Golang gpg decrypt (crypto/openpgp)

gpg-decrypt.go

package gpg

import (
	"bytes"
	"encoding/base64"
	"errors"
	"golang.org/x/crypto/openpgp"
	"golang.org/x/crypto/openpgp/packet"
	"io/ioutil"
	"os"
)

type DecryptOption struct {
	PrivateKeyPath   string
	FileToDecrypt    string
	PassPhraseBase64 string
	OutputFileName   string
}

type Decrypt struct {
	DecryptOption
	privateKeyEntity     *openpgp.Entity
	privateKeyEntityList openpgp.EntityList
}

func NewGpgDecrypt(gpgDecryptOption DecryptOption) (*Decrypt, error) {
	gpgDecrypt := Decrypt{DecryptOption: gpgDecryptOption}
	if gpgDecrypt.PrivateKeyPath == "" {
		return nil, errors.New("you must reference a private key")
	}
	if gpgDecrypt.FileToDecrypt == "" {
		return nil, errors.New("you must reference file to encrypt")
	}
	if gpgDecrypt.PassPhraseBase64 == "" {
		return nil, errors.New("you must reference pass phrase (base64)")
	}
	if gpgDecrypt.OutputFileName == "" {
		return nil, errors.New("you must reference output file name")
	}
	gpgDecrypt.openPrivateKey()
	return &gpgDecrypt, nil
}

func (g *Decrypt) openPrivateKey() error {
	privateKeyFile, err := os.Open(g.PrivateKeyPath)
	if err != nil {
		return err
	}
	defer privateKeyFile.Close()
	g.privateKeyEntityList, err = openpgp.ReadKeyRing(privateKeyFile)
	if err != nil {
		return err
	}
	g.privateKeyEntity = g.privateKeyEntityList[0]
	return g.decryptingPrivateKeyWithPassPhrase()
}

func (g *Decrypt) decryptingPrivateKeyWithPassPhrase() error {
	passphraseDecodedByte, err := g.PassPhraseDecode()

	if err != nil {
		return err
	}
	err = g.privateKeyEntity.PrivateKey.Decrypt(passphraseDecodedByte)
	if err != nil {
		return err
	}
	for _, subkey := range g.privateKeyEntity.Subkeys {
		err = subkey.PrivateKey.Decrypt(passphraseDecodedByte)
		if err != nil {
			return err
		}
	}
	return nil
}

func (g *Decrypt) PassPhraseDecode() ([]byte, error) {
	decodedPassPhrase, err := base64.StdEncoding.DecodeString(g.PassPhraseBase64)
	if err != nil {
		return []byte{}, err
	}
	return decodedPassPhrase, nil
}

func (g *Decrypt) saveDecodedFile(content []byte) error {
	f, err := os.Create(g.OutputFileName)
	if err != nil {
		return err
	}
	defer f.Close()
	_, err = f.Write(content)
	return err
}

func (g *Decrypt) Decrypt() error {
	content, err := ioutil.ReadFile(g.FileToDecrypt)
	if err != nil {
		return err
	}

	md, err := openpgp.ReadMessage(bytes.NewBuffer(content), g.privateKeyEntityList, nil, &packet.Config{DefaultCipher:packet.CipherAES256})
	if err != nil {
		return err
	}
	fileDecoded, err := ioutil.ReadAll(md.UnverifiedBody)
	if err != nil {
		return err
	}
	return g.saveDecodedFile(fileDecoded)
}