I am working with SagePay Forms and currently converting the VB examples they have to c#. I have made good progress so the encryption part of my project works fine (SagePay can decrypt it).
The issue I am having is that when I attempt to decrypt the string, it turns to garbage. If anyone has done this before I would really appreciate some help with my decryption code. I have included the encryption code which works and the first two lines are the setup and call from another method.
I haven't added the VB code but if this is required I could add it. Didn't want a huge post if not required.
Utility Methods:
public string byteArrayToHexString(byte[] ba)
{
return BitConverter.ToString(ba).Replace("-", "");
}
public static byte[] StringToByteArray(string hex)
{
return Enumerable.Range(0, hex.Length)
.Where(x => x % 2 == 0)
.Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
.ToArray();
}
Main Encryption Method with first couple of lines being the calling of it extracted from a larger method.
string crypt = "blahblahblah"
string EncryptAndEncode = "@" + byteArrayToHexString(aesEncrypt(crypt));
private byte[] aesEncrypt(string inputText)
{
RijndaelManaged AES = new RijndaelManaged();
//set the mode, padding and block size for the key
AES.Padding = PaddingMode.PKCS7;
AES.Mode = CipherMode.CBC;
AES.KeySize = 128;
AES.BlockSize = 128;
//convert key and plain text input into byte arrays
Byte[] keyAndIvBytes = UTF8Encoding.UTF8.GetBytes("tR7nR6wZHGjYMCuV");
Byte[] inputBytes = UTF8Encoding.UTF8.GetBytes(inputText);//AbHLlc5uLone0D1q
//create streams and encryptor object
MemoryStream memoryStream = new MemoryStream();
CryptoStream cryptoStream = new CryptoStream(memoryStream, AES.CreateEncryptor(keyAndIvBytes, keyAndIvBytes), CryptoStreamMode.Write);
//perform encryption
cryptoStream.Write(inputBytes, 0, inputBytes.Length);
cryptoStream.FlushFinalBlock();
//get encrypted stream into byte array
Byte[] outBytes = memoryStream.ToArray();
//close streams
memoryStream.Close();
cryptoStream.Close();
AES.Clear();
return outBytes;
}
Decoding and Decrypting methods
public string DecodeAndDecrypt(string strIn)
{
//** HEX decoding then AES decryption, CBC blocking with PKCS5 padding - DEFAULT **
string DecodeAndDecrypt = aesDecrypt(StringToByteArray(strIn.Substring(1)));
return (DecodeAndDecrypt);
}
private string aesDecrypt(Byte[] inputBytes)
{
RijndaelManaged AES = new RijndaelManaged();
Byte[] keyAndIvBytes = UTF8Encoding.UTF8.GetBytes("tR7nR6wZHGjYMCuV");
Byte[] outputBytes = inputBytes;//Convert.FromBase64String(inputBytes);
//set the mode, padding and block size
AES.Padding = PaddingMode.PKCS7;
AES.Mode = CipherMode.CBC;
AES.KeySize = 128;
AES.BlockSize = 128;
//create streams and decryptor object
MemoryStream memoryStream = new MemoryStream(outputBytes);
CryptoStream cryptoStream = new CryptoStream(memoryStream, AES.CreateEncryptor(keyAndIvBytes, keyAndIvBytes), CryptoStreamMode.Read);
//perform decryption
cryptoStream.Read(outputBytes, 0, outputBytes.Length);
Trace.WriteLine(outputBytes);
//close streams
memoryStream.Close();
cryptoStream.Close();
AES.Clear();
//return System.Text.Encoding.UTF8.GetString(outputBytes);
string plainText = Encoding.UTF8.GetString(outputBytes,
0,
outputBytes.Length);
return plainText;
}
Answer
There are actually multiple problems with your code. First in your decrypt method you're creating an encryptor, that should be a decryptor. Secondly you're reading the entire block including the padding of your algorithm into the buffer when you do the decryption. Below is a class with the items fixed and should be returning the proper result. I do however suggest you find a better way of storing the key, putting in your code and generating it the way you'r edoing it is a no no. You should generate your key with an RNG (RNGCryptoServiceProvider) then hash it with a secure hashing algorithm such as SHA512, use that output for your key. You then need to find a good place to store it, I would look into encrypting your web.config file.
public static class EncryptionHelper
{
private static byte[] keyAndIvBytes;
static EncryptionHelper()
{
// You'll need a more secure way of storing this, I hope this isn't
// the real key
keyAndIvBytes = UTF8Encoding.UTF8.GetBytes("tR7nR6wZHGjYMCuV");
}
public static string ByteArrayToHexString(byte[] ba)
{
return BitConverter.ToString(ba).Replace("-", "");
}
public static byte[] StringToByteArray(string hex)
{
return Enumerable.Range(0, hex.Length)
.Where(x => x % 2 == 0)
.Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
.ToArray();
}
public static string DecodeAndDecrypt(string cipherText)
{
string DecodeAndDecrypt = AesDecrypt(StringToByteArray(cipherText));
return (DecodeAndDecrypt);
}
public static string EncryptAndEncode(string plaintext)
{
return ByteArrayToHexString(AesEncrypt(plaintext));
}
public static string AesDecrypt(Byte[] inputBytes)
{
Byte[] outputBytes = inputBytes;
string plaintext = string.Empty;
using (MemoryStream memoryStream = new MemoryStream(outputBytes))
{
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, GetCryptoAlgorithm().CreateDecryptor(keyAndIvBytes, keyAndIvBytes), CryptoStreamMode.Read))
{
using (StreamReader srDecrypt = new StreamReader(cryptoStream))
{
plaintext = srDecrypt.ReadToEnd();
}
}
}
return plaintext;
}
public static byte[] AesEncrypt(string inputText)
{
byte[] inputBytes = UTF8Encoding.UTF8.GetBytes(inputText);//AbHLlc5uLone0D1q
byte[] result = null;
using (MemoryStream memoryStream = new MemoryStream())
{
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, GetCryptoAlgorithm().CreateEncryptor(keyAndIvBytes, keyAndIvBytes), CryptoStreamMode.Write))
{
cryptoStream.Write(inputBytes, 0, inputBytes.Length);
cryptoStream.FlushFinalBlock();
result = memoryStream.ToArray();
}
}
return result;
}
private static RijndaelManaged GetCryptoAlgorithm()
{
RijndaelManaged algorithm = new RijndaelManaged();
//set the mode, padding and block size
algorithm.Padding = PaddingMode.PKCS7;
algorithm.Mode = CipherMode.CBC;
algorithm.KeySize = 128;
algorithm.BlockSize = 128;
return algorithm;
}
}
Calling it is easy:
string crypt = "blahblahblah";
string EncryptAndEncode = EncryptionHelper.EncryptAndEncode(crypt);
Console.WriteLine(EncryptAndEncode);
Console.WriteLine(EncryptionHelper.DecodeAndDecrypt(EncryptAndEncode));
Console.ReadLine();