Digital signature with itextsharp

Question

Can someone explain the following code..

What will that return statement do.

 public byte[] sign(string text)
 {
    string password = "1234";
    X509Certificate2 cert = new X509Certificate2("c:\\certificate.pfx", password);
    RSACryptoServiceProvider crypt = (RSACryptoServiceProvider)cert.PrivateKey;
    SHA1Managed sha1 = new SHA1Managed();
    UnicodeEncoding encoding = new UnicodeEncoding();
    byte[] data = encoding.GetBytes(text);
    byte[] hash = sha1.ComputeHash(data);
    return crypt.SignHash(hash, CryptoConfig.MapNameToOID("SHA1"));
}

Answer 1

    public byte[] sign(string text)
         {
//Password for the PFX certificate
            string password = "1234";
//Importing the PFX certificate that contains the private key which will be used for creating the digital signature
            X509Certificate2 cert = new X509Certificate2("c:\\certificate.pfx", password);
//declaring RSA cryptographic service provider
            RSACryptoServiceProvider crypt = (RSACryptoServiceProvider)cert.PrivateKey;
//cryptographic hash of type SHA1
            SHA1Managed sha1 = new SHA1Managed();
//encoding the data to be signed
            UnicodeEncoding encoding = new UnicodeEncoding();
            byte[] data = encoding.GetBytes(text);
//generate Hash
            byte[] hash = sha1.ComputeHash(data);
//sign Hash
            return crypt.SignHash(hash, CryptoConfig.MapNameToOID("SHA1"));
        }

Answer 2

The SignHash(byte[], string) method will compute the signature for the hash value you pass as the first argument based on the private key read from your certificate. See here:

RSACryptoServiceProvider.SignHash Method

The result of this (which is subsequently returned) will be a byte[] containing the signature which you can send along with your data so that the signature can be verified by someone else using your public key.