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AES review corrections

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-Do not reuse any part of randomized number, use separate byte for
 each purpose.
-Combine some separate loops together to get rid of gap between them
-Extend usage of flow_control
This commit is contained in:
Arto Kinnunen 2020-01-16 15:04:11 +02:00
parent 98c93af1ef
commit 2b24f4280f
1 changed files with 33 additions and 46 deletions
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79
library/aes.c
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@ -545,18 +545,17 @@ static void aes_gen_tables( void )
*/
static int aes_sca_cm_data_randomize( uint8_t *tbl, uint8_t tbl_len )
{
int i = 0, j = 0, is_even_pos, dummy_rounds;
int i = 0, j, is_even_pos, dummy_rounds;
#if AES_SCA_CM_ROUNDS != 0
int num;
#endif
mbedtls_platform_memset( tbl, 0, tbl_len );
#if AES_SCA_CM_ROUNDS != 0
num = mbedtls_platform_random_in_range( 0x1f );
// get random from 0xfff (each byte will be used separately)
num = mbedtls_platform_random_in_range( 0x1000 );
// Randomize execution order of initial round key addition
if ( ( num & 0x10 ) == 0 )
if ( ( num & 0x0100 ) == 0 )
{
tbl[i++] = 0x10; // dummy data
tbl[i++] = 0x00 | 0x03; // real data + stop marker
@ -565,24 +564,28 @@ static int aes_sca_cm_data_randomize( uint8_t *tbl, uint8_t tbl_len )
tbl[i++] = 0x10 | 0x03; // dummy data + stop marker
}
// Randomize AES rounds
dummy_rounds = AES_SCA_CM_ROUNDS - ( num & 0x01 );
// Randomize number of dummy AES rounds
dummy_rounds = AES_SCA_CM_ROUNDS - ( ( num >> 8 ) & 0x01 );
tbl_len = tbl_len - (AES_SCA_CM_ROUNDS - dummy_rounds);
num = num % ( dummy_rounds + 1 );
// add dummy rounds to the start (if needed)
// randomize positions for the dummy rounds
num = ( num & 0x00f ) % ( dummy_rounds + 1 );
// add dummy rounds after initial round key addition (if needed)
for ( ; i < num + 2; i++ )
{
tbl[i] = 0x10; // dummy data
}
// add dummy rounds to the last, (AES_SCA_CM_ROUNDS - num) rounds if needed
// add dummy rounds to the end, (AES_SCA_CM_ROUNDS - num) rounds if needed
for ( j = tbl_len - dummy_rounds + num; j < tbl_len; j++ )
{
tbl[j] = 0x10; // dummy data
}
#else /* AES_SCA_CM_ROUNDS != 0 */
mbedtls_platform_memset( tbl, 0, tbl_len );
dummy_rounds = 0;
j = 0;
tbl[i++] = 0x03; // real data + stop marker for the round key addition
#endif /* AES_SCA_CM_ROUNDS != 0 */
@ -1081,21 +1084,19 @@ int mbedtls_internal_aes_encrypt( mbedtls_aes_context *ctx,
#endif
// Get AES calculation control bytes
dummy_rounds = aes_sca_cm_data_randomize( round_ctrl_table, round_ctrl_table_len );
dummy_rounds = aes_sca_cm_data_randomize( round_ctrl_table,
round_ctrl_table_len );
flow_control = dummy_rounds;
mbedtls_platform_memset( aes_data_real.xy_values, 0, 16 );
offset = mbedtls_platform_random_in_range( 4 );
for( i = offset; i < 4; i++ )
i = offset;
do
{
GET_UINT32_LE( aes_data_real.xy_values[i], input, ( i * 4 ) );
}
for( i = 0; i < offset; i++ )
{
GET_UINT32_LE( aes_data_real.xy_values[i], input, ( i * 4 ) );
}
flow_control++;
} while( ( i = ( i + 1 ) % 4 ) != offset );
tindex = 0;
do
@ -1155,19 +1156,14 @@ int mbedtls_internal_aes_encrypt( mbedtls_aes_context *ctx,
mbedtls_platform_memset( output, 0, 16 );
offset = mbedtls_platform_random_in_range( 4 );
for( i = offset; i < 4; i++ )
i = offset;
do
{
PUT_UINT32_LE( aes_data_real.xy_values[i], output, ( i * 4 ) );
flow_control++;
}
} while( ( i = ( i + 1 ) % 4 ) != offset );
for( i = 0; i < offset; i++ )
{
PUT_UINT32_LE( aes_data_real.xy_values[i], output, ( i * 4 ) );
flow_control++;
}
if( flow_control == tindex + dummy_rounds + 4 )
if( flow_control == tindex + dummy_rounds + 8 )
{
/* Validate control path due possible fault injection */
return 0;
@ -1274,22 +1270,18 @@ int mbedtls_internal_aes_decrypt( mbedtls_aes_context *ctx,
// Get AES calculation control bytes
dummy_rounds = aes_sca_cm_data_randomize( round_ctrl_table,
round_ctrl_table_len );
round_ctrl_table_len );
flow_control = dummy_rounds;
mbedtls_platform_memset( aes_data_real.xy_values, 0, 16 );
offset = mbedtls_platform_random_in_range( 4 );
for( i = offset; i < 4; i++ )
i = offset;
do
{
GET_UINT32_LE( aes_data_real.xy_values[i], input, ( i * 4 ) );
}
for( i = 0; i < offset; i++ )
{
GET_UINT32_LE( aes_data_real.xy_values[i], input, ( i * 4 ) );
}
flow_control++;
} while( ( i = ( i + 1 ) % 4 ) != offset );
tindex = 0;
do
@ -1349,19 +1341,14 @@ int mbedtls_internal_aes_decrypt( mbedtls_aes_context *ctx,
mbedtls_platform_memset( output, 0, 16 );
offset = mbedtls_platform_random_in_range( 4 );
for( i = offset; i < 4; i++ )
i = offset;
do
{
PUT_UINT32_LE( aes_data_real.xy_values[i], output, ( i * 4 ) );
flow_control++;
}
} while( ( i = ( i + 1 ) % 4 ) != offset );
for( i = 0; i < offset; i++ )
{
PUT_UINT32_LE( aes_data_real.xy_values[i], output, ( i * 4 ) );
flow_control++;
}
if( flow_control == tindex + dummy_rounds + 4 )
if( flow_control == tindex + dummy_rounds + 8 )
{
/* Validate control path due possible fault injection */
return 0;