HOW to Sign data in C# in wp8

Question

I am developing wp8 app. I send public key to server in 1st login request.In response server sends token (its simple base64 string with around 1200-1300 characters) which I need to sign with private key and send back to server in next request.Now server verifies that token with corresponding public key I sent in 1st request. I have working java code which does above thing.

String privateKey = sharedPref.getString("privateKey", "");

byte [] decoded = Base64.decode(privateKey, Base64.NO_WRAP);

KeyFactory kf = KeyFactory.getInstance("RSA");
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(decoded);
PrivateKey privateKeyNew = kf.generatePrivate(keySpec);

String tokenSp = sharedPref.getString("token", "");
byte[] tokenBytes = tokenSp.getBytes();
Signature dsa = Signature.getInstance("SHA1withRSA");
dsa.initSign(privateKeyNew);
dsa.update(tokenBytes);
byte[] signedData = dsa.sign();

ByteArrayOutputStream baos = new ByteArrayOutputStream();
baos.write(tokenBytes);
baos.write(signedData);

byte[] finalout = baos.toByteArray();
signedToken = new String(Base64.encode(finalout, 0, finalout.length, Base64.NO_WRAP));

I want achieve same in c#. Code I have written is :

UnicodeEncoding ByteConverter = new UnicodeEncoding();

CspParameters parameters = new CspParameters();
parameters.KeyContainerName = "MyContainer";
RSACryptoServiceProvider obj = new RSACryptoServiceProvider(parameters);

byte[] dataToEncrypt=ByteConverter.GetBytes(s[0]);
byte[] SignedData=obj.SignData(dataToEncrypt, "SHA256");

MemoryStream stream = new MemoryStream();
stream.Write(dataToEncrypt,0,dataToEncrypt.Count());
stream.Write(SignedData,0,SignedData.Count());

byte[] finalBytesToSend = stream.ToArray();

string s2 = Convert.ToBase64String(finalBytesToSend);
return s2;

And to server I send "SHA256" as public key to verify.Is it correct what I have done in c#?

score 0 · Answer 1 · answered Feb 13 '14 at 14:13

I believe what you need is something like below. You may need to examine publicKeyXml and work a little about the format.

// create a RSA provider with a 1024 bits key
using(RSACryptoServiceProvider rsaProv = new RSACryptoServiceProvider(1024))
{
    // export public key and send it to server to obtain base64 token
    string publicKeyXml = rsaProv.ToXmlString(false);
    string base64TokenFromServer = GetTokenFromServer(publicKeyXml);

    // decode base64 token
    byte[] tokenBytes = Convert.FromBase64String(base64TokenFromServer);

    // sign token bytes using RSA provider's private key and SHA1
    byte[] tokenSignatureBytes;
    using (var ms = new MemoryStream(tokenBytes))
    {
        tokenSignatureBytes = rsaProv.SignData(ms, SHA1.Create());
    }

    // concat token bytes and signature bytes
    byte[] finalOut;
    using (var ms = new MemoryStream())
    {
        ms.Write(tokenBytes, 0, tokenBytes.Length);
        ms.Write(tokenSignatureBytes, 0, tokenSignatureBytes.Length);
        ms.Flush();
        finalOut = ms.ToArray();
    }

    // encode final out to base64
    string signedToken = Convert.ToBase64String(finalOut);
}

While Signing there is no method named Create() in abstarct SHA1 class in wp8 api — Vaibhav, Feb 14 '14 at 06:42
This is standard .NET Framework code. Can you try `new System.Security.Cryptography.SHA1Managed()` — Mehmet Ataş, Feb 14 '14 at 07:44
SHA1,SHA1managed,SHA256,SHA256Managed are there.But they do not have create method.I want to implement in windows phone 8. — Vaibhav, Feb 17 '14 at 10:34

HOW to Sign data in C# in wp8

1 Answers1