using System;

using System.Security.Cryptography;

​

class EcSignatureString {

    static void Main() {

​

        Console.WriteLine("EC signature string (ECDSA with SHA256)");

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

        var dataToSign = System.Text.Encoding.UTF8.GetBytes(dataToSignString);

​

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

​

        try {

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

            string ecPrivateKeyPem = loadEcPrivateKeyPem();

            string signatureBase64 = ecSignP1363ToBase64(ecPrivateKeyPem, dataToSign);

            Console.WriteLine("used private key:");

            Console.WriteLine(ecPrivateKeyPem);

            Console.WriteLine("\nsignature (Base64): " + signatureBase64);

​

            // verify

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

            string signatureReceivedBase64 = signatureBase64;

            string ecPublicKeyPem = loadEcPublicKeyPem();

            Console.WriteLine("used public key:");

            Console.WriteLine(ecPublicKeyPem);

            bool signatureVerified = ecVerifySignatureFromBase64(ecPublicKeyPem, dataToSign, signatureReceivedBase64);

            Console.WriteLine("\nsignature verified: " + signatureVerified);

        }

        catch(ArgumentNullException) {

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

        }

    }

​

    private static string ecSignP1363ToBase64(string ecPrivateKeyPem, byte[] messageByte) {

        byte[] ecPrivateKeyByte = getEcPrivateKeyEncodedFromPem(ecPrivateKeyPem);

        var ecDsaKeypair = ECDsa.Create(ECCurve.NamedCurves.nistP256);

        int _out;

        ecDsaKeypair.ImportPkcs8PrivateKey(ecPrivateKeyByte, out _out);

        byte[] hashedData = null;

        byte[] signature = null;

        HashAlgorithm hashAlgo = new SHA256Managed();

        hashedData = hashAlgo.ComputeHash(messageByte);

        signature = ecDsaKeypair.SignHash(hashedData);

        return Base64Encoding(signature);

    }

​

    private static bool ecVerifySignatureFromBase64(string ecPublicKeyPem, byte[] messageByte, String signatureBase64) {

        byte[] hashedData = null;

        HashAlgorithm hashAlgo = new SHA256Managed();

        hashedData = hashAlgo.ComputeHash(messageByte);

        var ecDsaVerify = ECDsa.Create(ECCurve.NamedCurves.nistP256);

        byte[] ecPublicKeyByte = getEcPublicKeyFromPem(ecPublicKeyPem);

        ecDsaVerify.ImportSubjectPublicKeyInfo(ecPublicKeyByte, out _);

        return ecDsaVerify.VerifyHash(hashedData, Base64Decoding(signatureBase64));

    }

​

    private static byte[] getEcPrivateKeyEncodedFromPem(string ecPrivateKeyPem) {

        string ecPrivateKeyHeaderPem = "-----BEGIN EC PRIVATE KEY-----\n";

        string ecPrivateKeyFooterPem = "-----END EC PRIVATE KEY-----";

        string ecPrivateKeyDataPem = ecPrivateKeyPem.Replace(ecPrivateKeyHeaderPem, "").Replace(ecPrivateKeyFooterPem, "").Replace("\n", "");

        return Base64Decoding(ecPrivateKeyDataPem);

    }

​

    private static byte[] getEcPublicKeyFromPem(string ecPublicKeyPem) {

        string ecPublicKeyHeaderPem = "-----BEGIN PUBLIC KEY-----\n";

        string ecPublicKeyFooterPem = "-----END PUBLIC KEY-----";

        string ecPublicKeyDataPem = ecPublicKeyPem.Replace(ecPublicKeyHeaderPem, "").Replace(ecPublicKeyFooterPem, "").Replace("\n", "");

        return Base64Decoding(ecPublicKeyDataPem);

    }

​

    private static string loadEcPrivateKeyPem() {

        // this is a sample key - don't worry !

        return "-----BEGIN EC PRIVATE KEY-----\n"

            + "MEECAQAwEwYHKoZIzj0CAQYIKoZIzj0DAQcEJzAlAgEBBCAU2f8tzo99Z1HoxJlY\n"

            + "96yXUhFY5vppVjw1iPKRfk1wHA==\n"

            + "-----END EC PRIVATE KEY-----";

    }

​

    private static string loadEcPublicKeyPem() {

        // this is a sample key - don't worry !

        return "-----BEGIN PUBLIC KEY-----\n"

            + "MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEzb7yAFWup6iDqJiEq764rAumsV2M\n"

            + "rspZxaP3WGpwHaC4Uff3N4UbJZF7Zac1c6W7KJl0eeCP0205Q3UEpwxndQ==\n"

            + "-----END PUBLIC KEY-----";

    }

​

    static string Base64Encoding(byte[] input) {

        return Convert.ToBase64String(input);

    }

​

    static byte[] Base64Decoding(String input) {

        return Convert.FromBase64String(input);

    }

}