You may use:
byte[] process(bool encrypt, byte[] input, byte[] key)
{
var cipher = CipherUtilities.GetCipher("Blowfish");
cipher.Init(false, new KeyParameter(key));
return cipher.DoFinal(input);
}
// Encrypt:
byte[] encrypted = process(true, clear, key);
// Decrypt:
byte[] decrypted = process(false, encrypted, key);
See: https://github.com/wernight/decrypt-toolbox/blob/master/dtDecrypt/Program.cs