How to decrypt byte array using PHP which i has encrypted on c# ? As show on below code

Question

public string Encrypt(string text, string pass)
    {
        byte[] hash = SHA256.Create().ComputeHash(Encoding.UTF8.GetBytes(pass));
        byte[] iv = new byte[16];
        return this.EncryptString(text, hash, iv);
    }

    public string EncryptString(string plainText, byte[] key, byte[] iv)
    {
        Aes aes = Aes.Create();
        aes.Mode = CipherMode.CBC;
        byte[] numArray = new byte[32];
        Array.Copy(key, 0, numArray, 0, 32);
        aes.Key = numArray;
        aes.IV = iv;
        MemoryStream memoryStream = new MemoryStream();
        ICryptoTransform encryptor = aes.CreateEncryptor();
        CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
        byte[] bytes = Encoding.UTF8.GetBytes(plainText);
        cryptoStream.Write(bytes, 0, bytes.Length);
        cryptoStream.FlushFinalBlock();
        byte[] array = memoryStream.ToArray();
        memoryStream.Close();
        cryptoStream.Close();
        return Convert.ToBase64String(array, 0, array.Length);
    }

    public string DecryptString(string cipherText, byte[] key, byte[] iv)
    {
        Aes aes = Aes.Create();
        aes.Mode = CipherMode.CBC;
        byte[] numArray = new byte[32];
        Array.Copy(key, 0, numArray, 0, 32);
        aes.Key = numArray;
        aes.IV = iv;
        MemoryStream memoryStream = new MemoryStream();
        ICryptoTransform decryptor = aes.CreateDecryptor();
        CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Write);
        string empty = string.Empty;
        try
        {
            byte[] buffer = Convert.FromBase64String(cipherText);
            cryptoStream.Write(buffer, 0, buffer.Length);
            cryptoStream.FlushFinalBlock();
            byte[] array = memoryStream.ToArray();
            return Encoding.UTF8.GetString(array, 0, array.Length);
        }
        finally
        {
            memoryStream.Close();
            cryptoStream.Close();
        }
    }

These are the function which I have created to encrypt and decrypt on c# But how can I decrypt the encrypted data using PHP? I have gone through:

https://www.geeksforgeeks.org/how-to-encrypt-and-decrypt-a-php-string/

https://www.php.net/manual/en/function.openssl-encrypt.php

 private void btnEncrypt_Click(object sender, EventArgs e)
    {
        string text = richTextBoxEncrypt.Text;
        string pass = "DecyptionPass";
        richTextBoxEncrypt.Text= Encrypt(text, pass);
    }

    private void btnDecrypt_Click(object sender, EventArgs e)
    {
        byte[] hash = SHA256.Create().ComputeHash(Encoding.UTF8.GetBytes("DecyptionPass"));
        byte[] iv = new byte[16];
        richTextBoxDecrypt.Text = DecryptString(richTextBoxDecrypt.Text, hash, iv);
    }

Here is the example of the Plain text, encrypted text and the IV used

plaintext = "This is what i encrypted." 
Encrypted Text = "COz8V8eqkCS2U9TrH6FDA4ZD648m1WSB7QUoDoGyr7k="
Key = "ivdecrypt"

Update: This is the PHP Code that im trying but i dont know the actual value for IV

<?php

// Store a string into the variable which
// need to be Encrypted
$simple_string = "This is what i encrypted.";

// Display the original string
echo "Original String: " . $simple_string;

// Store the cipher method
$ciphering = "AES-128-CBC";

// Use OpenSSl Encryption method
$iv_length = openssl_cipher_iv_length($ciphering);
$options = 0;

// Non-NULL Initialization Vector for encryption
$encryption_iv = 'I dont know';

// Store the encryption key
$encryption_key = "ivdecrypt";

// Use openssl_encrypt() function to encrypt the data
$encryption = openssl_encrypt($simple_string, $ciphering,
    $encryption_key, $options, $encryption_iv);

// Display the encrypted string
echo "Encrypted String: " . $encryption . "\n";

// Non-NULL Initialization Vector for decryption
$decryption_iv = 'I dont know';

// Store the decryption key
$decryption_key = "ivdecrypt";

// Use openssl_decrypt() function to decrypt the data
$decryption=openssl_decrypt ($encryption, $ciphering,
    $decryption_key, $options, $decryption_iv);

// Display the decrypted string
echo "Decrypted String: " . $decryption;

?>

Welcome to Stackoverflow. Kindly share additionally one complete testdataset (plaintext, encryptedtext, key and iv used on C#-side, thanks. — Michael Fehr
– Michael Fehr, Commented Jul 23, 2020 at 7:41
You are encrypting on one system and decrypting on another. You need to explicitly set all parameters on both systems so they match. Do not use system defaults, as they are not guaranteed to match. This includes character encoding, endianness, padding etc. — rossum
– rossum, Commented Jul 23, 2020 at 8:37
Thanks for additional data. In your PHP code you are using "DecyptionPass" as source for your pass and in the example data: Key = "ivdecrypt" ? The initvector IV seems to be a byte array of 16 * 'x00', right ? — Michael Fehr
– Michael Fehr, Commented Jul 24, 2020 at 7:49
Yes thats right IV is the byte array of 16 and key i used for demo is ivdecrypt — Binay7587
– Binay7587, Commented Jul 24, 2020 at 8:01
I have updated my question with PHP code please look after that. Thank you — Binay7587
– Binay7587, Commented Jul 24, 2020 at 8:12

Michael Fehr · Accepted Answer · 2020-07-24 10:02:43Z

2

I wrote a sample program to show how encryption and decryption in PHP took place with similar result (encrypted string) to C#.

In your PHP source you are using AES 128 CBC but C# is using AES 256 CBC. You are using a string "I dont know" as source for the initialization vector (IV) but in C# it's a 16 length byte array filled with 16 "x00"s.

Here is the result:

pass:ivdecrypt
password:7b39fbd3f7a82a38dc565a10c236267a977e19fb0ba063f1e882cb6faaadf16f
plaintext=This is what i encrypted.
cipher=aes-256-cbc
encrypted to: COz8V8eqkCS2U9TrH6FDA4ZD648m1WSB7QUoDoGyr7k=
enc expected: COz8V8eqkCS2U9TrH6FDA4ZD648m1WSB7QUoDoGyr7k=
decrypted to: This is what i encrypted.

and the code. Beware that there is no proper error handling. Crypto warning: The usage of a static IV is UNSECURE.

<?php
// https://stackoverflow.com/questions/63033173/how-to-decrypt-byte-array-using-php-which-i-has-encrypted-on-c-sharp-as-show-o
// How to decrypt byte array using PHP which i has encrypted on c# ? As show on below code
$plaintext = 'This is what i encrypted.';
$pass = 'ivdecrypt';
$method = 'aes-256-cbc';

// Must be exact 32 chars (256 bit)
$password = substr(hash('sha256', $pass, true), 0, 32);
echo "pass:" . $pass . "\n";
echo "password:" . bin2hex($password) . "\n";

// IV must be exact 16 chars (128 bit)
$iv = chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0) . chr(0x0);

// encryption
$encrypted = base64_encode(openssl_encrypt($plaintext, $method, $password, OPENSSL_RAW_DATA, $iv));
// decryption
$decrypted = openssl_decrypt(base64_decode($encrypted), $method, $password, OPENSSL_RAW_DATA, $iv);

// output
echo 'plaintext: ' . $plaintext . "\n";
echo 'cipher: ' . $method . "\n";
echo 'encrypted to: ' . $encrypted . "\n";
echo 'enc expected: ' . "COz8V8eqkCS2U9TrH6FDA4ZD648m1WSB7QUoDoGyr7k=" . "\n";
echo 'decrypted to: ' . $decrypted . "\n\n";
?>

answered Jul 24, 2020 at 10:02

Michael Fehr

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2 Comments

Binay7587 Over a year ago

Thanks for your demo it worked. But how can I make that IV dynamic or random bytes for encryption on c# and then decryption on PHP?

Michael Fehr Over a year ago

On C#-side it's Crypto.getRandomValues() and the resulting value should get concated with the ciphertext so that it is available on (PHP) decryption side.

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