C# How to Simply Encrypt a Text File With a Pgp Public Key

C# How to simply encrypt a text file with a PGP Public Key?

I found a tutorial here but it requires both Secret Key and Public Key to encrypt data. However I've modified the codes a bit to only require public key (no signing, no compress) and thought I should publish it here in case anyone also looking for a solution for this question. Belows is the modified codes, all the credits for the author - Mr. Kim.

public class PgpEncrypt
    {
        private PgpEncryptionKeys m_encryptionKeys;
        private const int BufferSize = 0x10000; 
        /// <summary>
        /// Instantiate a new PgpEncrypt class with initialized PgpEncryptionKeys.
        /// </summary>
        /// <param name="encryptionKeys"></param>
        /// <exception cref="ArgumentNullException">encryptionKeys is null</exception>
        public PgpEncrypt(PgpEncryptionKeys encryptionKeys)
        {
            if (encryptionKeys == null)
            {
                throw new ArgumentNullException("encryptionKeys", "encryptionKeys is null.");
            }
            m_encryptionKeys = encryptionKeys;
        }
        /// <summary>
        /// Encrypt and sign the file pointed to by unencryptedFileInfo and
        /// write the encrypted content to outputStream.
        /// </summary>
        /// <param name="outputStream">The stream that will contain the
        /// encrypted data when this method returns.</param>
        /// <param name="fileName">FileInfo of the file to encrypt</param>
        public void Encrypt(Stream outputStream, FileInfo unencryptedFileInfo)
        {
            if (outputStream == null)
            {
                throw new ArgumentNullException("outputStream", "outputStream is null.");
            }
            if (unencryptedFileInfo == null)
            {
                throw new ArgumentNullException("unencryptedFileInfo", "unencryptedFileInfo is null.");
            }
            if (!File.Exists(unencryptedFileInfo.FullName))
            {
                throw new ArgumentException("File to encrypt not found.");
            }
            using (Stream encryptedOut = ChainEncryptedOut(outputStream))
            {
                using (Stream literalOut = ChainLiteralOut(encryptedOut, unencryptedFileInfo))
                using (FileStream inputFile = unencryptedFileInfo.OpenRead())
                {
                    WriteOutput(literalOut, inputFile);
                }
            }
        }

        private static void WriteOutput(Stream literalOut,
            FileStream inputFile)
        {
            int length = 0;
            byte[] buf = new byte[BufferSize];
            while ((length = inputFile.Read(buf, 0, buf.Length)) > 0)
            {
                literalOut.Write(buf, 0, length);
            }
        }

        private Stream ChainEncryptedOut(Stream outputStream)
        {
            PgpEncryptedDataGenerator encryptedDataGenerator;
            encryptedDataGenerator =
                new PgpEncryptedDataGenerator(SymmetricKeyAlgorithmTag.TripleDes,
                                              new SecureRandom());
            encryptedDataGenerator.AddMethod(m_encryptionKeys.PublicKey);
            return encryptedDataGenerator.Open(outputStream, new byte[BufferSize]);
        }

        private static Stream ChainLiteralOut(Stream encryptedOut, FileInfo file)
        {
            PgpLiteralDataGenerator pgpLiteralDataGenerator = new PgpLiteralDataGenerator();
            return pgpLiteralDataGenerator.Open(encryptedOut, PgpLiteralData.Binary, 

file);
            } 
}

Of course to run these codes you have to include BouncyCastle library in your project.

I've tested encrypting and then decrypting and it runs fine :)

Using two public keys to encrypt a file

On high level (if you use any PGP API), yes, you can pass two or more public PGP keys to OpenPGP API (or software) and have the data encrypted. Then you would be able to use a PGP secret key that corresponds to any of used public PGP keys to decrypt the data.

On lower level - OpenPGP always generates a symmetric key for encryption of data, and then this key is encrypted using one or more public PGP keys, consequently there's no difference how many keys to use.

Now, what to use depends on what platform and development environment you are using (as this is a programming site we assume that you are going to encrypt data in code). For Linux and C there exists GnuPG library. For Java and C# there's some PGP support in BouncyCastle. Finally, OpenPGPBlackbox of our SecureBlackbox library provides full scope of OpenPGP functionality for a number of platforms and languages, including .NET, VCL, ActiveX and C++.

On a side note, the answer you've accepted is completely wrong so I strongly suggest de-accepting it.

.net core PGP Encryption Decryption

I'm using by this way:

I think can help you!

Helper:

public static void EncryptPgpFile(string inputFile, string outputFile, string publicKeyFile, bool armor, bool withIntegrityCheck)
{
    using (Stream publicKeyStream = File.OpenRead(publicKeyFile))
    {
        PgpPublicKey pubKey = ReadPublicKey(publicKeyStream);

        using (MemoryStream outputBytes = new MemoryStream())
        {
            PgpCompressedDataGenerator dataCompressor = new PgpCompressedDataGenerator(CompressionAlgorithmTag.Zip);
            PgpUtilities.WriteFileToLiteralData(dataCompressor.Open(outputBytes), PgpLiteralData.Binary, new FileInfo(inputFile));

            dataCompressor.Close();
            PgpEncryptedDataGenerator dataGenerator = new PgpEncryptedDataGenerator(SymmetricKeyAlgorithmTag.Cast5, withIntegrityCheck, new SecureRandom());

            dataGenerator.AddMethod(pubKey);
            byte[] dataBytes = outputBytes.ToArray();

            using (Stream outputStream = File.Create(outputFile))
            {
                if (armor)
                {
                    using (ArmoredOutputStream armoredStream = new ArmoredOutputStream(outputStream))                   
                    using (Stream outputStream = dataGenerator.Open(armoredStream, dataBytes.Length))
                        outputStream.Write(dataBytes, 0, dataBytes.Length);
                }
                else
                {
                    using (Stream outputStream = dataGenerator.Open(armoredStream, dataBytes.Length))
                        outputStream.Write(dataBytes, 0, dataBytes.Length);
                }
            }
        }
    }
}

private static PgpPublicKey ReadPublicKey(Stream inputStream)
{
    inputStream = PgpUtilities.GetDecoderStream(inputStream);
    PgpPublicKeyRingBundle pgpPub = new PgpPublicKeyRingBundle(inputStream);

    foreach (PgpPublicKeyRing keyRing in pgpPub.GetKeyRings())
    {
        foreach (PgpPublicKey key in keyRing.GetPublicKeys())
        {
            if (key.IsEncryptionKey)
                return key;
        }
    }

    throw new ArgumentException("Can't find encryption key in key ring.");
}

Usage:

EncryptPgpFile(inputFile, outputFile, publicKeyPath, true, true);

How to encrypt for OpenPGP keys using C#?

Although OpenPGP takes advantage of RSA and other standard algorithms, you cannot use the default C# RSACryptoServiceProvider. RSA is only one possible algorithm for OpenPGP, and furthermore you need some symmetric encryption algorithm like AES (which would also be available). But there are further problems: you'd need to implement a generator for the OpenPGP message format, and OpenPGP defined its own cipher mode. Implementing all this on your own will not only be a hassle involving incompatibilities (an incomplete list exists in the RFC, but also has lots of ways to include security issues (and a bunch of further interesting attacks have been proposed and mitigated with existing implementations like GnuPG).

If you want to use OpenPGP from C#, in the end it boils down to following alternatives:

• use GnuPG through GPGME (but the wrapper still seems to be in alpha state),
• use BouncyCastle which has native implementations of several cryptographic protocols including OpenPGP for both C# and Java, but the C#-implementation seems to be less wide-spread and is not as capable,
• SharpPrivacy is another implementation, but seems dead
• interface the GnuPG command line directly

All of those have advantages and disadvantages. Probably BouncyCastle will be the best way to go, if it does not support the required features, you'll probably have to drop calling command GnuPG on the command line.

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