diff --git a/library/ccm.c b/library/ccm.c index e54a9955b..87fe16dd8 100644 --- a/library/ccm.c +++ b/library/ccm.c @@ -114,6 +114,41 @@ void mbedtls_ccm_free( mbedtls_ccm_context *ctx ) 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. * 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 * (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 \ 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 ) \ 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 * 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. */ -#define CTR_CRYPT( dst, src, len ) \ +#define CTR_CRYPT( dst, src, len ) \ do \ { \ + mbedtls_generate_permutation( perm_table, len ); \ + mbedtls_generate_masks( mask_table, len ); \ if( ( ret = mbedtls_cipher_update( &ctx->cipher_ctx, ctr, \ 16, b, &olen ) ) != 0 ) \ { \ return( ret ); \ } \ \ - for( i = 0; i < (len); i++ ) \ - (dst)[i] = (src)[i] ^ b[i]; \ + for( i = 0; i < len; 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 ) /* @@ -164,6 +224,8 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length, unsigned char b[16]; unsigned char y[16]; unsigned char ctr[16]; + unsigned char perm_table[16]; + unsigned char mask_table[16]; const unsigned char *src; 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 * 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_platform_memcpy( b + 1, iv, iv_len ); + 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]; + 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 ); @@ -226,12 +289,16 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length, 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; @@ -239,10 +306,12 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length, 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; @@ -281,8 +350,10 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length, 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; } @@ -290,8 +361,10 @@ static int ccm_auth_crypt( mbedtls_ccm_context *ctx, int mode, size_t length, 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; }