mbedtls/library/hmac_drbg.c
Hanno Becker a823d4c7f0 HMAC DRBG: Split entropy-gathering requests to reduce request sizes
According to SP800-90A, the DRBG seeding process should use a nonce
of length `security_strength / 2` bits as part of the DRBG seed. It
further notes that this nonce may be drawn from the same source of
entropy that is used for the first `security_strength` bits of the
DRBG seed. The present HMAC DRBG implementation does that, requesting
`security_strength * 3 / 2` bits of entropy from the configured entropy
source in total to form the initial part of the DRBG seed.

However, some entropy sources may have thresholds in terms of how much
entropy they can provide in a single call to their entropy gathering
function which may be exceeded by the present HMAC DRBG implementation
even if the threshold is not smaller than `security_strength` bits.
Specifically, this is the case for our own entropy module implementation
which only allows requesting at most 32 Bytes of entropy at a time
in configurations disabling SHA-512, and this leads to runtime failure
of HMAC DRBG when used with Mbed Crypto' own entropy callbacks in such
configurations.

This commit fixes this by splitting the seed entropy acquisition into
two calls, one requesting `security_strength` bits first, and another
one requesting `security_strength / 2` bits for the nonce.

Fixes #237.
2019-08-30 11:16:24 +01:00

623 lines
19 KiB
C

/*
* HMAC_DRBG implementation (NIST SP 800-90)
*
* 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 NIST SP 800-90A DRBGs are described in the following publication.
* http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf
* References below are based on rev. 1 (January 2012).
*/
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#if defined(MBEDTLS_HMAC_DRBG_C)
#include "mbedtls/hmac_drbg.h"
#include "mbedtls/platform_util.h"
#include <string.h>
#if defined(MBEDTLS_FS_IO)
#include <stdio.h>
#endif
#if defined(MBEDTLS_SELF_TEST)
#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdio.h>
#define mbedtls_printf printf
#endif /* MBEDTLS_SELF_TEST */
#endif /* MBEDTLS_PLATFORM_C */
/*
* HMAC_DRBG context initialization
*/
void mbedtls_hmac_drbg_init( mbedtls_hmac_drbg_context *ctx )
{
memset( ctx, 0, sizeof( mbedtls_hmac_drbg_context ) );
#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_init( &ctx->mutex );
#endif
}
/*
* HMAC_DRBG update, using optional additional data (10.1.2.2)
*/
int mbedtls_hmac_drbg_update_ret( mbedtls_hmac_drbg_context *ctx,
const unsigned char *additional,
size_t add_len )
{
size_t md_len = mbedtls_md_get_size( ctx->md_ctx.md_info );
unsigned char rounds = ( additional != NULL && add_len != 0 ) ? 2 : 1;
unsigned char sep[1];
unsigned char K[MBEDTLS_MD_MAX_SIZE];
int ret;
for( sep[0] = 0; sep[0] < rounds; sep[0]++ )
{
/* Step 1 or 4 */
if( ( ret = mbedtls_md_hmac_reset( &ctx->md_ctx ) ) != 0 )
goto exit;
if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
ctx->V, md_len ) ) != 0 )
goto exit;
if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
sep, 1 ) ) != 0 )
goto exit;
if( rounds == 2 )
{
if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
additional, add_len ) ) != 0 )
goto exit;
}
if( ( ret = mbedtls_md_hmac_finish( &ctx->md_ctx, K ) ) != 0 )
goto exit;
/* Step 2 or 5 */
if( ( ret = mbedtls_md_hmac_starts( &ctx->md_ctx, K, md_len ) ) != 0 )
goto exit;
if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
ctx->V, md_len ) ) != 0 )
goto exit;
if( ( ret = mbedtls_md_hmac_finish( &ctx->md_ctx, ctx->V ) ) != 0 )
goto exit;
}
exit:
mbedtls_platform_zeroize( K, sizeof( K ) );
return( ret );
}
#if !defined(MBEDTLS_DEPRECATED_REMOVED)
void mbedtls_hmac_drbg_update( mbedtls_hmac_drbg_context *ctx,
const unsigned char *additional,
size_t add_len )
{
(void) mbedtls_hmac_drbg_update_ret( ctx, additional, add_len );
}
#endif /* MBEDTLS_DEPRECATED_REMOVED */
/*
* Simplified HMAC_DRBG initialisation (for use with deterministic ECDSA)
*/
int mbedtls_hmac_drbg_seed_buf( mbedtls_hmac_drbg_context *ctx,
const mbedtls_md_info_t * md_info,
const unsigned char *data, size_t data_len )
{
int ret;
if( ( ret = mbedtls_md_setup( &ctx->md_ctx, md_info, 1 ) ) != 0 )
return( ret );
/*
* Set initial working state.
* Use the V memory location, which is currently all 0, to initialize the
* MD context with an all-zero key. Then set V to its initial value.
*/
if( ( ret = mbedtls_md_hmac_starts( &ctx->md_ctx, ctx->V,
mbedtls_md_get_size( md_info ) ) ) != 0 )
return( ret );
memset( ctx->V, 0x01, mbedtls_md_get_size( md_info ) );
if( ( ret = mbedtls_hmac_drbg_update_ret( ctx, data, data_len ) ) != 0 )
return( ret );
return( 0 );
}
/*
* Internal function used both for seeding and reseeding the DRBG.
* Comments starting with arabic numbers refer to section 10.1.2.4
* of SP800-90A, while roman numbers refer to section 9.2.
*/
static int hmac_drbg_reseed_core( mbedtls_hmac_drbg_context *ctx,
const unsigned char *additional, size_t len,
int use_nonce )
{
unsigned char seed[MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT];
size_t seedlen = 0;
int ret;
{
size_t total_entropy_len;
if( use_nonce == 0 )
total_entropy_len = ctx->entropy_len;
else
total_entropy_len = ctx->entropy_len * 3 / 2;
/* III. Check input length */
if( len > MBEDTLS_HMAC_DRBG_MAX_INPUT ||
total_entropy_len + len > MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT )
{
return( MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG );
}
}
memset( seed, 0, MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT );
/* IV. Gather entropy_len bytes of entropy for the seed */
if( ( ret = ctx->f_entropy( ctx->p_entropy,
seed, ctx->entropy_len ) ) != 0 )
{
return( MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
}
seedlen += ctx->entropy_len;
/* For initial seeding, allow adding of nonce generated
* from the entropy source. See Sect 8.6.7 in SP800-90A. */
if( use_nonce )
{
/* Note: We don't merge the two calls to f_entropy() in order
* to avoid requesting too much entropy from f_entropy()
* at once. Specifically, if the underlying digest is not
* SHA-1, 3 / 2 * entropy_len is at least 36 Bytes, which
* is larger than the maximum of 32 Bytes that our own
* entropy source implementation can emit in a single
* call in configurations disabling SHA-512. */
if( ( ret = ctx->f_entropy( ctx->p_entropy,
seed + seedlen,
ctx->entropy_len / 2 ) ) != 0 )
{
return( MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
}
seedlen += ctx->entropy_len / 2;
}
/* 1. Concatenate entropy and additional data if any */
if( additional != NULL && len != 0 )
{
memcpy( seed + seedlen, additional, len );
seedlen += len;
}
/* 2. Update state */
if( ( ret = mbedtls_hmac_drbg_update_ret( ctx, seed, seedlen ) ) != 0 )
goto exit;
/* 3. Reset reseed_counter */
ctx->reseed_counter = 1;
exit:
/* 4. Done */
mbedtls_platform_zeroize( seed, seedlen );
return( ret );
}
/*
* HMAC_DRBG reseeding: 10.1.2.4 + 9.2
*/
int mbedtls_hmac_drbg_reseed( mbedtls_hmac_drbg_context *ctx,
const unsigned char *additional, size_t len )
{
return( hmac_drbg_reseed_core( ctx, additional, len, 0 ) );
}
/*
* HMAC_DRBG initialisation (10.1.2.3 + 9.1)
*
* The nonce is not passed as a separate parameter but extracted
* from the entropy source as suggested in 8.6.7.
*/
int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
const mbedtls_md_info_t * md_info,
int (*f_entropy)(void *, unsigned char *, size_t),
void *p_entropy,
const unsigned char *custom,
size_t len )
{
int ret;
size_t md_size;
if( ( ret = mbedtls_md_setup( &ctx->md_ctx, md_info, 1 ) ) != 0 )
return( ret );
md_size = mbedtls_md_get_size( md_info );
/*
* Set initial working state.
* Use the V memory location, which is currently all 0, to initialize the
* MD context with an all-zero key. Then set V to its initial value.
*/
if( ( ret = mbedtls_md_hmac_starts( &ctx->md_ctx, ctx->V, md_size ) ) != 0 )
return( ret );
memset( ctx->V, 0x01, md_size );
ctx->f_entropy = f_entropy;
ctx->p_entropy = p_entropy;
ctx->reseed_interval = MBEDTLS_HMAC_DRBG_RESEED_INTERVAL;
/*
* 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.
*
* (This also matches the sizes used in the NIST test vectors.)
*/
ctx->entropy_len = md_size <= 20 ? 16 : /* 160-bits hash -> 128 bits */
md_size <= 28 ? 24 : /* 224-bits hash -> 192 bits */
32; /* better (256+) -> 256 bits */
if( ( ret = hmac_drbg_reseed_core( ctx, custom, len,
1 /* add nonce */ ) ) != 0 )
{
return( ret );
}
return( 0 );
}
/*
* Set prediction resistance
*/
void mbedtls_hmac_drbg_set_prediction_resistance( mbedtls_hmac_drbg_context *ctx,
int resistance )
{
ctx->prediction_resistance = resistance;
}
/*
* Set entropy length grabbed for reseeds
*/
void mbedtls_hmac_drbg_set_entropy_len( mbedtls_hmac_drbg_context *ctx, size_t len )
{
ctx->entropy_len = len;
}
/*
* Set reseed interval
*/
void mbedtls_hmac_drbg_set_reseed_interval( mbedtls_hmac_drbg_context *ctx, int interval )
{
ctx->reseed_interval = interval;
}
/*
* HMAC_DRBG random function with optional additional data:
* 10.1.2.5 (arabic) + 9.3 (Roman)
*/
int mbedtls_hmac_drbg_random_with_add( void *p_rng,
unsigned char *output, size_t out_len,
const unsigned char *additional, size_t add_len )
{
int ret;
mbedtls_hmac_drbg_context *ctx = (mbedtls_hmac_drbg_context *) p_rng;
size_t md_len = mbedtls_md_get_size( ctx->md_ctx.md_info );
size_t left = out_len;
unsigned char *out = output;
/* II. Check request length */
if( out_len > MBEDTLS_HMAC_DRBG_MAX_REQUEST )
return( MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG );
/* III. Check input length */
if( add_len > MBEDTLS_HMAC_DRBG_MAX_INPUT )
return( MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG );
/* 1. (aka VII and IX) Check reseed counter and PR */
if( ctx->f_entropy != NULL && /* For no-reseeding instances */
( ctx->prediction_resistance == MBEDTLS_HMAC_DRBG_PR_ON ||
ctx->reseed_counter > ctx->reseed_interval ) )
{
if( ( ret = mbedtls_hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
return( ret );
add_len = 0; /* VII.4 */
}
/* 2. Use additional data if any */
if( additional != NULL && add_len != 0 )
{
if( ( ret = mbedtls_hmac_drbg_update_ret( ctx,
additional, add_len ) ) != 0 )
goto exit;
}
/* 3, 4, 5. Generate bytes */
while( left != 0 )
{
size_t use_len = left > md_len ? md_len : left;
if( ( ret = mbedtls_md_hmac_reset( &ctx->md_ctx ) ) != 0 )
goto exit;
if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
ctx->V, md_len ) ) != 0 )
goto exit;
if( ( ret = mbedtls_md_hmac_finish( &ctx->md_ctx, ctx->V ) ) != 0 )
goto exit;
memcpy( out, ctx->V, use_len );
out += use_len;
left -= use_len;
}
/* 6. Update */
if( ( ret = mbedtls_hmac_drbg_update_ret( ctx,
additional, add_len ) ) != 0 )
goto exit;
/* 7. Update reseed counter */
ctx->reseed_counter++;
exit:
/* 8. Done */
return( ret );
}
/*
* HMAC_DRBG random function
*/
int mbedtls_hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len )
{
int ret;
mbedtls_hmac_drbg_context *ctx = (mbedtls_hmac_drbg_context *) p_rng;
#if defined(MBEDTLS_THREADING_C)
if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
return( ret );
#endif
ret = mbedtls_hmac_drbg_random_with_add( ctx, output, out_len, NULL, 0 );
#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
#endif
return( ret );
}
/*
* Free an HMAC_DRBG context
*/
void mbedtls_hmac_drbg_free( mbedtls_hmac_drbg_context *ctx )
{
if( ctx == NULL )
return;
#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_free( &ctx->mutex );
#endif
mbedtls_md_free( &ctx->md_ctx );
mbedtls_platform_zeroize( ctx, sizeof( mbedtls_hmac_drbg_context ) );
}
#if defined(MBEDTLS_FS_IO)
int mbedtls_hmac_drbg_write_seed_file( mbedtls_hmac_drbg_context *ctx, const char *path )
{
int ret;
FILE *f;
unsigned char buf[ MBEDTLS_HMAC_DRBG_MAX_INPUT ];
if( ( f = fopen( path, "wb" ) ) == NULL )
return( MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR );
if( ( ret = mbedtls_hmac_drbg_random( ctx, buf, sizeof( buf ) ) ) != 0 )
goto exit;
if( fwrite( buf, 1, sizeof( buf ), f ) != sizeof( buf ) )
{
ret = MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR;
goto exit;
}
ret = 0;
exit:
fclose( f );
mbedtls_platform_zeroize( buf, sizeof( buf ) );
return( ret );
}
int mbedtls_hmac_drbg_update_seed_file( mbedtls_hmac_drbg_context *ctx, const char *path )
{
int ret = 0;
FILE *f = NULL;
size_t n;
unsigned char buf[ MBEDTLS_HMAC_DRBG_MAX_INPUT ];
unsigned char c;
if( ( f = fopen( path, "rb" ) ) == NULL )
return( MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR );
n = fread( buf, 1, sizeof( buf ), f );
if( fread( &c, 1, 1, f ) != 0 )
{
ret = MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG;
goto exit;
}
if( n == 0 || ferror( f ) )
{
ret = MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR;
goto exit;
}
fclose( f );
f = NULL;
ret = mbedtls_hmac_drbg_update_ret( ctx, buf, n );
exit:
mbedtls_platform_zeroize( buf, sizeof( buf ) );
if( f != NULL )
fclose( f );
if( ret != 0 )
return( ret );
return( mbedtls_hmac_drbg_write_seed_file( ctx, path ) );
}
#endif /* MBEDTLS_FS_IO */
#if defined(MBEDTLS_SELF_TEST)
#if !defined(MBEDTLS_SHA1_C)
/* Dummy checkup routine */
int mbedtls_hmac_drbg_self_test( int verbose )
{
(void) verbose;
return( 0 );
}
#else
#define OUTPUT_LEN 80
/* From a NIST PR=true test vector */
static const unsigned char entropy_pr[] = {
0xa0, 0xc9, 0xab, 0x58, 0xf1, 0xe2, 0xe5, 0xa4, 0xde, 0x3e, 0xbd, 0x4f,
0xf7, 0x3e, 0x9c, 0x5b, 0x64, 0xef, 0xd8, 0xca, 0x02, 0x8c, 0xf8, 0x11,
0x48, 0xa5, 0x84, 0xfe, 0x69, 0xab, 0x5a, 0xee, 0x42, 0xaa, 0x4d, 0x42,
0x17, 0x60, 0x99, 0xd4, 0x5e, 0x13, 0x97, 0xdc, 0x40, 0x4d, 0x86, 0xa3,
0x7b, 0xf5, 0x59, 0x54, 0x75, 0x69, 0x51, 0xe4 };
static const unsigned char result_pr[OUTPUT_LEN] = {
0x9a, 0x00, 0xa2, 0xd0, 0x0e, 0xd5, 0x9b, 0xfe, 0x31, 0xec, 0xb1, 0x39,
0x9b, 0x60, 0x81, 0x48, 0xd1, 0x96, 0x9d, 0x25, 0x0d, 0x3c, 0x1e, 0x94,
0x10, 0x10, 0x98, 0x12, 0x93, 0x25, 0xca, 0xb8, 0xfc, 0xcc, 0x2d, 0x54,
0x73, 0x19, 0x70, 0xc0, 0x10, 0x7a, 0xa4, 0x89, 0x25, 0x19, 0x95, 0x5e,
0x4b, 0xc6, 0x00, 0x1d, 0x7f, 0x4e, 0x6a, 0x2b, 0xf8, 0xa3, 0x01, 0xab,
0x46, 0x05, 0x5c, 0x09, 0xa6, 0x71, 0x88, 0xf1, 0xa7, 0x40, 0xee, 0xf3,
0xe1, 0x5c, 0x02, 0x9b, 0x44, 0xaf, 0x03, 0x44 };
/* From a NIST PR=false test vector */
static const unsigned char entropy_nopr[] = {
0x79, 0x34, 0x9b, 0xbf, 0x7c, 0xdd, 0xa5, 0x79, 0x95, 0x57, 0x86, 0x66,
0x21, 0xc9, 0x13, 0x83, 0x11, 0x46, 0x73, 0x3a, 0xbf, 0x8c, 0x35, 0xc8,
0xc7, 0x21, 0x5b, 0x5b, 0x96, 0xc4, 0x8e, 0x9b, 0x33, 0x8c, 0x74, 0xe3,
0xe9, 0x9d, 0xfe, 0xdf };
static const unsigned char result_nopr[OUTPUT_LEN] = {
0xc6, 0xa1, 0x6a, 0xb8, 0xd4, 0x20, 0x70, 0x6f, 0x0f, 0x34, 0xab, 0x7f,
0xec, 0x5a, 0xdc, 0xa9, 0xd8, 0xca, 0x3a, 0x13, 0x3e, 0x15, 0x9c, 0xa6,
0xac, 0x43, 0xc6, 0xf8, 0xa2, 0xbe, 0x22, 0x83, 0x4a, 0x4c, 0x0a, 0x0a,
0xff, 0xb1, 0x0d, 0x71, 0x94, 0xf1, 0xc1, 0xa5, 0xcf, 0x73, 0x22, 0xec,
0x1a, 0xe0, 0x96, 0x4e, 0xd4, 0xbf, 0x12, 0x27, 0x46, 0xe0, 0x87, 0xfd,
0xb5, 0xb3, 0xe9, 0x1b, 0x34, 0x93, 0xd5, 0xbb, 0x98, 0xfa, 0xed, 0x49,
0xe8, 0x5f, 0x13, 0x0f, 0xc8, 0xa4, 0x59, 0xb7 };
/* "Entropy" from buffer */
static size_t test_offset;
static int hmac_drbg_self_test_entropy( void *data,
unsigned char *buf, size_t len )
{
const unsigned char *p = data;
memcpy( buf, p + test_offset, len );
test_offset += len;
return( 0 );
}
#define CHK( c ) if( (c) != 0 ) \
{ \
if( verbose != 0 ) \
mbedtls_printf( "failed\n" ); \
return( 1 ); \
}
/*
* Checkup routine for HMAC_DRBG with SHA-1
*/
int mbedtls_hmac_drbg_self_test( int verbose )
{
mbedtls_hmac_drbg_context ctx;
unsigned char buf[OUTPUT_LEN];
const mbedtls_md_info_t *md_info = mbedtls_md_info_from_type( MBEDTLS_MD_SHA1 );
mbedtls_hmac_drbg_init( &ctx );
/*
* PR = True
*/
if( verbose != 0 )
mbedtls_printf( " HMAC_DRBG (PR = True) : " );
test_offset = 0;
CHK( mbedtls_hmac_drbg_seed( &ctx, md_info,
hmac_drbg_self_test_entropy, (void *) entropy_pr,
NULL, 0 ) );
mbedtls_hmac_drbg_set_prediction_resistance( &ctx, MBEDTLS_HMAC_DRBG_PR_ON );
CHK( mbedtls_hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
CHK( mbedtls_hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
CHK( memcmp( buf, result_pr, OUTPUT_LEN ) );
mbedtls_hmac_drbg_free( &ctx );
mbedtls_hmac_drbg_free( &ctx );
if( verbose != 0 )
mbedtls_printf( "passed\n" );
/*
* PR = False
*/
if( verbose != 0 )
mbedtls_printf( " HMAC_DRBG (PR = False) : " );
mbedtls_hmac_drbg_init( &ctx );
test_offset = 0;
CHK( mbedtls_hmac_drbg_seed( &ctx, md_info,
hmac_drbg_self_test_entropy, (void *) entropy_nopr,
NULL, 0 ) );
CHK( mbedtls_hmac_drbg_reseed( &ctx, NULL, 0 ) );
CHK( mbedtls_hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
CHK( mbedtls_hmac_drbg_random( &ctx, buf, OUTPUT_LEN ) );
CHK( memcmp( buf, result_nopr, OUTPUT_LEN ) );
mbedtls_hmac_drbg_free( &ctx );
mbedtls_hmac_drbg_free( &ctx );
if( verbose != 0 )
mbedtls_printf( "passed\n" );
if( verbose != 0 )
mbedtls_printf( "\n" );
return( 0 );
}
#endif /* MBEDTLS_SHA1_C */
#endif /* MBEDTLS_SELF_TEST */
#endif /* MBEDTLS_HMAC_DRBG_C */