Add mix columns

multiplatform-crypto/src/commonMain/kotlin/com/ionspin/kotlin/crypto/symmetric/Aes.kt

@@ -92,6 +92,24 @@ class Aes {
         stateMatrix[3] = arrayOf(stateMatrix[3][3], stateMatrix[3][0], stateMatrix[3][1], stateMatrix[3][2])
     }
 
+    fun mixColumns() {
+        val stateMixed : Array<Array<UByte>> = (0 until 4).map {
+            Array<UByte>(4) { 0U }
+        }.toTypedArray()
+        for (c in 0 .. 3) {
+
+            stateMixed[0][c] = (2U gfm stateMatrix[0][c]) xor galoisFieldMultiply(3U, stateMatrix[1][c]) xor stateMatrix[2][c] xor stateMatrix[3][c]
+            stateMixed[1][c] = stateMatrix[0][c] xor (2U gfm stateMatrix[1][c]) xor (3U gfm stateMatrix[2][c]) xor stateMatrix[3][c]
+            stateMixed[2][c] = stateMatrix[0][c] xor stateMatrix[1][c] xor (2U gfm stateMatrix[2][c]) xor (3U gfm stateMatrix[3][c])
+            stateMixed[3][c] = 3U gfm stateMatrix[0][c] xor stateMatrix[1][c] xor stateMatrix[2][c] xor (2U gfm stateMatrix[3][c])
+        }
+        stateMixed.copyInto(stateMatrix)
+    }
+
+    fun galoisFieldAdd(first : UByte, second : UByte) : UByte {
+        return first xor second
+    }
+
     fun galoisFieldMultiply(first : UByte, second : UByte) : UByte {
         var result : UInt = 0U
         var firstInt = first.toUInt()
@@ -112,6 +130,10 @@ class Aes {
         return result.toUByte()
     }
 
+    infix fun UInt.gfm(second : UByte) : UByte {
+        return galoisFieldMultiply(this.toUByte(), second)
+    }
+
     fun expandKey(key: AesKey) {
 
     }

multiplatform-crypto/src/commonTest/kotlin/com/ionspin/kotlin/crypto/symmetric/AesTest.kt

@@ -20,7 +20,7 @@ class AesTest {
         val aes = Aes()
         fakeState.copyInto(aes.stateMatrix)
         aes.subBytes()
-        aes.stateMatrix.forEach{
+        aes.stateMatrix.forEach {
             println(it.joinToString { it.toString(16) })
         }
         assertTrue {
@@ -45,7 +45,7 @@ class AesTest {
         val aes = Aes()
         fakeState.copyInto(aes.stateMatrix)
         aes.shiftRows()
-        aes.stateMatrix.forEach{
+        aes.stateMatrix.forEach {
             println(it.joinToString { it.toString(16) })
         }
         assertTrue {
@@ -55,12 +55,52 @@ class AesTest {
 
     @Test
     fun testGaloisMultiply() {
+        //Samples from FIPS-197
+        assertTrue {
             val a = 0x57U
             val b = 0x83U
             val aes = Aes()
             val c = aes.galoisFieldMultiply(a.toUByte(), b.toUByte())
-        assertTrue {
             c == 0xC1U.toUByte()
         }
+
+        assertTrue {
+            val a = 0x57U
+            val b = 0x13U
+            val aes = Aes()
+            val c = aes.galoisFieldMultiply(a.toUByte(), b.toUByte())
+            c == 0xFEU.toUByte()
+        }
+
+
+    }
+
+    @Test
+    fun testMixColumns() {
+        //Test vectors from wikipedia
+        val fakeState = arrayOf(
+            ubyteArrayOf(0xdbU, 0xf2U, 0x01U, 0xc6U).toTypedArray(),
+            ubyteArrayOf(0x13U, 0x0aU, 0x01U, 0xc6U).toTypedArray(),
+            ubyteArrayOf(0x53U, 0x22U, 0x01U, 0xc6U).toTypedArray(),
+            ubyteArrayOf(0x45U, 0x5cU, 0x01U, 0xc6U).toTypedArray()
+        )
+
+        val expectedState = arrayOf(
+            ubyteArrayOf(0x8eU, 0x9fU, 0x01U, 0xc6U).toTypedArray(),
+            ubyteArrayOf(0x4dU, 0xdcU, 0x01U, 0xc6U).toTypedArray(),
+            ubyteArrayOf(0xa1U, 0x58U, 0x01U, 0xc6U).toTypedArray(),
+            ubyteArrayOf(0xbcU, 0x9dU, 0x01U, 0xc6U).toTypedArray()
+        )
+
+        val aes = Aes()
+        fakeState.copyInto(aes.stateMatrix)
+        aes.mixColumns()
+        aes.stateMatrix.forEach {
+            println(it.joinToString { it.toString(16) })
+        }
+        assertTrue {
+            aes.stateMatrix.contentDeepEquals(expectedState)
+        }
+
     }
 }