using System;

using System.Security.Cryptography;

​

class EcSignatureString {

    static void Main() {

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

    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 * * *");

​

    // get the private key

    string ecPrivateKeyPem = loadEcPrivateKeyPem();

    //CngKey ecPrivateKey = getEcPrivateKeyFromPem(ecPrivateKeyPem);

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

    //ecDsaKeypair = ECDsa.Create(ecPrivateKey);

​

    // Normally here:

    //ecDsaKeypair.ImportFromPem();

    int _out;

    byte[] ecPrivateKeyByte = getEcPrivateKeyEncodedFromPem(ecPrivateKeyPem);

    ecDsaKeypair.ImportPkcs8PrivateKey(ecPrivateKeyByte, out _out);

​

    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 ecDsaPublicKeyParameters = Convert.ToBase64String(ecDsaKeypair.ExportSubjectPublicKeyInfo());

​

    // verify

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

​

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

    bool signatureVerified = false;

​

    // Normally here:

    //ecDsaKeypair.ImportFromPem()

    //var publicKey = Convert.FromBase64String(ecDsaPublicKeyParameters);

    // get the private key

    string ecPublicKeyPem = loadEcPublicKeyPem();

    byte[] publicKeyByte = getEcPublicKeyFromPem(ecPublicKeyPem);

    ecDsaVerify.ImportSubjectPublicKeyInfo(publicKeyByte, out _);

​

    signatureVerified = ecDsaVerify.VerifyHash(hashedData, signature);

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

}

catch (ArgumentNullException)

{

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

}

  }

    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);

  }

}

​