Use GnuPG Tools or C# Code for PGP Encryption and Signature

For PGP encryption and signature, usually we use PGP command line tools for test purpose and finally use C# application for production.

Mine is a Net Core 2.0 console application using NuGet package PgpCore,  https://github.com/mattosaurus/PgpCore. PgpCore is based on BouncyCastle.NetCore which supports the standard OpenPGP keys. Here w use the popular GnuPG (GPG) tools to generate OpenPGP key pair.

Download and Install GPG for Windows

Download from https://gpg4win.org/download.html. By default the installation will create two folders (here we use command line tools only):

• Gpg4Win UI (Kleopatra): C:\Program Files (x86)\Gpg4win
• Command line tools: C:\Program Files (x86)\GnuPG\bin

Generate a GPG Key Pair

For GnuPG 2.2.1 and above:
    C:\Program Files (x86)\GnuPG\bin> gpg --full-generate-key
For old versions of GnuPG:
    C:\Program Files (x86)\GnuPG\bin> gpg --gen-key

Common GPG Commands

List public keys: gpg --list-key or gpg -k
List private keys: gpg --list-secretkey or gpg -K
List and check signatures:  gpg --check-sigs
To delete a key pair, please delete private first, then delete public:
    Delete a private key: gpg --delete-secret-key keyname
    Delete a public key: gpg --delete-key keyname

Export GPG Public Key File

C:\Program Files (x86)\GnuPG\bin>gpg --export -a -o PGPPublicKey.asc keyname
Please send this public key file to the remote server so that the server can validate our signature.

Export GPG Private Key File (if using C# code)

C:\Program Files (x86)\GnuPG\bin>gpg --export-secret-key -a -o PGPPrivateKey.asc keyname

This private key file will be used by the PgpCore package for file signature.

Please note that we don't need to export the private key if we use GPG command line tools only.

Import, Sign and Trust Remote Server's GPG Public Key (if using GPG command tools)

C:\Program Files (x86)\GnuPG\bin>gpg --import RemoteServersPGPPublicKeyFilePath
C:\Program Files (x86)\GnuPG\bin>gpg --sign-key RemoteServersPGPKeyName
C:\Program Files (x86)\GnuPG\bin>gpg --edit-key RemoteServersPGPKeyName (then type trust and quit)

Please note that we don't need to import remote server's public key if we use C# code for encryption and signature.

Encryption and Signature using GPG command tools

Encrypt and Sign:
    C:\Program Files (x86)\GnuPG\bin>gpg -r RecipientKeyName -a -u SenderKeyName -s -e -o encryptedAndSignedFile sourceFile

Descrypt:
    Decrypt: C:\Program Files (x86)\GnuPG\bin>gpg -d -o destinationFile encryptedFile

Encryption and Signature using C# Code

using PgpCore;

using (PGP pgp = new PGP()) {

    pgp.EncryptFileAndSign(Source, EncryptedAndSignedFile, RemoteServersPGPPublicKeyFilePath, ClientsPGPPrivateKeyFilePath, ClientsPGPPrivateKeyPassPhrase, Armor?, IntegrityCheck?);

}