using System;

using System.Security.Cryptography;

​

class EcSignatureString {

    static void Main() {

    Console.WriteLine("EC signature curve secp256r1 / P-256 string");

    string dataToSignString = "The quick brown fox jumps over the lazy dog";

    byte[] dataToSign = System.Text.Encoding.UTF8.GetBytes(dataToSignString);

    Console.WriteLine("dataToSign: " + dataToSignString);

    try {

        Console.WriteLine("\n* * * sign the plaintext with the EC private key * * *");

​

        ECDsaCng ecDsaKeypair = new ECDsaCng(256);

        Console.WriteLine("EC keysize: " + ecDsaKeypair.KeySize);

        byte[] hashedData = null;

        byte[] signature = null;

        // create new instance of SHA256 hash algorithm to compute hash

        HashAlgorithm hashAlgo = new SHA256Managed();

        hashedData = hashAlgo.ComputeHash(dataToSign);

        // sign Data using private key 

        signature = ecDsaKeypair.SignHash(hashedData);

        string signatureBase64 = Convert.ToBase64String(signature);

        Console.WriteLine("signature (Base64): " + signatureBase64);

        // get public key from private key

        string ecDsaPublicKeyParametersXml = ecDsaKeypair.ToXmlString(ECKeyXmlFormat.Rfc4050);

        // verify

        Console.WriteLine("\n* * *verify the signature against hash of plaintext with the EC public key * * *");

        ECDsaCng ecDsaVerify = new ECDsaCng();

        bool signatureVerified = false;

        ecDsaVerify.FromXmlString(ecDsaPublicKeyParametersXml, ECKeyXmlFormat.Rfc4050);

        signatureVerified = ecDsaVerify.VerifyHash(hashedData, signature);

        Console.WriteLine("signature verified: " + signatureVerified);

        }

        catch(ArgumentNullException) {

            Console.WriteLine("The data was not signed or verified");

        }

    }

}