simple AES encryption/decryption example with PBKDF2 key derivation in Go, Javascript, and Python

aes.go

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"strings"

	"golang.org/x/crypto/pbkdf2"
)

func deriveKey(passphrase string, salt []byte) ([]byte, []byte) {
	if salt == nil {
		salt = make([]byte, 8)
		// http://www.ietf.org/rfc/rfc2898.txt
		// Salt.
		rand.Read(salt)
	}
	return pbkdf2.Key([]byte(passphrase), salt, 1000, 32, sha256.New), salt
}

func encrypt(passphrase, plaintext string) string {
	key, salt := deriveKey(passphrase, nil)
	iv := make([]byte, 12)
	// http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf
	// Section 8.2
	rand.Read(iv)
	b, _ := aes.NewCipher(key)
	aesgcm, _ := cipher.NewGCM(b)
	data := aesgcm.Seal(nil, iv, []byte(plaintext), nil)
	return hex.EncodeToString(salt) + "-" + hex.EncodeToString(iv) + "-" + hex.EncodeToString(data)
}

func decrypt(passphrase, ciphertext string) string {
	arr := strings.Split(ciphertext, "-")
	salt, _ := hex.DecodeString(arr[0])
	iv, _ := hex.DecodeString(arr[1])
	data, _ := hex.DecodeString(arr[2])
	key, _ := deriveKey(passphrase, salt)
	b, _ := aes.NewCipher(key)
	aesgcm, _ := cipher.NewGCM(b)
	data, _ = aesgcm.Open(nil, iv, data, nil)
	return string(data)
}

func main() {
	c := encrypt("hello", "world")
	fmt.Println(c)
	fmt.Println(decrypt("hello", c))
	fmt.Println(decrypt("hello", "c2932347953ad4a4-25f496d260de9c150fc9e4c6-20bc1f8439796cc914eb783b9996a8d9c32d45e2df"))
}

aes.js

/**
 * Encodes a utf8 string as a byte array.
 * @param {String} str 
 * @returns {Uint8Array}
 */
function str2buf(str) {
  return new TextEncoder("utf-8").encode(str);
}

/**
 * Decodes a byte array as a utf8 string.
 * @param {Uint8Array} buffer 
 * @returns {String}
 */
function buf2str(buffer) {
  return new TextDecoder("utf-8").decode(buffer);
}

/**
 * Decodes a string of hex to a byte array.
 * @param {String} hexStr
 * @returns {Uint8Array} 
 */
function hex2buf(hexStr) {
  return new Uint8Array(hexStr.match(/.{2}/g).map(h => parseInt(h, 16)));
}

/**
 * Encodes a byte array as a string of hex.
 * @param {Uint8Array} buffer
 * @returns {String} 
 */
function buf2hex(buffer) {
  return Array.prototype.slice
    .call(new Uint8Array(buffer))
    .map(x => [x >> 4, x & 15])
    .map(ab => ab.map(x => x.toString(16)).join(""))
    .join("");
}

/**
 * Given a passphrase, this generates a crypto key
 * using `PBKDF2` with SHA256 and 1000 iterations.
 * If no salt is given, a new one is generated.
 * The return value is an array of `[key, salt]`.
 * @param {String} passphrase 
 * @param {UInt8Array} salt [salt=random bytes]
 * @returns {Promise<[CryptoKey,UInt8Array]>} 
 */
function deriveKey(passphrase, salt) {
  salt = salt || crypto.getRandomValues(new Uint8Array(8));
  return crypto.subtle
    .importKey("raw", str2buf(passphrase), "PBKDF2", false, ["deriveKey"])
    .then(key =>
      crypto.subtle.deriveKey(
        { name: "PBKDF2", salt, iterations: 1000, hash: "SHA-256" },
        key,
        { name: "AES-GCM", length: 256 },
        false,
        ["encrypt", "decrypt"],
      ),
    )
    .then(key => [key, salt]);
}

/**
 * Given a passphrase and some plaintext, this derives a key
 * (generating a new salt), and then encrypts the plaintext with the derived
 * key using AES-GCM. The ciphertext, salt, and iv are hex encoded and joined
 * by a "-". So the result is `"salt-iv-ciphertext"`.
 * @param {String} passphrase 
 * @param {String} plaintext
 * @returns {Promise<String>} 
 */
function encrypt(passphrase, plaintext) {
  const iv = crypto.getRandomValues(new Uint8Array(12));
  const data = str2buf(plaintext);
  return deriveKey(passphrase).then(([key, salt]) =>
    crypto.subtle
      .encrypt({ name: "AES-GCM", iv }, key, data)
      .then(ciphertext => `${buf2hex(salt)}-${buf2hex(iv)}-${buf2hex(ciphertext)}`),
  );
}

/**
 * Given a key and ciphertext (in the form of a string) as given by `encrypt`,
 * this decrypts the ciphertext and returns the original plaintext
 * @param {String} passphrase 
 * @param {String} saltIvCipherHex 
 * @returns {Promise<String>}
 */
function decrypt(passphrase, saltIvCipherHex) {
  const [salt, iv, data] = saltIvCipherHex.split("-").map(hex2buf);
  return deriveKey(passphrase, salt)
    .then(([key]) => crypto.subtle.decrypt({ name: "AES-GCM", iv }, key, data))
    .then(v => buf2str(new Uint8Array(v)));
}

// EXAMPLE
/*
encrypt("hello", "world")
  .then(v => console.log("ENCRYPTED", v) || v)
  .then(v => decrypt("hello", v))
  .then(v => console.log("DECRYPTED ", v) || v);
  
  decrypt(
    "hello",
    "6102677198e41d98-84c95e2d7caf6f2d4ccbfe3c-3093cef35d0dba7a24d37f7d4580b5ad83c154329c",
  ).then(console.log);
*/

aes.py

import hashlib
import os
from binascii import hexlify, unhexlify
from cryptography.hazmat.primitives.ciphers.aead import AESGCM


def deriveKey(passphrase: str, salt: bytes=None) -> [str, bytes]:
    if salt is None:
        salt = os.urandom(8)
    return hashlib.pbkdf2_hmac("sha256", passphrase.encode("utf8"), salt, 1000), salt


def encrypt(passphrase: str, plaintext: str) -> str:
    key, salt = deriveKey(passphrase)
    aes = AESGCM(key)
    iv = os.urandom(12)
    plaintext = plaintext.encode("utf8")
    ciphertext = aes.encrypt(iv, plaintext, None)
    return "%s-%s-%s" % (hexlify(salt).decode("utf8"), hexlify(iv).decode("utf8"), hexlify(ciphertext).decode("utf8"))


def decrypt(passphrase: str, ciphertext: str) -> str:
    salt, iv, ciphertext = map(unhexlify, ciphertext.split("-"))
    key, _ = deriveKey(passphrase, salt)
    aes = AESGCM(key)
    plaintext = aes.decrypt(iv, ciphertext, None)
    return plaintext.decode("utf8")


if __name__ == "__main__":
    ciphertext = encrypt("hello", "world")
    print(ciphertext)
    print(decrypt("hello", ciphertext))
    print(decrypt("hello", "6102677198e41d98-84c95e2d7caf6f2d4ccbfe3c-3093cef35d0dba7a24d37f7d4580b5ad83c154329c"))