If you cannot enable SSL for whatever reason, you might still want to encrypt your sensitive information (such as passwords) over the wire. In this post I tried to put together a solution with working examples from various languages to make the client server communication secure using public cryptography with RSA.

This post focuses on C# and Javascript interoperability. Below is a C# example using Bouncycastle project:

const string PrivateKey = @"-----BEGIN RSA PRIVATE KEY-----
MIICXgIBAAKBgQDOFfwbqHOmQWYc50XxsR+dLyNUSwsaQ3tx225AvYEOs9bSS3VV
....
4/uGrlWiOG8EHeL1RUW/s5LezT1RFlL15RuSq4tHH/GI6w==
-----END RSA PRIVATE KEY-----
";

readonly Lazy<IAsymmetricBlockCipher> _cipher = new Lazy<IAsymmetricBlockCipher>(() =>
{
    var rsa = new Pkcs1Encoding(new RsaEngine());
    var pemReader = new PemReader(new StringReader(PrivateKey));
    var keyPair = (AsymmetricCipherKeyPair)pemReader.ReadObject();
    rsa.Init(false, keyPair.Private);
    return rsa;
});

string Decrypt(string base64Input)
{
    var buf = Convert.FromBase64String(base64Input);
    byte[] block = _cipher.Value.ProcessBlock(buf, 0, buf.Length);

    return Encoding.UTF8.GetString(block);
}

As for the client side I used the JSEncrypt project which has a extremely simple API:

var crypt = new JSEncrypt();
crypt.setPublicKey('-----BEGIN PUBLIC KEY-----....-----END PUBLIC KEY-----');
var enc = crypt.encrypt($scope.secret);

All the examples keys can be generated using OpenSSL. You can also validate encryption and decryption results too.

# Generate new keys:
> openssl genrsa -out key.pem 1024
> openssl rsa -pubout -in key.pem -out public_key.pem

# Encrypt using public key:
> echo "Text to encript" | openssl rsautl -encrypt -inkey public_key.pem -pubin -out enc.bin
> openssl base64 -e -in out.enc -out enc.txt

# Decrypt using private key:
> openssl base64 -d -in enc.txt -out enc.bin
> openssl rsautl -decrypt -inkey key.pem -in enc.bin

It sounds like it could be easy to find other examples in various languages too. For Objective-C examples check out Launckey documentation for encryption.

You can find a simple web application (in ASP.Net WebAPI) under mtmk GitHub secpassx repository.

Enjoy