library/ssl_tls13_generic.c

/*
 *  TLS 1.3 functionality shared between client and server
 *
 *  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_TLS_C)

#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)

#include "mbedtls/error.h"
#include "mbedtls/debug.h"

#include "ssl_misc.h"


int mbedtls_ssl_tls13_start_handshake_msg( mbedtls_ssl_context *ssl,
                                           unsigned hs_type,
                                           unsigned char **buf,
                                           size_t *buf_len )
{
    /*
     * Reserve 4 bytes for hanshake header. ( Section 4,RFC 8446 )
     *    ...
     *    HandshakeType msg_type;
     *    uint24 length;
     *    ...
     */
    *buf = ssl->out_msg + 4;
    *buf_len = MBEDTLS_SSL_OUT_CONTENT_LEN - 4;

    ssl->out_msgtype = MBEDTLS_SSL_MSG_HANDSHAKE;
    ssl->out_msg[0]  = hs_type;

    return( 0 );
}

int mbedtls_ssl_tls13_finish_handshake_msg( mbedtls_ssl_context *ssl,
                                            size_t buf_len,
                                            size_t msg_len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    size_t msg_len_with_header;
    ((void) buf_len);

    /* Add reserved 4 bytes for handshake header */
    msg_len_with_header = msg_len + 4;
    ssl->out_msglen = msg_len_with_header;
    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_write_handshake_msg_ext( ssl, 0 ) );

cleanup:
    return( ret );
}

void mbedtls_ssl_tls13_add_hs_hdr_to_checksum( mbedtls_ssl_context *ssl,
                                               unsigned hs_type,
                                               size_t total_hs_len )
{
    unsigned char hs_hdr[4];

    /* Build HS header for checksum update. */
    hs_hdr[0] = MBEDTLS_BYTE_0( hs_type );
    hs_hdr[1] = MBEDTLS_BYTE_2( total_hs_len );
    hs_hdr[2] = MBEDTLS_BYTE_1( total_hs_len );
    hs_hdr[3] = MBEDTLS_BYTE_0( total_hs_len );

    ssl->handshake->update_checksum( ssl, hs_hdr, sizeof( hs_hdr ) );
}

#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)

/*
 * mbedtls_ssl_tls13_write_sig_alg_ext( )
 *
 * enum {
 *    ....
 *   ecdsa_secp256r1_sha256( 0x0403 ),
 *   ecdsa_secp384r1_sha384( 0x0503 ),
 *   ecdsa_secp521r1_sha512( 0x0603 ),
 *    ....
 * } SignatureScheme;
 *
 * struct {
 *    SignatureScheme supported_signature_algorithms<2..2^16-2>;
 * } SignatureSchemeList;
 *
 * Only if we handle at least one key exchange that needs signatures.
 */

int mbedtls_ssl_tls13_write_sig_alg_ext( mbedtls_ssl_context *ssl,
                                         unsigned char *buf,
                                         unsigned char *end,
                                         size_t *olen )
{
    unsigned char *p = buf;
    unsigned char *sig_alg_ptr; /* Start of supported_signature_algorithms */
    size_t sig_alg_len = 0;     /* Length of supported_signature_algorithms */

    *olen = 0;

    /* Skip the extension on the client if all allowed key exchanges
     * are PSK-based. */
#if defined(MBEDTLS_SSL_CLI_C)
    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT &&
        !mbedtls_ssl_conf_tls13_some_ephemeral_enabled( ssl ) )
    {
        return( 0 );
    }
#endif /* MBEDTLS_SSL_CLI_C */

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "adding signature_algorithms extension" ) );

    /* Check there is space for extension header */
    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 6 );
    p += 6;

    /*
     * Write supported_signature_algorithms
     */
    sig_alg_ptr = p;
    for( const uint16_t *sig_alg = ssl->conf->tls13_sig_algs;
         *sig_alg != MBEDTLS_TLS13_SIG_NONE; sig_alg++ )
    {
        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
        MBEDTLS_PUT_UINT16_BE( *sig_alg, p, 0 );
        p += 2;
        MBEDTLS_SSL_DEBUG_MSG( 3, ( "signature scheme [%x]", *sig_alg ) );
    }

    /* Length of supported_signature_algorithms*/
    sig_alg_len = p - sig_alg_ptr;
    if( sig_alg_len == 0 )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "No signature algorithms defined." ) );
        return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
    }

    /* Write extension_type */
    MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_SIG_ALG, buf, 0 );
    /* Write extension_data_length */
    MBEDTLS_PUT_UINT16_BE( sig_alg_len + 2, buf, 2 );
    /* Write length of supported_signature_algorithms */
    MBEDTLS_PUT_UINT16_BE( sig_alg_len, buf, 4 );

    /* Output the total length of signature algorithms extension. */
    *olen = p - buf;

    ssl->handshake->extensions_present |= MBEDTLS_SSL_EXT_SIG_ALG;
    return( 0 );
}

#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */

#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */

#endif /* MBEDTLS_SSL_TLS_C */