crypt.go

// Copyright (c) 2023 Qiying Wang

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package confcrypt

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/md5"
	"crypto/rand"
	"encoding/base64"
	"encoding/hex"
	"errors"
	"io"
)

var (
	ErrInvalidCipherText = errors.New("invalid text to decrypt")
)

// Encrypt encrypts data with passphrase using AES-256 algorithm.
func Encrypt(data []byte, passphrase string) (string, error) {
	block, err := aes.NewCipher([]byte(createHash(passphrase)))
	if err != nil {
		return "", err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
		return "", err
	}
	seal := gcm.Seal(nonce, nonce, data, nil)
	return base64.StdEncoding.EncodeToString(seal), nil
}

// Decrypt decrypts text with passphrase using AES-256 algorithm.
func Decrypt(text string, passphrase string) ([]byte, error) {
	data, err := base64.StdEncoding.DecodeString(text)
	if err != nil {
		return nil, ErrInvalidCipherText
	}
	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, nil
}

// EncryptString encrypts string with passphrase using AES-256 algorithm and prepends "ENC~" to the result.
func EncryptString(s string, key string) (string, error) {
	encrypted, err := Encrypt([]byte(s), key)
	if err != nil {
		return "", err
	}
	return "ENC~" + string(encrypted), nil
}

func createHash(key string) string {
	hasher := md5.New()
	hasher.Write([]byte(key))
	return hex.EncodeToString(hasher.Sum(nil))
}