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hmac_drbg: make no reseeding behaviour explicit

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Add a flag to the hmac_drbg context that will signal that reseeding is not required.
Change tests and one ecdsa call to not use reseeding, as was the previous case.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
This commit is contained in:
Andrzej Kurek 2020-07-19 04:58:58 -04:00
parent f6265441b0
commit 4353b698ed
No known key found for this signature in database
GPG Key ID: 89A90840DC388527
4 changed files with 46 additions and 9 deletions
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19
include/mbedtls/hmac_drbg.h
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@ -77,6 +77,9 @@
#define MBEDTLS_HMAC_DRBG_PR_OFF 0x55555555 /**< No prediction resistance */
#define MBEDTLS_HMAC_DRBG_PR_ON 0x2AAAAAAA /**< Prediction resistance enabled */
#define MBEDTLS_HMAC_DRBG_RESEED 0x78547854 /**< Default environment, reseeding enabled */
#define MBEDTLS_HMAC_DRBG_NO_RESEED 0x07AB87F0 /**< Reseeding disabled, no f_entropy required */
#ifdef __cplusplus
extern "C" {
#endif
@ -91,7 +94,7 @@ typedef struct mbedtls_hmac_drbg_context
mbedtls_md_context_t md_ctx; /*!< HMAC context (inc. K) */
unsigned char V[MBEDTLS_MD_MAX_SIZE]; /*!< V in the spec */
int reseed_counter; /*!< reseed counter */
int reseed_flag; /*!< disables reseeding if set to MBEDTLS_HMAC_DRBG_NO_RESEED */
/* Administrative state */
size_t entropy_len; /*!< entropy bytes grabbed on each (re)seed */
int prediction_resistance; /*!< enable prediction resistance (Automatic
@ -220,6 +223,20 @@ int mbedtls_hmac_drbg_seed_buf( mbedtls_hmac_drbg_context *ctx,
void mbedtls_hmac_drbg_set_prediction_resistance( mbedtls_hmac_drbg_context *ctx,
int resistance );
/**
* \brief This function turns reseeding on or off.
* Default value is on.
*
* \note If set to MBEDTLS_HMAC_DRBG_NO_RESEED, this function
* disables reseeding, providing a no_reseed environment.
* f_entropy can then be null.
*
* \param ctx The HMAC_DRBG context.
* \param reseed_flag #MBEDTLS_HMAC_DRBG_NO_RESEED or #MBEDTLS_HMAC_DRBG_RESEED
*/
void mbedtls_hmac_drbg_set_reseeding( mbedtls_hmac_drbg_context *ctx,
int reseed_flag );
/**
* \brief This function sets the amount of entropy grabbed on each
* seed or reseed.

2
library/ecdsa.c
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@ -482,6 +482,7 @@ sign:
mbedtls_hmac_drbg_context rng_ctx_blind;
mbedtls_hmac_drbg_init( &rng_ctx_blind );
mbedtls_hmac_drbg_set_reseeding( &rng_ctx_blind, MBEDTLS_HMAC_DRBG_NO_RESEED );
p_rng_blind_det = &rng_ctx_blind;
mbedtls_hmac_drbg_seed_buf( p_rng_blind_det, md_info,
@ -509,6 +510,7 @@ sign:
* a valid ECDSA signature.
*/
p_rng_blind_det = p_rng;
mbedtls_hmac_drbg_set_reseeding( p_rng_blind_det, MBEDTLS_HMAC_DRBG_NO_RESEED );
#endif /* MBEDTLS_ECP_RESTARTABLE */
/*

30
library/hmac_drbg.c
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@ -63,6 +63,7 @@ void mbedtls_hmac_drbg_init( mbedtls_hmac_drbg_context *ctx )
memset( ctx, 0, sizeof( mbedtls_hmac_drbg_context ) );
ctx->prediction_resistance = MBEDTLS_HMAC_DRBG_PR_OFF;
ctx->reseed_flag = MBEDTLS_HMAC_DRBG_RESEED;
#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_init( &ctx->mutex );
#endif
@ -388,6 +389,15 @@ void mbedtls_hmac_drbg_set_prediction_resistance( mbedtls_hmac_drbg_context *ctx
ctx->prediction_resistance = resistance;
}
/*
* Set the reseeding flag
*/
void mbedtls_hmac_drbg_set_reseeding( mbedtls_hmac_drbg_context *ctx,
int reseed_flag )
{
ctx->reseed_flag = reseed_flag;
}
/*
* Set entropy length grabbed for seeding
*/
@ -434,14 +444,20 @@ int mbedtls_hmac_drbg_random_with_add( void *p_rng,
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( ctx->reseed_flag != MBEDTLS_HMAC_DRBG_NO_RESEED &&
( 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 */
if( ctx->f_entropy == NULL )
{
return( MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
}
else
{
if( ( ret = mbedtls_hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
return( ret );
add_len = 0; /* VII.4 */
}
}
/* 2. Use additional data if any */

4
tests/suites/test_suite_hmac_drbg.function
View File

@ -149,6 +149,7 @@ void hmac_drbg_buf( int md_alg )
TEST_ASSERT( mbedtls_hmac_drbg_seed_buf( &ctx, md_info, buf, sizeof( buf ) ) == 0 );
/* Make sure it never tries to reseed (would segfault otherwise) */
mbedtls_hmac_drbg_set_reseeding( &ctx, MBEDTLS_HMAC_DRBG_NO_RESEED );
mbedtls_hmac_drbg_set_reseed_interval( &ctx, 3 );
mbedtls_hmac_drbg_set_prediction_resistance( &ctx, MBEDTLS_HMAC_DRBG_PR_ON );
@ -172,7 +173,7 @@ void hmac_drbg_no_reseed( int md_alg, data_t * entropy,
mbedtls_hmac_drbg_context ctx;
mbedtls_hmac_drbg_init( &ctx );
mbedtls_hmac_drbg_set_reseeding( &ctx, MBEDTLS_HMAC_DRBG_NO_RESEED );
p_entropy.p = entropy->x;
p_entropy.len = entropy->len;
@ -219,6 +220,7 @@ void hmac_drbg_nopr( int md_alg, data_t * entropy, data_t * custom,
mbedtls_hmac_drbg_context ctx;
mbedtls_hmac_drbg_init( &ctx );
mbedtls_hmac_drbg_set_reseeding( &ctx, MBEDTLS_HMAC_DRBG_NO_RESEED );
p_entropy.p = entropy->x;
p_entropy.len = entropy->len;