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Update AES SCA random number function

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-Replace usage of rand() with mbedtls_platform_random_in_range()
-Prevent for-ever loop by hardcoding SCA countermeasure position in
 case of used random function is always returning constant number.
This commit is contained in:
Arto Kinnunen 2019-12-05 10:10:31 +02:00
parent f44f7d465a
commit 76deef9fca
1 changed files with 13 additions and 6 deletions
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19
library/aes.c
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@ -544,24 +544,31 @@ static void aes_sca_cm_data_randomize( uint8_t *tbl, uint8_t tbl_len )
// Randomize SCA CM positions to tbl // Randomize SCA CM positions to tbl
for( i = 0; i < AES_SCA_CM_ROUNDS; i++ ) for( i = 0; i < AES_SCA_CM_ROUNDS; i++ )
{ {
is_unique_number = 0;
do do
{ {
is_unique_number = 1; is_unique_number++;
/* TODO - Use proper random. This is now ONLY FOR TESTING as mbedtls_platform_random_in_range is alwyays returning 0 */ num = mbedtls_platform_random_in_range( tbl_len - 4 );
num = /* mbedtls_platform_random_in_range( tbl_len - 4 ) */rand() % (tbl_len - 4);
if( is_unique_number > 10 )
{
// prevent forever loop if random returns constant
is_unique_number = 0;
tbl[i] = 0x10; // fake data
}
if( tbl[num] == 0 ) if( tbl[num] == 0 )
{ {
is_unique_number = 0; is_unique_number = 0;
tbl[num] = 0x10; tbl[num] = 0x10; // fake data
} }
} while( is_unique_number == 1 ); } while( is_unique_number != 0 );
} }
// randomize control data for start and final round // randomize control data for start and final round
for( i = 1; i <= 2; i++ ) for( i = 1; i <= 2; i++ )
{ {
num = /* mbedtls_platform_random_in_range( 0xff ) */rand() % 0xff; num = mbedtls_platform_random_in_range( 0xff );
if( ( num % 2 ) == 0 ) if( ( num % 2 ) == 0 )
{ {
tbl[tbl_len - ( i * 2 - 0 )] = 0x10; // fake data tbl[tbl_len - ( i * 2 - 0 )] = 0x10; // fake data