private byte[] InverseSecondRound(byte[] cipherText, byte[] roundKey)
{
var inversedRoundKey = Aes16Helper.AddRoundKey(cipherText, roundKey);
var inversedShiftRow = Aes16Helper.ShiftRow(inversedRoundKey);
var inversedNibbleSubstitution = Aes16Helper.InverseNibbleSubstitution(inversedShiftRow);
return(inversedNibbleSubstitution);
}
private byte[] GetThirdSubKey(byte[] key)
{
var secondSubKey = GetSecondSubKey(key);
var firstByte = (byte)(secondSubKey[0] ^ 0b00110000 ^ Aes16Helper.SubNib(Aes16Helper.RotNib(secondSubKey[1])));
var secondByte = (byte)(firstByte ^ secondSubKey[1]);
return(new[] { firstByte, secondByte });
}
private byte[] InverseFirstRound(byte[] firstRoundCipherText, byte[] roundKey)
{
var inversedRoundKey = Aes16Helper.AddRoundKey(firstRoundCipherText, roundKey);
var inversedMixColumns = Aes16Helper.InverseMixColumns(inversedRoundKey);
var inversedShiftRow = Aes16Helper.ShiftRow(inversedMixColumns);
var inversedNibbleSubstitution = Aes16Helper.InverseNibbleSubstitution(inversedShiftRow);
return(inversedNibbleSubstitution);
}
private byte[] GetSecondRoundResult(byte[] firstRoundResult, byte[] subKey)
{
var nibbled = Aes16Helper.NibbleSubstitution(firstRoundResult);
var secondFourBitsOfFirstByte = (byte)(nibbled[0] & 0b00001111);
var secondFourBitsOfSecondByte = (byte)(nibbled[1] & 0b00001111);
var newFirstByte = (byte)((nibbled[0] & 0b11110000) | secondFourBitsOfSecondByte);
var newSecondByte = (byte)((nibbled[1] & 0b11110000) | secondFourBitsOfFirstByte);
var shiftedBytes = new[] { newFirstByte, newSecondByte };
return(Aes16Helper.AddRoundKey(shiftedBytes, subKey));
}
private byte[] GetFirstRoundResult(byte[] zeroRoundResult, byte[] roundKey)
{
// Nibble substitution
var nibbled = Aes16Helper.NibbleSubstitution(zeroRoundResult);
// Shift row
var shiftedRowBytes = Aes16Helper.ShiftRow(nibbled);
var mixedBytes = Aes16Helper.MixColumns(shiftedRowBytes);
return(Aes16Helper.AddRoundKey(new[] { mixedBytes[0], mixedBytes[1] }, roundKey));
}
private byte[] GetSecondSubKey(byte[] key)
{
var firstSubKey = GetFirstSubKey(key);
var a = (byte)(firstSubKey[0] ^ 0b10000000);
var c = Aes16Helper.RotNib(firstSubKey[1]);
var b = Aes16Helper.SubNib(c);
var firstByte = (byte)(a ^ b);
var secondByte = (byte)(firstByte ^ firstSubKey[1]);
return(new[] { firstByte, secondByte });
}
private byte[] InverseZeroRound(byte[] zeroRoundCipherText, byte[] roundKey)
{
var inversedRoundKey = Aes16Helper.AddRoundKey(zeroRoundCipherText, roundKey);
return(inversedRoundKey);
}
private byte[] GetZeroRoundResult(byte[] plainText, byte[] roundKey)
{
return(Aes16Helper.AddRoundKey(plainText, roundKey));
}