/* * TLS server tickets callbacks implementation * * Copyright (C) 2015, ARM Limited, All Rights Reserved * * This file is part of mbed TLS (https://tls.mbed.org) * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License along * with this program; if not, write to the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. */ #if !defined(MBEDTLS_CONFIG_FILE) #include "mbedtls/config.h" #else #include MBEDTLS_CONFIG_FILE #endif #if defined(MBEDTLS_SSL_TICKET_C) #include "mbedtls/ssl_ticket.h" #if defined(MBEDTLS_PLATFORM_C) #include "mbedtls/platform.h" #else #define mbedtls_malloc malloc #define mbedtls_free free #endif #include /* * Serialize a session in the following format: * 0 . n-1 session structure, n = sizeof(mbedtls_ssl_session) * n . n+2 peer_cert length = m (0 if no certificate) * n+3 . n+2+m peer cert ASN.1 * * Assumes ticket is NULL (always true on server side). */ static int ssl_save_session( const mbedtls_ssl_session *session, unsigned char *buf, size_t buf_len, size_t *olen ) { unsigned char *p = buf; size_t left = buf_len; #if defined(MBEDTLS_X509_CRT_PARSE_C) size_t cert_len; #endif /* MBEDTLS_X509_CRT_PARSE_C */ if( left < sizeof( mbedtls_ssl_session ) ) return( -1 ); memcpy( p, session, sizeof( mbedtls_ssl_session ) ); p += sizeof( mbedtls_ssl_session ); left -= sizeof( mbedtls_ssl_session ); #if defined(MBEDTLS_X509_CRT_PARSE_C) if( session->peer_cert == NULL ) cert_len = 0; else cert_len = session->peer_cert->raw.len; if( left < 3 + cert_len ) return( -1 ); *p++ = (unsigned char)( cert_len >> 16 & 0xFF ); *p++ = (unsigned char)( cert_len >> 8 & 0xFF ); *p++ = (unsigned char)( cert_len & 0xFF ); if( session->peer_cert != NULL ) memcpy( p, session->peer_cert->raw.p, cert_len ); p += cert_len; #endif /* MBEDTLS_X509_CRT_PARSE_C */ *olen = p - buf; return( 0 ); } /* * Unserialise session, see ssl_save_session() */ static int ssl_load_session( mbedtls_ssl_session *session, const unsigned char *buf, size_t len ) { const unsigned char *p = buf; const unsigned char * const end = buf + len; #if defined(MBEDTLS_X509_CRT_PARSE_C) size_t cert_len; #endif /* MBEDTLS_X509_CRT_PARSE_C */ if( p + sizeof( mbedtls_ssl_session ) > end ) return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA ); memcpy( session, p, sizeof( mbedtls_ssl_session ) ); p += sizeof( mbedtls_ssl_session ); #if defined(MBEDTLS_X509_CRT_PARSE_C) if( p + 3 > end ) return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA ); cert_len = ( p[0] << 16 ) | ( p[1] << 8 ) | p[2]; p += 3; if( cert_len == 0 ) { session->peer_cert = NULL; } else { int ret; if( p + cert_len > end ) return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA ); session->peer_cert = mbedtls_malloc( sizeof( mbedtls_x509_crt ) ); if( session->peer_cert == NULL ) return( MBEDTLS_ERR_SSL_MALLOC_FAILED ); mbedtls_x509_crt_init( session->peer_cert ); if( ( ret = mbedtls_x509_crt_parse_der( session->peer_cert, p, cert_len ) ) != 0 ) { mbedtls_x509_crt_free( session->peer_cert ); mbedtls_free( session->peer_cert ); session->peer_cert = NULL; return( ret ); } p += cert_len; } #endif /* MBEDTLS_X509_CRT_PARSE_C */ if( p != end ) return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA ); return( 0 ); } /* * Create session ticket, secured as recommended in RFC 5077 section 4: * * struct { * opaque key_name[16]; * opaque iv[16]; * opaque encrypted_state<0..2^16-1>; * opaque mac[32]; * } ticket; * * (the internal state structure differs, however). */ int mbedtls_ssl_ticket_write( const mbedtls_ssl_config *conf, const mbedtls_ssl_session *session, unsigned char *start, const unsigned char *end, size_t *tlen ) { int ret; unsigned char *p = start; unsigned char *state; unsigned char iv[16]; size_t clear_len, enc_len, pad_len, i; *tlen = 0; if( conf->ticket_keys == NULL ) return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA ); /* We need at least 16 bytes for key_name, 16 for IV, 2 for len * 16 for padding, 32 for MAC, in addition to session itself, * that will be checked when writing it. */ if( end - start < 16 + 16 + 2 + 16 + 32 ) return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL ); /* Write key name */ memcpy( p, conf->ticket_keys->key_name, 16 ); p += 16; /* Generate and write IV (with a copy for aes_crypt) */ if( ( ret = conf->f_rng( conf->p_rng, p, 16 ) ) != 0 ) return( ret ); memcpy( iv, p, 16 ); p += 16; /* Dump session state */ state = p + 2; if( ssl_save_session( session, state, end - state, &clear_len ) != 0 ) return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL ); /* Apply PKCS padding */ pad_len = 16 - clear_len % 16; enc_len = clear_len + pad_len; for( i = clear_len; i < enc_len; i++ ) state[i] = (unsigned char) pad_len; /* Encrypt */ if( ( ret = mbedtls_aes_crypt_cbc( &conf->ticket_keys->enc, MBEDTLS_AES_ENCRYPT, enc_len, iv, state, state ) ) != 0 ) { return( ret ); } /* Write length */ *p++ = (unsigned char)( ( enc_len >> 8 ) & 0xFF ); *p++ = (unsigned char)( ( enc_len ) & 0xFF ); p = state + enc_len; /* Compute and write MAC( key_name + iv + enc_state_len + enc_state ) */ if( ( ret = mbedtls_md_hmac( mbedtls_md_info_from_type( MBEDTLS_MD_SHA256 ), conf->ticket_keys->mac_key, 16, start, p - start, p ) ) != 0 ) { return( ret ); } p += 32; *tlen = p - start; return( 0 ); } /* * Load session ticket (see mbedtls_ssl_ticket_write for structure) */ int mbedtls_ssl_ticket_parse( const mbedtls_ssl_config *conf, mbedtls_ssl_session *session, unsigned char *buf, size_t len ) { int ret; unsigned char *key_name = buf; unsigned char *iv = buf + 16; unsigned char *enc_len_p = iv + 16; unsigned char *ticket = enc_len_p + 2; unsigned char *mac; unsigned char computed_mac[32]; size_t enc_len, clear_len, i; unsigned char pad_len, diff; if( len < 34 || conf->ticket_keys == NULL ) return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA ); enc_len = ( enc_len_p[0] << 8 ) | enc_len_p[1]; mac = ticket + enc_len; if( len != enc_len + 66 ) return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA ); /* Check name, in constant time though it's not a big secret */ diff = 0; for( i = 0; i < 16; i++ ) diff |= key_name[i] ^ conf->ticket_keys->key_name[i]; /* don't return yet, check the MAC anyway */ /* Check mac, with constant-time buffer comparison */ if( ( ret = mbedtls_md_hmac( mbedtls_md_info_from_type( MBEDTLS_MD_SHA256 ), conf->ticket_keys->mac_key, 16, buf, len - 32, computed_mac ) ) != 0 ) { return( ret ); } for( i = 0; i < 32; i++ ) diff |= mac[i] ^ computed_mac[i]; /* Now return if ticket is not authentic, since we want to avoid * decrypting arbitrary attacker-chosen data */ if( diff != 0 ) return( MBEDTLS_ERR_SSL_INVALID_MAC ); /* Decrypt */ if( ( ret = mbedtls_aes_crypt_cbc( &conf->ticket_keys->dec, MBEDTLS_AES_DECRYPT, enc_len, iv, ticket, ticket ) ) != 0 ) { return( ret ); } /* Check PKCS padding */ pad_len = ticket[enc_len - 1]; ret = 0; for( i = 2; i < pad_len; i++ ) if( ticket[enc_len - i] != pad_len ) ret = MBEDTLS_ERR_SSL_BAD_INPUT_DATA; if( ret != 0 ) return( ret ); clear_len = enc_len - pad_len; /* Actually load session */ if( ( ret = ssl_load_session( session, ticket, clear_len ) ) != 0 ) return( ret ); #if defined(MBEDTLS_HAVE_TIME) /* Check if still valid */ if( (int) ( time( NULL) - session->start ) > conf->ticket_lifetime ) return( MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED ); #endif return( 0 ); } #endif /* MBEDTLS_SSL_TICKET_C */