library/ssl_ticket.c

/*
 *  TLS server tickets callbacks implementation
 *
 *  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_TICKET_C)

#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdlib.h>
#define mbedtls_calloc    calloc
#define mbedtls_free      free
#endif

#include "ssl_misc.h"
#include "mbedtls/ssl_ticket.h"
#include "mbedtls/error.h"
#include "mbedtls/platform_util.h"

#include <string.h>

/*
 * Initialze context
 */
void mbedtls_ssl_ticket_init( mbedtls_ssl_ticket_context *ctx )
{
    memset( ctx, 0, sizeof( mbedtls_ssl_ticket_context ) );

#if defined(MBEDTLS_THREADING_C)
    mbedtls_mutex_init( &ctx->mutex );
#endif
}

#define MAX_KEY_BYTES           MBEDTLS_SSL_TICKET_MAX_KEY_BYTES

#define TICKET_KEY_NAME_BYTES   MBEDTLS_SSL_TICKET_KEY_NAME_BYTES
#define TICKET_IV_BYTES         12
#define TICKET_CRYPT_LEN_BYTES   2
#define TICKET_AUTH_TAG_BYTES   16

#define TICKET_MIN_LEN ( TICKET_KEY_NAME_BYTES  +        \
                         TICKET_IV_BYTES        +        \
                         TICKET_CRYPT_LEN_BYTES +        \
                         TICKET_AUTH_TAG_BYTES )
#define TICKET_ADD_DATA_LEN ( TICKET_KEY_NAME_BYTES  +        \
                              TICKET_IV_BYTES        +        \
                              TICKET_CRYPT_LEN_BYTES )

/*
 * Generate/update a key
 */
static int ssl_ticket_gen_key( mbedtls_ssl_ticket_context *ctx,
                               unsigned char index )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char buf[MAX_KEY_BYTES];
    mbedtls_ssl_ticket_key *key = ctx->keys + index;

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
#endif

#if defined(MBEDTLS_HAVE_TIME)
    key->generation_time = (uint32_t) mbedtls_time( NULL );
#endif

    if( ( ret = ctx->f_rng( ctx->p_rng, key->name, sizeof( key->name ) ) ) != 0 )
        return( ret );

    if( ( ret = ctx->f_rng( ctx->p_rng, buf, sizeof( buf ) ) ) != 0 )
        return( ret );

#if defined(MBEDTLS_USE_PSA_CRYPTO)

    psa_set_key_usage_flags( &attributes,
                             PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_DECRYPT );
    psa_set_key_algorithm( &attributes, key->alg );
    psa_set_key_type( &attributes, key->key_type );
    psa_set_key_bits( &attributes, key->key_bits );

    ret = psa_ssl_status_to_mbedtls(
            psa_import_key( &attributes, buf,
                            PSA_BITS_TO_BYTES( key->key_bits ),
                            &key->key ) );

#else

    /* With GCM and CCM, same context can encrypt & decrypt */
    ret = mbedtls_cipher_setkey( &key->ctx, buf,
                                 mbedtls_cipher_get_key_bitlen( &key->ctx ),
                                 MBEDTLS_ENCRYPT );

#endif /* MBEDTLS_USE_PSA_CRYPTO */

    mbedtls_platform_zeroize( buf, sizeof( buf ) );

    return( ret );
}

/*
 * Rotate/generate keys if necessary
 */
static int ssl_ticket_update_keys( mbedtls_ssl_ticket_context *ctx )
{
#if !defined(MBEDTLS_HAVE_TIME)
    ((void) ctx);
#else
    if( ctx->ticket_lifetime != 0 )
    {
        uint32_t current_time = (uint32_t) mbedtls_time( NULL );
        uint32_t key_time = ctx->keys[ctx->active].generation_time;

#if defined(MBEDTLS_USE_PSA_CRYPTO)
        int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
#endif

        if( current_time >= key_time &&
            current_time - key_time < ctx->ticket_lifetime )
        {
            return( 0 );
        }

        ctx->active = 1 - ctx->active;

#if defined(MBEDTLS_USE_PSA_CRYPTO)

        if( ( ret = psa_ssl_status_to_mbedtls(
                        psa_destroy_key( ctx->keys[ctx->active].key ) ) ) != 0 )
            return( ret );

#endif /* MBEDTLS_USE_PSA_CRYPTO */

        return( ssl_ticket_gen_key( ctx, ctx->active ) );
    }
    else
#endif /* MBEDTLS_HAVE_TIME */
        return( 0 );
}

/*
 * Rotate active session ticket encryption key
 */
int mbedtls_ssl_ticket_rotate( mbedtls_ssl_ticket_context *ctx,
    const unsigned char *name, size_t nlength,
    const unsigned char *k, size_t klength,
    uint32_t lifetime )
{
    const unsigned char idx = 1 - ctx->active;
    mbedtls_ssl_ticket_key * const key = ctx->keys + idx;
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
    const int bitlen = key->key_bits;
#else
    const int bitlen = mbedtls_cipher_get_key_bitlen( &key->ctx );
#endif

    if( nlength < TICKET_KEY_NAME_BYTES || klength * 8 < (size_t)bitlen )
        return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );

#if defined(MBEDTLS_USE_PSA_CRYPTO)

    if( ( ret = psa_ssl_status_to_mbedtls(
                    psa_destroy_key( key->key ) ) ) != 0 )
        return( ret );

    psa_set_key_usage_flags( &attributes,
                             PSA_KEY_USAGE_ENCRYPT | PSA_KEY_USAGE_DECRYPT );
    psa_set_key_algorithm( &attributes, key->alg );
    psa_set_key_type( &attributes, key->key_type );
    psa_set_key_bits( &attributes, key->key_bits );

    if( ( ret = psa_ssl_status_to_mbedtls(
                    psa_import_key( &attributes, k,
                                    PSA_BITS_TO_BYTES( key->key_bits ),
                                    &key->key ) ) ) != 0 )
        return( ret );

#else

    ret = mbedtls_cipher_setkey( &key->ctx, k, bitlen, MBEDTLS_ENCRYPT );
    if( ret != 0 )
        return( ret );

#endif /* MBEDTLS_USE_PSA_CRYPTO */

    ctx->active = idx;
    ctx->ticket_lifetime = lifetime;
    memcpy( key->name, name, TICKET_KEY_NAME_BYTES );
#if defined(MBEDTLS_HAVE_TIME)
    key->generation_time = (uint32_t) mbedtls_time( NULL );
#endif
    return 0;
}

/*
 * Setup context for actual use
 */
int mbedtls_ssl_ticket_setup( mbedtls_ssl_ticket_context *ctx,
    int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
    mbedtls_cipher_type_t cipher,
    uint32_t lifetime )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    const mbedtls_cipher_info_t *cipher_info;

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    psa_algorithm_t alg;
    psa_key_type_t key_type;
    size_t key_bits;
#endif

    ctx->f_rng = f_rng;
    ctx->p_rng = p_rng;

    ctx->ticket_lifetime = lifetime;

    cipher_info = mbedtls_cipher_info_from_type( cipher );

    if( mbedtls_cipher_info_get_mode( cipher_info ) != MBEDTLS_MODE_GCM &&
        mbedtls_cipher_info_get_mode( cipher_info ) != MBEDTLS_MODE_CCM )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    if( mbedtls_cipher_info_get_key_bitlen( cipher_info ) > 8 * MAX_KEY_BYTES )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

#if defined(MBEDTLS_USE_PSA_CRYPTO)

    if( mbedtls_ssl_cipher_to_psa( cipher_info->type, TICKET_AUTH_TAG_BYTES,
                                   &alg, &key_type, &key_bits ) != PSA_SUCCESS )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    ctx->keys[0].alg = alg;
    ctx->keys[0].key_type = key_type;
    ctx->keys[0].key_bits = key_bits;

    ctx->keys[1].alg = alg;
    ctx->keys[1].key_type = key_type;
    ctx->keys[1].key_bits = key_bits;

#else

    if( ( ret = mbedtls_cipher_setup( &ctx->keys[0].ctx, cipher_info ) ) != 0 )
        return( ret );

    if( ( ret = mbedtls_cipher_setup( &ctx->keys[1].ctx, cipher_info ) ) != 0 )
        return( ret );

#endif /* MBEDTLS_USE_PSA_CRYPTO */

    if( ( ret = ssl_ticket_gen_key( ctx, 0 ) ) != 0 ||
        ( ret = ssl_ticket_gen_key( ctx, 1 ) ) != 0 )
    {
        return( ret );
    }

    return( 0 );
}

/*
 * Create session ticket, with the following structure:
 *
 *    struct {
 *        opaque key_name[4];
 *        opaque iv[12];
 *        opaque encrypted_state<0..2^16-1>;
 *        opaque tag[16];
 *    } ticket;
 *
 * The key_name, iv, and length of encrypted_state are the additional
 * authenticated data.
 */

int mbedtls_ssl_ticket_write( void *p_ticket,
                              const mbedtls_ssl_session *session,
                              unsigned char *start,
                              const unsigned char *end,
                              size_t *tlen,
                              uint32_t *ticket_lifetime )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_ssl_ticket_context *ctx = p_ticket;
    mbedtls_ssl_ticket_key *key;
    unsigned char *key_name = start;
    unsigned char *iv = start + TICKET_KEY_NAME_BYTES;
    unsigned char *state_len_bytes = iv + TICKET_IV_BYTES;
    unsigned char *state = state_len_bytes + TICKET_CRYPT_LEN_BYTES;
    size_t clear_len, ciph_len;

    *tlen = 0;

    if( ctx == NULL || ctx->f_rng == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    /* We need at least 4 bytes for key_name, 12 for IV, 2 for len 16 for tag,
     * in addition to session itself, that will be checked when writing it. */
    MBEDTLS_SSL_CHK_BUF_PTR( start, end, TICKET_MIN_LEN );

#if defined(MBEDTLS_THREADING_C)
    if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
        return( ret );
#endif

    if( ( ret = ssl_ticket_update_keys( ctx ) ) != 0 )
        goto cleanup;

    key = &ctx->keys[ctx->active];

    *ticket_lifetime = ctx->ticket_lifetime;

    memcpy( key_name, key->name, TICKET_KEY_NAME_BYTES );

    if( ( ret = ctx->f_rng( ctx->p_rng, iv, TICKET_IV_BYTES ) ) != 0 )
        goto cleanup;

    /* Dump session state */
    if( ( ret = mbedtls_ssl_session_save( session,
                                          state, end - state,
                                          &clear_len ) ) != 0 ||
        (unsigned long) clear_len > 65535 )
    {
         goto cleanup;
    }
    MBEDTLS_PUT_UINT16_BE( clear_len, state_len_bytes, 0 );

    /* Encrypt and authenticate */
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    if( ( ret = psa_ssl_status_to_mbedtls(
                    psa_aead_encrypt( key->key, key->alg, iv, TICKET_IV_BYTES,
                                      key_name, TICKET_ADD_DATA_LEN,
                                      state, clear_len,
                                      state, end - state, &ciph_len ) ) ) != 0 )
#else
    if( ( ret = mbedtls_cipher_auth_encrypt_ext( &key->ctx,
                    iv, TICKET_IV_BYTES,
                    /* Additional data: key name, IV and length */
                    key_name, TICKET_ADD_DATA_LEN,
                    state, clear_len,
                    state, end - state, &ciph_len,
                    TICKET_AUTH_TAG_BYTES ) ) != 0 )
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    {
        goto cleanup;
    }

    if( ciph_len != clear_len + TICKET_AUTH_TAG_BYTES )
    {
        ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        goto cleanup;
    }

    *tlen = TICKET_MIN_LEN + ciph_len - TICKET_AUTH_TAG_BYTES;

cleanup:
#if defined(MBEDTLS_THREADING_C)
    if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
        return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
#endif

    return( ret );
}

/*
 * Select key based on name
 */
static mbedtls_ssl_ticket_key *ssl_ticket_select_key(
        mbedtls_ssl_ticket_context *ctx,
        const unsigned char name[4] )
{
    unsigned char i;

    for( i = 0; i < sizeof( ctx->keys ) / sizeof( *ctx->keys ); i++ )
        if( memcmp( name, ctx->keys[i].name, 4 ) == 0 )
            return( &ctx->keys[i] );

    return( NULL );
}

/*
 * Load session ticket (see mbedtls_ssl_ticket_write for structure)
 */
int mbedtls_ssl_ticket_parse( void *p_ticket,
                              mbedtls_ssl_session *session,
                              unsigned char *buf,
                              size_t len )
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_ssl_ticket_context *ctx = p_ticket;
    mbedtls_ssl_ticket_key *key;
    unsigned char *key_name = buf;
    unsigned char *iv = buf + TICKET_KEY_NAME_BYTES;
    unsigned char *enc_len_p = iv + TICKET_IV_BYTES;
    unsigned char *ticket = enc_len_p + TICKET_CRYPT_LEN_BYTES;
    size_t enc_len, clear_len;

    if( ctx == NULL || ctx->f_rng == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    if( len < TICKET_MIN_LEN )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

#if defined(MBEDTLS_THREADING_C)
    if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
        return( ret );
#endif

    if( ( ret = ssl_ticket_update_keys( ctx ) ) != 0 )
        goto cleanup;

    enc_len = ( enc_len_p[0] << 8 ) | enc_len_p[1];

    if( len != TICKET_MIN_LEN + enc_len )
    {
        ret = MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
        goto cleanup;
    }

    /* Select key */
    if( ( key = ssl_ticket_select_key( ctx, key_name ) ) == NULL )
    {
        /* We can't know for sure but this is a likely option unless we're
         * under attack - this is only informative anyway */
        ret = MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED;
        goto cleanup;
    }

    /* Decrypt and authenticate */
#if defined(MBEDTLS_USE_PSA_CRYPTO)
    if( ( ret = psa_ssl_status_to_mbedtls(
                    psa_aead_decrypt( key->key, key->alg, iv, TICKET_IV_BYTES,
                                      key_name, TICKET_ADD_DATA_LEN,
                                      ticket, enc_len + TICKET_AUTH_TAG_BYTES,
                                      ticket, enc_len, &clear_len ) ) ) != 0 )
#else
    if( ( ret = mbedtls_cipher_auth_decrypt_ext( &key->ctx,
                    iv, TICKET_IV_BYTES,
                    /* Additional data: key name, IV and length */
                    key_name, TICKET_ADD_DATA_LEN,
                    ticket, enc_len + TICKET_AUTH_TAG_BYTES,
                    ticket, enc_len, &clear_len,
                    TICKET_AUTH_TAG_BYTES ) ) != 0 )
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    {
        if( ret == MBEDTLS_ERR_CIPHER_AUTH_FAILED )
            ret = MBEDTLS_ERR_SSL_INVALID_MAC;

        goto cleanup;
    }
    if( clear_len != enc_len )
    {
        ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        goto cleanup;
    }

    /* Actually load session */
    if( ( ret = mbedtls_ssl_session_load( session, ticket, clear_len ) ) != 0 )
        goto cleanup;

#if defined(MBEDTLS_HAVE_TIME)
    {
        /* Check for expiration */
        mbedtls_time_t current_time = mbedtls_time( NULL );

        if( current_time < session->start ||
            (uint32_t)( current_time - session->start ) > ctx->ticket_lifetime )
        {
            ret = MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED;
            goto cleanup;
        }
    }
#endif

cleanup:
#if defined(MBEDTLS_THREADING_C)
    if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
        return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
#endif

    return( ret );
}

/*
 * Free context
 */
void mbedtls_ssl_ticket_free( mbedtls_ssl_ticket_context *ctx )
{
#if defined(MBEDTLS_USE_PSA_CRYPTO)

    psa_destroy_key( ctx->keys[0].key );
    psa_destroy_key( ctx->keys[1].key );

#else

    mbedtls_cipher_free( &ctx->keys[0].ctx );
    mbedtls_cipher_free( &ctx->keys[1].ctx );

#endif /* MBEDTLS_USE_PSA_CRYPTO */

#if defined(MBEDTLS_THREADING_C)
    mbedtls_mutex_free( &ctx->mutex );
#endif

    mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ssl_ticket_context ) );
}

#endif /* MBEDTLS_SSL_TICKET_C */