Finding a way to encrypt messages in C# and decrypting them in PHP or vice versa seems to be a "challenge" for many users. I wrote this tutorial to provide some help with this: below, you can find how to encrypt / decrypt messages in C# / PHP using AES256 with CBC mode.
1.Basic Information
AES 256 with CBC mode requires 3 values: the message, a key (32 bytes long) and an initialization vector (IV). Note that you must use the same IV when encrypting / decrypting a message: otherwise the message is lost. Sending the IV with the message is perfectly safe but it always has to be a random value. Since it has a fixed size, I always place the IV at the end of the encrypted text.
The encrypted messages should be encoded using base64 before being sent.
Encryption steps:
- encrypt the text
- add the IV at the end
- encode everything (base64)
Decryption steps:
- decode the message
- get & remove the IV
- proceed to decypt
Ok, enough talking, let's see some code...
2.PHP Encryption/Decryption Code
PHP accepts keys that are not 32 bytes long and simply extends them to the correct length. Well...C# doesn't, so you'll have to use a key that is 32 bytes long.
Encryption
-
function encrypt($text, $pkey)
- {
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$key = $pkey;
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$IV = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CBC), MCRYPT_RAND);
-
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return base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_CBC, $IV)."-[--IV-[-".$IV);
- }
Decryption
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function decrypt($text, $pkey)
- {
-
$key = $pkey;
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$text = base64_decode($text);
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$IV = substr($text, strrpos($text, "-[--IV-[-") + 9);
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$text = str_replace("-[--IV-[-".$IV, "", $text);
-
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return rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_CBC, $IV), "\0");
- }
3.C# Encryption/Decryption Code
As I said before, C# doesn't accept keys that aren't 32 bytes long - it will throw an error. Also, many people get tricked here because of the encoding (most of the times you have to use Encoding.Default).
Encryption
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public static string EncryptMessage(byte[] text, string key)
- {
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RijndaelManaged aes = new RijndaelManaged();
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aes.KeySize = 256;
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aes.BlockSize = 256;
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aes.Padding = PaddingMode.Zeros;
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aes.Mode = CipherMode.CBC;
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aes.Key = Encoding.Default.GetBytes(key);
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aes.GenerateIV();
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string IV = ("-[--IV-[-" + Encoding.Default.GetString(aes.IV));
-
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ICryptoTransform AESEncrypt = aes.CreateEncryptor(aes.Key, aes.IV);
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byte[] buffer = text;
-
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return
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Convert.ToBase64String(Encoding.Default.GetBytes(Encoding.Default.GetString(AESEncrypt.TransformFinalBlock(buffer, 0, buffer.Length)) + IV));
-
- }
Decryption
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public static string DecryptMessage(string text, string key)
- {
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RijndaelManaged aes = new RijndaelManaged();
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aes.KeySize = 256;
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aes.BlockSize = 256;
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aes.Padding = PaddingMode.Zeros;
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aes.Mode = CipherMode.CBC;
-
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aes.Key = Encoding.Default.GetBytes(key);
-
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text = Encoding.Default.GetString(Convert.FromBase64String(text));
-
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string IV = text;
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IV = IV.Substring(IV.IndexOf("-[--IV-[-") + 9);
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text = text.Replace("-[--IV-[-" + IV, "");
-
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text = Convert.ToBase64String(Encoding.Default.GetBytes(text));
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aes.IV = Encoding.Default.GetBytes(IV);
-
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ICryptoTransform AESDecrypt = aes.CreateDecryptor(aes.Key, aes.IV);
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byte[] buffer = Convert.FromBase64String(text);
-
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return Encoding.Default.GetString(AESDecrypt.TransformFinalBlock(buffer, 0, buffer.Length));
- }
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