cosmopolitan/third_party/mbedtls/ssl_ticket.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:4;tab-width:4;coding:utf-8 -*-│
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright The Mbed TLS Contributors                                          │
│                                                                              │
│ 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 "libc/time.h"
#include "third_party/mbedtls/common.h"
#include "third_party/mbedtls/error.h"
#include "third_party/mbedtls/platform.h"
#include "third_party/mbedtls/ssl_internal.h"
#include "third_party/mbedtls/ssl_ticket.h"
__static_yoink("mbedtls_notice");

/*
 *  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.
 */

#if defined(MBEDTLS_SSL_TICKET_C)

/*
 * Initialze context
 */
void mbedtls_ssl_ticket_init( mbedtls_ssl_ticket_context *ctx )
{
    mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ssl_ticket_context ) );
}

#define MAX_KEY_BYTES 32    /* 256 bits */

#define TICKET_KEY_NAME_BYTES    4
#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_THIS_CORRUPTION;
    unsigned char buf[MAX_KEY_BYTES];
    mbedtls_ssl_ticket_key *key = ctx->keys + index;

#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 );

    /* 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 );

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

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

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

/**
 * \brief           Prepare context to be actually used
 *
 * \param ctx       Context to be set up
 * \param f_rng     RNG callback function
 * \param p_rng     RNG callback context
 * \param cipher    AEAD cipher to use for ticket protection.
 *                  Recommended value: MBEDTLS_CIPHER_AES_256_GCM.
 * \param lifetime  Tickets lifetime in seconds
 *                  Recommended value: 86400 (one day).
 *
 * \note            It is highly recommended to select a cipher that is at
 *                  least as strong as the the strongest ciphersuite
 *                  supported. Usually that means a 256-bit key.
 *
 * \note            The lifetime of the keys is twice the lifetime of tickets.
 *                  It is recommended to pick a reasonnable lifetime so as not
 *                  to negate the benefits of forward secrecy.
 *
 * \return          0 if successful,
 *                  or a specific MBEDTLS_ERR_XXX error code
 */
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_THIS_CORRUPTION;
    const mbedtls_cipher_info_t *cipher_info;

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

    ctx->ticket_lifetime = lifetime;

    cipher_info = mbedtls_cipher_info_from_type( cipher);
    if( cipher_info == NULL )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

    if( cipher_info->mode != MBEDTLS_MODE_GCM &&
        cipher_info->mode != MBEDTLS_MODE_CCM )
    {
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
    }

    if( cipher_info->key_bitlen > 8 * MAX_KEY_BYTES )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    ret = mbedtls_cipher_setup_psa( &ctx->keys[0].ctx,
                                    cipher_info, TICKET_AUTH_TAG_BYTES );
    if( ret != 0 && ret != MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE )
        return( ret );
    /* We don't yet expect to support all ciphers through PSA,
     * so allow fallback to ordinary mbedtls_cipher_setup(). */
    if( ret == MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE )
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    if( ( ret = mbedtls_cipher_setup( &ctx->keys[0].ctx, cipher_info ) ) != 0 )
        return( ret );

#if defined(MBEDTLS_USE_PSA_CRYPTO)
    ret = mbedtls_cipher_setup_psa( &ctx->keys[1].ctx,
                                    cipher_info, TICKET_AUTH_TAG_BYTES );
    if( ret != 0 && ret != MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE )
        return( ret );
    if( ret == MBEDTLS_ERR_CIPHER_FEATURE_UNAVAILABLE )
#endif /* MBEDTLS_USE_PSA_CRYPTO */
    if( ( ret = mbedtls_cipher_setup( &ctx->keys[1].ctx, cipher_info ) ) != 0 )
        return( ret );

    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_THIS_CORRUPTION;
    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( ( 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;
    }
    state_len_bytes[0] = ( clear_len >> 8 ) & 0xff;
    state_len_bytes[1] = ( clear_len      ) & 0xff;

    /* Encrypt and authenticate */
    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 )
    {
        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:
    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( timingsafe_bcmp( 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_THIS_CORRUPTION;
    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( ( 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( ( 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 )
    {
        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:
    return( ret );
}

/*
 * Free context
 */
void mbedtls_ssl_ticket_free( mbedtls_ssl_ticket_context *ctx )
{
    mbedtls_cipher_free( &ctx->keys[0].ctx );
    mbedtls_cipher_free( &ctx->keys[1].ctx );
    mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ssl_ticket_context ) );
}

#endif /* MBEDTLS_SSL_TICKET_C */