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Reduce HMAC buffer usage in PSA version of mbedtls_ct_hmac()

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Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
This commit is contained in:
Neil Armstrong 2022-03-17 17:04:37 +01:00
parent 72c2f76c43
commit 9ebb9ff60c
1 changed files with 15 additions and 19 deletions
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34
library/constant_time.c
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@ -474,8 +474,7 @@ int mbedtls_ct_hmac( mbedtls_svc_key_id_t key,
*/ */
psa_algorithm_t hash_alg = PSA_ALG_HMAC_GET_HASH( mac_alg ); psa_algorithm_t hash_alg = PSA_ALG_HMAC_GET_HASH( mac_alg );
const size_t block_size = PSA_HASH_BLOCK_LENGTH( hash_alg ); const size_t block_size = PSA_HASH_BLOCK_LENGTH( hash_alg );
unsigned char ikey[MAX_HASH_BLOCK_LENGTH]; unsigned char key_buf[MAX_HASH_BLOCK_LENGTH];
unsigned char okey[MAX_HASH_BLOCK_LENGTH];
const size_t hash_size = PSA_HASH_LENGTH( hash_alg ); const size_t hash_size = PSA_HASH_LENGTH( hash_alg );
psa_hash_operation_t operation = PSA_HASH_OPERATION_INIT; psa_hash_operation_t operation = PSA_HASH_OPERATION_INIT;
size_t hash_length; size_t hash_length;
@ -485,7 +484,6 @@ int mbedtls_ct_hmac( mbedtls_svc_key_id_t key,
size_t offset; size_t offset;
psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED; psa_status_t status = PSA_ERROR_CORRUPTION_DETECTED;
unsigned char mac_key[MAX_HASH_BLOCK_LENGTH];
size_t mac_key_length; size_t mac_key_length;
size_t i; size_t i;
@ -501,24 +499,18 @@ int mbedtls_ct_hmac( mbedtls_svc_key_id_t key,
* which is never more than the block size, thus we use block_size * which is never more than the block size, thus we use block_size
* as the key buffer size. * as the key buffer size.
*/ */
PSA_CHK( psa_export_key( key, mac_key, block_size, &mac_key_length ) ); PSA_CHK( psa_export_key( key, key_buf, block_size, &mac_key_length ) );
/* Calculate ikey/okey */
memset( ikey, 0x36, block_size );
memset( okey, 0x5C, block_size );
/* Calculate ikey */
for( i = 0; i < mac_key_length; i++ ) for( i = 0; i < mac_key_length; i++ )
{ key_buf[i] = (unsigned char)( key_buf[i] ^ 0x36 );
ikey[i] = (unsigned char)( ikey[i] ^ mac_key[i] ); for(; i < block_size; ++i )
okey[i] = (unsigned char)( okey[i] ^ mac_key[i] ); key_buf[i] = 0x36;
}
mbedtls_platform_zeroize( mac_key, MAX_HASH_BLOCK_LENGTH );
PSA_CHK( psa_hash_setup( &operation, hash_alg ) ); PSA_CHK( psa_hash_setup( &operation, hash_alg ) );
/* Now compute inner_hash = HASH(ikey + msg) */ /* Now compute inner_hash = HASH(ikey + msg) */
PSA_CHK( psa_hash_update( &operation, ikey, block_size ) ); PSA_CHK( psa_hash_update( &operation, key_buf, block_size ) );
PSA_CHK( psa_hash_update( &operation, add_data, add_data_len ) ); PSA_CHK( psa_hash_update( &operation, add_data, add_data_len ) );
PSA_CHK( psa_hash_update( &operation, data, min_data_len ) ); PSA_CHK( psa_hash_update( &operation, data, min_data_len ) );
@ -539,18 +531,22 @@ int mbedtls_ct_hmac( mbedtls_svc_key_id_t key,
/* Abort current operation to prepare for final operation */ /* Abort current operation to prepare for final operation */
PSA_CHK( psa_hash_abort( &operation ) ); PSA_CHK( psa_hash_abort( &operation ) );
/* Calculate okey */
for( i = 0; i < mac_key_length; i++ )
key_buf[i] = (unsigned char)( ( key_buf[i] ^ 0x36 ) ^ 0x5C );
for(; i < block_size; ++i )
key_buf[i] = 0x5C;
/* Now compute HASH(okey + inner_hash) */ /* Now compute HASH(okey + inner_hash) */
PSA_CHK( psa_hash_setup( &operation, hash_alg ) ); PSA_CHK( psa_hash_setup( &operation, hash_alg ) );
PSA_CHK( psa_hash_update( &operation, okey, block_size ) ); PSA_CHK( psa_hash_update( &operation, key_buf, block_size ) );
PSA_CHK( psa_hash_update( &operation, output, hash_size ) ); PSA_CHK( psa_hash_update( &operation, output, hash_size ) );
PSA_CHK( psa_hash_finish( &operation, output, hash_size, &hash_length ) ); PSA_CHK( psa_hash_finish( &operation, output, hash_size, &hash_length ) );
#undef PSA_CHK #undef PSA_CHK
cleanup: cleanup:
mbedtls_platform_zeroize( mac_key, MAX_HASH_BLOCK_LENGTH ); mbedtls_platform_zeroize( key_buf, MAX_HASH_BLOCK_LENGTH );
mbedtls_platform_zeroize( ikey, MAX_HASH_BLOCK_LENGTH );
mbedtls_platform_zeroize( okey, MAX_HASH_BLOCK_LENGTH );
mbedtls_platform_zeroize( aux_out, PSA_HASH_MAX_SIZE ); mbedtls_platform_zeroize( aux_out, PSA_HASH_MAX_SIZE );
psa_hash_abort( &operation ); psa_hash_abort( &operation );