Merge branch 'fix-tweakey-m4'

1 files changed, 20 insertions, 0 deletions

diff --git a/src/ref/multiplications.h b/src/ref/multiplications.h
index 4de1848..c0645b9 100644
--- a/src/ref/multiplications.h
+++ b/src/ref/multiplications.h
@@ -71,6 +71,26 @@ static void _multiply_M3(const uint8_t x[LANE_BYTES], uint8_t y[LANE_BYTES])
     y[0] = x[5];
 }
 
+static void _multiply_M4(const uint8_t x[LANE_BYTES], uint8_t y[LANE_BYTES])
+{
+    uint8_t a_5  = x[5]<<3  ^ x[4];
+    uint8_t a_4  = x[4]>>3  ^ x[3];
+    uint8_t b_5 = a_5<<3 ^ a_4;
+    uint8_t b_4 = a_4>>3 ^ x[2];
+
+    uint8_t c_4 = b_4>>3 ^ x[6]<<2 ^ x[1];
+    uint8_t c_5 = b_5<<3 ^ b_4;
+
+    y[7] = b_5;
+    y[6] = c_5;
+    y[5] = c_5<<3 ^ c_4;
+    y[4] = c_4>>3 ^ x[5]<<2 ^ x[0];
+    y[3] = a_5<<2 ^ x[7];
+    y[2] = b_5<<2 ^ x[6];
+    y[1] = x[5];
+    y[0] = a_5;
+}
+
 static void _multiply_MR(const uint8_t x[LANE_BYTES], uint8_t y[LANE_BYTES])
 {
     y[0] = x[1];