library/ccm.c

/*
 *  NIST SP800-38C compliant CCM implementation
 *
 *  Copyright (C) 2014, 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.
 */

/*
 * Definition of CCM:
 * http://csrc.nist.gov/publications/nistpubs/800-38C/SP800-38C_updated-July20_2007.pdf
 * RFC 3610 "Counter with CBC-MAC (CCM)"
 *
 * Related:
 * RFC 5116 "An Interface and Algorithms for Authenticated Encryption"
 */

#if !defined(POLARSSL_CONFIG_FILE)
#include "polarssl/config.h"
#else
#include POLARSSL_CONFIG_FILE
#endif

#if defined(POLARSSL_CCM_C)

#include "polarssl/ccm.h"

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

#define CCM_ENCRYPT 0
#define CCM_DECRYPT 1

/*
 * Initialize context
 */
int ccm_init( ccm_context *ctx, cipher_id_t cipher,
              const unsigned char *key, unsigned int keysize )
{
    int ret;
    const cipher_info_t *cipher_info;

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

    cipher_info = cipher_info_from_values( cipher, keysize, POLARSSL_MODE_ECB );
    if( cipher_info == NULL )
        return( POLARSSL_ERR_CCM_BAD_INPUT );

    if( cipher_info->block_size != 16 )
        return( POLARSSL_ERR_CCM_BAD_INPUT );

    if( ( ret = cipher_init_ctx( &ctx->cipher_ctx, cipher_info ) ) != 0 )
        return( ret );

    if( ( ret = cipher_setkey( &ctx->cipher_ctx, key, keysize,
                               POLARSSL_ENCRYPT ) ) != 0 )
    {
        return( ret );
    }

    return( 0 );
}

/*
 * Free context
 */
void ccm_free( ccm_context *ctx )
{
    (void) cipher_free_ctx( &ctx->cipher_ctx );
    polarssl_zeroize( ctx, sizeof( ccm_context ) );
}

/*
 * Macros for common operations.
 * Results in smaller compiled code than static inline functions.
 */

/*
 * Update the CBC-MAC state in y using a block in b
 * (Always using b as the source helps the compiler optimise a bit better.)
 */
#define UPDATE_CBC_MAC                                                      \
    for( i = 0; i < 16; i++ )                                               \
        y[i] ^= b[i];                                                       \
                                                                            \
    if( ( ret = cipher_update( &ctx->cipher_ctx, y, 16, y, &olen ) ) != 0 ) \
        return( ret );

/*
 * Encrypt or decrypt a partial block with CTR
 * Warning: using b for temporary storage! src and dst must not be b!
 * This avoids allocating one more 16 bytes buffer while allowing src == dst.
 */
#define CTR_CRYPT( dst, src, len  )                                            \
    if( ( ret = cipher_update( &ctx->cipher_ctx, ctr, 16, b, &olen ) ) != 0 )  \
        return( ret );                                                         \
                                                                               \
    for( i = 0; i < len; i++ )                                                 \
        dst[i] = src[i] ^ b[i];

/*
 * Authenticated encryption or decryption
 */
static int ccm_auth_crypt( ccm_context *ctx, int mode, size_t length,
                           const unsigned char *iv, size_t iv_len,
                           const unsigned char *add, size_t add_len,
                           const unsigned char *input, unsigned char *output,
                           unsigned char *tag, size_t tag_len )
{
    int ret;
    unsigned char i;
    unsigned char q = 16 - 1 - iv_len;
    size_t len_left, olen;
    unsigned char b[16];
    unsigned char y[16];
    unsigned char ctr[16];
    const unsigned char *src;
    unsigned char *dst;

    /*
     * Check length requirements: SP800-38C A.1
     * Additional requirement: a < 2^16 - 2^8 to simplify the code.
     * 'length' checked later (when writing it to the first block)
     */
    if( tag_len < 4 || tag_len > 16 || tag_len % 2 != 0 )
        return( POLARSSL_ERR_CCM_BAD_INPUT );

    /* Also implies q is within bounds */
    if( iv_len < 7 || iv_len > 13 )
        return( POLARSSL_ERR_CCM_BAD_INPUT );

    if( add_len > 0xFF00 )
        return( POLARSSL_ERR_CCM_BAD_INPUT );

    /*
     * First block B_0:
     * 0        .. 0        flags
     * 1        .. iv_len   nonce (aka iv)
     * iv_len+1 .. 15       length
     *
     * With flags as (bits):
     * 7        0
     * 6        add present?
     * 5 .. 3   (t - 2) / 2
     * 2 .. 0   q - 1
     */
    b[0] = 0;
    b[0] |= ( add_len > 0 ) << 6;
    b[0] |= ( ( tag_len - 2 ) / 2 ) << 3;
    b[0] |= q - 1;

    memcpy( b + 1, iv, iv_len );

    for( i = 0, len_left = length; i < q; i++, len_left >>= 8 )
        b[15-i] = (unsigned char)( len_left & 0xFF );

    if( len_left > 0 )
        return( POLARSSL_ERR_CCM_BAD_INPUT );


    /* Start CBC-MAC with first block */
    memset( y, 0, 16 );
    UPDATE_CBC_MAC;

    /*
     * If there is additional data, update CBC-MAC with
     * add_len, add, 0 (padding to a block boundary)
     */
    if( add_len > 0 )
    {
        size_t use_len;
        len_left = add_len;
        src = add;

        memset( b, 0, 16 );
        b[0] = (unsigned char)( ( add_len >> 8 ) & 0xFF );
        b[1] = (unsigned char)( ( add_len      ) & 0xFF );

        use_len = len_left < 16 - 2 ? len_left : 16 - 2;
        memcpy( b + 2, src, use_len );
        len_left -= use_len;
        src += use_len;

        UPDATE_CBC_MAC;

        while( len_left > 0 )
        {
            use_len = len_left > 16 ? 16 : len_left;

            memset( b, 0, 16 );
            memcpy( b, src, use_len );
            UPDATE_CBC_MAC;

            len_left -= use_len;
            src += use_len;
        }
    }

    /*
     * Prepare counter block for encryption:
     * 0        .. 0        flags
     * 1        .. iv_len   nonce (aka iv)
     * iv_len+1 .. 15       counter (initially 1)
     *
     * With flags as (bits):
     * 7 .. 3   0
     * 2 .. 0   q - 1
     */
    ctr[0] = q - 1;
    memcpy( ctr + 1, iv, iv_len );
    memset( ctr + 1 + iv_len, 0, q );
    ctr[15] = 1;

    /*
     * Authenticate and {en,de}crypt the message.
     *
     * The only difference between encryption and decryption is
     * the respective order of authentication and {en,de}cryption.
     */
    len_left = length;
    src = input;
    dst = output;

    while( len_left > 0 )
    {
        unsigned char use_len = len_left > 16 ? 16 : len_left;

        if( mode == CCM_ENCRYPT )
        {
            memset( b, 0, 16 );
            memcpy( b, src, use_len );
            UPDATE_CBC_MAC;
        }

        CTR_CRYPT( dst, src, use_len );

        if( mode == CCM_DECRYPT )
        {
            memset( b, 0, 16 );
            memcpy( b, dst, use_len );
            UPDATE_CBC_MAC;
        }

        dst += use_len;
        src += use_len;
        len_left -= use_len;

        /*
         * Increment counter.
         * No need to check for overflow thanks to the length check above.
         */
        for( i = 0; i < q; i++ )
            if( ++ctr[15-i] != 0 )
                break;
    }

    /*
     * Authentication: reset counter and crypt/mask internal tag
     */
    for( i = 0; i < q; i++ )
        ctr[15-i] = 0;

    CTR_CRYPT( y, y, 16 );
    memcpy( tag, y, tag_len );

    return( 0 );
}

/*
 * Authenticated encryption
 */
int ccm_encrypt_and_tag( ccm_context *ctx, size_t length,
                         const unsigned char *iv, size_t iv_len,
                         const unsigned char *add, size_t add_len,
                         const unsigned char *input, unsigned char *output,
                         unsigned char *tag, size_t tag_len )
{
    return( ccm_auth_crypt( ctx, CCM_ENCRYPT, length, iv, iv_len,
                            add, add_len, input, output, tag, tag_len ) );
}

/*
 * Authenticated decryption
 */
int ccm_auth_decrypt( ccm_context *ctx, size_t length,
                      const unsigned char *iv, size_t iv_len,
                      const unsigned char *add, size_t add_len,
                      const unsigned char *input, unsigned char *output,
                      const unsigned char *tag, size_t tag_len )
{
    int ret;
    unsigned char check_tag[16];
    unsigned char i;
    int diff;

    if( ( ret = ccm_auth_crypt( ctx, CCM_DECRYPT, length,
                                iv, iv_len, add, add_len,
                                input, output, check_tag, tag_len ) ) != 0 )
    {
        return( ret );
    }

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

    if( diff != 0 )
    {
        polarssl_zeroize( output, length );
        return( POLARSSL_ERR_CCM_AUTH_FAILED );
    }

    return( 0 );
}


#if defined(POLARSSL_SELF_TEST) && defined(POLARSSL_AES_C)

#if defined(POLARSSL_PLATFORM_C)
#include "polarssl/platform.h"
#else
#define polarssl_printf printf
#endif

/*
 * Examples 1 to 3 from SP800-38C Appendix C
 */

#define NB_TESTS 3

/*
 * The data is the same for all tests, only the used length changes
 */
static const unsigned char key[] = {
    0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
    0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f
};

static const unsigned char iv[] = {
    0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
    0x18, 0x19, 0x1a, 0x1b
};

static const unsigned char ad[] = {
    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
    0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
    0x10, 0x11, 0x12, 0x13
};

static const unsigned char msg[] = {
    0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
    0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
    0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
};

static const size_t iv_len [NB_TESTS] = { 7, 8,  12 };
static const size_t add_len[NB_TESTS] = { 8, 16, 20 };
static const size_t msg_len[NB_TESTS] = { 4, 16, 24 };
static const size_t tag_len[NB_TESTS] = { 4, 6,  8  };

static const unsigned char res[NB_TESTS][32] = {
    {   0x71, 0x62, 0x01, 0x5b, 0x4d, 0xac, 0x25, 0x5d },
    {   0xd2, 0xa1, 0xf0, 0xe0, 0x51, 0xea, 0x5f, 0x62,
        0x08, 0x1a, 0x77, 0x92, 0x07, 0x3d, 0x59, 0x3d,
        0x1f, 0xc6, 0x4f, 0xbf, 0xac, 0xcd },
    {   0xe3, 0xb2, 0x01, 0xa9, 0xf5, 0xb7, 0x1a, 0x7a,
        0x9b, 0x1c, 0xea, 0xec, 0xcd, 0x97, 0xe7, 0x0b,
        0x61, 0x76, 0xaa, 0xd9, 0xa4, 0x42, 0x8a, 0xa5,
        0x48, 0x43, 0x92, 0xfb, 0xc1, 0xb0, 0x99, 0x51 }
};

int ccm_self_test( int verbose )
{
    ccm_context ctx;
    unsigned char out[32];
    size_t i;
    int ret;

    if( ccm_init( &ctx, POLARSSL_CIPHER_ID_AES, key, 8 * sizeof key ) != 0 )
    {
        if( verbose != 0 )
            polarssl_printf( "  CCM: setup failed" );

        return( 1 );
    }

    for( i = 0; i < NB_TESTS; i++ )
    {
        if( verbose != 0 )
            polarssl_printf( "  CCM-AES #%u: ", (unsigned int) i + 1 );

        ret = ccm_encrypt_and_tag( &ctx, msg_len[i],
                                   iv, iv_len[i], ad, add_len[i],
                                   msg, out,
                                   out + msg_len[i], tag_len[i] );

        if( ret != 0 ||
            memcmp( out, res[i], msg_len[i] + tag_len[i] ) != 0 )
        {
            if( verbose != 0 )
                polarssl_printf( "failed\n" );

            return( 1 );
        }

        ret = ccm_auth_decrypt( &ctx, msg_len[i],
                                iv, iv_len[i], ad, add_len[i],
                                res[i], out,
                                res[i] + msg_len[i], tag_len[i] );

        if( ret != 0 ||
            memcmp( out, msg, msg_len[i] ) != 0 )
        {
            if( verbose != 0 )
                polarssl_printf( "failed\n" );

            return( 1 );
        }

        if( verbose != 0 )
            polarssl_printf( "passed\n" );
    }

    ccm_free( &ctx );

    if( verbose != 0 )
        polarssl_printf( "\n" );

    return( 0 );
}

#endif /* POLARSSL_SELF_TEST && POLARSSL_AES_C */

#endif /* POLARSSL_CCM_C */