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

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 on开发者_运维百科ly want to encrypt with the public key (because I don't have the private key to use it)!

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 :)

Here is perhaps a cleaner approach:

        var pkr = asciiPublicKeyToRing(ascfilein);
        if (pkr != null)
        {
            try
            {
                EncryptFile(
                tbUnencryptedFile.Text, tbEncryptedFile.Text, getFirstPublicEncryptionKeyFromRing(pkr), true, true);

                MessageBox.Show("File Encrypted.");
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error: " + ex.Message);
            }
        }
        else
        {
             MessageBox.Show(ascfilein + " is not a public key.");
        }

    private PgpPublicKeyRing asciiPublicKeyToRing(string ascfilein)
    {
        using (Stream pubFis = File.OpenRead(ascfilein))
        {
            var pubArmoredStream = new ArmoredInputStream(pubFis);

            PgpObjectFactory pgpFact = new PgpObjectFactory(pubArmoredStream);
            Object opgp = pgpFact.NextPgpObject();
            var pkr = opgp as PgpPublicKeyRing;
            return pkr;
        }
    }

    private PgpPublicKey getFirstPublicEncryptionKeyFromRing(PgpPublicKeyRing pkr)
    {
        foreach (PgpPublicKey k in pkr.GetPublicKeys())
        {
            if (k.IsEncryptionKey)
                return k;
        }
        throw new ArgumentException("Can't find encryption key in key ring.");
    }

    public static void EncryptFile(string inputFile, string outputFile, PgpPublicKey encKey, bool armor,
        bool withIntegrityCheck)
    {
        using (MemoryStream bOut = new MemoryStream())
        {
            PgpCompressedDataGenerator comData = new PgpCompressedDataGenerator(CompressionAlgorithmTag.Zip);
            PgpUtilities.WriteFileToLiteralData(comData.Open(bOut), PgpLiteralData.Binary,
                new FileInfo(inputFile));

            comData.Close();
            PgpEncryptedDataGenerator cPk = new PgpEncryptedDataGenerator(SymmetricKeyAlgorithmTag.Aes256,
                withIntegrityCheck, new SecureRandom());

            cPk.AddMethod(encKey);
            byte[] bytes = bOut.ToArray();

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

Did you take a look at the bouncycastle pgp? http://www.bouncycastle.org/

There is a source example here of enrypting a file taken from the BouncyCastle site: Need example for BouncyCastle PGP File encryption in C#

If you want to do both encryption and decryption in dotnet core, this is the article I followed: https://nightbaker.github.io/pgp/cryptography/.net/core/2019/02/08/pgp-encryption/

The encryption part does not require the private key.

All credits go to the original author NightBaker.

Install-Package  BouncyCastle.NetCore
Install-Package  BouncyCastle.NetCoreSdk

public class Pgp
{
    public static void EncryptFile(
        string outputFileName,
        string inputFileName,
        string encKeyFileName,
        bool armor,
        bool withIntegrityCheck)
    {
        PgpPublicKey encKey = PgpExampleUtilities.ReadPublicKey(encKeyFileName);

        using (Stream output = File.Create(outputFileName))
        {
            EncryptFile(output, inputFileName, encKey, armor, withIntegrityCheck);
        }
    }

    private static void EncryptFile(
        Stream outputStream,
        string fileName,
        PgpPublicKey encKey,
        bool armor,
        bool withIntegrityCheck)
    {
        if (armor)
        {
            outputStream = new ArmoredOutputStream(outputStream);
        }

        try
        {
            byte[] bytes = PgpExampleUtilities.CompressFile(fileName, CompressionAlgorithmTag.Zip);

            PgpEncryptedDataGenerator encGen = new PgpEncryptedDataGenerator(
                SymmetricKeyAlgorithmTag.Cast5, withIntegrityCheck, new SecureRandom());
            encGen.AddMethod(encKey);

            Stream cOut = encGen.Open(outputStream, bytes.Length);

            cOut.Write(bytes, 0, bytes.Length);
            cOut.Close();

            if (armor)
            {
                outputStream.Close();
            }
        }
        catch (PgpException e)
        {
            Console.Error.WriteLine(e);

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

public class PgpExampleUtilities
{
    internal static PgpPublicKey ReadPublicKey(string fileName)
    {
        using (Stream keyIn = File.OpenRead(fileName))
        {
            return ReadPublicKey(keyIn);
        }
    }

    internal static PgpPublicKey ReadPublicKey(Stream input)
    {
        PgpPublicKeyRingBundle pgpPub = new PgpPublicKeyRingBundle(
            PgpUtilities.GetDecoderStream(input));

        //
        // we just loop through the collection till we find a key suitable for encryption, in the real
        // world you would probably want to be a bit smarter about this.
        //

        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.");
    }


    internal static byte[] CompressFile(string fileName, CompressionAlgorithmTag algorithm)
    {
        MemoryStream bOut = new MemoryStream();
        PgpCompressedDataGenerator comData = new PgpCompressedDataGenerator(algorithm);
        PgpUtilities.WriteFileToLiteralData(comData.Open(bOut), PgpLiteralData.Binary,
            new FileInfo(fileName));
        comData.Close();
        return bOut.ToArray();
    }
}

Usage:

Pgp.EncryptFile("Resources/output.txt", "Resources/input.txt", "Resources/publicKey.txt", true, true);

If you are looking for a simple dotnet library to do pgp encryption take a look at PgpCore. Its a wrapper around Bouncy Castle - just making it a little bit easier than needing to know the internals of Bouncy Castle.