Update AES SCA countermeasures
-Add dummy rounds to the start and/or end of the AES calculation
rounds.
diff --git a/library/aes.c b/library/aes.c
index c96f29e..ece7a82 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -95,7 +95,7 @@
#if defined(MBEDTLS_AES_SCA_COUNTERMEASURES)
/* Number of additional AES calculation rounds added for SCA CM */
-#define AES_SCA_CM_ROUNDS 3
+#define AES_SCA_CM_ROUNDS 4
#else /* MBEDTLS_AES_SCA_COUNTERMEASURES */
#define AES_SCA_CM_ROUNDS 0
#endif /* MBEDTLS_AES_SCA_COUNTERMEASURES */
@@ -513,97 +513,99 @@
#endif /* MBEDTLS_AES_ROM_TABLES */
/**
- * Randomize positions when to use AES SCA countermeasures.
- * Each byte indicates one AES round as follows:
- * first ( tbl_len - 4 ) bytes are reserved for middle AES rounds:
- * -4 high bit = table to use 0x10 for SCA CM data, 0 otherwise
- * -4 low bits = offset based on order, 4 for even position, 0 otherwise
- * Last 4 bytes for first(2) and final(2) round calculation
- * -4 high bit = table to use, 0x10 for SCA CM data, otherwise real data
- * -4 low bits = not used
+ * Randomize positions for AES SCA countermeasures if AES countermeasures are
+ * enabled. If countermeasures are not enabled then fill given table with real
+ * data values.
+ *
+ * Dummy rounds are added as follows:
+ * 1. One dummy round added to the initial round key addition (executed in
+ * random order).
+ * 2. Random number of dummy rounds added as first and/or last AES calculation
+ * round. Total number of dummy rounds is AES_SCA_CM_ROUNDS.
+ *
+ * Description of the bytes in the table are as follows:
+ * - 2 bytes for initial round key addition
+ * - remaining bytes for AES calculation with real or dummy data
+ *
+ * Each byte indicates one AES calculation round:
+ * -4 high bit = table to use 0x10 for dummy data, 0x00 real data
+ * -bit 2 = offset for even/odd rounds
+ * -bit 0-1: stop mark (0x03) to indicate calculation end
*
* Return Number of additional AES rounds
*
* Example of the control bytes:
- * Control data when only real data (R) is used:
- * | R | R | R | R | R | R | R | R | Start | Final |
- * |0x04|0x00|0x00|0x04|0x00|0x04|0x00|0x04|0x00|0x00|0x00|0x00|
+ * 1. No countermeasures enabled and AES-128, only real data (R) used:
+ * | Ri | R | R | R | R | R | R | R | R | R | R |
+ * |0x03|0x04|0x00|0x04|0x00|0x04|0x00|0x04|0x00|0x07|0x03|
*
- * Control data with 5 (F) dummy rounds and randomized start and final round:
- * | R | F | R | F | F | R | R | R | R | R | R | START RF| FINAL FR|
- * |0x04|0x10|0x04|0x10|0x10|0x00|0x04|0x00|0x04|0x00|0x04|0x00|0x10|0x10|0x00|
+ * 2. Countermeasures enabled, 3 (F) dummy rounds in start and 1 at end:
+ * | Fi | Ri | F | F | F | R | R | ... | R | R | R | R | F |
+ * |0x10|0x03 |0x10|0x10|0x10|0x04|0x00| ... |0x04|0x00|0x04|0x03|0x07|
*/
static int aes_sca_cm_data_randomize( uint8_t *tbl, uint8_t tbl_len )
{
- int i, is_even_pos;
+ int i = 0, j = 0, is_even_pos;
#if AES_SCA_CM_ROUNDS != 0
- int is_unique_number;
int num;
#endif
mbedtls_platform_memset( tbl, 0, tbl_len );
#if AES_SCA_CM_ROUNDS != 0
- // Randomize SCA CM positions to tbl
- for( i = 0; i < AES_SCA_CM_ROUNDS; i++ )
+ num = mbedtls_platform_random_in_range( 0x1f );
+
+ // Randomize execution order of initial round key addition
+ if ( ( num & 0x10 ) == 0 )
{
- is_unique_number = 0;
- do
- {
- is_unique_number++;
- num = mbedtls_platform_random_in_range( 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 )
- {
- is_unique_number = 0;
- tbl[num] = 0x10; // fake data
- }
- } while( is_unique_number != 0 );
+ tbl[i++] = 0x10; // dummy data
+ tbl[i++] = 0x00 | 0x03; // real data + stop marker
+ } else {
+ tbl[i++] = 0x00; // real data
+ tbl[i++] = 0x10 | 0x03; // dummy data + stop marker
}
- // randomize control data for start and final round
- for( i = 1; i <= 2; i++ )
+ // Randomize AES rounds
+ num = num % ( AES_SCA_CM_ROUNDS + 1 );
+
+ // add dummy rounds to the start (if needed)
+ for ( ; i < num + 2; i++ )
{
- num = mbedtls_platform_random_in_range( 0xff );
- if( ( num % 2 ) == 0 )
- {
- tbl[tbl_len - ( i * 2 - 0 )] = 0x10; // fake data
- tbl[tbl_len - ( i * 2 - 1 )] = 0x00; // real data
- }
- else
- {
- tbl[tbl_len - ( i * 2 - 0 )] = 0x00; // real data
- tbl[tbl_len - ( i * 2 - 1 )] = 0x10; // fake data
- }
+ tbl[i] = 0x10; // dummy data
}
+
+ // add dummy rounds to the last, (AES_SCA_CM_ROUNDS - num) rounds if needed
+ for ( j = tbl_len - AES_SCA_CM_ROUNDS + num; j < tbl_len; j++ )
+ {
+ tbl[j] = 0x10; // dummy data
+ }
+#else /* AES_SCA_CM_ROUNDS != 0 */
+ tbl[i++] = 0x03; // real data + stop marker for the round key addition
#endif /* AES_SCA_CM_ROUNDS != 0 */
- // Fill real AES round data to the remaining places
+ // Fill real AES data to the remaining places
is_even_pos = 1;
- for( i = 0; i < tbl_len - 4; i++ )
+ for( ; i < tbl_len; i++ )
{
if( tbl[i] == 0 )
{
if( is_even_pos == 1 )
{
- tbl[i] = 0x04; // real data, offset 4
+ tbl[i] = 0x04; // real data, offset for rounds 1,3,5, etc...
is_even_pos = 0;
}
else
{
- tbl[i] = 0x00; // real data, offset 0
+ tbl[i] = 0x00; // real data, offset for rounds 2,4,6,...
is_even_pos = 1;
}
+ j = i; // remember the final round position in table
}
}
+ tbl[( tbl_len - 1)] |= 0x03; // Stop marker for the last item in tbl
+ tbl[( j - 1 )] |= 0x03; // stop marker for final - 1 real data
+
return( AES_SCA_CM_ROUNDS );
}
@@ -1051,30 +1053,31 @@
const unsigned char input[16],
unsigned char output[16] )
{
- int i, j, offset, start_fin_loops = 1;
+ int i, tindex, offset, stop_mark;
aes_r_data_t aes_data_real; // real data
#if AES_SCA_CM_ROUNDS != 0
aes_r_data_t aes_data_fake; // fake data
#endif /* AES_SCA_CM_ROUNDS != 0 */
- aes_r_data_t *aes_data_ptr; // pointer to aes_data_real or aes_data_fake
+ aes_r_data_t *aes_data_ptr; // pointer to real or fake data
aes_r_data_t *aes_data_table[2]; // pointers to real and fake data
- int round_ctrl_table_len = ctx->nr - 1 + AES_SCA_CM_ROUNDS + 2 + 2;
+ int round_ctrl_table_len = ctx->nr + 1;
volatile int flow_control;
- // control bytes for AES rounds, reserve based on max ctx->nr
- uint8_t round_ctrl_table[ 14 - 1 + AES_SCA_CM_ROUNDS + 2 + 2];
+ // control bytes for AES calculation rounds,
+ // reserve based on max rounds + dummy rounds + 2 (for initial key addition)
+ uint8_t round_ctrl_table[( 14 + AES_SCA_CM_ROUNDS + 2 )];
aes_data_real.rk_ptr = ctx->rk;
aes_data_table[0] = &aes_data_real;
#if AES_SCA_CM_ROUNDS != 0
+ round_ctrl_table_len += ( AES_SCA_CM_ROUNDS + 1 );
aes_data_table[1] = &aes_data_fake;
aes_data_fake.rk_ptr = ctx->rk;
- start_fin_loops = 2;
for( i = 0; i < 4; i++ )
aes_data_fake.xy_values[i] = mbedtls_platform_random_in_range( 0xffffffff );
#endif
- // Get randomized AES calculation control bytes
+ // Get AES calculation control bytes
flow_control = aes_sca_cm_data_randomize( round_ctrl_table,
round_ctrl_table_len );
@@ -1091,22 +1094,29 @@
GET_UINT32_LE( aes_data_real.xy_values[i], input, ( i * 4 ) );
}
- for( i = 0; i < 4; i++ )
+ tindex = 0;
+ do
{
- for( j = 0; j < start_fin_loops; j++ )
- {
- aes_data_ptr =
- aes_data_table[round_ctrl_table[ round_ctrl_table_len - 2 + j ] >> 4];
- aes_data_ptr->xy_values[i] ^= *aes_data_ptr->rk_ptr++;
- flow_control++;
- }
- }
+ // Get pointer to the real or fake data
+ aes_data_ptr = aes_data_table[round_ctrl_table[tindex] >> 4];
+ stop_mark = round_ctrl_table[tindex] & 0x03;
- for( i = 0; i < ( ctx->nr - 1 + AES_SCA_CM_ROUNDS ); i++ )
+ // initial round key addition
+ for( i = 0; i < 4; i++ )
+ {
+ aes_data_ptr->xy_values[i] ^= *aes_data_ptr->rk_ptr++;
+ }
+ tindex++;
+ flow_control++;
+ } while( stop_mark == 0 );
+
+ // Calculate AES rounds (9, 11 or 13 rounds) + dummy rounds
+ do
{
- // Read AES control data
- aes_data_ptr = aes_data_table[round_ctrl_table[i] >> 4];
- offset = round_ctrl_table[i] & 0x0f;
+ // Get pointer to the real or fake data
+ aes_data_ptr = aes_data_table[round_ctrl_table[tindex] >> 4];
+ offset = round_ctrl_table[tindex] & 0x04;
+ stop_mark = round_ctrl_table[tindex] & 0x03;
aes_data_ptr->rk_ptr = aes_fround( aes_data_ptr->rk_ptr,
&aes_data_ptr->xy_values[0 + offset],
@@ -1117,12 +1127,15 @@
aes_data_ptr->xy_values[5 - offset],
aes_data_ptr->xy_values[6 - offset],
aes_data_ptr->xy_values[7 - offset] );
+ tindex++;
flow_control++;
- }
+ } while( stop_mark == 0 );
- for( j = 0; j < start_fin_loops; j++ )
+ // Calculate final AES round + dummy rounds
+ do
{
- aes_data_ptr = aes_data_table[round_ctrl_table[ i + j ] >> 4];
+ aes_data_ptr = aes_data_table[round_ctrl_table[tindex] >> 4];
+ stop_mark = round_ctrl_table[tindex] & 0x03;
aes_fround_final( aes_data_ptr->rk_ptr,
&aes_data_ptr->xy_values[0],
&aes_data_ptr->xy_values[1],
@@ -1133,7 +1146,8 @@
aes_data_ptr->xy_values[6],
aes_data_ptr->xy_values[7] );
flow_control++;
- }
+ tindex++;
+ } while( stop_mark == 0 );
mbedtls_platform_memset( output, 0, 16 );
offset = mbedtls_platform_random_in_range( 4 );
@@ -1150,8 +1164,7 @@
flow_control++;
}
- if( flow_control == ( AES_SCA_CM_ROUNDS + ( 4 * start_fin_loops ) +
- ctx->nr - 1 + AES_SCA_CM_ROUNDS + start_fin_loops + 4 ) )
+ if( flow_control == round_ctrl_table_len + AES_SCA_CM_ROUNDS + 4 )
{
/* Validate control path due possible fault injection */
return 0;
@@ -1232,50 +1245,70 @@
const unsigned char input[16],
unsigned char output[16] )
{
- int i, j, offset, start_fin_loops = 1;
+ int i, tindex, offset, stop_mark;
aes_r_data_t aes_data_real; // real data
#if AES_SCA_CM_ROUNDS != 0
aes_r_data_t aes_data_fake; // fake data
#endif /* AES_SCA_CM_ROUNDS != 0 */
- aes_r_data_t *aes_data_ptr; // pointer to aes_data_real or aes_data_fake
+ aes_r_data_t *aes_data_ptr; // pointer to real or fake data
aes_r_data_t *aes_data_table[2]; // pointers to real and fake data
- int round_ctrl_table_len = ctx->nr - 1 + AES_SCA_CM_ROUNDS + 2 + 2;
- // control bytes for AES rounds, reserve based on max ctx->nr
+ int round_ctrl_table_len = ctx->nr + 1;
volatile int flow_control;
- uint8_t round_ctrl_table[ 14 - 1 + AES_SCA_CM_ROUNDS + 2 + 2 ];
+ // control bytes for AES calculation rounds,
+ // reserve based on max rounds + dummy rounds + 2 (for initial key addition)
+ uint8_t round_ctrl_table[( 14 + AES_SCA_CM_ROUNDS + 2 )];
aes_data_real.rk_ptr = ctx->rk;
aes_data_table[0] = &aes_data_real;
#if AES_SCA_CM_ROUNDS != 0
+ round_ctrl_table_len += ( AES_SCA_CM_ROUNDS + 1 );
aes_data_table[1] = &aes_data_fake;
aes_data_fake.rk_ptr = ctx->rk;
- start_fin_loops = 2;
for( i = 0; i < 4; i++ )
aes_data_fake.xy_values[i] = mbedtls_platform_random_in_range( 0xffffffff );
#endif
- // Get randomized AES calculation control bytes
+ // Get AES calculation control bytes
flow_control = aes_sca_cm_data_randomize( round_ctrl_table,
round_ctrl_table_len );
- for( i = 0; i < 4; i++ )
+ mbedtls_platform_memset( aes_data_real.xy_values, 0, 16 );
+ offset = mbedtls_platform_random_in_range( 4 );
+
+ for( i = offset; i < 4; i++ )
{
GET_UINT32_LE( aes_data_real.xy_values[i], input, ( i * 4 ) );
- for( j = 0; j < start_fin_loops; j++ )
- {
- aes_data_ptr =
- aes_data_table[round_ctrl_table[ round_ctrl_table_len - 4 + j ] >> 4];
- aes_data_ptr->xy_values[i] ^= *aes_data_ptr->rk_ptr++;
- flow_control++;
- }
}
- for( i = 0; i < ( ctx->nr - 1 + AES_SCA_CM_ROUNDS ); i++ )
+ for( i = 0; i < offset; i++ )
{
- // Read AES control data
- aes_data_ptr = aes_data_table[round_ctrl_table[i] >> 4];
- offset = round_ctrl_table[i] & 0x0f;
+ GET_UINT32_LE( aes_data_real.xy_values[i], input, ( i * 4 ) );
+ }
+
+ tindex = 0;
+ do
+ {
+ // Get pointer to the real or fake data
+ aes_data_ptr = aes_data_table[round_ctrl_table[tindex] >> 4];
+ stop_mark = round_ctrl_table[tindex] & 0x03;
+
+ // initial round key addition
+ for( i = 0; i < 4; i++ )
+ {
+ aes_data_ptr->xy_values[i] ^= *aes_data_ptr->rk_ptr++;
+ }
+ tindex++;
+ flow_control++;
+ } while( stop_mark == 0 );
+
+ // Calculate AES rounds (9, 11 or 13 rounds) + dummy rounds
+ do
+ {
+ // Get pointer to the real or fake data
+ aes_data_ptr = aes_data_table[round_ctrl_table[tindex] >> 4];
+ offset = round_ctrl_table[tindex] & 0x04;
+ stop_mark = round_ctrl_table[tindex] & 0x03;
aes_data_ptr->rk_ptr = aes_rround( aes_data_ptr->rk_ptr,
&aes_data_ptr->xy_values[0 + offset],
@@ -1286,12 +1319,15 @@
aes_data_ptr->xy_values[5 - offset],
aes_data_ptr->xy_values[6 - offset],
aes_data_ptr->xy_values[7 - offset] );
+ tindex++;
flow_control++;
- }
+ } while( stop_mark == 0 );
- for( j = 0; j < start_fin_loops; j++ )
+ // Calculate final AES round + dummy rounds
+ do
{
- aes_data_ptr = aes_data_table[round_ctrl_table[ i + j ] >> 4];
+ aes_data_ptr = aes_data_table[round_ctrl_table[tindex] >> 4];
+ stop_mark = round_ctrl_table[tindex] & 0x03;
aes_rround_final( aes_data_ptr->rk_ptr,
&aes_data_ptr->xy_values[0],
&aes_data_ptr->xy_values[1],
@@ -1302,16 +1338,25 @@
aes_data_ptr->xy_values[6],
aes_data_ptr->xy_values[7] );
flow_control++;
- }
+ tindex++;
+ } while( stop_mark == 0 );
- for( i = 0; i < 4; i++ )
+ mbedtls_platform_memset( output, 0, 16 );
+ offset = mbedtls_platform_random_in_range( 4 );
+
+ for( i = offset; i < 4; i++ )
{
PUT_UINT32_LE( aes_data_real.xy_values[i], output, ( i * 4 ) );
flow_control++;
}
- if( flow_control == ( AES_SCA_CM_ROUNDS + ( 4 * start_fin_loops ) +
- ctx->nr - 1 + AES_SCA_CM_ROUNDS + start_fin_loops + 4 ) )
+ for( i = 0; i < offset; i++ )
+ {
+ PUT_UINT32_LE( aes_data_real.xy_values[i], output, ( i * 4 ) );
+ flow_control++;
+ }
+
+ if( flow_control == round_ctrl_table_len + AES_SCA_CM_ROUNDS + 4 )
{
/* Validate control path due possible fault injection */
return 0;