library/ssl_ticket.c

/*
 *  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
#include <stdlib.h>
#define mbedtls_calloc    calloc
#define mbedtls_free       free
#endif

#include <string.h>

/* Implementation that should never be optimized out by the compiler */
static void mbedtls_zeroize( void *v, size_t n ) {
    volatile unsigned char *p = v; while( n-- ) *p++ = 0;
}

/*
 * 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 32    /* 256 bits */

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

#if defined(MBEDTLS_HAVE_TIME)
    key->generation_time = (uint32_t) 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_size( &key->ctx ),
                                 MBEDTLS_ENCRYPT );

    mbedtls_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) 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 );
}

/*
 * 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;
    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_length > 8 * MAX_KEY_BYTES )
        return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );

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

/*
 * 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
 */
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( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );

    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( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );

    *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_calloc( 1, sizeof( mbedtls_x509_crt ) );

        if( session->peer_cert == NULL )
            return( MBEDTLS_ERR_SSL_ALLOC_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, 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_ssl_ticket_context *ctx = p_ticket;
    mbedtls_ssl_ticket_key *key;
    unsigned char *key_name = start;
    unsigned char *iv = start + 4;
    unsigned char *state_len_bytes = iv + 12;
    unsigned char *state = state_len_bytes + 2;
    unsigned char *tag;
    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. */
    if( end - start < 4 + 12 + 2 + 16 )
        return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );

#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, 4 );

    if( ( ret = ctx->f_rng( ctx->p_rng, iv, 12 ) ) != 0 )
        goto cleanup;

    /* Dump session state */
    if( ( ret = ssl_save_session( 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 */
    tag = state + clear_len;
    if( ( ret = mbedtls_cipher_auth_encrypt( &key->ctx,
                    iv, 12, key_name, 4 + 12 + 2,
                    state, clear_len, state, &ciph_len, tag, 16 ) ) != 0 )
    {
        goto cleanup;
    }
    if( ciph_len != clear_len )
    {
        ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
        goto cleanup;
    }

    *tlen = 4 + 12 + 2 + 16 + ciph_len;

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_ssl_ticket_context *ctx = p_ticket;
    mbedtls_ssl_ticket_key *key;
    unsigned char *key_name = buf;
    unsigned char *iv = buf + 4;
    unsigned char *enc_len_p = iv + 12;
    unsigned char *ticket = enc_len_p + 2;
    unsigned char *tag;
    size_t enc_len, clear_len;

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

    /* See mbedtls_ssl_ticket_write() */
    if( len < 4 + 12 + 2 + 16 )
        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];
    tag = ticket + enc_len;

    if( len != 4 + 12 + 2 + enc_len + 16 )
    {
        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( &key->ctx, iv, 12,
                    key_name, 4 + 12 + 2, ticket, enc_len,
                    ticket, &clear_len, tag, 16 ) ) != 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 = ssl_load_session( session, ticket, clear_len ) ) != 0 )
        goto cleanup;

#if defined(MBEDTLS_HAVE_TIME)
    {
        /* Check for expiration */
        time_t current_time = 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 )
{
    mbedtls_cipher_free( &ctx->keys[0].ctx );
    mbedtls_cipher_free( &ctx->keys[1].ctx );

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

    mbedtls_zeroize( ctx, sizeof( mbedtls_ssl_ticket_context ) );
}

#endif /* MBEDTLS_SSL_TICKET_C */