Commit e9baceab authored by Andy Polyakov's avatar Andy Polyakov
Browse files

s3_cbc.c: get rid of expensive divisions [from master].

parent b05561c4

ssl/s3_cbc.c

+21 −14
Original line number Diff line number Diff line
@@ -76,6 +76,13 @@ 
#define DUPLICATE_MSB_TO_ALL(x) ( (unsigned)( (int)(x) >> (sizeof(int)*8-1) ) )

#define DUPLICATE_MSB_TO_ALL_8(x) ((unsigned char)(DUPLICATE_MSB_TO_ALL(x)))



/* constant_time_lt returns 0xff if a<b and 0x00 otherwise. */

static unsigned constant_time_lt(unsigned a, unsigned b)

	{

	a -= b;

	return DUPLICATE_MSB_TO_ALL(a);

	}



/* constant_time_ge returns 0xff if a>=b and 0x00 otherwise. */

static unsigned constant_time_ge(unsigned a, unsigned b)

	{
@@ -84,7 +91,7 @@ static unsigned constant_time_ge(unsigned a, unsigned b) 
	}



/* constant_time_eq_8 returns 0xff if a==b and 0x00 otherwise. */

static unsigned char constant_time_eq_8(unsigned char a, unsigned char b)

static unsigned char constant_time_eq_8(unsigned a, unsigned b)

	{

	unsigned c = a ^ b;

	c--;
@@ -288,16 +295,13 @@ void ssl3_cbc_copy_mac(unsigned char* out, 
	rotate_offset = (div_spoiler + mac_start - scan_start) % md_size;



	memset(rotated_mac, 0, md_size);

	for (i = scan_start; i < orig_len;)

		{

		for (j = 0; j < md_size && i < orig_len; i++, j++)

	for (i = scan_start, j = 0; i < orig_len; i++)

		{

		unsigned char mac_started = constant_time_ge(i, mac_start);

		unsigned char mac_ended = constant_time_ge(i, mac_end);

			unsigned char b = 0;

			b = rec->data[i];

			rotated_mac[j] |= b & mac_started & ~mac_ended;

			}

		unsigned char b = rec->data[i];

		rotated_mac[j++] |= b & mac_started & ~mac_ended;

		j &= constant_time_lt(j,md_size);

		}



	/* Now rotate the MAC */
@@ -305,16 +309,19 @@ void ssl3_cbc_copy_mac(unsigned char* out, 
	j = 0;

	for (i = 0; i < md_size; i++)

		{

		unsigned char offset = (div_spoiler + rotate_offset + i) % md_size;

		out[j++] = rotated_mac[offset];

		out[j++] = rotated_mac[rotate_offset++];

		rotate_offset &= constant_time_lt(rotate_offset,md_size);

		}

#else

	memset(out, 0, md_size);

	rotate_offset = md_size - rotate_offset;

	rotate_offset &= constant_time_lt(rotate_offset,md_size);

	for (i = 0; i < md_size; i++)

		{

		unsigned char offset = (div_spoiler + md_size - rotate_offset + i) % md_size;

		for (j = 0; j < md_size; j++)

			out[j] |= rotated_mac[i] & constant_time_eq_8(j, offset);

			out[j] |= rotated_mac[i] & constant_time_eq_8(j, rotate_offset);

		rotate_offset++;

		rotate_offset &= constant_time_lt(rotate_offset,md_size);

		}

#endif

	}