---

utils/invMixColumns.ts

@@ -0,0 +1,39 @@
+import { galoisMultiplyBy2 } from './mixColumns'
+
+const galoisMultiplyBy9 = (value: number): number => {
+  return galoisMultiplyBy2(galoisMultiplyBy2(galoisMultiplyBy2(value))) ^ value
+}
+
+const galoisMultiplyBy11 = (value: number): number => {
+  return galoisMultiplyBy2(galoisMultiplyBy2(galoisMultiplyBy2(value)) ^ value) ^ value
+}
+
+const galoisMultiplyBy13 = (value: number): number => {
+  return galoisMultiplyBy2(galoisMultiplyBy2(galoisMultiplyBy2(value) ^ value)) ^ value
+}
+
+const galoisMultiplyBy14 = (value: number): number => {
+  return galoisMultiplyBy2(galoisMultiplyBy2(galoisMultiplyBy2(value) ^ value) ^ value)
+}
+
+const clampToByte = (value: number): number => {
+  return value & 0xFF
+}
+
+export const invMixColumns = (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(galoisMultiplyBy14(state[0][col]) ^ galoisMultiplyBy11(state[1][col]) ^ galoisMultiplyBy13(state[2][col]) ^ galoisMultiplyBy9(state[3][col]))
+    result[1][col] = clampToByte(galoisMultiplyBy9(state[0][col]) ^ galoisMultiplyBy14(state[1][col]) ^ galoisMultiplyBy11(state[2][col]) ^ galoisMultiplyBy13(state[3][col]))
+    result[2][col] = clampToByte(galoisMultiplyBy13(state[0][col]) ^ galoisMultiplyBy9(state[1][col]) ^ galoisMultiplyBy14(state[2][col]) ^ galoisMultiplyBy11(state[3][col]))
+    result[3][col] = clampToByte(galoisMultiplyBy11(state[0][col]) ^ galoisMultiplyBy13(state[1][col]) ^ galoisMultiplyBy9(state[2][col]) ^ galoisMultiplyBy14(state[3][col]))
+  }
+
+  return result
+}