ccm: add masking to the UPDATE_CBC_MAC macro
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/library/ccm.c b/library/ccm.c
index edd7b8f..d785866 100644
--- a/library/ccm.c
+++ b/library/ccm.c
@@ -156,18 +156,34 @@
/*
* 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.)
+ * Initial b masking happens outside of this macro due to various sources of it.
*/
#define UPDATE_CBC_MAC \
- mbedtls_generate_permutation( perm_table, 16 ); \
for( i = 0; i < 16; 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 ) \
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_uint32() % 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
* 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.
@@ -243,15 +259,16 @@
* 5 .. 3 (t - 2) / 2
* 2 .. 0 q - 1
*/
- b[0] = 0;
- b[0] |= ( add_len > 0 ) << 6;
- b[0] |= ( ( tag_len - 2 ) / 2 ) << 3;
- b[0] |= q - 1;
+ mbedtls_generate_masks( mask_table, 16 );
+ mbedtls_generate_permutation( perm_table, 16 );
+ b[0] = (unsigned char) ( ( ( add_len > 0 ) << 6 ) |
+ ( ( ( 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 )
- b[15-i] = (unsigned char)( len_left & 0xFF );
+ b[15-i] = (unsigned char)( ( len_left & 0xFF ) ) ^ mask_table[15-i];
if( len_left > 0 )
return( MBEDTLS_ERR_CCM_BAD_INPUT );
@@ -271,12 +288,16 @@
len_left = add_len;
src = add;
+ mbedtls_generate_masks( mask_table, 16 );
+ mbedtls_generate_permutation( perm_table, 16 );
mbedtls_platform_memset( b, 0, 16 );
- b[0] = (unsigned char)( ( add_len >> 8 ) & 0xFF );
- b[1] = (unsigned char)( ( add_len ) & 0xFF );
+ b[0] = (unsigned char)( ( ( add_len >> 8 ) & 0xFF ) ^ mask_table[0] );
+ b[1] = (unsigned char)( ( ( add_len ) & 0xFF ) ^ mask_table[1] );
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;
src += use_len;
@@ -284,10 +305,12 @@
while( len_left > 0 )
{
+ mbedtls_generate_masks( mask_table, 16 );
+ mbedtls_generate_permutation( perm_table, 16 );
use_len = len_left > 16 ? 16 : len_left;
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;
len_left -= use_len;
@@ -326,8 +349,10 @@
if( mode == CCM_ENCRYPT )
{
+ mbedtls_generate_masks( mask_table, 16 );
+ mbedtls_generate_permutation( perm_table, 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;
}
@@ -335,8 +360,10 @@
if( mode == CCM_DECRYPT )
{
+ mbedtls_generate_masks( mask_table, 16 );
+ mbedtls_generate_permutation( perm_table, 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;
}