Encrypt in JavaScript will not decrypt in C#

Question

I am trying to use RSA encryption in JavaScript and then decrypt it in C#. In JavaScript I am using the library jsencrypt. In C# I using the API "bouncy castle". When I do the encryption/decryption within the same language everything works. I get back the correct text when I decrypt it. When I try to decrypt in C# what was encrypted in JavaScript I get nothing close. I am sure the keys are the same between the two. An example of the code is below. Any help on how to solve this would be greatly appreciated.

JavaScript

//using jsencrypt.min.js

var encrypt = new JSEncrypt();
encrypt.setPublicKey($('#pubkey').val());
var encrypted = encrypt.encrypt($('#input').val());

take the value I get from JavaScript "encrypted" and use it in C# for "encyp"

    AsymmetricCipherKeyPair KeyParameterPrivate;
        byte[] cipheredBytes = Convert.FromBase64String(encyp);


        string privateKeyFileName = @"C:\private.pem";
        using (var fileStream2 = File.OpenText(privateKeyFileName))
        {
            PemReader pemReader2 = new Org.BouncyCastle.OpenSsl.PemReader(fileStream2);
            KeyParameterPrivate = (Org.BouncyCastle.Crypto.AsymmetricCipherKeyPair)pemReader2.ReadObject();
        }
        IAsymmetricBlockCipher cipher2 = new Org.BouncyCastle.Crypto.Engines.RsaEngine();
        RsaKeyParameters privateKey2 = (RsaKeyParameters)KeyParameterPrivate.Private;
        //cipher.Init(false, publicKey4);
        cipher2.Init(false, privateKey2);
        byte[] deciphered = cipher2.ProcessBlock(cipheredBytes, 0, cipheredBytes.Length);
        string decipheredText = utf8enc.GetString(deciphered);

Answer 1

You'll have to use new PKCS1Encoding(cipher2). The RSAEngine only produces plain (also known as raw or textbook) RSA.

Answer 2

My advice is to keep it as simple as possible and not use Bouncy Castle for this. You need to create a public key for encryption, private key for decryption and a certificate to fetch the private key from.

First, create private key and certificate PEM files using OpenSSL:

openssl req -newkey rsa:1024 -nodes -keyout private_key.pem -x509 -days 365 -out certificate.pem

Then create a public key PEM file from the certificate that you created:

openssl x509 -pubkey -noout -in certificate.pem > public_key.pem

Then export a PFX file using the private key and certificate PEM files that you created:

openssl pkcs12 -export -out certificate.pfx -inkey private_key.pem -in certificate.pem

When you do the export, you'll be asked to provide a certificate password.

Now here is how to do the RSA decryption in C#:

var cert = new X509Certificate2(@"C:\path\to\certificate.pfx", "password");
var rsaCng = (RSACng)cert.PrivateKey;
var decryptedText = Encoding.UTF8.GetString(rsaCng.Decrypt(Convert.FromBase64String(encryptedText), RSAEncryptionPadding.Pkcs1));

Answer 3

Tell me if it works for you.

public string Decrypt(RSACryptoServiceProvider provider, string toDecrypt)
{
    var input = Convert.FromBase64String(toDecrypt);
    IEnumerable<byte> output = new List<byte>();
    for (var i = 0; i < input.Length; i = i + input.Length)
    {
        var length = Math.Max(input.Length - i, 128);
        var block = new byte[length];
        Buffer.BlockCopy(input, i, block, 0, length);
        var chunk = provider.Decrypt(block, false);
        output = output.Concat(chunk);
    }
    return Encoding.UTF8.GetString(output.ToArray());
}

Answer 4

Why would you want to torture yourself using BC for this?

The easiest approach to decryption here is :

 // store is a X509Store pointing to the correct store on the target machine
 // You have to ensure that the security principal for your app has access to the private key to decrypt
 X509Certificate2 cert = store.Certificates.Find(X509FindType.FindByThumbprint, "sha1hash", false)[0];

 var prov = (RSACryptoServiceProvider)cert.PrivateKey;
 var decipheredText = Encoding.UTF8.GetString(prov.Decrypt(Convert.FromBase64String(target), false));

Obviously you can get your X509Certificate2 from file or any other means, e.g. X509Certificate2 cert = new X509Certificate2(@"C:\someCert.pfx", "somePass");

If you followed jsencrypt tutorial, use this openssl command to get the pfx out of the pems you have:

openssl pkcs12 -export -out certificate.pfx -inkey privateKey.pem -in publicKey.pem