From 2e58e8ee345894ee224694cf727b1443de3d3423 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Manuel=20P=C3=A9gouri=C3=A9-Gonnard?= Date: Mon, 18 Jun 2018 11:16:43 +0200 Subject: [PATCH] Implement ChachaPoly mode in TLS --- library/ssl_tls.c | 150 +++++++++++++++++++++++++++++++++------------- 1 file changed, 109 insertions(+), 41 deletions(-) diff --git a/library/ssl_tls.c b/library/ssl_tls.c index e5119fcda..c6e5f9702 100644 --- a/library/ssl_tls.c +++ b/library/ssl_tls.c @@ -688,18 +688,32 @@ int mbedtls_ssl_derive_keys( mbedtls_ssl_context *ssl ) transform->keylen = cipher_info->key_bitlen / 8; if( cipher_info->mode == MBEDTLS_MODE_GCM || - cipher_info->mode == MBEDTLS_MODE_CCM ) + cipher_info->mode == MBEDTLS_MODE_CCM || + cipher_info->mode == MBEDTLS_MODE_CHACHAPOLY ) { + size_t taglen, explicit_ivlen; + transform->maclen = 0; mac_key_len = 0; + /* All modes haves 96-bit IVs; + * GCM and CCM has 4 implicit and 8 explicit bytes + * ChachaPoly has all 12 bytes implicit + */ transform->ivlen = 12; - transform->fixed_ivlen = 4; + if( cipher_info->mode == MBEDTLS_MODE_CHACHAPOLY ) + transform->fixed_ivlen = 12; + else + transform->fixed_ivlen = 4; - /* Minimum length is expicit IV + tag */ - transform->minlen = transform->ivlen - transform->fixed_ivlen - + ( transform->ciphersuite_info->flags & - MBEDTLS_CIPHERSUITE_SHORT_TAG ? 8 : 16 ); + /* All modes have 128-bit tags, except CCM_8 (ciphersuite flag) */ + taglen = transform->ciphersuite_info->flags & + MBEDTLS_CIPHERSUITE_SHORT_TAG ? 8 : 16; + + + /* Minimum length of encrypted record */ + explicit_ivlen = transform->ivlen - transform->fixed_ivlen; + transform->minlen = explicit_ivlen + taglen; } else { @@ -1394,17 +1408,26 @@ static int ssl_encrypt_buf( mbedtls_ssl_context *ssl ) } else #endif /* MBEDTLS_ARC4_C || MBEDTLS_CIPHER_NULL_CIPHER */ -#if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CCM_C) +#if defined(MBEDTLS_GCM_C) || \ + defined(MBEDTLS_CCM_C) || \ + defined(MBEDTLS_CHACHAPOLY_C) if( mode == MBEDTLS_MODE_GCM || - mode == MBEDTLS_MODE_CCM ) + mode == MBEDTLS_MODE_CCM || + mode == MBEDTLS_MODE_CHACHAPOLY ) { int ret; size_t enc_msglen, olen; unsigned char *enc_msg; unsigned char add_data[13]; - unsigned char taglen = ssl->transform_out->ciphersuite_info->flags & + unsigned char iv[12]; + mbedtls_ssl_transform *transform = ssl->transform_out; + unsigned char taglen = transform->ciphersuite_info->flags & MBEDTLS_CIPHERSUITE_SHORT_TAG ? 8 : 16; + size_t explicit_ivlen = transform->ivlen - transform->fixed_ivlen; + /* + * Prepare additional authenticated data + */ memcpy( add_data, ssl->out_ctr, 8 ); add_data[8] = ssl->out_msgtype; mbedtls_ssl_write_version( ssl->major_ver, ssl->minor_ver, @@ -1412,44 +1435,57 @@ static int ssl_encrypt_buf( mbedtls_ssl_context *ssl ) add_data[11] = ( ssl->out_msglen >> 8 ) & 0xFF; add_data[12] = ssl->out_msglen & 0xFF; - MBEDTLS_SSL_DEBUG_BUF( 4, "additional data used for AEAD", - add_data, 13 ); + MBEDTLS_SSL_DEBUG_BUF( 4, "additional data for AEAD", add_data, 13 ); /* * Generate IV */ - if( ssl->transform_out->ivlen - ssl->transform_out->fixed_ivlen != 8 ) + if( transform->ivlen == 12 && transform->fixed_ivlen == 4 ) + { + /* GCM and CCM: concatenate fixed + explicit (=seqnum) */ + memcpy( iv, transform->iv_enc, transform->fixed_ivlen ); + memcpy( iv + transform->fixed_ivlen, ssl->out_ctr, 8 ); + memcpy( ssl->out_iv, ssl->out_ctr, 8 ); + + } + else if( transform->ivlen == 12 && transform->fixed_ivlen == 12 ) + { + /* ChachaPoly: XOR fixed + sequence number */ + unsigned char i; + + memcpy( iv, transform->iv_enc, transform->fixed_ivlen ); + + for( i = 0; i < 8; i++ ) + iv[i+4] ^= ssl->out_ctr[i]; + } + else { /* Reminder if we ever add an AEAD mode with a different size */ MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) ); return( MBEDTLS_ERR_SSL_INTERNAL_ERROR ); } - memcpy( ssl->transform_out->iv_enc + ssl->transform_out->fixed_ivlen, - ssl->out_ctr, 8 ); - memcpy( ssl->out_iv, ssl->out_ctr, 8 ); - - MBEDTLS_SSL_DEBUG_BUF( 4, "IV used", ssl->out_iv, - ssl->transform_out->ivlen - ssl->transform_out->fixed_ivlen ); + MBEDTLS_SSL_DEBUG_BUF( 4, "IV used (internal)", + iv, transform->ivlen ); + MBEDTLS_SSL_DEBUG_BUF( 4, "IV used (transmitted)", + ssl->out_iv, explicit_ivlen ); /* - * Fix pointer positions and message length with added IV + * Fix message length with added IV */ enc_msg = ssl->out_msg; enc_msglen = ssl->out_msglen; - ssl->out_msglen += ssl->transform_out->ivlen - - ssl->transform_out->fixed_ivlen; + ssl->out_msglen += explicit_ivlen; MBEDTLS_SSL_DEBUG_MSG( 3, ( "before encrypt: msglen = %d, " - "including %d bytes of padding", - ssl->out_msglen, 0 ) ); + "including 0 bytes of padding", + ssl->out_msglen ) ); /* * Encrypt and authenticate */ - if( ( ret = mbedtls_cipher_auth_encrypt( &ssl->transform_out->cipher_ctx_enc, - ssl->transform_out->iv_enc, - ssl->transform_out->ivlen, + if( ( ret = mbedtls_cipher_auth_encrypt( &transform->cipher_ctx_enc, + iv, transform->ivlen, add_data, 13, enc_msg, enc_msglen, enc_msg, &olen, @@ -1609,7 +1645,6 @@ static int ssl_encrypt_buf( mbedtls_ssl_context *ssl ) static int ssl_decrypt_buf( mbedtls_ssl_context *ssl ) { - size_t i; mbedtls_cipher_mode_t mode; int auth_done = 0; #if defined(SSL_SOME_MODES_USE_MAC) @@ -1659,20 +1694,27 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl ) } else #endif /* MBEDTLS_ARC4_C || MBEDTLS_CIPHER_NULL_CIPHER */ -#if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CCM_C) +#if defined(MBEDTLS_GCM_C) || \ + defined(MBEDTLS_CCM_C) || \ + defined(MBEDTLS_CHACHAPOLY_C) if( mode == MBEDTLS_MODE_GCM || - mode == MBEDTLS_MODE_CCM ) + mode == MBEDTLS_MODE_CCM || + mode == MBEDTLS_MODE_CHACHAPOLY ) { int ret; size_t dec_msglen, olen; unsigned char *dec_msg; unsigned char *dec_msg_result; unsigned char add_data[13]; - unsigned char taglen = ssl->transform_in->ciphersuite_info->flags & + unsigned char iv[12]; + mbedtls_ssl_transform *transform = ssl->transform_in; + unsigned char taglen = transform->ciphersuite_info->flags & MBEDTLS_CIPHERSUITE_SHORT_TAG ? 8 : 16; - size_t explicit_iv_len = ssl->transform_in->ivlen - - ssl->transform_in->fixed_ivlen; + size_t explicit_iv_len = transform->ivlen - transform->fixed_ivlen; + /* + * Compute and update sizes + */ if( ssl->in_msglen < explicit_iv_len + taglen ) { MBEDTLS_SSL_DEBUG_MSG( 1, ( "msglen (%d) < explicit_iv_len (%d) " @@ -1686,6 +1728,9 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl ) dec_msg_result = ssl->in_msg; ssl->in_msglen = dec_msglen; + /* + * Prepare additional authenticated data + */ memcpy( add_data, ssl->in_ctr, 8 ); add_data[8] = ssl->in_msgtype; mbedtls_ssl_write_version( ssl->major_ver, ssl->minor_ver, @@ -1693,23 +1738,43 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl ) add_data[11] = ( ssl->in_msglen >> 8 ) & 0xFF; add_data[12] = ssl->in_msglen & 0xFF; - MBEDTLS_SSL_DEBUG_BUF( 4, "additional data used for AEAD", - add_data, 13 ); + MBEDTLS_SSL_DEBUG_BUF( 4, "additional data for AEAD", add_data, 13 ); - memcpy( ssl->transform_in->iv_dec + ssl->transform_in->fixed_ivlen, - ssl->in_iv, - ssl->transform_in->ivlen - ssl->transform_in->fixed_ivlen ); + /* + * Prepare IV + */ + if( transform->ivlen == 12 && transform->fixed_ivlen == 4 ) + { + /* GCM and CCM: concatenate fixed + explicit (transmitted) */ + memcpy( iv, transform->iv_dec, transform->fixed_ivlen ); + memcpy( iv + transform->fixed_ivlen, ssl->in_iv, 8 ); - MBEDTLS_SSL_DEBUG_BUF( 4, "IV used", ssl->transform_in->iv_dec, - ssl->transform_in->ivlen ); + } + else if( transform->ivlen == 12 && transform->fixed_ivlen == 12 ) + { + /* ChachaPoly: XOR fixed + sequence number */ + unsigned char i; + + memcpy( iv, transform->iv_dec, transform->fixed_ivlen ); + + for( i = 0; i < 8; i++ ) + iv[i+4] ^= ssl->in_ctr[i]; + } + else + { + /* Reminder if we ever add an AEAD mode with a different size */ + MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) ); + return( MBEDTLS_ERR_SSL_INTERNAL_ERROR ); + } + + MBEDTLS_SSL_DEBUG_BUF( 4, "IV used", iv, transform->ivlen ); MBEDTLS_SSL_DEBUG_BUF( 4, "TAG used", dec_msg + dec_msglen, taglen ); /* * Decrypt and authenticate */ if( ( ret = mbedtls_cipher_auth_decrypt( &ssl->transform_in->cipher_ctx_dec, - ssl->transform_in->iv_dec, - ssl->transform_in->ivlen, + iv, transform->ivlen, add_data, 13, dec_msg, dec_msglen, dec_msg_result, &olen, @@ -1827,6 +1892,7 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl ) */ if( ssl->minor_ver >= MBEDTLS_SSL_MINOR_VERSION_2 ) { + unsigned char i; dec_msglen -= ssl->transform_in->ivlen; ssl->in_msglen -= ssl->transform_in->ivlen; @@ -1901,6 +1967,7 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl ) */ size_t pad_count = 0, real_count = 1; size_t padding_idx = ssl->in_msglen - padlen - 1; + size_t i; /* * Padding is guaranteed to be incorrect if: @@ -2077,6 +2144,7 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl ) else #endif { + unsigned char i; for( i = 8; i > ssl_ep_len( ssl ); i-- ) if( ++ssl->in_ctr[i - 1] != 0 ) break;