public static string DecryptASCII(byte[] cipherText, byte[] key)
{
if (cipherText == null)
{
throw new ArgumentNullException("cipherText");
}
if (key == null)
{
throw new ArgumentNullException("key");
}
var convKey = KeyToShiftValues(key).ToArray();
if (convKey.Length == 0)
{
throw new ArgumentException("Converted key is empty. Please use alphabetic characters.");
}
// copy byte array into work buffer for manipulation
byte[] buff = new byte[cipherText.Length];
Buffer.BlockCopy(cipherText, 0, buff, 0, cipherText.Length);
int keyNdx = 0;
for (int z = 0; z < buff.Length; z++)
{
if (Utils.IsAsciiByteUpper(buff[z]) || Utils.IsAsciiByteLower(buff[z]))
{
buff[z] = Caesar.DecryptOneByteCaesarASCII(buff[z], convKey[keyNdx++]);
if (keyNdx >= convKey.Length)
{
keyNdx = 0; // wrap key back to beginning
}
}
}
return(Encoding.ASCII.GetString(buff));
}
public static string EncryptASCII(byte[] plainText, byte[] key)
{
if (plainText == null)
{
throw new ArgumentNullException("plaintext");
}
if (key == null)
{
throw new ArgumentNullException("key");
}
// select all alpha, convert to upper case, and turn characters into individual shift values for Caesar byte-by-byte encryption
var convKey = KeyToShiftValues(key).ToArray();
if (convKey.Length == 0)
{
throw new ArgumentException("Converted key is empty. Please use alphabetic characters.");
}
// copy byte array into work buffer for manipulation
byte[] buff = new byte[plainText.Length];
Buffer.BlockCopy(plainText, 0, buff, 0, plainText.Length);
int keyNdx = 0;
for (int z = 0; z < buff.Length; z++)
{
if (Utils.IsAsciiByteUpper(buff[z]) || Utils.IsAsciiByteLower(buff[z]))
{
buff[z] = Caesar.EncryptOneByteCaesarASCII(buff[z], convKey[keyNdx++]);
if (keyNdx >= convKey.Length)
{
keyNdx = 0; // wrap key back to beginning
}
}
}
return(Encoding.ASCII.GetString(buff));
}
