library/sha256.c

/*
 *  FIPS-180-2 compliant SHA-256 implementation
 *
 *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
 *  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.
 *
 *  This file is part of mbed TLS (https://tls.mbed.org)
 */
/*
 *  The SHA-256 Secure Hash Standard was published by NIST in 2002.
 *
 *  http://csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf
 */

#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif

#if defined(MBEDTLS_SHA256_C)

#include "mbedtls/sha256.h"
#include "mbedtls/platform_util.h"
#include "mbedtls/platform.h"

#include <string.h>

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

#define SHA256_VALIDATE_RET(cond)                           \
    MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_SHA256_BAD_INPUT_DATA )
#define SHA256_VALIDATE(cond)  MBEDTLS_INTERNAL_VALIDATE( cond )

#if !defined(MBEDTLS_SHA256_ALT)

void mbedtls_sha256_init( mbedtls_sha256_context *ctx )
{
    SHA256_VALIDATE( ctx != NULL );

    memset( ctx, 0, sizeof( mbedtls_sha256_context ) );
}

void mbedtls_sha256_free( mbedtls_sha256_context *ctx )
{
    if( ctx == NULL )
        return;

    mbedtls_platform_zeroize( ctx, sizeof( mbedtls_sha256_context ) );
}

void mbedtls_sha256_clone( mbedtls_sha256_context *dst,
                           const mbedtls_sha256_context *src )
{
    SHA256_VALIDATE( dst != NULL );
    SHA256_VALIDATE( src != NULL );

    *dst = *src;
}

/*
 * SHA-256 context setup
 */
int mbedtls_sha256_starts_ret( mbedtls_sha256_context *ctx, int is224 )
{
    SHA256_VALIDATE_RET( ctx != NULL );
#if defined(MBEDTLS_SHA256_NO_SHA224)
    SHA256_VALIDATE_RET( is224 == 0 );
    (void) is224;
#else
    SHA256_VALIDATE_RET( is224 == 0 || is224 == 1 );
#endif

    ctx->total[0] = 0;
    ctx->total[1] = 0;

#if !defined(MBEDTLS_SHA256_NO_SHA224)
    ctx->is224 = is224;

    if( is224 == 1 )
    {
        /* SHA-224 */
        ctx->state[0] = 0xC1059ED8;
        ctx->state[1] = 0x367CD507;
        ctx->state[2] = 0x3070DD17;
        ctx->state[3] = 0xF70E5939;
        ctx->state[4] = 0xFFC00B31;
        ctx->state[5] = 0x68581511;
        ctx->state[6] = 0x64F98FA7;
        ctx->state[7] = 0xBEFA4FA4;
    }
    else
#endif
    {
        /* SHA-256 */
        ctx->state[0] = 0x6A09E667;
        ctx->state[1] = 0xBB67AE85;
        ctx->state[2] = 0x3C6EF372;
        ctx->state[3] = 0xA54FF53A;
        ctx->state[4] = 0x510E527F;
        ctx->state[5] = 0x9B05688C;
        ctx->state[6] = 0x1F83D9AB;
        ctx->state[7] = 0x5BE0CD19;
    }

    return( 0 );
}

#if !defined(MBEDTLS_DEPRECATED_REMOVED)
void mbedtls_sha256_starts( mbedtls_sha256_context *ctx,
                            int is224 )
{
    mbedtls_sha256_starts_ret( ctx, is224 );
}
#endif

#if !defined(MBEDTLS_SHA256_PROCESS_ALT)
static const uint32_t K[] =
{
    0x428A2F98, 0x71374491, 0xB5C0FBCF, 0xE9B5DBA5,
    0x3956C25B, 0x59F111F1, 0x923F82A4, 0xAB1C5ED5,
    0xD807AA98, 0x12835B01, 0x243185BE, 0x550C7DC3,
    0x72BE5D74, 0x80DEB1FE, 0x9BDC06A7, 0xC19BF174,
    0xE49B69C1, 0xEFBE4786, 0x0FC19DC6, 0x240CA1CC,
    0x2DE92C6F, 0x4A7484AA, 0x5CB0A9DC, 0x76F988DA,
    0x983E5152, 0xA831C66D, 0xB00327C8, 0xBF597FC7,
    0xC6E00BF3, 0xD5A79147, 0x06CA6351, 0x14292967,
    0x27B70A85, 0x2E1B2138, 0x4D2C6DFC, 0x53380D13,
    0x650A7354, 0x766A0ABB, 0x81C2C92E, 0x92722C85,
    0xA2BFE8A1, 0xA81A664B, 0xC24B8B70, 0xC76C51A3,
    0xD192E819, 0xD6990624, 0xF40E3585, 0x106AA070,
    0x19A4C116, 0x1E376C08, 0x2748774C, 0x34B0BCB5,
    0x391C0CB3, 0x4ED8AA4A, 0x5B9CCA4F, 0x682E6FF3,
    0x748F82EE, 0x78A5636F, 0x84C87814, 0x8CC70208,
    0x90BEFFFA, 0xA4506CEB, 0xBEF9A3F7, 0xC67178F2,
};

#define  SHR(x,n) (((x) & 0xFFFFFFFF) >> (n))
#define ROTR(x,n) (SHR(x,n) | ((x) << (32 - (n))))

#define S0(x) (ROTR(x, 7) ^ ROTR(x,18) ^  SHR(x, 3))
#define S1(x) (ROTR(x,17) ^ ROTR(x,19) ^  SHR(x,10))

#define S2(x) (ROTR(x, 2) ^ ROTR(x,13) ^ ROTR(x,22))
#define S3(x) (ROTR(x, 6) ^ ROTR(x,11) ^ ROTR(x,25))

#define F0(x,y,z) (((x) & (y)) | ((z) & ((x) | (y))))
#define F1(x,y,z) ((z) ^ ((x) & ((y) ^ (z))))

#define R(t)                                    \
    (                                           \
        W[t] = S1(W[(t) -  2]) + W[(t) -  7] +  \
               S0(W[(t) - 15]) + W[(t) - 16]    \
    )

#define P(a,b,c,d,e,f,g,h,x,K)                          \
    do                                                  \
    {                                                   \
        temp1 = (h) + S3(e) + F1((e),(f),(g)) + (K) + (x);      \
        temp2 = S2(a) + F0((a),(b),(c));                        \
        (d) += temp1; (h) = temp1 + temp2;              \
    } while( 0 )

int mbedtls_internal_sha256_process( mbedtls_sha256_context *ctx,
                                const unsigned char data[64] )
{
    uint32_t temp1, temp2, W[64];
    uint32_t A[8];
    uint32_t flow_ctrl = 0;
    unsigned int i;

    SHA256_VALIDATE_RET( ctx != NULL );
    SHA256_VALIDATE_RET( (const unsigned char *)data != NULL );

    for( i = 0; i < 8; i++ )
        A[i] = ctx->state[i];

#if defined(MBEDTLS_SHA256_SMALLER)
    {
        uint32_t offset = mbedtls_platform_random_in_range(16);
        mbedtls_platform_memset( W, 0, sizeof( W ) );

        for( i = offset; i < 16; i++ )
        {
            W[i] = (uint32_t)mbedtls_platform_get_uint32_be( &data[4 * i] );
            flow_ctrl++;
        }
        for( i = 0; i < offset; i++ )
        {
            W[i] = (uint32_t)mbedtls_platform_get_uint32_be( &data[4 * i] );
            flow_ctrl++;
        }
    }

    if( flow_ctrl != 16 )
    {
        return MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
    }

    for( i = 0; i < 64; i++ )
    {
        if( i >= 16 )
            R( i );

        P( A[0], A[1], A[2], A[3], A[4], A[5], A[6], A[7], W[i], K[i] );

        temp1 = A[7]; A[7] = A[6]; A[6] = A[5]; A[5] = A[4]; A[4] = A[3];
        A[3] = A[2]; A[2] = A[1]; A[1] = A[0]; A[0] = temp1;
        flow_ctrl++;
    }

    if( flow_ctrl != 80 )
    {
        return MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
    }

#else /* MBEDTLS_SHA256_SMALLER */
    for( i = 0; i < 16; i++ )
    {
        W[i] = (uint32_t)mbedtls_platform_get_uint32_be( &data[4 * i] );
        flow_ctrl++;
    }

    for( i = 0; i < 16; i += 8 )
    {
        P( A[0], A[1], A[2], A[3], A[4], A[5], A[6], A[7], W[i+0], K[i+0] );
        P( A[7], A[0], A[1], A[2], A[3], A[4], A[5], A[6], W[i+1], K[i+1] );
        P( A[6], A[7], A[0], A[1], A[2], A[3], A[4], A[5], W[i+2], K[i+2] );
        P( A[5], A[6], A[7], A[0], A[1], A[2], A[3], A[4], W[i+3], K[i+3] );
        P( A[4], A[5], A[6], A[7], A[0], A[1], A[2], A[3], W[i+4], K[i+4] );
        P( A[3], A[4], A[5], A[6], A[7], A[0], A[1], A[2], W[i+5], K[i+5] );
        P( A[2], A[3], A[4], A[5], A[6], A[7], A[0], A[1], W[i+6], K[i+6] );
        P( A[1], A[2], A[3], A[4], A[5], A[6], A[7], A[0], W[i+7], K[i+7] );
        flow_ctrl++;
    }

    for( i = 16; i < 64; i += 8 )
    {
        P( A[0], A[1], A[2], A[3], A[4], A[5], A[6], A[7], R(i+0), K[i+0] );
        P( A[7], A[0], A[1], A[2], A[3], A[4], A[5], A[6], R(i+1), K[i+1] );
        P( A[6], A[7], A[0], A[1], A[2], A[3], A[4], A[5], R(i+2), K[i+2] );
        P( A[5], A[6], A[7], A[0], A[1], A[2], A[3], A[4], R(i+3), K[i+3] );
        P( A[4], A[5], A[6], A[7], A[0], A[1], A[2], A[3], R(i+4), K[i+4] );
        P( A[3], A[4], A[5], A[6], A[7], A[0], A[1], A[2], R(i+5), K[i+5] );
        P( A[2], A[3], A[4], A[5], A[6], A[7], A[0], A[1], R(i+6), K[i+6] );
        P( A[1], A[2], A[3], A[4], A[5], A[6], A[7], A[0], R(i+7), K[i+7] );
        flow_ctrl++;
    }

    /* 16 from the first loop, 2 from the second and 6 from the third. */
    if( flow_ctrl != 24 )
    {
        return MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
    }
#endif /* MBEDTLS_SHA256_SMALLER */
    flow_ctrl = 0;

    for( i = 0; i < 8; i++ )
    {
        ctx->state[i] += A[i];
        flow_ctrl++;
    }

    if( flow_ctrl == 8 )
    {
        return( 0 );
    }

    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
}

#if !defined(MBEDTLS_DEPRECATED_REMOVED)
void mbedtls_sha256_process( mbedtls_sha256_context *ctx,
                             const unsigned char data[64] )
{
    mbedtls_internal_sha256_process( ctx, data );
}
#endif
#endif /* !MBEDTLS_SHA256_PROCESS_ALT */

/*
 * SHA-256 process buffer
 */
int mbedtls_sha256_update_ret( mbedtls_sha256_context *ctx,
                               const unsigned char *input,
                               size_t ilen )
{
    int ret;
    size_t fill;
    uint32_t left;
    volatile const unsigned char *input_dup = input;
    volatile size_t ilen_dup = ilen;
    size_t ilen_change;
    SHA256_VALIDATE_RET( ctx != NULL );
    SHA256_VALIDATE_RET( ilen == 0 || input != NULL );

    if( ilen == 0 )
        return( 0 );

    left = ctx->total[0] & 0x3F;
    fill = 64 - left;

    ctx->total[0] += (uint32_t) ilen;
    ctx->total[0] &= 0xFFFFFFFF;

    if( ctx->total[0] < (uint32_t) ilen )
        ctx->total[1]++;

    if( left && ilen >= fill )
    {
        mbedtls_platform_memcpy( (void *) (ctx->buffer + left), input, fill );

        if( ( ret = mbedtls_internal_sha256_process( ctx, ctx->buffer ) ) != 0 )
            return( ret );

        input += fill;
        ilen  -= fill;
        left = 0;
    }

    while( ilen >= 64 )
    {
        if( ( ret = mbedtls_internal_sha256_process( ctx, input ) ) != 0 )
            return( ret );

        input += 64;
        ilen  -= 64;
    }

    if( ilen > 0 )
        mbedtls_platform_memcpy( (void *) (ctx->buffer + left), input, ilen );

    /* Re-check ilen to protect from a FI attack */
    if( ilen < 64 )
    {
        /* Re-check that the calculated offsets are correct */
        ilen_change = ilen_dup - ilen;
        if( ( input_dup + ilen_change ) == input )
        {
            return( 0 );
        }
    }
    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
}

#if !defined(MBEDTLS_DEPRECATED_REMOVED)
void mbedtls_sha256_update( mbedtls_sha256_context *ctx,
                            const unsigned char *input,
                            size_t ilen )
{
    mbedtls_sha256_update_ret( ctx, input, ilen );
}
#endif

/*
 * SHA-256 final digest
 */
int mbedtls_sha256_finish_ret( mbedtls_sha256_context *ctx,
                               unsigned char output[32] )
{
    int ret, s_pos, o_pos;
    uint32_t used;
    uint32_t high, low;
    uint32_t offset = 0;
    uint32_t flow_ctrl = 0;

    SHA256_VALIDATE_RET( ctx != NULL );
    SHA256_VALIDATE_RET( (unsigned char *)output != NULL );

    /*
     * Add padding: 0x80 then 0x00 until 8 bytes remain for the length
     */
    used = ctx->total[0] & 0x3F;

    ctx->buffer[used++] = 0x80;
    flow_ctrl++;

    if( used <= 56 )
    {
        /* Enough room for padding + length in current block */
        mbedtls_platform_memset( ctx->buffer + used, 0, 56 - used );
    }
    else
    {
        /* We'll need an extra block */
        mbedtls_platform_memset( ctx->buffer + used, 0, 64 - used );

        if( ( ret = mbedtls_internal_sha256_process( ctx, ctx->buffer ) ) != 0 )
            return( ret );

        mbedtls_platform_memset( ctx->buffer, 0, 56 );
    }

    /*
     * Add message length
     */
    high = ( ctx->total[0] >> 29 )
         | ( ctx->total[1] <<  3 );
    low  = ( ctx->total[0] <<  3 );

    (void)mbedtls_platform_put_uint32_be( ctx->buffer + 56, high );
    (void)mbedtls_platform_put_uint32_be( ctx->buffer + 60, low );
    flow_ctrl++;

    if( ( ret = mbedtls_internal_sha256_process( ctx, ctx->buffer ) ) != 0 )
        return( ret );

    /*
     * Output final state
     */
    offset = mbedtls_platform_random_in_range(7);

    mbedtls_platform_memset( output, 0, 32 );

    for( s_pos = offset, o_pos = offset * 4; s_pos < 7;
            s_pos++, o_pos += 4 )
    {
        (void)mbedtls_platform_put_uint32_be( &output[o_pos],
                                            ctx->state[s_pos] );
        flow_ctrl++;
    }

#if !defined(MBEDTLS_SHA256_NO_SHA224)
    if( ctx->is224 == 0 )
#endif
        (void)mbedtls_platform_put_uint32_be( &output[28], ctx->state[7] );

    for( s_pos = 0, o_pos = 0; s_pos < (int)offset; s_pos++, o_pos += 4 )
    {
        (void)mbedtls_platform_put_uint32_be( &output[o_pos],
                                            ctx->state[s_pos] );
        flow_ctrl++;
    }
    /* flow ctrl was incremented twice and then 7 times in two loops */
    if( flow_ctrl == 9 )
    {
        return( 0 );
    }
    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
}

#if !defined(MBEDTLS_DEPRECATED_REMOVED)
void mbedtls_sha256_finish( mbedtls_sha256_context *ctx,
                            unsigned char output[32] )
{
    mbedtls_sha256_finish_ret( ctx, output );
}
#endif

#endif /* !MBEDTLS_SHA256_ALT */

/*
 * output = SHA-256( input buffer )
 */
int mbedtls_sha256_ret( const unsigned char *input,
                        size_t ilen,
                        unsigned char output[32],
                        int is224 )
{
    int ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
    mbedtls_sha256_context ctx;
    volatile const unsigned char *input_dup = input;
    volatile size_t ilen_dup = ilen;

    SHA256_VALIDATE_RET( is224 == 0 || is224 == 1 );
    SHA256_VALIDATE_RET( ilen == 0 || input != NULL );
    SHA256_VALIDATE_RET( (unsigned char *)output != NULL );

    mbedtls_sha256_init( &ctx );

    if( ( ret = mbedtls_sha256_starts_ret( &ctx, is224 ) ) != 0 )
        goto exit;

    if( ( ret = mbedtls_sha256_update_ret( &ctx, input, ilen ) ) != 0 )
        goto exit;

    if( ( ret = mbedtls_sha256_finish_ret( &ctx, output ) ) != 0 )
        goto exit;

exit:
    mbedtls_sha256_free( &ctx );

    if( input_dup == input && ilen_dup == ilen )
    {
        return( ret );
    }
    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
}

#if !defined(MBEDTLS_DEPRECATED_REMOVED)
void mbedtls_sha256( const unsigned char *input,
                     size_t ilen,
                     unsigned char output[32],
                     int is224 )
{
    mbedtls_sha256_ret( input, ilen, output, is224 );
}
#endif

#if defined(MBEDTLS_SELF_TEST)
/*
 * FIPS-180-2 test vectors
 */
static const unsigned char sha256_test_buf[3][57] =
{
    { "abc" },
    { "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq" },
    { "" }
};

static const size_t sha256_test_buflen[3] =
{
    3, 56, 1000
};

static const unsigned char sha256_test_sum[][32] =
{
#if !defined(MBEDTLS_SHA256_NO_SHA224)
    /*
     * SHA-224 test vectors
     */
    { 0x23, 0x09, 0x7D, 0x22, 0x34, 0x05, 0xD8, 0x22,
      0x86, 0x42, 0xA4, 0x77, 0xBD, 0xA2, 0x55, 0xB3,
      0x2A, 0xAD, 0xBC, 0xE4, 0xBD, 0xA0, 0xB3, 0xF7,
      0xE3, 0x6C, 0x9D, 0xA7 },
    { 0x75, 0x38, 0x8B, 0x16, 0x51, 0x27, 0x76, 0xCC,
      0x5D, 0xBA, 0x5D, 0xA1, 0xFD, 0x89, 0x01, 0x50,
      0xB0, 0xC6, 0x45, 0x5C, 0xB4, 0xF5, 0x8B, 0x19,
      0x52, 0x52, 0x25, 0x25 },
    { 0x20, 0x79, 0x46, 0x55, 0x98, 0x0C, 0x91, 0xD8,
      0xBB, 0xB4, 0xC1, 0xEA, 0x97, 0x61, 0x8A, 0x4B,
      0xF0, 0x3F, 0x42, 0x58, 0x19, 0x48, 0xB2, 0xEE,
      0x4E, 0xE7, 0xAD, 0x67 },
#endif /* !MBEDTLS_SHA256_NO_SHA224 */

    /*
     * SHA-256 test vectors
     */
    { 0xBA, 0x78, 0x16, 0xBF, 0x8F, 0x01, 0xCF, 0xEA,
      0x41, 0x41, 0x40, 0xDE, 0x5D, 0xAE, 0x22, 0x23,
      0xB0, 0x03, 0x61, 0xA3, 0x96, 0x17, 0x7A, 0x9C,
      0xB4, 0x10, 0xFF, 0x61, 0xF2, 0x00, 0x15, 0xAD },
    { 0x24, 0x8D, 0x6A, 0x61, 0xD2, 0x06, 0x38, 0xB8,
      0xE5, 0xC0, 0x26, 0x93, 0x0C, 0x3E, 0x60, 0x39,
      0xA3, 0x3C, 0xE4, 0x59, 0x64, 0xFF, 0x21, 0x67,
      0xF6, 0xEC, 0xED, 0xD4, 0x19, 0xDB, 0x06, 0xC1 },
    { 0xCD, 0xC7, 0x6E, 0x5C, 0x99, 0x14, 0xFB, 0x92,
      0x81, 0xA1, 0xC7, 0xE2, 0x84, 0xD7, 0x3E, 0x67,
      0xF1, 0x80, 0x9A, 0x48, 0xA4, 0x97, 0x20, 0x0E,
      0x04, 0x6D, 0x39, 0xCC, 0xC7, 0x11, 0x2C, 0xD0 }
};

#define SHA256_TEST_SUM_N \
    ( sizeof( sha256_test_sum ) / sizeof( sha256_test_sum[0] ) )

/*
 * Checkup routine
 */
int mbedtls_sha256_self_test( int verbose )
{
    int i, j, k, buflen, ret = 0;
    unsigned char *buf;
    unsigned char sha256sum[32];
    mbedtls_sha256_context ctx;

    buf = mbedtls_calloc( 1024, sizeof(unsigned char) );
    if( NULL == buf )
    {
        if( verbose != 0 )
            mbedtls_printf( "Buffer allocation failed\n" );

        return( 1 );
    }

    mbedtls_sha256_init( &ctx );

    for( i = 0; i < (int) SHA256_TEST_SUM_N; i++ )
    {
        j = i % 3;
#if !defined(MBEDTLS_SHA256_NO_SHA224)
        k = i < 3;
#else
        k = 0;
#endif

        if( verbose != 0 )
            mbedtls_printf( "  SHA-%d test #%d: ", 256 - k * 32, j + 1 );

        if( ( ret = mbedtls_sha256_starts_ret( &ctx, k ) ) != 0 )
            goto fail;

        if( j == 2 )
        {
            memset( buf, 'a', buflen = 1000 );

            for( j = 0; j < 1000; j++ )
            {
                ret = mbedtls_sha256_update_ret( &ctx, buf, buflen );
                if( ret != 0 )
                    goto fail;
            }

        }
        else
        {
            ret = mbedtls_sha256_update_ret( &ctx, sha256_test_buf[j],
                                             sha256_test_buflen[j] );
            if( ret != 0 )
                 goto fail;
        }

        if( ( ret = mbedtls_sha256_finish_ret( &ctx, sha256sum ) ) != 0 )
            goto fail;


        if( memcmp( sha256sum, sha256_test_sum[i], 32 - k * 4 ) != 0 )
        {
            ret = 1;
            goto fail;
        }

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

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

    goto exit;

fail:
    if( verbose != 0 )
        mbedtls_printf( "failed\n" );

exit:
    mbedtls_sha256_free( &ctx );
    mbedtls_free( buf );

    return( ret );
}

#endif /* MBEDTLS_SELF_TEST */

#endif /* MBEDTLS_SHA256_C */