Bouncy Castle C# PGP Decryption example

Question

I have been looking all day yesterday, and I can't seem to find a working example of PGP decryption using Bouncy Castle in c#

Answer 1

Finally got it to work. The main issue I had with other samples was the fact that the private key ring I had included a key for signing which was coming up first when trying to load the key for decryption. This is why why I had to add a check for the ElGamalPrivateKeyParameters type on the key.

Below is my code. Not very clean, but it works.

        private static PgpPrivateKey GetPrivateKey(string privateKeyPath)
    {
        using (Stream keyIn = File.OpenRead(privateKeyPath))
        using (Stream inputStream = PgpUtilities.GetDecoderStream(keyIn))
        {
            PgpSecretKeyRingBundle secretKeyRingBundle = new PgpSecretKeyRingBundle(inputStream);

            PgpSecretKey key = null;
            foreach (PgpSecretKeyRing kRing in secretKeyRingBundle.GetKeyRings())
            {
                foreach (PgpSecretKey secretKey in kRing.GetSecretKeys())
                {
                    PgpPrivateKey privKey = secretKey.ExtractPrivateKey("1234567890".ToCharArray());

                    if (privKey.Key.GetType() ==
                        typeof (Org.BouncyCastle.Crypto.Parameters.ElGamalPrivateKeyParameters))
                        //Org.BouncyCastle.Crypto.Parameters.ElGamalPrivateKeyParameters
                    {
                        return privKey;
                    }
                }

            }
        }
        
        return null;
    }





    public static void Decrypt(Stream input, string outputpath, String privateKeyPath)
    {
        input = PgpUtilities.GetDecoderStream(input);
        try
        {
            PgpObjectFactory pgpObjF = new PgpObjectFactory(input);
            PgpEncryptedDataList enc;
            PgpObject obj = pgpObjF.NextPgpObject();
            if (obj is PgpEncryptedDataList)
            {
                enc = (PgpEncryptedDataList)obj;
            }
            else
            {
                enc = (PgpEncryptedDataList)pgpObjF.NextPgpObject();
            }

       


            
            PgpPrivateKey privKey = GetPrivateKey(privateKeyPath);


            PgpPublicKeyEncryptedData pbe = enc.GetEncryptedDataObjects().Cast<PgpPublicKeyEncryptedData>().First();
            Stream clear;
            clear = pbe.GetDataStream(privKey);
            PgpObjectFactory plainFact = new PgpObjectFactory(clear);
            PgpObject message = plainFact.NextPgpObject();
            if (message is PgpCompressedData)
            {
                PgpCompressedData cData = (PgpCompressedData)message;
                Stream compDataIn = cData.GetDataStream();
                PgpObjectFactory o = new PgpObjectFactory(compDataIn);
                message = o.NextPgpObject();
                if (message is PgpOnePassSignatureList)
                {
                    message = o.NextPgpObject();
                    PgpLiteralData Ld = null;
                    Ld = (PgpLiteralData)message;
                    Stream output = File.Create(outputpath + "\\" + Ld.FileName);
                    Stream unc = Ld.GetInputStream();
                    Streams.PipeAll(unc, output);
                }
                else
                {
                    PgpLiteralData Ld = null;
                    Ld = (PgpLiteralData)message;
                    //Stream output = File.Create(outputpath + "\\" + Ld.FileName);
                    Stream output = File.Create(outputpath);
                    Stream unc = Ld.GetInputStream();
                    Streams.PipeAll(unc, output);
                }
            }
        }
        catch (Exception e)
        {
            throw new Exception(e.Message);
        }
    }