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Harden hmac_drbg and md against fault injection

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-Add flow monitor, loop integrity check and variable doubling to
 harden mbedtls_hmac_drbg_update_ret.

-Use longer hamming distance for nonce usage in hmac_drbg_reseed_core

-Return actual value instead of success in mbedtls_hmac_drbg_seed and
 mbedtls_hmac_drbg_seed_buf

-Check illegal condition in hmac_drbg_reseed_core.

-Double buf/buf_len variables in mbedtls_hmac_drbg_random_with_add

-Add more hamming distance to MBEDTLS_HMAC_DRBG_PR_ON/OFF
This commit is contained in:
Arto Kinnunen 2019-11-20 16:13:13 +02:00
parent 72a8c9e7dc
commit 5b36693774
3 changed files with 101 additions and 30 deletions
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14
include/mbedtls/hmac_drbg.h
View file

@ -70,8 +70,8 @@
/* \} name SECTION: Module settings */
#define MBEDTLS_HMAC_DRBG_PR_OFF 0 /**< No prediction resistance */
#define MBEDTLS_HMAC_DRBG_PR_ON 1 /**< Prediction resistance enabled */
#define MBEDTLS_HMAC_DRBG_PR_OFF 0x55555555 /**< No prediction resistance */
#define MBEDTLS_HMAC_DRBG_PR_ON 0x2AAAAAAA /**< Prediction resistance enabled */
#ifdef __cplusplus
extern "C" {
@ -202,7 +202,8 @@ void mbedtls_hmac_drbg_set_reseed_interval( mbedtls_hmac_drbg_context *ctx,
* \param add_len Length of additional data, or 0
*
* \return \c 0 on success, or an error from the underlying
* hash calculation.
* hash calculation or
* MBEDTLS_ERR_PLATFORM_FAULT_DETECTED.
*
* \note Additional data is optional, pass NULL and 0 as second
* third argument if no additional data is being used.
@ -237,7 +238,8 @@ int mbedtls_hmac_drbg_reseed( mbedtls_hmac_drbg_context *ctx,
* \return 0 if successful, or
* MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or
* MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG, or
* MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG.
* MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG, or
* MBEDTLS_ERR_PLATFORM_FAULT_DETECTED.
*/
int mbedtls_hmac_drbg_random_with_add( void *p_rng,
unsigned char *output, size_t output_len,
@ -255,7 +257,9 @@ int mbedtls_hmac_drbg_random_with_add( void *p_rng,
*
* \return 0 if successful, or
* MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or
* MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG
* MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG,
* MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG, or
* MBEDTLS_ERR_PLATFORM_FAULT_DETECTED.
*/
int mbedtls_hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len );

102
library/hmac_drbg.c
View file

@ -51,6 +51,9 @@
#endif /* MBEDTLS_SELF_TEST */
#endif /* MBEDTLS_PLATFORM_C */
#define HMAC_NONCE_YES 0x4AAAAAAA
#define HMAC_NONCE_NO 0x75555555
/*
* HMAC_DRBG context initialization
*/
@ -74,40 +77,74 @@ int mbedtls_hmac_drbg_update_ret( mbedtls_hmac_drbg_context *ctx,
mbedtls_md_get_handle( &ctx->md_ctx ) );
unsigned char rounds = ( additional != NULL && add_len != 0 ) ? 2 : 1;
unsigned char sep[1];
volatile unsigned char flow_counter = 0;
unsigned char K[MBEDTLS_MD_MAX_SIZE];
int ret;
int ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
for( sep[0] = 0; sep[0] < rounds; sep[0]++ )
{
/* Step 1 or 4 */
flow_counter++;
if( ( ret = mbedtls_md_hmac_reset( &ctx->md_ctx ) ) != 0 )
goto exit;
flow_counter++;
if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
ctx->V, md_len ) ) != 0 )
goto exit;
flow_counter++;
if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
sep, 1 ) ) != 0 )
goto exit;
if( rounds == 2 )
{
flow_counter++;
if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
additional, add_len ) ) != 0 )
goto exit;
}
flow_counter++;
if( ( ret = mbedtls_md_hmac_finish( &ctx->md_ctx, K ) ) != 0 )
goto exit;
/* Step 2 or 5 */
flow_counter++;
if( ( ret = mbedtls_md_hmac_starts( &ctx->md_ctx, K, md_len ) ) != 0 )
goto exit;
flow_counter++;
if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
ctx->V, md_len ) ) != 0 )
goto exit;
flow_counter++;
if( ( ret = mbedtls_md_hmac_finish( &ctx->md_ctx, ctx->V ) ) != 0 )
goto exit;
}
exit:
if( ret == 0 )
{
ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
/* Check for possible attack.
* Counters needs to have correct values when returning success
*/
if ( ( ( flow_counter == 7 ) && ( sep[0] == 1 ) ) ||
( ( flow_counter == 16 ) && ( sep[0] == 2 ) ) )
{
flow_counter = flow_counter - sep[0];
// Double check flow_counter
if ( ( flow_counter == 6 ) || ( flow_counter == 14 ) )
{
ret = 0;
}
}
}
mbedtls_platform_zeroize( K, sizeof( K ) );
return( ret );
}
@ -125,10 +162,10 @@ void mbedtls_hmac_drbg_update( mbedtls_hmac_drbg_context *ctx,
* Simplified HMAC_DRBG initialisation (for use with deterministic ECDSA)
*/
int mbedtls_hmac_drbg_seed_buf( mbedtls_hmac_drbg_context *ctx,
mbedtls_md_handle_t md_info,
const unsigned char *data, size_t data_len )
mbedtls_md_handle_t md_info,
const unsigned char *data, size_t data_len )
{
int ret;
int ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
if( ( ret = mbedtls_md_setup( &ctx->md_ctx, md_info, 1 ) ) != 0 )
return( ret );
@ -146,7 +183,7 @@ int mbedtls_hmac_drbg_seed_buf( mbedtls_hmac_drbg_context *ctx,
if( ( ret = mbedtls_hmac_drbg_update_ret( ctx, data, data_len ) ) != 0 )
return( ret );
return( 0 );
return( ret );
}
/*
@ -160,22 +197,19 @@ static int hmac_drbg_reseed_core( mbedtls_hmac_drbg_context *ctx,
{
unsigned char seed[MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT];
size_t seedlen = 0;
size_t total_entropy_len;
int ret;
if( use_nonce == HMAC_NONCE_NO )
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 )
{
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 );
}
return( MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG );
}
memset( seed, 0, MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT );
@ -190,7 +224,7 @@ static int hmac_drbg_reseed_core( mbedtls_hmac_drbg_context *ctx,
/* For initial seeding, allow adding of nonce generated
* from the entropy source. See Sect 8.6.7 in SP800-90A. */
if( use_nonce )
if( use_nonce == HMAC_NONCE_YES )
{
/* Note: We don't merge the two calls to f_entropy() in order
* to avoid requesting too much entropy from f_entropy()
@ -225,6 +259,11 @@ static int hmac_drbg_reseed_core( mbedtls_hmac_drbg_context *ctx,
ctx->reseed_counter = 1;
exit:
if (ret == 0 && ctx->reseed_counter != 1)
{
/* Illegal condition, possible attack detected */
ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
}
/* 4. Done */
mbedtls_platform_zeroize( seed, seedlen );
return( ret );
@ -236,8 +275,7 @@ exit:
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 /* no nonce */ ) );
return( hmac_drbg_reseed_core( ctx, additional, len, HMAC_NONCE_NO ) );
}
/*
@ -286,13 +324,12 @@ int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
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 )
if( ( ret = hmac_drbg_reseed_core( ctx, custom, len, HMAC_NONCE_YES ) ) != 0 )
{
return( ret );
}
return( 0 );
return( ret );
}
/*
@ -329,6 +366,8 @@ int mbedtls_hmac_drbg_random_with_add( void *p_rng,
const unsigned char *additional, size_t add_len )
{
int ret;
volatile unsigned char *output_fi = output;
volatile size_t out_len_fi = out_len;
mbedtls_hmac_drbg_context *ctx = (mbedtls_hmac_drbg_context *) p_rng;
size_t md_len = mbedtls_md_get_size(
mbedtls_md_get_handle( &ctx->md_ctx ) );
@ -390,6 +429,21 @@ int mbedtls_hmac_drbg_random_with_add( void *p_rng,
exit:
/* 8. Done */
if (ret == 0)
{
/*
* Check doubled variables and illegal conditions in case of possible
* attack.
*/
ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
if ( ( out_len_fi == out_len ) && ( output_fi == output) &&
( left == 0 ) )
{
ret = 0;
}
}
return( ret );
}

15
library/md.c
View file

@ -575,15 +575,28 @@ int mbedtls_md_hmac_starts( mbedtls_md_context_t *ctx, const unsigned char *key,
if( ( ret = mbedtls_md_info_starts( md_info, ctx->md_ctx ) ) != 0 )
goto cleanup;
i++; // Use i as flow control
if( ( ret = mbedtls_md_info_update( md_info, ctx->md_ctx, ipad,
mbedtls_md_info_block_size( md_info ) ) ) != 0 )
{
goto cleanup;
}
i++; // Use i as flow control now
cleanup:
mbedtls_platform_zeroize( sum, sizeof( sum ) );
if ( ret == 0 )
{
ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
/* Check possible fault injection */
if ( ( i - 2 ) == keylen ) {
ret = 0;
}
}
return( ret );
}
@ -653,7 +666,7 @@ int mbedtls_md_hmac_finish( mbedtls_md_context_t *ctx, unsigned char *output )
if( ( ret = mbedtls_md_info_finish( md_info, ctx->md_ctx, output ) ) != 0 )
return( ret );
return( 0 );
return( ret );
}
int mbedtls_md_hmac_reset( mbedtls_md_context_t *ctx )