---

utils/mixColumns.ts

@@ -0,0 +1,29 @@
+export const galoisMultiplyBy2 = (value: number): number => {
+  return (value << 1) ^ ((value & 0x80) ? 0x1b : 0x00)
+}
+
+export const galoisMultiplyBy3 = (value: number): number => {
+  return galoisMultiplyBy2(value) ^ value
+}
+
+const clampToByte = (value: number): number => {
+  return value & 0xFF
+}
+
+export const mixColumns = (state: number[][]): number[][] => {
+  const result: number[][] = [
+    [0, 0, 0, 0],
+    [0, 0, 0, 0],
+    [0, 0, 0, 0],
+    [0, 0, 0, 0]
+  ]
+
+  for (let col = 0; col < 4; col++) {
+    result[0][col] = clampToByte(galoisMultiplyBy2(state[0][col]) ^ galoisMultiplyBy3(state[1][col]) ^ state[2][col] ^ state[3][col])
+    result[1][col] = clampToByte(state[0][col] ^ galoisMultiplyBy2(state[1][col]) ^ galoisMultiplyBy3(state[2][col]) ^ state[3][col])
+    result[2][col] = clampToByte(state[0][col] ^ state[1][col] ^ galoisMultiplyBy2(state[2][col]) ^ galoisMultiplyBy3(state[3][col]))
+    result[3][col] = clampToByte(galoisMultiplyBy3(state[0][col]) ^ state[1][col] ^ state[2][col] ^ galoisMultiplyBy2(state[3][col]))
+  }
+
+  return result
+}