library/cipher.c

/**
 * \file cipher.c
 * 
 * \brief Generic cipher wrapper for PolarSSL
 *
 * \author Adriaan de Jong <dejong@fox-it.com>
 *
 *  Copyright (C) 2006-2013, Brainspark B.V.
 *
 *  This file is part of PolarSSL (http://www.polarssl.org)
 *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
 *
 *  All rights reserved.
 *
 *  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.
 */

#include "polarssl/config.h"

#if defined(POLARSSL_CIPHER_C)

#include "polarssl/cipher.h"
#include "polarssl/cipher_wrap.h"

#if defined(POLARSSL_GCM_C)
#include "polarssl/gcm.h"
#endif

#include <stdlib.h>

#if defined(POLARSSL_ARC4_C) || defined(POLARSSL_CIPHER_NULL_CIPHER)
#define POLARSSL_CIPHER_MODE_STREAM
#endif

#if defined _MSC_VER && !defined strcasecmp
#define strcasecmp _stricmp
#endif

static const int supported_ciphers[] = {

#if defined(POLARSSL_AES_C)
        POLARSSL_CIPHER_AES_128_CBC,
        POLARSSL_CIPHER_AES_192_CBC,
        POLARSSL_CIPHER_AES_256_CBC,

#if defined(POLARSSL_CIPHER_MODE_CFB)
        POLARSSL_CIPHER_AES_128_CFB128,
        POLARSSL_CIPHER_AES_192_CFB128,
        POLARSSL_CIPHER_AES_256_CFB128,
#endif /* defined(POLARSSL_CIPHER_MODE_CFB) */

#if defined(POLARSSL_CIPHER_MODE_CTR)
        POLARSSL_CIPHER_AES_128_CTR,
        POLARSSL_CIPHER_AES_192_CTR,
        POLARSSL_CIPHER_AES_256_CTR,
#endif /* defined(POLARSSL_CIPHER_MODE_CTR) */

#endif /* defined(POLARSSL_AES_C) */

#if defined(POLARSSL_ARC4_C)
        POLARSSL_CIPHER_ARC4_128,
#endif

#if defined(POLARSSL_CAMELLIA_C)
        POLARSSL_CIPHER_CAMELLIA_128_CBC,
        POLARSSL_CIPHER_CAMELLIA_192_CBC,
        POLARSSL_CIPHER_CAMELLIA_256_CBC,

#if defined(POLARSSL_CIPHER_MODE_CFB)
        POLARSSL_CIPHER_CAMELLIA_128_CFB128,
        POLARSSL_CIPHER_CAMELLIA_192_CFB128,
        POLARSSL_CIPHER_CAMELLIA_256_CFB128,
#endif /* defined(POLARSSL_CIPHER_MODE_CFB) */

#if defined(POLARSSL_CIPHER_MODE_CTR)
        POLARSSL_CIPHER_CAMELLIA_128_CTR,
        POLARSSL_CIPHER_CAMELLIA_192_CTR,
        POLARSSL_CIPHER_CAMELLIA_256_CTR,
#endif /* defined(POLARSSL_CIPHER_MODE_CTR) */

#endif /* defined(POLARSSL_CAMELLIA_C) */

#if defined(POLARSSL_DES_C)
        POLARSSL_CIPHER_DES_CBC,
        POLARSSL_CIPHER_DES_EDE_CBC,
        POLARSSL_CIPHER_DES_EDE3_CBC,
#endif /* defined(POLARSSL_DES_C) */

#if defined(POLARSSL_BLOWFISH_C)
        POLARSSL_CIPHER_BLOWFISH_CBC,

#if defined(POLARSSL_CIPHER_MODE_CFB)
        POLARSSL_CIPHER_BLOWFISH_CFB64,
#endif /* defined(POLARSSL_CIPHER_MODE_CFB) */

#if defined(POLARSSL_CIPHER_MODE_CTR)
        POLARSSL_CIPHER_BLOWFISH_CTR,
#endif /* defined(POLARSSL_CIPHER_MODE_CTR) */

#endif /* defined(POLARSSL_BLOWFISH_C) */

#if defined(POLARSSL_CIPHER_NULL_CIPHER)
        POLARSSL_CIPHER_NULL,
#endif /* defined(POLARSSL_CIPHER_NULL_CIPHER) */

        0
};

const int *cipher_list( void )
{
    return supported_ciphers;
}

const cipher_info_t *cipher_info_from_type( const cipher_type_t cipher_type )
{
    /* Find static cipher information */
    switch ( cipher_type )
    {
#if defined(POLARSSL_AES_C)
        case POLARSSL_CIPHER_AES_128_CBC:
            return &aes_128_cbc_info;
        case POLARSSL_CIPHER_AES_192_CBC:
            return &aes_192_cbc_info;
        case POLARSSL_CIPHER_AES_256_CBC:
            return &aes_256_cbc_info;

#if defined(POLARSSL_CIPHER_MODE_CFB)
        case POLARSSL_CIPHER_AES_128_CFB128:
            return &aes_128_cfb128_info;
        case POLARSSL_CIPHER_AES_192_CFB128:
            return &aes_192_cfb128_info;
        case POLARSSL_CIPHER_AES_256_CFB128:
            return &aes_256_cfb128_info;
#endif /* defined(POLARSSL_CIPHER_MODE_CFB) */

#if defined(POLARSSL_CIPHER_MODE_CTR)
        case POLARSSL_CIPHER_AES_128_CTR:
            return &aes_128_ctr_info;
        case POLARSSL_CIPHER_AES_192_CTR:
            return &aes_192_ctr_info;
        case POLARSSL_CIPHER_AES_256_CTR:
            return &aes_256_ctr_info;
#endif /* defined(POLARSSL_CIPHER_MODE_CTR) */

#if defined(POLARSSL_GCM_C)
        case POLARSSL_CIPHER_AES_128_GCM:
            return &aes_128_gcm_info;
        case POLARSSL_CIPHER_AES_256_GCM:
            return &aes_256_gcm_info;
#endif /* defined(POLARSSL_GCM_C) */

#endif

#if defined(POLARSSL_CAMELLIA_C)
        case POLARSSL_CIPHER_CAMELLIA_128_CBC:
            return &camellia_128_cbc_info;
        case POLARSSL_CIPHER_CAMELLIA_192_CBC:
            return &camellia_192_cbc_info;
        case POLARSSL_CIPHER_CAMELLIA_256_CBC:
            return &camellia_256_cbc_info;

#if defined(POLARSSL_CIPHER_MODE_CFB)
        case POLARSSL_CIPHER_CAMELLIA_128_CFB128:
            return &camellia_128_cfb128_info;
        case POLARSSL_CIPHER_CAMELLIA_192_CFB128:
            return &camellia_192_cfb128_info;
        case POLARSSL_CIPHER_CAMELLIA_256_CFB128:
            return &camellia_256_cfb128_info;
#endif /* defined(POLARSSL_CIPHER_MODE_CFB) */

#if defined(POLARSSL_CIPHER_MODE_CTR)
        case POLARSSL_CIPHER_CAMELLIA_128_CTR:
            return &camellia_128_ctr_info;
        case POLARSSL_CIPHER_CAMELLIA_192_CTR:
            return &camellia_192_ctr_info;
        case POLARSSL_CIPHER_CAMELLIA_256_CTR:
            return &camellia_256_ctr_info;
#endif /* defined(POLARSSL_CIPHER_MODE_CTR) */

#endif

#if defined(POLARSSL_DES_C)
        case POLARSSL_CIPHER_DES_CBC:
            return &des_cbc_info;
        case POLARSSL_CIPHER_DES_EDE_CBC:
            return &des_ede_cbc_info;
        case POLARSSL_CIPHER_DES_EDE3_CBC:
            return &des_ede3_cbc_info;
#endif

#if defined(POLARSSL_ARC4_C)
        case POLARSSL_CIPHER_ARC4_128:
            return &arc4_128_info;
#endif

#if defined(POLARSSL_BLOWFISH_C)
        case POLARSSL_CIPHER_BLOWFISH_CBC:
            return &blowfish_cbc_info;

#if defined(POLARSSL_CIPHER_MODE_CFB)
        case POLARSSL_CIPHER_BLOWFISH_CFB64:
            return &blowfish_cfb64_info;
#endif /* defined(POLARSSL_CIPHER_MODE_CFB) */

#if defined(POLARSSL_CIPHER_MODE_CTR)
        case POLARSSL_CIPHER_BLOWFISH_CTR:
            return &blowfish_ctr_info;
#endif /* defined(POLARSSL_CIPHER_MODE_CTR) */

#endif

#if defined(POLARSSL_CIPHER_NULL_CIPHER)
        case POLARSSL_CIPHER_NULL:
            return &null_cipher_info;
#endif /* defined(POLARSSL_CIPHER_NULL_CIPHER) */

        default:
            return NULL;
    }
}

const cipher_info_t *cipher_info_from_string( const char *cipher_name )
{
    if( NULL == cipher_name )
        return NULL;

    /* Get the appropriate cipher information */
#if defined(POLARSSL_CAMELLIA_C)
    if( !strcasecmp( "CAMELLIA-128-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_CAMELLIA_128_CBC );
    if( !strcasecmp( "CAMELLIA-192-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_CAMELLIA_192_CBC );
    if( !strcasecmp( "CAMELLIA-256-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_CAMELLIA_256_CBC );

#if defined(POLARSSL_CIPHER_MODE_CFB)
    if( !strcasecmp( "CAMELLIA-128-CFB128", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_CAMELLIA_128_CFB128 );
    if( !strcasecmp( "CAMELLIA-192-CFB128", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_CAMELLIA_192_CFB128 );
    if( !strcasecmp( "CAMELLIA-256-CFB128", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_CAMELLIA_256_CFB128 );
#endif /* defined(POLARSSL_CIPHER_MODE_CFB) */

#if defined(POLARSSL_CIPHER_MODE_CTR)
    if( !strcasecmp( "CAMELLIA-128-CTR", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_CAMELLIA_128_CTR );
    if( !strcasecmp( "CAMELLIA-192-CTR", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_CAMELLIA_192_CTR );
    if( !strcasecmp( "CAMELLIA-256-CTR", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_CAMELLIA_256_CTR );
#endif /* defined(POLARSSL_CIPHER_MODE_CTR) */
#endif

#if defined(POLARSSL_AES_C)
    if( !strcasecmp( "AES-128-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_128_CBC );
    if( !strcasecmp( "AES-192-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_192_CBC );
    if( !strcasecmp( "AES-256-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_256_CBC );

#if defined(POLARSSL_CIPHER_MODE_CFB)
    if( !strcasecmp( "AES-128-CFB128", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_128_CFB128 );
    if( !strcasecmp( "AES-192-CFB128", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_192_CFB128 );
    if( !strcasecmp( "AES-256-CFB128", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_256_CFB128 );
#endif /* defined(POLARSSL_CIPHER_MODE_CFB) */

#if defined(POLARSSL_CIPHER_MODE_CTR)
    if( !strcasecmp( "AES-128-CTR", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_128_CTR );
    if( !strcasecmp( "AES-192-CTR", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_192_CTR );
    if( !strcasecmp( "AES-256-CTR", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_256_CTR );
#endif /* defined(POLARSSL_CIPHER_MODE_CTR) */

#if defined(POLARSSL_GCM_C)
    if( !strcasecmp( "AES-128-GCM", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_128_GCM );
    if( !strcasecmp( "AES-256-GCM", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_AES_256_GCM );
#endif
#endif /* POLARSSL_AES_C */

#if defined(POLARSSL_ARC4_C)
    if( !strcasecmp( "ARC4-128", cipher_name ) )
        return( cipher_info_from_type( POLARSSL_CIPHER_ARC4_128 ) );
#endif

#if defined(POLARSSL_DES_C)
    if( !strcasecmp( "DES-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_DES_CBC );
    if( !strcasecmp( "DES-EDE-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_DES_EDE_CBC );
    if( !strcasecmp( "DES-EDE3-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_DES_EDE3_CBC );
#endif

#if defined(POLARSSL_BLOWFISH_C)
    if( !strcasecmp( "BLOWFISH-CBC", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_BLOWFISH_CBC );

#if defined(POLARSSL_CIPHER_MODE_CFB)
    if( !strcasecmp( "BLOWFISH-CFB64", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_BLOWFISH_CFB64 );
#endif /* defined(POLARSSL_CIPHER_MODE_CFB) */

#if defined(POLARSSL_CIPHER_MODE_CTR)
    if( !strcasecmp( "BLOWFISH-CTR", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_BLOWFISH_CTR );
#endif /* defined(POLARSSL_CIPHER_MODE_CTR) */
#endif

#if defined(POLARSSL_CIPHER_NULL_CIPHER)
    if( !strcasecmp( "NULL", cipher_name ) )
        return cipher_info_from_type( POLARSSL_CIPHER_NULL );
#endif /* defined(POLARSSL_CIPHER_NULL_CIPHER) */

    return NULL;
}

int cipher_init_ctx( cipher_context_t *ctx, const cipher_info_t *cipher_info )
{
    if( NULL == cipher_info || NULL == ctx )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    memset( ctx, 0, sizeof( cipher_context_t ) );

    if( NULL == ( ctx->cipher_ctx = cipher_info->base->ctx_alloc_func() ) )
        return POLARSSL_ERR_CIPHER_ALLOC_FAILED;

    ctx->cipher_info = cipher_info;

    /*
     * Ignore possible errors caused by a cipher mode that doesn't use padding
     */
#if defined(POLARSSL_CIPHER_PADDING_PKCS7)
    (void) cipher_set_padding_mode( ctx, POLARSSL_PADDING_PKCS7 );
#else
    (void) cipher_set_padding_mode( ctx, POLARSSL_PADDING_NONE );
#endif

    return 0;
}

int cipher_free_ctx( cipher_context_t *ctx )
{
    if( ctx == NULL || ctx->cipher_info == NULL )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    ctx->cipher_info->base->ctx_free_func( ctx->cipher_ctx );

    return 0;
}

int cipher_setkey( cipher_context_t *ctx, const unsigned char *key,
        int key_length, const operation_t operation )
{
    if( NULL == ctx || NULL == ctx->cipher_info )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    ctx->key_length = key_length;
    ctx->operation = operation;

    /*
     * For CFB and CTR mode always use the encryption key schedule
     */
    if( POLARSSL_ENCRYPT == operation ||
        POLARSSL_MODE_CFB == ctx->cipher_info->mode ||
        POLARSSL_MODE_CTR == ctx->cipher_info->mode )
    {
        return ctx->cipher_info->base->setkey_enc_func( ctx->cipher_ctx, key,
                ctx->key_length );
    }

    if( POLARSSL_DECRYPT == operation )
        return ctx->cipher_info->base->setkey_dec_func( ctx->cipher_ctx, key,
                ctx->key_length );

    return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
}

int cipher_set_iv( cipher_context_t *ctx,
                   const unsigned char *iv, size_t iv_len )
{
    size_t actual_iv_size;

    if( NULL == ctx || NULL == ctx->cipher_info || NULL == iv )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    if( ctx->cipher_info->accepts_variable_iv_size )
        actual_iv_size = iv_len;
    else
        actual_iv_size = ctx->cipher_info->iv_size;

    memcpy( ctx->iv, iv, actual_iv_size );
    ctx->iv_size = actual_iv_size;

    return 0;
}

int cipher_reset( cipher_context_t *ctx )
{
    if( NULL == ctx || NULL == ctx->cipher_info )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    ctx->unprocessed_len = 0;

    return 0;
}

int cipher_update_ad( cipher_context_t *ctx,
                      const unsigned char *ad, size_t ad_len )
{
    if( NULL == ctx || NULL == ctx->cipher_info )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

#if defined(POLARSSL_GCM_C)
    if( POLARSSL_MODE_GCM == ctx->cipher_info->mode )
    {
        /* Make sure we're called right after cipher_reset() */
        if( ((gcm_context *) ctx->cipher_ctx)->len != 0 ||
            ((gcm_context *) ctx->cipher_ctx)->add_len != 0 )
        {
            return POLARSSL_ERR_CIPHER_FEATURE_UNAVAILABLE;
        }

        return gcm_starts( ctx->cipher_ctx, ctx->operation,
                           ctx->iv, ctx->iv_size, ad, ad_len );
    }
#else
    ((void) ad);
    ((void) ad_len);
#endif

    return 0;
}

int cipher_update( cipher_context_t *ctx, const unsigned char *input, size_t ilen,
        unsigned char *output, size_t *olen )
{
    int ret;
    size_t copy_len = 0;

    *olen = 0;

    if( NULL == ctx || NULL == ctx->cipher_info || NULL == olen )
    {
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
    }

    if( input == output &&
       ( ctx->unprocessed_len != 0 || ilen % cipher_get_block_size( ctx ) ) )
    {
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
    }

    if( ctx->cipher_info->mode == POLARSSL_MODE_CBC ||
        ctx->cipher_info->mode == POLARSSL_MODE_GCM )
    {
        /*
         * If there is not enough data for a full block, cache it.
         */
        if( ( ctx->operation == POLARSSL_DECRYPT &&
                ilen + ctx->unprocessed_len <= cipher_get_block_size( ctx ) ) ||
             ( ctx->operation == POLARSSL_ENCRYPT &&
                ilen + ctx->unprocessed_len < cipher_get_block_size( ctx ) ) )
        {
            memcpy( &( ctx->unprocessed_data[ctx->unprocessed_len] ), input,
                    ilen );

            ctx->unprocessed_len += ilen;
            return 0;
        }

        /*
         * Process cached data first
         */
        if( ctx->unprocessed_len != 0 )
        {
            copy_len = cipher_get_block_size( ctx ) - ctx->unprocessed_len;

            memcpy( &( ctx->unprocessed_data[ctx->unprocessed_len] ), input,
                    copy_len );

#if defined(POLARSSL_GCM_C)
            if( ctx->cipher_info->mode == POLARSSL_MODE_GCM )
            {
                if( 0 != ( ret = gcm_update( ctx->cipher_ctx,
                                cipher_get_block_size( ctx ),
                                ctx->unprocessed_data, output ) ) )
                {
                    return ret;
                }
            }
            else
#endif
            if( 0 != ( ret = ctx->cipher_info->base->cbc_func( ctx->cipher_ctx,
                    ctx->operation, cipher_get_block_size( ctx ), ctx->iv,
                    ctx->unprocessed_data, output ) ) )
            {
                return ret;
            }

            *olen += cipher_get_block_size( ctx );
            output += cipher_get_block_size( ctx );
            ctx->unprocessed_len = 0;

            input += copy_len;
            ilen -= copy_len;
        }

        /*
         * Cache final, incomplete block
         */
        if( 0 != ilen )
        {
            copy_len = ilen % cipher_get_block_size( ctx );
            if( copy_len == 0 && ctx->operation == POLARSSL_DECRYPT )
                copy_len = cipher_get_block_size(ctx);

            memcpy( ctx->unprocessed_data, &( input[ilen - copy_len] ),
                    copy_len );

            ctx->unprocessed_len += copy_len;
            ilen -= copy_len;
        }

        /*
         * Process remaining full blocks
         */
        if( ilen )
        {
#if defined(POLARSSL_GCM_C)
            if( ctx->cipher_info->mode == POLARSSL_MODE_GCM )
            {
                if( 0 != ( ret = gcm_update( ctx->cipher_ctx,
                                             ilen, input, output ) ) )
                {
                    return ret;
                }
            }
            else
#endif
            if( 0 != ( ret = ctx->cipher_info->base->cbc_func( ctx->cipher_ctx,
                    ctx->operation, ilen, ctx->iv, input, output ) ) )
            {
                return ret;
            }

            *olen += ilen;
        }

        return 0;
    }

#if defined(POLARSSL_CIPHER_MODE_CFB)
    if( ctx->cipher_info->mode == POLARSSL_MODE_CFB )
    {
        if( 0 != ( ret = ctx->cipher_info->base->cfb_func( ctx->cipher_ctx,
                ctx->operation, ilen, &ctx->unprocessed_len, ctx->iv,
                input, output ) ) )
        {
            return ret;
        }

        *olen = ilen;

        return 0;
    }
#endif

#if defined(POLARSSL_CIPHER_MODE_CTR)
    if( ctx->cipher_info->mode == POLARSSL_MODE_CTR )
    {
        if( 0 != ( ret = ctx->cipher_info->base->ctr_func( ctx->cipher_ctx,
                ilen, &ctx->unprocessed_len, ctx->iv,
                ctx->unprocessed_data, input, output ) ) )
        {
            return ret;
        }

        *olen = ilen;

        return 0;
    }
#endif

#if defined(POLARSSL_CIPHER_MODE_STREAM)
    if( ctx->cipher_info->mode == POLARSSL_MODE_STREAM )
    {
        if( 0 != ( ret = ctx->cipher_info->base->stream_func( ctx->cipher_ctx,
                                                    ilen, input, output ) ) )
        {
            return ret;
        }

        *olen = ilen;

        return 0;
    }
#endif

    return POLARSSL_ERR_CIPHER_FEATURE_UNAVAILABLE;
}

#if defined(POLARSSL_CIPHER_PADDING_PKCS7)
/*
 * PKCS7 (and PKCS5) padding: fill with ll bytes, with ll = padding_len
 */
static void add_pkcs_padding( unsigned char *output, size_t output_len,
        size_t data_len )
{
    size_t padding_len = output_len - data_len;
    unsigned char i = 0;

    for( i = 0; i < padding_len; i++ )
        output[data_len + i] = (unsigned char) padding_len;
}

static int get_pkcs_padding( unsigned char *input, size_t input_len,
        size_t *data_len )
{
    unsigned int i, padding_len = 0;

    if( NULL == input || NULL == data_len )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    padding_len = input[input_len - 1];

    if( padding_len > input_len || padding_len == 0 )
        return POLARSSL_ERR_CIPHER_INVALID_PADDING;

    for( i = input_len - padding_len; i < input_len; i++ )
        if( input[i] != padding_len )
            return POLARSSL_ERR_CIPHER_INVALID_PADDING;

    *data_len = input_len - padding_len;

    return 0;
}
#endif /* POLARSSL_CIPHER_PADDING_PKCS7 */

#if defined(POLARSSL_CIPHER_PADDING_ONE_AND_ZEROS)
/*
 * One and zeros padding: fill with 80 00 ... 00
 */
static void add_one_and_zeros_padding( unsigned char *output,
                                       size_t output_len, size_t data_len )
{
    size_t padding_len = output_len - data_len;
    unsigned char i = 0;

    output[data_len] = 0x80;
    for( i = 1; i < padding_len; i++ )
        output[data_len + i] = 0x00;
}

static int get_one_and_zeros_padding( unsigned char *input, size_t input_len,
                                      size_t *data_len )
{
    unsigned char *p = input + input_len - 1;

    if( NULL == input || NULL == data_len )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    while( *p == 0x00 && p > input )
        --p;

    if( *p != 0x80 )
        return POLARSSL_ERR_CIPHER_INVALID_PADDING;

    *data_len = p - input;

    return 0;
}
#endif /* POLARSSL_CIPHER_PADDING_ONE_AND_ZEROS */

#if defined(POLARSSL_CIPHER_PADDING_ZEROS_AND_LEN)
/*
 * Zeros and len padding: fill with 00 ... 00 ll, where ll is padding length
 */
static void add_zeros_and_len_padding( unsigned char *output,
                                       size_t output_len, size_t data_len )
{
    size_t padding_len = output_len - data_len;
    unsigned char i = 0;

    for( i = 1; i < padding_len; i++ )
        output[data_len + i - 1] = 0x00;
    output[output_len - 1] = (unsigned char) padding_len;
}

static int get_zeros_and_len_padding( unsigned char *input, size_t input_len,
                                      size_t *data_len )
{
    unsigned int i, padding_len = 0;

    if( NULL == input || NULL == data_len )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    padding_len = input[input_len - 1];

    if( padding_len > input_len || padding_len == 0 )
        return POLARSSL_ERR_CIPHER_INVALID_PADDING;

    for( i = input_len - padding_len; i < input_len - 1; i++ )
        if( input[i] != 0x00 )
            return POLARSSL_ERR_CIPHER_INVALID_PADDING;

    *data_len = input_len - padding_len;

    return 0;
}
#endif /* POLARSSL_CIPHER_PADDING_ZEROS_AND_LEN */

#if defined(POLARSSL_CIPHER_PADDING_ZEROS)
/*
 * Zero padding: fill with 00 ... 00
 */
static void add_zeros_padding( unsigned char *output,
                               size_t output_len, size_t data_len )
{
    unsigned char i;

    for( i = data_len; i < output_len; i++ )
        output[i] = 0x00;
}

static int get_zeros_padding( unsigned char *input, size_t input_len,
                              size_t *data_len )
{
    unsigned char *p = input + input_len - 1;
    if( NULL == input || NULL == data_len )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    while( *p == 0x00 && p > input )
        --p;

    *data_len = *p == 0x00 ? 0 : p - input + 1;

    return 0;
}
#endif /* POLARSSL_CIPHER_PADDING_ZEROS */

/*
 * No padding: don't pad :)
 *
 * There is no add_padding function (check for NULL in cipher_finish)
 * but a trivial get_padding function
 */
static int get_no_padding( unsigned char *input, size_t input_len,
                              size_t *data_len )
{
    if( NULL == input || NULL == data_len )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    *data_len = input_len;

    return 0;
}

int cipher_finish( cipher_context_t *ctx,
                   unsigned char *output, size_t *olen,
                   unsigned char *tag, size_t tag_len )
{
    int ret = 0;

    if( NULL == ctx || NULL == ctx->cipher_info || NULL == olen )
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;

    *olen = 0;

    if( POLARSSL_MODE_CFB == ctx->cipher_info->mode ||
        POLARSSL_MODE_CTR == ctx->cipher_info->mode ||
        POLARSSL_MODE_STREAM == ctx->cipher_info->mode )
    {
        return 0;
    }

#if defined(POLARSSL_GCM_C)
    if( POLARSSL_MODE_GCM == ctx->cipher_info->mode )
    {
        unsigned char check_tag[16];
        size_t i;
        int diff;

        if( 0 != ( ret = gcm_update( ctx->cipher_ctx,
                        ctx->unprocessed_len, ctx->unprocessed_data,
                        output ) ) )
        {
            return( ret );
        }

        *olen += ctx->unprocessed_len;

        if( 0 != ( ret = gcm_finish( ctx->cipher_ctx, check_tag, tag_len ) ) )
            return( ret );

        /* On encryption, write the tag */
        if( POLARSSL_ENCRYPT == ctx->operation )
        {
            if( tag_len != 0 )
                memcpy( tag, check_tag, tag_len );
            return( 0 );
        }

        /* On decryption, check the tag (in "constant-time") */
        for( diff = 0, i = 0; i < tag_len; i++ )
            diff |= tag[i] ^ check_tag[i];

        if( diff != 0 )
            return( POLARSSL_ERR_GCM_AUTH_FAILED );

        return( 0 );
    }
#else
    ((void) tag);
    ((void) tag_len);
#endif

    if( POLARSSL_MODE_CBC == ctx->cipher_info->mode )
    {
        if( POLARSSL_ENCRYPT == ctx->operation )
        {
            /* check for 'no padding' mode */
            if( NULL == ctx->add_padding )
            {
                if( 0 != ctx->unprocessed_len )
                    return POLARSSL_ERR_CIPHER_FULL_BLOCK_EXPECTED;

                return 0;
            }

            ctx->add_padding( ctx->unprocessed_data, cipher_get_iv_size( ctx ),
                    ctx->unprocessed_len );
        }
        else if ( cipher_get_block_size( ctx ) != ctx->unprocessed_len )
        {
            /*
             * For decrypt operations, expect a full block,
             * or an empty block if no padding
             */
            if( NULL == ctx->add_padding && 0 == ctx->unprocessed_len )
                return 0;

            return POLARSSL_ERR_CIPHER_FULL_BLOCK_EXPECTED;
        }

        /* cipher block */
        if( 0 != ( ret = ctx->cipher_info->base->cbc_func( ctx->cipher_ctx,
                ctx->operation, cipher_get_block_size( ctx ), ctx->iv,
                ctx->unprocessed_data, output ) ) )
        {
            return ret;
        }

        /* Set output size for decryption */
        if( POLARSSL_DECRYPT == ctx->operation )
            return ctx->get_padding( output, cipher_get_block_size( ctx ),
                                     olen );

        /* Set output size for encryption */
        *olen = cipher_get_block_size( ctx );
        return 0;
    }

    return POLARSSL_ERR_CIPHER_FEATURE_UNAVAILABLE;
}

int cipher_set_padding_mode( cipher_context_t *ctx, cipher_padding_t mode )
{
    if( NULL == ctx ||
        POLARSSL_MODE_CBC != ctx->cipher_info->mode )
    {
        return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
    }

    switch( mode )
    {
#if defined(POLARSSL_CIPHER_PADDING_PKCS7)
    case POLARSSL_PADDING_PKCS7:
        ctx->add_padding = add_pkcs_padding;
        ctx->get_padding = get_pkcs_padding;
        break;
#endif
#if defined(POLARSSL_CIPHER_PADDING_ONE_AND_ZEROS)
    case POLARSSL_PADDING_ONE_AND_ZEROS:
        ctx->add_padding = add_one_and_zeros_padding;
        ctx->get_padding = get_one_and_zeros_padding;
        break;
#endif
#if defined(POLARSSL_CIPHER_PADDING_ZEROS_AND_LEN)
    case POLARSSL_PADDING_ZEROS_AND_LEN:
        ctx->add_padding = add_zeros_and_len_padding;
        ctx->get_padding = get_zeros_and_len_padding;
        break;
#endif
#if defined(POLARSSL_CIPHER_PADDING_ZEROS)
    case POLARSSL_PADDING_ZEROS:
        ctx->add_padding = add_zeros_padding;
        ctx->get_padding = get_zeros_padding;
        break;
#endif
    case POLARSSL_PADDING_NONE:
        ctx->add_padding = NULL;
        ctx->get_padding = get_no_padding;
        break;

    default:
        return POLARSSL_ERR_CIPHER_FEATURE_UNAVAILABLE;
    }

    return 0;
}

#if defined(POLARSSL_SELF_TEST)

#include <stdio.h>

#define ASSERT(x) if (!(x)) { \
        printf( "failed with %i at %s\n", value, (#x) ); \
    return( 1 ); \
}
/*
 * Checkup routine
 */

int cipher_self_test( int verbose )
{
    ((void) verbose);

    return( 0 );
}

#endif

#endif