I need to decrypt a string as part of an authorization process.
The documentation specifies that the authorization string was encrypted with the following settings:
PKCS*7
The C# example:
/// <summary>
/// Decrypts a string.
/// </summary>
/// <param name="content">The string to decrypt.</param>
/// <param name="password">The password to use.</param>
/// <returns>The decrypted string.</returns>
private static string DecryptString(string content, string password)
{
Rijndael aes;
byte[] retVal = null;
byte[] contentBytes;
byte[] passwordBytes;
byte[] ivBytes;
try
{
contentBytes = Convert.FromBase64String(content);
//Create the password and initial vector bytes
passwordBytes = new byte[32];
ivBytes = new byte[16];
Array.Copy(Encoding.Unicode.GetBytes(password), passwordBytes, Encoding.Unicode.GetBytes(password).Length);
Array.Copy(passwordBytes, ivBytes, 16);
//Create the cryptograpy object
using (aes = Rijndael.Create())
{
aes.Key = passwordBytes;
aes.IV = ivBytes;
aes.Padding = PaddingMode.PKCS7;
//Decrypt
retVal = aes.CreateDecryptor().TransformFinalBlock(contentBytes, 0, contentBytes.Length);
}
}
catch
{
}
return Encoding.Unicode.GetString(retVal);
}
The same function was discussed here, but for JAVA: Decrypt C# RIJNDAEL encoded text
I tried to decrypt it with the following function but the result is different than expected:
function decrypt($string, $pass){
$iv = substr($pass, 0, 16);
$data = mcrypt_decrypt(MCRYPT_RIJNDAEL_256,
$pass,
base64_decode($string),
MCRYPT_MODE_CBC,
$iv);
$pad = ord($data[strlen($data) - 1]);
return substr($data, 0, -$pad);
}
The ecrypted string "7iTdZnp0DtGnIfwwqY4W/glbLLVZ0+asVLAuz13PzrW0wM6HC7rNuQvcG8JDSehyYeBJARdXHgLo9hRL9sBz3fN5LJ8cro3o0kFnAao2YRU="
should decrypt to
"ldYWMFlSbcki6LMl3rkNfGavnt8VqmZd"
using the password "GAT"
I think it has something to do with the password / iv / encoding
function decrypt($string, $pass)
{
$encodedPass = mb_convert_encoding($pass, 'utf-16le');
$encodedPass = substr($encodedPass, 0, 32);
$encodedPass = str_pad($encodedPass, 32, "\0", STR_PAD_RIGHT);
$iv = substr($encodedPass, 0, 16);
$data = mcrypt_decrypt(MCRYPT_RIJNDAEL_128,
$encodedPass,
base64_decode($string),
MCRYPT_MODE_CBC,
$iv);
$pad = ord($data[strlen($data) - 1]);
return substr($data, 0, -$pad);
}
In PHP, the MCRYPT_RIJNDAEL_128
/ MCRYPT_RIJNDAEL_256
isn't the size of the key, but the size of the block (see https://www.chilkatsoft.com/p/php_aes.asp ). C# normally uses 16 bytes blocks, so MCRYPT_RIJNDAEL_128
. The size of the key is auto-detected. Note that I've moved the encoding/resizing of the password inside the method.
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