// Generating 26 length string of random characters for the Secret Key
public static byte[] GenerateSecretKey(string username)
{
Dictionary <double, char> numberToCharacter = Utils.numberToCharacter;
StringBuilder secretKey = new StringBuilder();
for (int i = 0; i < SECRET_KEY_LENGTH; i++)
{
byte[] randomNumber = new byte[8];
rngCsp.GetBytes(randomNumber);
double generatedNumber = Math.Abs((BitConverter.ToInt32(randomNumber, 0) % 31));
if (numberToCharacter.ContainsKey(generatedNumber))
{
secretKey.Append(numberToCharacter[generatedNumber]);
}
else
{
throw new Exception("Value not found in dictionary.");
}
}
byte[] expandedSecretKey = MyHKDF.KeyExpansion(32, Encoding.ASCII.GetBytes(secretKey.ToString()), username);
return(expandedSecretKey);
}
private static byte[] DeriveMasterUnlockKey(byte[] masterPassword, string username)
{
byte[] salt = DataStore.GetData(Globals.Salt);
byte[] hashedPassword = PBKDF2.PerformPBKDF(masterPassword, salt);
byte[] secretKey = DataStore.GetData(Globals.SecretKey);
byte[] expandedSecretKey = MyHKDF.KeyExpansion(32, secretKey);
return(XOR(hashedPassword, expandedSecretKey));
}
private static byte[] HandleSalt(byte[] salt)
{
if (salt.Length == OUTPUT_LENGTH_IN_BYTES)
{
return(salt);
}
else
{
return(MyHKDF.KeyExpansion(OUTPUT_LENGTH_IN_BYTES, salt));
}
}
private static void Decryption(byte[,] stateMatrix, byte[,] keyMatrix)
{
byte[] derivedRoundKeys = MyHKDF.KeyDerivation(16, MatrixToByteBlock(keyMatrix), 10);
// Initial round
AddRoundKey(stateMatrix, GetCurrentRoundKey(derivedRoundKeys, 10));
ShiftRows(stateMatrix);
SubBytes(stateMatrix);
// 9 main rounds (depends on key length) of substitution and permutation
for (int i = 1; i <= NUM_MAIN_ROUNDS; i++)
{
byte[,] roundKey = GetCurrentRoundKey(derivedRoundKeys, NUM_MAIN_ROUNDS - i + 1);
AddRoundKey(stateMatrix, roundKey);
MixColumns(stateMatrix);
ShiftRows(stateMatrix);
SubBytes(stateMatrix);
}
// Final round
AddRoundKey(stateMatrix, keyMatrix);
}
