Add C# signing example using Bouncy Castle library (qzind#880)

assets/signing/sign-message.bouncycastle.cs

@@ -0,0 +1,60 @@
+// #########################################################
+// #             WARNING   WARNING   WARNING               #
+// #########################################################
+// #                                                       #
+// # This file is intended for demonstration purposes      #
+// # only.                                                 #
+// #                                                       #
+// # It is the SOLE responsibility of YOU, the programmer  #
+// # to prevent against unauthorized access to any signing #
+// # functions.                                            #
+// #                                                       #
+// # Organizations that do not protect against un-         #
+// # authorized signing will be black-listed to prevent    #
+// # software piracy.                                      #
+// #                                                       #
+// # -QZ Industries, LLC                                   #
+// #                                                       #
+// #########################################################
+
+using System;
+using System.Text;
+using Org.BouncyCastle.Crypto;
+using Org.BouncyCastle.OpenSsl;
+using Org.BouncyCastle.Security;
+
+
+// Public method for signing the input string with the private key
+// ===============================================================
+
+string privateKey = "private-key.pem"; // PKCS#8 PEM file
+
+string SignMessage(string msg)
+{
+    // Convert the input string to a byte array
+    byte[] input = Encoding.ASCII.GetBytes(msg);
+
+    // Initialize the signer with the algorithm and the private key
+    ISigner sig = SignerUtilities.GetSigner("SHA512withRSA");
+    sig.Init(true, getPrivateKey());
+
+    // Generate signature and return it as a base64 string
+    sig.BlockUpdate(input, 0, input.Length);
+    return Convert.ToBase64String(sig.GenerateSignature());
+}
+
+AsymmetricKeyParameter getPrivateKey() {
+    using (var reader = System.IO.File.OpenText(privateKey))
+        return (new PemReader(reader, null).ReadObject() as AsymmetricCipherKeyPair).Private;
+}
+
+
+// Public method for returning the certificate
+// ===========================================
+
+string certificate = "digital-certificate.txt";
+
+string GetCertificate() {
+    using (var reader = System.IO.File.OpenText(certificate))
+        return reader.ReadToEnd();
+}