUG_RET( 1, ( "ssl_tls13_parse_supported_versions_ext" ), ret ); return( ret ); } ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_SUPPORTED_VERSIONS; break; #if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED) case MBEDTLS_TLS_EXT_SIG_ALG: MBEDTLS_SSL_DEBUG_MSG( 3, ( "found signature_algorithms extension" ) ); ret = mbedtls_ssl_tls13_parse_sig_alg_ext( ssl, p, extension_data_end ); if( ret != 0 ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "ssl_parse_supported_signature_algorithms_server_ext ( %d )", ret ) ); return( ret ); } ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_SIG_ALG; break; #endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */ default: MBEDTLS_SSL_DEBUG_MSG( 3, ( "unknown extension found: %ud ( ignoring )", extension_type ) ); } p += extension_data_len; } /* Update checksum with either * - The entire content of the CH message, if no PSK extension is present * - The content up to but excluding the PSK extension, if present. */ mbedtls_ssl_add_hs_msg_to_checksum( ssl, MBEDTLS_SSL_HS_CLIENT_HELLO, buf, p - buf ); /* List all the extensions we have received */ #if defined(MBEDTLS_DEBUG_C) ssl_tls13_debug_print_client_hello_exts( ssl ); #endif /* MBEDTLS_DEBUG_C */ /* * Here we only support the ephemeral or (EC)DHE key echange mode */ if( !ssl_tls13_check_ephemeral_key_exchange( ssl ) ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "ClientHello message misses mandatory extensions." ) ); MBEDTLS_SSL_PEND_FATAL_ALERT( MBEDTLS_SSL_ALERT_MSG_MISSING_EXTENSION , MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER ); return( MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER ); } return( 0 ); } static int ssl_tls13_postprocess_client_hello( mbedtls_ssl_context* ssl ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; ret = mbedtls_ssl_tls13_key_schedule_stage_early( ssl ); if( ret != 0 ) { MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_tls1_3_key_schedule_stage_early", ret ); return( ret ); } return( 0 ); } /* * Main entry point from the state machine; orchestrates the otherfunctions. */ static int ssl_tls13_process_client_hello( mbedtls_ssl_context *ssl ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; unsigned char* buf = NULL; size_t buflen = 0; MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse client hello" ) ); MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_tls13_fetch_handshake_msg( ssl, MBEDTLS_SSL_HS_CLIENT_HELLO, &buf, &buflen ) ); MBEDTLS_SSL_PROC_CHK_NEG( ssl_tls13_parse_client_hello( ssl, buf, buf + buflen ) ); MBEDTLS_SSL_PROC_CHK( ssl_tls13_postprocess_client_hello( ssl ) ); mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_HELLO ); cleanup: MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= parse client hello" ) ); return( ret ); } /* * Handler for MBEDTLS_SSL_SERVER_HELLO */ static int ssl_tls13_prepare_server_hello( mbedtls_ssl_context *ssl ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; unsigned char *server_randbytes = ssl->handshake->randbytes + MBEDTLS_CLIENT_HELLO_RANDOM_LEN; if( ssl->conf->f_rng == NULL ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided" ) ); return( MBEDTLS_ERR_SSL_NO_RNG ); } if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng, server_randbytes, MBEDTLS_SERVER_HELLO_RANDOM_LEN ) ) != 0 ) { MBEDTLS_SSL_DEBUG_RET( 1, "f_rng", ret ); return( ret ); } MBEDTLS_SSL_DEBUG_BUF( 3, "server hello, random bytes", server_randbytes, MBEDTLS_SERVER_HELLO_RANDOM_LEN ); #if defined(MBEDTLS_HAVE_TIME) ssl->session_negotiate->start = time( NULL ); #endif /* MBEDTLS_HAVE_TIME */ return( ret ); } /* * ssl_tls13_write_server_hello_supported_versions_ext (): * * struct { * ProtocolVersion selected_version; * } SupportedVersions; */ static int ssl_tls13_write_server_hello_supported_versions_ext( mbedtls_ssl_context *ssl, unsigned char *buf, unsigned char *end, size_t *out_len ) { *out_len = 0; MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, write selected version" ) ); /* Check if we have space to write the extension: * - extension_type (2 bytes) * - extension_data_length (2 bytes) * - selected_version (2 bytes) */ MBEDTLS_SSL_CHK_BUF_PTR( buf, end, 6 ); MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_SUPPORTED_VERSIONS, buf, 0 ); MBEDTLS_PUT_UINT16_BE( 2, buf, 2 ); mbedtls_ssl_write_version( buf + 4, ssl->conf->transport, ssl->tls_version ); MBEDTLS_SSL_DEBUG_MSG( 3, ( "supported version: [%04x]", ssl->tls_version ) ); *out_len = 6; return( 0 ); } /* Generate and export a single key share. For hybrid KEMs, this can * be called multiple times with the different components of the hybrid. */ static int ssl_tls13_generate_and_write_key_share( mbedtls_ssl_context *ssl, uint16_t named_group, unsigned char *buf, unsigned char *end, size_t *out_len ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; *out_len = 0; #if defined(MBEDTLS_ECDH_C) if( mbedtls_ssl_tls13_named_group_is_ecdhe( named_group ) ) { ret = mbedtls_ssl_tls13_generate_and_write_ecdh_key_exchange( ssl, named_group, buf, end, out_len ); if( ret != 0 ) { MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_tls13_generate_and_write_ecdh_key_exchange", ret ); return( ret ); } } else #endif /* MBEDTLS_ECDH_C */ if( 0 /* Other kinds of KEMs */ ) { } else { ((void) ssl); ((void) named_group); ((void) buf); ((void) end); ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR; } return( ret ); } /* * ssl_tls13_write_key_share_ext * * Structure of key_share extension in ServerHello: * * struct { * NamedGroup group; * opaque key_exchange<1..2^16-1>; * } KeyShareEntry; * struct { * KeyShareEntry server_share; * } KeyShareServerHello; */ static int ssl_tls13_write_key_share_ext( mbedtls_ssl_context *ssl, unsigned char *buf, unsigned char *end, size_t *out_len ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; unsigned char *p = buf; uint16_t group = ssl->handshake->offered_group_id; unsigned char *server_share = buf + 4; size_t key_exchange_length; *out_len = 0; MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, adding key share extension" ) ); /* Check if we have space for header and length fields: * - extension_type (2 bytes) * - extension_data_length (2 bytes) * - group (2 bytes) * - key_exchange_length (2 bytes) */ MBEDTLS_SSL_CHK_BUF_PTR( p, end, 8 ); MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_KEY_SHARE, p, 0 ); MBEDTLS_PUT_UINT16_BE( group, server_share, 0 ); p += 8; /* When we introduce PQC-ECDHE hybrids, we'll want to call this * function multiple times. */ ret = ssl_tls13_generate_and_write_key_share( ssl, group, server_share + 4, end, &key_exchange_length ); if( ret != 0 ) return( ret ); p += key_exchange_length; MBEDTLS_PUT_UINT16_BE( key_exchange_length, server_share + 2, 0 ); MBEDTLS_PUT_UINT16_BE( p - server_share, buf, 2 ); *out_len = p - buf; return( 0 ); } /* * Structure of ServerHello message: * * struct { * ProtocolVersion legacy_version = 0x0303; // TLS v1.2 * Random random; * opaque legacy_session_id_echo<0..32>; * CipherSuite cipher_suite; * uint8 legacy_compression_method = 0; * Extension extensions<6..2^16-1>; * } ServerHello; */ static int ssl_tls13_write_server_hello_body( mbedtls_ssl_context *ssl, unsigned char *buf, unsigned char *end, size_t *out_len ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; unsigned char *p = buf; unsigned char *p_extensions_len; size_t output_len; /* Length of buffer used by function */ *out_len = 0; /* ... * ProtocolVersion legacy_version = 0x0303; // TLS 1.2 * ... * with ProtocolVersion defined as: * uint16 ProtocolVersion; */ MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 ); MBEDTLS_PUT_UINT16_BE( 0x0303, p, 0 ); p += 2; /* ... * Random random; * ... * with Random defined as: * opaque Random[MBEDTLS_SERVER_HELLO_RANDOM_LEN]; */ MBEDTLS_SSL_CHK_BUF_PTR( p, end, MBEDTLS_SERVER_HELLO_RANDOM_LEN ); memcpy( p, &ssl->handshake->randbytes[MBEDTLS_CLIENT_HELLO_RANDOM_LEN], MBEDTLS_SERVER_HELLO_RANDOM_LEN ); MBEDTLS_SSL_DEBUG_BUF( 3, "server hello, random bytes", p, MBEDTLS_SERVER_HELLO_RANDOM_LEN ); p += MBEDTLS_SERVER_HELLO_RANDOM_LEN; /* ... * opaque legacy_session_id_echo<0..32>; * ... */ MBEDTLS_SSL_CHK_BUF_PTR( p, end, 1 + ssl->session_negotiate->id_len ); *p++ = (unsigned char)ssl->session_negotiate->id_len; if( ssl->session_negotiate->id_len > 0 ) { memcpy( p, &ssl->session_negotiate->id[0], ssl->session_negotiate->id_len ); p += ssl->session_negotiate->id_len; MBEDTLS_SSL_DEBUG_BUF( 3, "session id", ssl->session_negotiate->id, ssl->session_negotiate->id_len ); } /* ... * CipherSuite cipher_suite; * ... * with CipherSuite defined as: * uint8 CipherSuite[2]; */ MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 ); MBEDTLS_PUT_UINT16_BE( ssl->session_negotiate->ciphersuite, p, 0 ); p += 2; MBEDTLS_SSL_DEBUG_MSG( 3, ( "server hello, chosen ciphersuite: %s ( id=%d )", mbedtls_ssl_get_ciphersuite_name( ssl->session_negotiate->ciphersuite ), ssl->session_negotiate->ciphersuite ) ); /* ... * uint8 legacy_compression_method = 0; * ... */ MBEDTLS_SSL_CHK_BUF_PTR( p, end, 1 ); *p++ = 0x0; /* ... * Extension extensions<6..2^16-1>; * ... * struct { * ExtensionType extension_type; (2 bytes) * opaque extension_data<0..2^16-1>; * } Extension; */ MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 ); p_extensions_len = p; p += 2; if( ( ret = ssl_tls13_write_server_hello_supported_versions_ext( ssl, p, end, &output_len ) ) != 0 ) { MBEDTLS_SSL_DEBUG_RET( 1, "ssl_tls13_write_server_hello_supported_versions_ext", ret ); return( ret ); } p += output_len; if( mbedtls_ssl_conf_tls13_some_ephemeral_enabled( ssl ) ) { ret = ssl_tls13_write_key_share_ext( ssl, p, end, &output_len ); if( ret != 0 ) return( ret ); p += output_len; } MBEDTLS_PUT_UINT16_BE( p - p_extensions_len - 2, p_extensions_len, 0 ); MBEDTLS_SSL_DEBUG_BUF( 4, "server hello extensions", p_extensions_len, p - p_extensions_len ); *out_len = p - buf; MBEDTLS_SSL_DEBUG_BUF( 3, "server hello", buf, *out_len ); return( ret ); } static int ssl_tls13_write_server_hello( mbedtls_ssl_context *ssl ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; unsigned char *buf; size_t buf_len, msg_len; MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write server hello" ) ); MBEDTLS_SSL_PROC_CHK( ssl_tls13_prepare_server_hello( ssl ) ); MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_start_handshake_msg( ssl, MBEDTLS_SSL_HS_SERVER_HELLO, &buf, &buf_len ) ); MBEDTLS_SSL_PROC_CHK( ssl_tls13_write_server_hello_body( ssl, buf, buf + buf_len, &msg_len ) ); mbedtls_ssl_add_hs_msg_to_checksum( ssl, MBEDTLS_SSL_HS_SERVER_HELLO, buf, msg_len ); MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_finish_handshake_msg( ssl, buf_len, msg_len ) ); mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_ENCRYPTED_EXTENSIONS ); cleanup: MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write server hello" ) ); return( ret ); } /* * TLS 1.3 State Machine -- server side */ int mbedtls_ssl_tls13_handshake_server_step( mbedtls_ssl_context *ssl ) { int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; if( ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER || ssl->handshake == NULL ) return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA ); MBEDTLS_SSL_DEBUG_MSG( 2, ( "tls13 server state: %s(%d)", mbedtls_ssl_states_str( ssl->state ), ssl->state ) ); switch( ssl->state ) { /* start state */ case MBEDTLS_SSL_HELLO_REQUEST: mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_CLIENT_HELLO ); ret = 0; break; case MBEDTLS_SSL_CLIENT_HELLO: ret = ssl_tls13_process_client_hello( ssl ); if( ret != 0 ) MBEDTLS_SSL_DEBUG_RET( 1, "ssl_tls13_process_client_hello", ret ); break; case MBEDTLS_SSL_SERVER_HELLO: ret = ssl_tls13_write_server_hello( ssl ); break; default: MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid state %d", ssl->state ) ); return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE ); } return( ret ); } #endif /* MBEDTLS_SSL_SRV_C && MBEDTLS_SSL_PROTO_TLS1_3 */