Replicate C# encryption/decryption in PHP

Question

I have been given a set of codes from a third party that need encrypting/decrypting however the sample encryption code they gave me was in C# and I am primarily a front-end PHP developer.

I have set-up a slimmed down working example of the code I was provided here using the sample key of A818163DD5E0DE87.

public static byte[] HexStringToByteArray(String hex)
{
int NumberChars = hex.Length;
byte[] bytes = new byte[NumberChars / 2];
for (int i = 0; i < NumberChars; i += 2) {
bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
}
return bytes;
}

// Convers a byte array to a HEX string
public static string ByteArrayToHexString(byte[] bytes)
{
StringBuilder hexString = new StringBuilder(bytes.Length * 2);
for (int i = 0; i < bytes.Length; i++)
{
hexString.Append(bytes[i].ToString("X2"));
}
return hexString.ToString();
}

public static byte[] Encrypt()
{
string plainText = "GROW06BP";
DESCryptoServiceProvider desCrypto = new DESCryptoServiceProvider();
desCrypto.Key = HexStringToByteArray("A818163DD5E0DE87");
desCrypto.IV = HexStringToByteArray("A818163DD5E0DE87");
desCrypto.Mode = CipherMode.CBC;
desCrypto.Padding = PaddingMode.Zeros;
// Create a buffer for the Plain Text using ASCIIEncoding
byte[] plaintextBytes = (new ASCIIEncoding()).GetBytes(plainText);
// Create a memory stream for the encrypted bytes
MemoryStream msEncrypt = new MemoryStream();
// Create a CryptoStream using the memory stream and the passed Algorithm
CryptoStream csEncrypt = new CryptoStream(msEncrypt, desCrypto.CreateEncryptor(), CryptoStreamMode.Write);
// Write the plaintext to the CryptoStream
csEncrypt.Write(plaintextBytes, 0, plaintextBytes.Length);
// Close the CryptoStream
csEncrypt.Close();
// Read the Encrypted bytes into our buffer
byte[] encryptedTextBytes = msEncrypt.ToArray();
// Close the Memory Stream
msEncrypt.Close();
// And return the encrypted buffer
return encryptedTextBytes;
}

I have scoured stack overflow and other sites in an attempt to replicate this in PHP but nothing comes close to the correct output. I'm also confused by which cipher I am meant to be using and how to convert the key and iv to match the C# example. Below is what I have attempted so far.

$key = unpack('H*', "A818163DD5E0DE87");
$key = "A818163DD5E0DE87";
$iv = $key;
$plaintext = "GROW06BP";
$ciphertext = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $plaintext,MCRYPT_MODE_CBC, $iv);
echo base64_encode($ciphertext);

Any help would be appreciated.

In C# you're using DES but in PHP you're using Rijndael (AES). They are different encryption algorithms! — Nasreddine
– Nasreddine, Commented May 26, 2016 at 7:22

VolkerK · Accepted Answer · 2016-05-26 07:37:53Z

1

Things you need to consider:

DESCryptoServiceProvider -> mcrypt_module_open('des'
desCrypto.Mode = CipherMode.CBC; -> mcrypt_module_open(...,..., 'cbc',
key,iv and the cipher output are "treated" with HexStringToByteArray(), pack('H*) can undo that

So, given the output of the .net fiddle (7860D97E56DA6A40) that leads to

<?php
$msgHex = '7860D97E56DA6A40'; 
$keyHex = 'A818163DD5E0DE87';
$ivHex = 'A818163DD5E0DE87';  // really? invalidates the use-case of an iv :-/

// this reverts the effect of HexStringToByteArray() 
$msg = pack('H*', $msgHex);
$key = pack('H*', $keyHex);
$iv = pack('H*', $ivHex);

// add error handing !
$module = mcrypt_module_open('des', '', 'cbc', '');
mcrypt_generic_init($module, $key, $iv);
$plaintext = mdecrypt_generic($module, $msg);
mcrypt_generic_deinit($module);

echo $plaintext;

output: GROW06BP

answered May 26, 2016 at 7:37

VolkerK

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1 Comment

Daniel Beilharz Over a year ago

Thank you very much VolkerK, this allows me to successfully decrypt the codes. I don't think I would have ever got this as I didn't come across those functions at all when searching for this.

Nasreddine · Accepted Answer · 2016-05-26 07:48:35Z

0

As I've already mentioned in my comment, you're using the wrong algorithm in your PHP code since it's Rijndael. What you should use is MCRYPT_DES.

$key = "A818163DD5E0DE87";
// Here you need pack instead of unpack
$packKey = pack("H*",$key);
// you should use the key as the initialization vector
// use something like mcrypt_create_iv to generate an IV
$iv = $packKey;
$plaintext = "GROW06BP";
// replaced MCRYPT_RIJNDAEL_128 with MCRYPT_DES
$ciphertext = mcrypt_encrypt(MCRYPT_DES, $packKey, $plaintext,MCRYPT_MODE_CBC, $iv);
echo base64_encode($ciphertext);

This will produce the same output as the C# code

answered May 26, 2016 at 7:48

Nasreddine

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1 Comment

Daniel Beilharz Over a year ago

Thanks for all your help Nasreddine. Your code looks great to me but seems to output a different result to the C# code, which is where a lot of my confusion came from with this.

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