PgP Encryption and Decryption using BouncyCastle c#

Question

I've seen a number of posts, followed a number of tutorials but none seems to work. Sometimes, they make reference to some classes which are not found. Can I be pointed to a place where I can get a simple tutorial showing how to encrypt and decrypt a file.

I'm very new to Pgp and any assistance is welcomed.

Answer 1

I know this question is years old but it is still #1 or #2 in Google for searches related to PGP Decryption using Bouncy Castle. Since it seems hard to find a complete, succinct example I wanted to share my working solution here for decrypting a PGP file. This is simply a modified version of the Bouncy Castle example included with their source files.

using System;
using System.IO;
using Org.BouncyCastle.Bcpg.OpenPgp;
using Org.BouncyCastle.Utilities.IO;

namespace PGPDecrypt
{
    class Program
    {
        static void Main(string[] args)
        {
            DecryptFile(
                @"path_to_encrypted_file.pgp",
                @"path_to_secret_key.asc",
                "your_password_here".ToCharArray(), 
                "output.txt"
            );
        }

        private static void DecryptFile(
            string inputFileName,
            string keyFileName,
            char[] passwd,
            string defaultFileName)
        {
            using (Stream input = File.OpenRead(inputFileName),
                   keyIn = File.OpenRead(keyFileName))
            {
                DecryptFile(input, keyIn, passwd, defaultFileName);
            }
        }

        private static void DecryptFile(
            Stream inputStream,
            Stream keyIn,
            char[] passwd,
            string defaultFileName)
        {
            inputStream = PgpUtilities.GetDecoderStream(inputStream);

            try
            {
                PgpObjectFactory pgpF = new PgpObjectFactory(inputStream);
                PgpEncryptedDataList enc;

                PgpObject o = pgpF.NextPgpObject();
                //
                // the first object might be a PGP marker packet.
                //
                if (o is PgpEncryptedDataList)
                {
                    enc = (PgpEncryptedDataList)o;
                }
                else
                {
                    enc = (PgpEncryptedDataList)pgpF.NextPgpObject();
                }

                //
                // find the secret key
                //
                PgpPrivateKey sKey = null;
                PgpPublicKeyEncryptedData pbe = null;
                PgpSecretKeyRingBundle pgpSec = new PgpSecretKeyRingBundle(
                    PgpUtilities.GetDecoderStream(keyIn));

                foreach (PgpPublicKeyEncryptedData pked in enc.GetEncryptedDataObjects())
                {
                    sKey = FindSecretKey(pgpSec, pked.KeyId, passwd);

                    if (sKey != null)
                    {
                        pbe = pked;
                        break;
                    }
                }

                if (sKey == null)
                {
                    throw new ArgumentException("secret key for message not found.");
                }

                Stream clear = pbe.GetDataStream(sKey);

                PgpObjectFactory plainFact = new PgpObjectFactory(clear);

                PgpObject message = plainFact.NextPgpObject();

                if (message is PgpCompressedData)
                {
                    PgpCompressedData cData = (PgpCompressedData)message;
                    PgpObjectFactory pgpFact = new PgpObjectFactory(cData.GetDataStream());

                    message = pgpFact.NextPgpObject();
                }

                if (message is PgpLiteralData)
                {
                    PgpLiteralData ld = (PgpLiteralData)message;

                    string outFileName = ld.FileName;
                    if (outFileName.Length == 0)
                    {
                        outFileName = defaultFileName;
                    }

                    Stream fOut = File.Create(outFileName);
                    Stream unc = ld.GetInputStream();
                    Streams.PipeAll(unc, fOut);
                    fOut.Close();
                }
                else if (message is PgpOnePassSignatureList)
                {
                    throw new PgpException("encrypted message contains a signed message - not literal data.");
                }
                else
                {
                    throw new PgpException("message is not a simple encrypted file - type unknown.");
                }

                if (pbe.IsIntegrityProtected())
                {
                    if (!pbe.Verify())
                    {
                        Console.Error.WriteLine("message failed integrity check");
                    }
                    else
                    {
                        Console.Error.WriteLine("message integrity check passed");
                    }
                }
                else
                {
                    Console.Error.WriteLine("no message integrity check");
                }
            }
            catch (PgpException e)
            {
                Console.Error.WriteLine(e);

                Exception underlyingException = e.InnerException;
                if (underlyingException != null)
                {
                    Console.Error.WriteLine(underlyingException.Message);
                    Console.Error.WriteLine(underlyingException.StackTrace);
                }
            }
        }

        private static PgpPrivateKey FindSecretKey(PgpSecretKeyRingBundle pgpSec, long keyID, char[] pass)
        {
            PgpSecretKey pgpSecKey = pgpSec.GetSecretKey(keyID);

            if (pgpSecKey == null)
            {
                return null;
            }

            return pgpSecKey.ExtractPrivateKey(pass);
        }
    }
}