mbedtls/library/hmac_drbg.c

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/*
* HMAC_DRBG implementation (NIST SP 800-90)
*
* 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.
*/
/*
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* The NIST SP 800-90A DRBGs are described in the following publication.
* http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf
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* References below are based on rev. 1 (January 2012).
*/
#include "polarssl/config.h"
#if defined(POLARSSL_HMAC_DRBG_C)
#include "polarssl/hmac_drbg.h"
/*
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* HMAC_DRBG update, using optional additional data (10.1.2.2)
*/
void hmac_drbg_update( hmac_drbg_context *ctx,
const unsigned char *additional, size_t add_len )
{
size_t md_len = ctx->md_ctx.md_info->size;
unsigned char rounds = ( additional != NULL && add_len != 0 ) ? 2 : 1;
unsigned char sep[1];
for( sep[0] = 0; sep[0] < rounds; sep[0]++ )
{
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/* Step 1 or 4 */
md_hmac_starts( &ctx->md_ctx, ctx->K, md_len );
md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
md_hmac_update( &ctx->md_ctx, sep, 1 );
if( rounds == 2 )
md_hmac_update( &ctx->md_ctx, additional, add_len );
md_hmac_finish( &ctx->md_ctx, ctx->K );
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/* Step 2 or 5 */
md_hmac_starts( &ctx->md_ctx, ctx->K, md_len );
md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
md_hmac_finish( &ctx->md_ctx, ctx->V );
}
}
/*
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* Simplified HMAC_DRBG initialisation (for use with deterministic ECDSA)
*/
int hmac_drbg_init_buf( hmac_drbg_context *ctx,
const md_info_t * md_info,
const unsigned char *data, size_t data_len )
{
int ret;
memset( ctx, 0, sizeof( hmac_drbg_context ) );
if( ( ret = md_init_ctx( &ctx->md_ctx, md_info ) ) != 0 )
return( ret );
memset( ctx->V, 0x01, md_info->size );
/* ctx->K is already 0 */
hmac_drbg_update( ctx, data, data_len );
return( 0 );
}
/*
* HMAC_DRBG initialisation
*/
int hmac_drbg_init( hmac_drbg_context *ctx,
const md_info_t * md_info,
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int (*f_entropy)(void *, unsigned char *, size_t),
void *p_entropy,
const unsigned char *custom,
size_t len )
{
int ret;
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unsigned char seed[HMAC_DRBG_MAX_SEED_INPUT];
size_t seedlen, init_entropy_len;
memset( ctx, 0, sizeof( hmac_drbg_context ) );
if( ( ret = md_init_ctx( &ctx->md_ctx, md_info ) ) != 0 )
return( ret );
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/*
* See SP800-57 5.6.1 (p. 65-66) for the security strength provided by
* each hash function, then according to SP800-90A rev1 10.1 table 2,
* min_entropy_len (in bits) is security_strength.
*/
ctx->entropy_len = md_info->size <= 20 ? 16 : /* 160-bits hash -> 128 */
md_info->size <= 28 ? 24 : /* 224-bits hash -> 192 */
32; /* better (256+) -> 256 */
ctx->f_entropy = f_entropy;
ctx->p_entropy = p_entropy;
/*
* For initialisation, use more entropy to emulate a nonce
*/
init_entropy_len = ctx->entropy_len * 3 / 2;
if( init_entropy_len + len > HMAC_DRBG_MAX_SEED_INPUT )
return( POLARSSL_ERR_HMAC_DRBG_INPUT_TOO_BIG );
memset( seed, 0, HMAC_DRBG_MAX_SEED_INPUT );
/*
* Gather init_entropy_len bytes of entropy for initial seed
*/
if( 0 != ctx->f_entropy( ctx->p_entropy, seed,
init_entropy_len ) )
{
return( POLARSSL_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
}
seedlen = init_entropy_len;
/*
* Add additional data
*/
if( custom != NULL && len != 0 )
{
memcpy( seed + seedlen, custom, len );
seedlen += len;
}
/*
* Set initial state and update it with initialisation data
*/
memset( ctx->V, 0x01, md_info->size );
/* ctx->K is already 0 */
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hmac_drbg_update( ctx, seed, seedlen );
return( 0 );
}
/*
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* HMAC_DRBG random function with optional additional data (10.1.2.5)
*/
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int hmac_drbg_random_with_add( void *p_rng,
unsigned char *output, size_t out_len,
const unsigned char *additional, size_t add_len )
{
hmac_drbg_context *ctx = (hmac_drbg_context *) p_rng;
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size_t md_len = md_get_size( ctx->md_ctx.md_info );
size_t left = out_len;
unsigned char *out = output;
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/* 1. Check reseed counter (TODO) */
/* 2. Use additional data if any */
if( additional != NULL && add_len != 0 )
hmac_drbg_update( ctx, additional, add_len );
/* 3, 4, 5. Generate bytes */
while( left != 0 )
{
size_t use_len = left > md_len ? md_len : left;
md_hmac_starts( &ctx->md_ctx, ctx->K, md_len );
md_hmac_update( &ctx->md_ctx, ctx->V, md_len );
md_hmac_finish( &ctx->md_ctx, ctx->V );
memcpy( out, ctx->V, use_len );
out += use_len;
left -= use_len;
}
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/* 6. Update */
hmac_drbg_update( ctx, additional, add_len );
/* 7. Update reseed counter (TODO) */
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/* 8. Done */
return( 0 );
}
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/*
* HMAC_DRBG random function
*/
int hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len )
{
return( hmac_drbg_random_with_add( p_rng, output, out_len, NULL, 0 ) );
}
/*
* Free an HMAC_DRBG context
*/
void hmac_drbg_free( hmac_drbg_context *ctx )
{
if( ctx == NULL )
return;
md_free_ctx( &ctx->md_ctx );
memset( ctx, 0, sizeof( hmac_drbg_context ) );
}
#if defined(POLARSSL_SELF_TEST)
#include <stdio.h>
/*
* Checkup routine
*/
int hmac_drbg_self_test( int verbose )
{
if( verbose != 0 )
printf( "\n" );
return( 0 );
}
#endif /* POLARSSL_SELF_TEST */
#endif /* POLARSSL_HMAC_DRBG_C */