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Merge pull request #3840 from AndrzejKurek/baremetal-aes-shuffling-2

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CCM countermeasures - shuffling and masking
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Andrzej Kurek 2020-11-25 11:33:53 +01:00 committed by GitHub
commit 21f64d3633
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1 changed files with 90 additions and 17 deletions
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107
library/ccm.c
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@ -114,6 +114,41 @@ void mbedtls_ccm_free( mbedtls_ccm_context *ctx )
mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ccm_context ) ); mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ccm_context ) );
} }
/* Durstenfeld's version of Fisher-Yates shuffle */
static void mbedtls_generate_permutation( unsigned char* table, size_t size )
{
size_t i, j;
for( i = 0; i < size; i++ )
{
table[i] = (unsigned char) i;
}
if( size < 2 )
{
return;
}
for( i = size - 1; i > 0; i-- )
{
unsigned char tmp;
j = mbedtls_platform_random_in_range( (uint32_t) i + 1 );
tmp = table[i];
table[i] = table[j];
table[j] = tmp;
}
}
static void mbedtls_generate_masks( unsigned char* table, size_t size )
{
size_t i;
for( i = 0; i < size; i++ )
{
table[i] = mbedtls_platform_random_in_range( 256 );
}
}
/* /*
* Macros for common operations. * Macros for common operations.
* Results in smaller compiled code than static inline functions. * Results in smaller compiled code than static inline functions.
@ -122,30 +157,55 @@ void mbedtls_ccm_free( mbedtls_ccm_context *ctx )
/* /*
* Update the CBC-MAC state in y using a block in b * Update the CBC-MAC state in y using a block in b
* (Always using b as the source helps the compiler optimise a bit better.) * (Always using b as the source helps the compiler optimise a bit better.)
* Initial b masking happens outside of this macro due to various sources of it.
*/ */
#define UPDATE_CBC_MAC \ #define UPDATE_CBC_MAC \
for( i = 0; i < 16; i++ ) \ for( i = 0; i < 16; i++ ) \
y[i] ^= b[i]; \ { \
y[perm_table[i]] ^= b[perm_table[i]]; \
y[perm_table[i]] ^= mask_table[perm_table[i]]; \
} \
\ \
if( ( ret = mbedtls_cipher_update( &ctx->cipher_ctx, y, 16, y, &olen ) ) != 0 ) \ if( ( ret = mbedtls_cipher_update( &ctx->cipher_ctx, y, 16, y, &olen ) ) != 0 ) \
return( ret ); return( ret );
/*
* Copy src to dst starting at a random offset, while masking the whole dst buffer.
*/
#define COPY_MASK( dst, src, mask, len_src, len_dst ) \
do \
{ \
unsigned j, offset = mbedtls_platform_random_in_range( 256 ); \
for( i = 0; i < len_src; i++ ) \
{ \
j = (i + offset) % len_src; \
(dst)[j] = (src)[j] ^ (mask)[j]; \
} \
for( ; i < len_dst; i++ ) \
(dst)[i] ^= (mask)[i]; \
} while( 0 )
/* /*
* Encrypt or decrypt a partial block with CTR * Encrypt or decrypt a partial block with CTR
* Warning: using b for temporary storage! src and dst must not be b! * Warning: using b for temporary storage! src and dst must not be b!
* This avoids allocating one more 16 bytes buffer while allowing src == dst. * This avoids allocating one more 16 bytes buffer while allowing src == dst.
*/ */
#define CTR_CRYPT( dst, src, len ) \ #define CTR_CRYPT( dst, src, len ) \
do \ do \
{ \ { \
mbedtls_generate_permutation( perm_table, len ); \
mbedtls_generate_masks( mask_table, len ); \
if( ( ret = mbedtls_cipher_update( &ctx->cipher_ctx, ctr, \ if( ( ret = mbedtls_cipher_update( &ctx->cipher_ctx, ctr, \
16, b, &olen ) ) != 0 ) \ 16, b, &olen ) ) != 0 ) \
{ \ { \
return( ret ); \ return( ret ); \
} \ } \
\ \
for( i = 0; i < (len); i++ ) \ for( i = 0; i < len; i++ ) \
(dst)[i] = (src)[i] ^ b[i]; \ { \
(dst)[perm_table[i]] = (src)[perm_table[i]] ^ mask_table[perm_table[i]];\
(dst)[perm_table[i]] ^= b[perm_table[i]]; \
(dst)[perm_table[i]] ^= mask_table[perm_table[i]]; \
} \
} while( 0 ) } while( 0 )
/* /*
@ -164,6 +224,8 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length,
unsigned char b[16]; unsigned char b[16];
unsigned char y[16]; unsigned char y[16];
unsigned char ctr[16]; unsigned char ctr[16];
unsigned char perm_table[16];
unsigned char mask_table[16];
const unsigned char *src; const unsigned char *src;
unsigned char *dst; unsigned char *dst;
@ -198,15 +260,16 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length,
* 5 .. 3 (t - 2) / 2 * 5 .. 3 (t - 2) / 2
* 2 .. 0 q - 1 * 2 .. 0 q - 1
*/ */
b[0] = 0; mbedtls_generate_masks( mask_table, 16 );
b[0] |= ( add_len > 0 ) << 6; mbedtls_generate_permutation( perm_table, 16 );
b[0] |= ( ( tag_len - 2 ) / 2 ) << 3; b[0] = (unsigned char) ( ( ( add_len > 0 ) << 6 ) |
b[0] |= q - 1; ( ( ( tag_len - 2 ) / 2 ) << 3 ) |
( q - 1 ) ) ^ mask_table[0];
mbedtls_platform_memcpy( b + 1, iv, iv_len );
for( i = 0; i < iv_len; i++ )
b[i+1] = iv[i] ^ mask_table[i+1];
for( i = 0, len_left = length; i < q; i++, len_left >>= 8 ) for( i = 0, len_left = length; i < q; i++, len_left >>= 8 )
b[15-i] = (unsigned char)( len_left & 0xFF ); b[15-i] = (unsigned char)( ( len_left & 0xFF ) ) ^ mask_table[15-i];
if( len_left > 0 ) if( len_left > 0 )
return( MBEDTLS_ERR_CCM_BAD_INPUT ); return( MBEDTLS_ERR_CCM_BAD_INPUT );
@ -226,12 +289,16 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length,
len_left = add_len; len_left = add_len;
src = add; src = add;
mbedtls_generate_masks( mask_table, 16 );
mbedtls_generate_permutation( perm_table, 16 );
mbedtls_platform_memset( b, 0, 16 ); mbedtls_platform_memset( b, 0, 16 );
b[0] = (unsigned char)( ( add_len >> 8 ) & 0xFF ); b[0] = (unsigned char)( ( ( add_len >> 8 ) & 0xFF ) ^ mask_table[0] );
b[1] = (unsigned char)( ( add_len ) & 0xFF ); b[1] = (unsigned char)( ( ( add_len ) & 0xFF ) ^ mask_table[1] );
use_len = len_left < 16 - 2 ? len_left : 16 - 2; use_len = len_left < 16 - 2 ? len_left : 16 - 2;
mbedtls_platform_memcpy( b + 2, src, use_len );
COPY_MASK( b+2, src, mask_table+2, use_len, 14 );
len_left -= use_len; len_left -= use_len;
src += use_len; src += use_len;
@ -239,10 +306,12 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length,
while( len_left > 0 ) while( len_left > 0 )
{ {
mbedtls_generate_masks( mask_table, 16 );
mbedtls_generate_permutation( perm_table, 16 );
use_len = len_left > 16 ? 16 : len_left; use_len = len_left > 16 ? 16 : len_left;
mbedtls_platform_memset( b, 0, 16 ); mbedtls_platform_memset( b, 0, 16 );
mbedtls_platform_memcpy( b, src, use_len ); COPY_MASK( b, src, mask_table, use_len, 16);
UPDATE_CBC_MAC; UPDATE_CBC_MAC;
len_left -= use_len; len_left -= use_len;
@ -281,8 +350,10 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length,
if( mode == CCM_ENCRYPT ) if( mode == CCM_ENCRYPT )
{ {
mbedtls_generate_masks( mask_table, 16 );
mbedtls_generate_permutation( perm_table, 16 );
mbedtls_platform_memset( b, 0, 16 ); mbedtls_platform_memset( b, 0, 16 );
mbedtls_platform_memcpy( b, src, use_len ); COPY_MASK( b, src, mask_table, use_len, 16 );
UPDATE_CBC_MAC; UPDATE_CBC_MAC;
} }
@ -290,8 +361,10 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length,
if( mode == CCM_DECRYPT ) if( mode == CCM_DECRYPT )
{ {
mbedtls_generate_masks( mask_table, 16 );
mbedtls_generate_permutation( perm_table, 16 );
mbedtls_platform_memset( b, 0, 16 ); mbedtls_platform_memset( b, 0, 16 );
mbedtls_platform_memcpy( b, dst, use_len ); COPY_MASK( b, dst, mask_table, use_len, 16 );
UPDATE_CBC_MAC; UPDATE_CBC_MAC;
} }