encryption.go

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/md5"
	"crypto/rand"
	"encoding/hex"
	"io"
	"os"
)

// Credit for code below goes to
// https://www.thepolyglotdeveloper.com/2018/02/encrypt-decrypt-data-golang-application-crypto-packages/
func createHash(key string) string {
	hasher := md5.New()
	hasher.Write([]byte(key))
	return hex.EncodeToString(hasher.Sum(nil))
}

func encrypt(data []byte, passphrase string) ([]byte, error) {
	block, _ := aes.NewCipher([]byte(createHash(passphrase)))
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
		return nil, err
	}
	ciphertext := gcm.Seal(nonce, nonce, data, nil)
	return ciphertext, nil
}

func decrypt(data []byte, passphrase string) ([]byte, error) {
	key := []byte(createHash(passphrase))
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	nonceSize := gcm.NonceSize()
	nonce, ciphertext := data[:nonceSize], data[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return nil, err
	}
	return plaintext, err
}

// EncryptFile takes plain text as byte slice and writes encrypetd file
func EncryptFile(filename string, data []byte, passphrase string) error {
	f, _ := os.Create(filename)
	defer f.Close()
	encrypted, err := encrypt(data, passphrase)
	if err == nil {
		f.Write(encrypted)
		return nil
	}
	return err
}

// DecryptFile reads encrypted file and returns plain text as byte slice
func DecryptFile(filename string, passphrase string) ([]byte, error) {
	data, err := os.ReadFile(filename)
	if err != nil {
		return nil, err
	}
	text, err := decrypt(data, passphrase)
	if err == nil {
		return text, err
	}
	return data, err
}