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

Question

I've researched a bit about how to achieve what I said in the question and found several APIs but most of them look very complicated and since I'm just a noobie in this area I just want a simple method like:

public String Encrypt(String message, PublicKey publicKey)

Don't know if this can be done? If not then please someone enlighten me another way to achieve this :)

Thank you.

UPDATE:

So far I have only seen that all of the library for OpenPGP encryption require both the public key and private key to do the encrypt while I only want to encrypt with the public key (because I don't have the private key to use it)!

Answer 1

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 :)