Mcrypt and base64 with PHP and c#

Question

I have written the same methods in two platforms which I believe should result same thing but its not happening. I have encrypted the same text with same key which result different. Can someone figure it out why is it happening ?

String: this is test

Key: 1234567812345678

PHP encrypted string: ybUaKwQlRNwOjJhxLWtLYQ==

C# encrypted string: r2YjEFPyDDacnPmDFcGTLA==

C# functions

static string Encrypt(string plainText, string key) { string cipherText; var rijndael = new RijndaelManaged() { Key = Encoding.UTF8.GetBytes(key), Mode = CipherMode.ECB, BlockSize = 128, }; ICryptoTransform encryptor = rijndael.CreateEncryptor(rijndael.Key, rijndael.IV); using (var memoryStream = new MemoryStream()) { using (var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write)) { using (var streamWriter = new StreamWriter(cryptoStream)) { streamWriter.Write(plainText); streamWriter.Flush(); } cipherText = Convert.ToBase64String(memoryStream.ToArray()); //cryptoStream.FlushFinalBlock(); } } return cipherText; } private static string Decrypt(string cipherText, string key) { string plainText; byte[] cipherArray = Convert.FromBase64String(cipherText); var rijndael = new RijndaelManaged() { Key = Encoding.UTF8.GetBytes(key), Mode = CipherMode.ECB, BlockSize = 128 }; ICryptoTransform decryptor = rijndael.CreateDecryptor(rijndael.Key, rijndael.IV); using (var memoryStream = new MemoryStream(cipherArray)) { using (var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read)) { using (var streamReader = new StreamReader(cryptoStream)) { plainText = streamReader.ReadToEnd(); } } } return plainText; }

PHP functions

function string_encrypt($string, $key) { $crypted_text = mcrypt_encrypt( MCRYPT_RIJNDAEL_128, $key, $string, MCRYPT_MODE_ECB ); return base64_encode($crypted_text); } function string_decrypt($encrypted_string, $key) { return mcrypt_decrypt( MCRYPT_RIJNDAEL_128, $key, base64_decode($encrypted_string), MCRYPT_MODE_ECB ); }

I am not so good in C# and I know the PHP function is working fine. So, there must be something done on C# functions. May be the string to be encrypted should converted to Latin chars.

Is there anything wrong with the answer you have been given hsuk? It seems rather extensive... — Maarten Bodewes
– Maarten Bodewes, Commented Sep 22, 2013 at 12:16
What about the second block of code written by StigM? That looks like C# to me. He first showed you the correct way, and then the way to make C# comply with the braindead PHP mcrypt_decrypt functionality. — Maarten Bodewes
– Maarten Bodewes, Commented Sep 22, 2013 at 16:25
Also note that you should explicitly define the character-encoding to be used within both PHP and C#. Also note that keys and passwords are not the same, and that ECB mode is not secure for encrypting text (or for most data, really). — Maarten Bodewes
– Maarten Bodewes, Commented Sep 22, 2013 at 16:27

Community · Accepted Answer · 2017-05-23 12:24:44Z

C# does Rijndael padding by default and uses PKCS7.

This means you have to pad your PHP side as per PKCS7, code below should work:

function string_encrypt($string, $key) { $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB); $padding = $block - (strlen($string) % $block); $string .= str_repeat(chr($padding), $padding); $crypted_text = mcrypt_encrypt( MCRYPT_RIJNDAEL_128, $key, $string, MCRYPT_MODE_ECB ); return base64_encode($crypted_text); }

For further information, see the first answer here

I should add also, that if you want to change the C# side and not use padding, make the below modification instead and leave the PHP side alone:

static string Encrypt(string plainText, string key) { string cipherText; var rijndael = new RijndaelManaged() { Key = Encoding.UTF8.GetBytes(key), Mode = CipherMode.ECB, BlockSize = 128, Padding = PaddingMode.Zeros, }; ICryptoTransform encryptor = rijndael.CreateEncryptor(rijndael.Key, null); using (var memoryStream = new MemoryStream()) { using (var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write)) { using (var streamWriter = new StreamWriter(cryptoStream)) { streamWriter.Write(plainText); streamWriter.Flush(); } //cipherText = Convert.ToBase64String(Encoding.UTF8.GetBytes(Encoding.UTF8.GetString(memoryStream.ToArray()))); cipherText = Convert.ToBase64String(memoryStream.ToArray()); //cryptoStream.FlushFinalBlock(); } } return cipherText; }

It would be great if the PaddingMode.Zeros was more prominent in this answer. Thanks!

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