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);

What do you get in C# in the deciphered variable if you print out the bytes in hexadecimals? — Maarten Bodewes
– Maarten Bodewes, Commented Jan 2, 2015 at 14:39

Sirar Salih · Accepted Answer · 2019-03-07 14:08:49Z

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));

answered Mar 7, 2019 at 14:08

Sirar Salih

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2 Comments

Denis Evseev Over a year ago

Thanks a lot, Sirar! I would like to add that OpenSSL is available in Git folder on Windows: C:\Program Files\Git\usr\bin\openssl.exe. No need to install it

hiFI Over a year ago

@hans did this sort your issue

zaitsman · Accepted Answer · 2014-12-31 23:37:47Z

0

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

answered Dec 31, 2014 at 23:37

zaitsman

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2 Comments

Sirar Salih Over a year ago

That openssl command doesn't work for me in Windows. I got "unable to load certificates" when I ran it.

Sirar Salih Over a year ago

Also the C# code doesn't work in .NET Core, it crashes at runtime when doing the RSA cast. Please see my answer below which has working code.

Maarten Bodewes · Accepted Answer · 2015-01-02 14:42:24Z

0

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

answered Jan 2, 2015 at 14:42

Maarten Bodewes

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Comments

Sirar Salih · Accepted Answer · 2019-03-07 08:47:20Z

0

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());
}

edited Mar 7, 2019 at 8:47

Sirar Salih

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answered Feb 7, 2015 at 18:21

Antonio Gabriele

11

1 Comment

Sirar Salih Over a year ago

You need to use a private key to decrypt. You're not doing that in your code. Also I can confirm that your code doesn't work, it crashes at runtime when trying to decrypt. Please next time understand the question first, test your code and then suggest a working example.

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