Converting php array substr to c#-CodePudding

I'm trying to decrypt in c#, using bouncycastle, the result of the following php code:

<?php
    $plaintext = 'The quick brown fox jumps over the lazy dog';
    $cipher = "AES-128-CTR";
    $key = "F5UgsDQddWGdgjdd";
    $iv = openssl_random_pseudo_bytes(16);
    $ciphertext = openssl_encrypt(
        $plaintext, 
        $cipher,   
        $key,
        0, 
        $iv
    );
    $ciphertext = base64_encode($iv.$ciphertext);
    echo $ciphertext."\n";
?>

in php, the following code works:

<?php
    $cipher = "AES-128-CTR";
    $key = "F5UgsDQddWGdgjdd";    
    $ciphertext = base64_decode( $_POST['ciphertext'] );
    $iv = substr($ciphertext, 0, 16);
    $content = substr($ciphertext, 16);
    $text = openssl_decrypt(
        $content, 
        $cipher,
        $key,  
        0, 
        $iv
      );
    
    echo $text."\n";
?>

However, when I do the following in C# the result is just gibberish.

public string Test(string cipherTextStr)
{
    var cipherText = Convert.FromBase64String(cipherTextStr);
    var iv = cipherText.Take(16).ToArray();
    var content = cipherText.Skip(16).ToArray();

    byte[] keyBytes = Encoding.UTF8.GetBytes("F5UgsDQddWGdgjdd");

    IBufferedCipher cipher = CipherUtilities.GetCipher("AES/CTR/NoPadding");

    cipher.Init(false, new ParametersWithIV(ParameterUtilities.CreateKeyParameter("AES", keyBytes), iv));

    byte[] decryptedBytes = cipher.DoFinal(content);

    return Encoding.UTF8.GetString(decryptedBytes);

}

The same C# code works if I don't have to separate iv and content which makes me think that I'm either doing the initial FromBase64String wrong or the take and skip from the byte array.

CodePudding user response：

When you pass $option = 0 to openssl_encrypt, the input data is PKCS#7 padded and the output data is base64 encoded. If you don't want any padding and base64 encoded output, use this option value:

$ciphertext = openssl_encrypt(
    $plaintext, 
    $cipher,   
    $key,
    OPENSSL_RAW_DATA | OPENSSL_ZERO_PADDING, 
    $iv
);

Update: modify C#, manually decode the encrypted data.

content = Convert.FromBase64String(Encoding.UTF8.GetString(content));