Get SHA1 for Public key of SSL Cert Xamarin.iOS

sslcertpinningios.cs

private byte[] rsa2048Asn1Header = new byte[] {0x30, 0x82, 0x01, 0x22, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86,
              0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x82, 0x01, 0x0f, 0x00};
 
public override void DidReceiveChallenge(NSUrlSession session, NSUrlAuthenticationChallenge challenge, Action<NSUrlSessionAuthChallengeDisposition, NSUrlCredential> completionHandler)
{    
	  //Sample implementation using SHA1Managed
    var secServerChain = challenge.ProtectionSpace.ServerSecTrust;
	  
	  int certCount = challenge.ProtectionSpace.ServerSecTrust.Count;
	  
	  var certData = secServerChain[i];
	  var policy = SecPolicy.CreateBasicX509Policy();
	  var secTrust = new SecTrust(certData, policy);

	  //get public key 
	  var publicKey = secTrust.GetPublicKey().GetExternalRepresentation();
	  var publicKeyBytes = new byte[publicKey.Length];
	  System.Runtime.InteropServices.Marshal.Copy(publicKey.Bytes, publicKeyBytes, 0, Convert.ToInt32(publicKey.Length));

	  //adding rsa2048Asn1 Header
	  var header = NSData.FromArray(rsa2048Asn1Header);
	  var headerBytes = new byte[header.Length];
	  System.Runtime.InteropServices.Marshal.Copy(header.Bytes, headerBytes, 0, Convert.ToInt32(header.Length));

	  //combine rsa2048Asn1 header and public key into one item
	  var allBytes = new byte[headerBytes.Length + publicKeyBytes.Length];
	  Buffer.BlockCopy(headerBytes, 0, allBytes, 0, headerBytes.Length);
	  Buffer.BlockCopy(publicKeyBytes, 0, allBytes, headerBytes.Length, publicKeyBytes.Length);
	  
	  string sha1forPublicKey;
	  using (var sha1 = new SHA1Managed())
	  {
		  var asnEncodedData = new AsnEncodedData(allBytes);

		  var hash = sha1.ComputeHash(asnEncodedData.RawData);
		  sha1forPublicKey = Convert.ToBase64String(hash);
	  }	  
}