golang gpg/openpgp encryption/decryption example

simple-gpg-enc.go

package main

import (
    "bytes"
    "code.google.com/p/go.crypto/openpgp"
    "encoding/base64"
    "io/ioutil"
    "log"
    "os"
)

// create gpg keys with
// $ gpg --gen-key
// ensure you correct paths and passphrase

const mySecretString = "this is so very secret!"
const prefix, passphrase = "/Users/stuart-warren/", "1234"
const secretKeyring = prefix + ".gnupg/secring.gpg"
const publicKeyring = prefix + ".gnupg/pubring.gpg"

func encTest(secretString string) (string, error) {
    log.Println("Secret to hide:", secretString)
    log.Println("Public Keyring:", publicKeyring)

    // Read in public key
    keyringFileBuffer, _ := os.Open(publicKeyring)
    defer keyringFileBuffer.Close()
    entityList, err := openpgp.ReadKeyRing(keyringFileBuffer)
    if err != nil {
        return "", err
    }

    // encrypt string
    buf := new(bytes.Buffer)
    w, err := openpgp.Encrypt(buf, entityList, nil, nil, nil)
    if err != nil {
        return "", err
    }
    _, err = w.Write([]byte(mySecretString))
    if err != nil {
        return "", err
    }
    err = w.Close()
    if err != nil {
        return "", err
    }

    // Encode to base64
    bytes, err := ioutil.ReadAll(buf)
    if err != nil {
        return "", err
    }
    encStr := base64.StdEncoding.EncodeToString(bytes)

    // Output encrypted/encoded string
    log.Println("Encrypted Secret:", encStr)

    return encStr, nil
}

func decTest(encString string) (string, error) {

    log.Println("Secret Keyring:", secretKeyring)
    log.Println("Passphrase:", passphrase)

    // init some vars
    var entity *openpgp.Entity
    var entityList openpgp.EntityList

    // Open the private key file
    keyringFileBuffer, err := os.Open(secretKeyring)
    if err != nil {
        return "", err
    }
    defer keyringFileBuffer.Close()
    entityList, err = openpgp.ReadKeyRing(keyringFileBuffer)
    if err != nil {
        return "", err
    }
    entity = entityList[0]

    // Get the passphrase and read the private key.
    // Have not touched the encrypted string yet
    passphraseByte := []byte(passphrase)
    log.Println("Decrypting private key using passphrase")
    entity.PrivateKey.Decrypt(passphraseByte)
    for _, subkey := range entity.Subkeys {
        subkey.PrivateKey.Decrypt(passphraseByte)
    }
    log.Println("Finished decrypting private key using passphrase")

    // Decode the base64 string
    dec, err := base64.StdEncoding.DecodeString(encString)
    if err != nil {
        return "", err
    }

    // Decrypt it with the contents of the private key
    md, err := openpgp.ReadMessage(bytes.NewBuffer(dec), entityList, nil, nil)
    if err != nil {
        return "", err
    }
    bytes, err := ioutil.ReadAll(md.UnverifiedBody)
    if err != nil {
        return "", err
    }
    decStr := string(bytes)

    return decStr, nil
}

func main() {
    encStr, err := encTest(mySecretString)
    if err != nil {
        log.Fatal(err)
    }
    decStr, err := decTest(encStr)
    if err != nil {
        log.Fatal(err)
    }
    // should be done
    log.Println("Decrypted Secret:", decStr)
}

Keys should be in binary NOT in base64, otherwise you'll get tag byte does not have MSB set error.

use openpgp.ReadArmoredKeyRing instead of openpgp.ReadKeyRing if you exported your gpg keys with --armor

thanks mates, now it finally works for me too..

If you have created your keyring with gnupg >=v2 you need to export the secret keys e.g. with

$ gpg --no-default-keyring --keyring ./ring.gpg --export-secret-keys > secret-key.gpg
$ file secret-key.gpg
secret-key.gpg: PGP	Secret Key - 2048b created on Thu Jan  9 01:46:30 2020 - RSA (Encrypt or Sign) e=65537 hashed AES with 128-bit key Salted&Iterated S2K SHA-1

🤦‍♂️

I believe the url has changed for the openpgp package to golang.org/x/crypto/openpgp

Awesome code snippet! Only comment was for anyone referencing this code to decrypt something other than a string, such as a big encrypted file. It would be safer and might save you a ton of time debugging if you read in the decrypted string using _, err := ioutil.copy(decryptWriter, md.UnverifiedBody) instead of bytes, err := ioutil.ReadAll(md.UnverifiedBody)

Thanks, this gist works! I had struggled a bit with generation of secring.gpg and pubring.gpg, though.

To generate throwaway keys for experiments, following commands can be used generate a new key in .gnupg as subdirectory of the current directory, and .gnupg/secring.gpg and .gnupg/pubring.gpg keyrings:

gpg --gen-key --homedir .gnupg
gpg --no-default-keyring --homedir ./.gnupg/ --export-secret-keys > ./.gnupg/secring.gpg
gpg --no-default-keyring --homedir ./.gnupg/ --export > ./.gnupg/pubring.gpg

Thanks, how about if I want to support dual keys?