1

i have a rsa private key and i wanted to sign the data with it. i wrote this code but it doesn't work:

public string Sign(string text)
{
    var sha = new SHA1Managed();
    var encoding = new UTF8Encoding();
    var bytes = encoding.GetBytes(text);
    var digest = sha.ComputeHash(bytes);

    var cert = new X509Certificate2(Convert.FromBase64String(PermissionKey));
    var rsa = (RSACryptoServiceProvider)cert.PrivateKey;
    var rsaFormatter = new RSAPKCS1SignatureFormatter(rsa);
    rsaFormatter.SetHashAlgorithm("SHA1");

    var SignedHashValue = rsa.SignData(digest, sha);
    return Convert.ToBase64String(SignedHashValue).Replace("=", "") + "\n";
}

i get this exception:

'Cannot find the requested object.

when i tried to create X509Certificate2:

var cert = new X509Certificate2(Convert.FromBase64String(PermissionKey));

PS: I'm tiring to simulate the android code in c#. here is the main android:

public static PrivateKey makePrivateKeyFromPermissionKey(String permissionKey)
        throws InvalidKeySpecException, NoSuchProviderException, NoSuchAlgorithmException {
    KeyFactory keyFactory;
    byte[] certificate = decode(
            permissionKey
                    .replaceAll("\\n", "")
                    .replace("-----BEGIN RSA PRIVATE KEY-----", "")
                    .replace("-----END RSA PRIVATE KEY-----", "")
    );
    if (Build.VERSION.SDK_INT < 27) {
        keyFactory = KeyFactory.getInstance("RSA", "BC");
    } else {
        keyFactory = KeyFactory.getInstance("RSA");
    }
    return keyFactory.generatePrivate(new PKCS8EncodedKeySpec(certificate));
}
President James K. Polk
  • 40,516
  • 21
  • 95
  • 125
Mohammad
  • 2,724
  • 6
  • 29
  • 55
  • 1
    Possible duplicate of [How do I use a private key in C#? "Cannot find the requested object."](https://stackoverflow.com/questions/13754685/how-do-i-use-a-private-key-in-c-cannot-find-the-requested-object) – bartonjs Nov 18 '18 at 18:48
  • 1
    The Android code contains bullshit. It doesn't contain a certificate at all; PKCS#8 just encoded the private key (as the PEM header indicates). It also *just returns* a private key - and such a private key does not include a certificate. – Maarten Bodewes Nov 19 '18 at 02:27

1 Answers1

0

I found the answer. i used CSharp_easy_RSA_PEM library in order to read the private key.

public static string Sign(string text)
{
    var privateRSAkey = Crypto.DecodeRsaPrivateKey(PermissionKey);
    var rsa = privateRSAkey;

    var hasher = new SHA1CryptoServiceProvider();
    var e = new UTF8Encoding(true);
    var bytesFirmados = rsa.SignData(e.GetBytes(text), hasher);

    return Convert.ToBase64String(bytesFirmados);
}
Mohammad
  • 2,724
  • 6
  • 29
  • 55