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Uses the SubtleCrypto interface of the Web Cryptography API to encrypt and decrypt text using AES-GCM (AES Galois counter mode).
/**
* Encrypts plaintext using AES-GCM with supplied password, for decryption with aesGcmDecrypt().
*
* @param {String} plaintext - Plaintext to be encrypted.
* @param {String} password - Password to use to encrypt plaintext.
* @returns {String} Encrypted ciphertext.
*
* @example
* const ciphertext = await aesGcmEncrypt('my secret text', 'pw');
*/
async function aesGcmEncrypt(plaintext, password) {
const pwUtf8 = new TextEncoder().encode(password); // encode password as UTF-8
const pwHash = await crypto.subtle.digest('SHA-256', pwUtf8); // hash the password
const iv = crypto.getRandomValues(new Uint8Array(12)); // get 96-bit random iv
const alg = { name: 'AES-GCM', iv: iv }; // specify algorithm to use
const key = await crypto.subtle.importKey('raw', pwHash, alg, false, ['encrypt']); // generate key from pw
const ptUint8 = new TextEncoder().encode(plaintext); // encode plaintext as UTF-8
const ctBuffer = await crypto.subtle.encrypt(alg, key, ptUint8); // encrypt plaintext using key
const ctArray = Array.from(new Uint8Array(ctBuffer)); // ciphertext as byte array
const ctStr = ctArray.map(byte => String.fromCharCode(byte)).join(''); // ciphertext as string
const ctBase64 = btoa(ctStr); // encode ciphertext as base64
const ivHex = Array.from(iv).map(b => ('00' + b.toString(16)).slice(-2)).join(''); // iv as hex string
return ivHex+ctBase64; // return iv+ciphertext
}
/**
* Decrypts ciphertext encrypted with aesGcmEncrypt() using supplied password.
*
* @param {String} ciphertext - Ciphertext to be decrypted.
* @param {String} password - Password to use to decrypt ciphertext.
* @returns {String} Decrypted plaintext.
*
* @example
* const plaintext = await aesGcmDecrypt(ciphertext, 'pw');
*/
async function aesGcmDecrypt(ciphertext, password) {
const pwUtf8 = new TextEncoder().encode(password); // encode password as UTF-8
const pwHash = await crypto.subtle.digest('SHA-256', pwUtf8); // hash the password
const iv = ciphertext.slice(0,24).match(/.{2}/g).map(byte => parseInt(byte, 16)); // get iv from ciphertext
const alg = { name: 'AES-GCM', iv: new Uint8Array(iv) }; // specify algorithm to use
const key = await crypto.subtle.importKey('raw', pwHash, alg, false, ['decrypt']); // use pw to generate key
const ctStr = atob(ciphertext.slice(24)); // decode base64 ciphertext
const ctUint8 = new Uint8Array(ctStr.match(/./g).map(ch => ch.charCodeAt(0))); // ciphertext as Uint8Array
// note: why doesn't ctUint8 = new TextEncoder().encode(ctStr) work?
const plainBuffer = await crypto.subtle.decrypt(alg, key, ctUint8); // decrypt ciphertext using key
const plaintext = new TextDecoder().decode(plainBuffer); // decode password from UTF-8
return plaintext; // return the plaintext
}
Owner

chrisveness commented Feb 17, 2017

Cryptography is indeed subtle. If I have made any errors, let me know and I will attempt to correct.

Thx to Tim Taubert @ Mozilla.

Owner

chrisveness commented Feb 28, 2017

With the benefit of node-webcrypto-ossl and text-encoding polyfills, these routines will run on Node.js, and will inter-operate between the browser and the server.

Simply add the following at the top of the file:

const TextEncoder = require('text-encoding').TextEncoder;
const TextDecoder = require('text-encoding').TextDecoder;
const WebCrypto = require("node-webcrypto-ossl");
const crypto = new WebCrypto();
module.exports = { aesGcmEncrypt, aesGcmDecrypt };

Then to use it,

const aesGcmEncrypt = require ('./crypto-aes-gcm.js').aesGcmEncrypt;
const aesGcmDecrypt = require ('./crypto-aes-gcm.js').aesGcmDecrypt;

const ciphertext = await aesGcmEncrypt('my secret text', 'pw');
const plaintext = await aesGcmDecrypt(ciphertext, 'pw');

majodi commented Nov 23, 2017

match(/./g) is leaving out whitespace chars, making the Decrypt fail when ctStr contains a return or linefeed for instance. For now I am using a for-loop with charCodeAt() but maybe there's a more efficient way.

Hi @chrisveness ,
I'm a newbie to GitHubGist...
Haven't yet tried out the above pieces of code, but it looks pretty useful.
What is the license for the code that you've shared above (even though it's a couple of lines of wrapper code around webcrypto)?
For some reason I'm unable to find clear information on this.
I'm planning to use this on an open source project, but still want to be clear on the licensing aspects.

Also by the way, I'm assuming that there is no known symmetric-key encryption system significantly more secure than AES-256-GCM.
Please confirm my understanding?
Also, can you recommend any similar gists for asymmetric key encryption?

Thanks,
Sohrab

Hi @majodi,
Can you please share your fix for decrypt?

Thanks,
Sohrab

i want to say a big thanks to you. this is the first time I found simple, useable and readable crypto libs made for casual users.
no need to bother with module api's, initialisation etc simply call encrypt/decrypt!

gnadelwartz commented Dec 2, 2017

hm, not so easy then expected. even your code use await internally it returns a promise, not a string. So i can't simply do an

result = aesGcmEncrypt('text', 'pw');
enSaveValue(result);

gives me in Firefox:
"EnSaveValue URL: https://dealz.rrr.de/enstyler/save.php?ID=-378385905&value=[object Promise]"

looks like I have to convert over everything to async :-(, because it seems not easy to getb the value a promise from for not async code ...

@majodi,

You can replace:

 const ctUint8 = new Uint8Array(ctStr.match(/./g).map(ch => ch.charCodeAt(0)));     // ciphertext as Uint8Array

...with:

const ctUint8 = new Uint8Array(ctStr.match(/[\s\S]/g).map(ch => ch.charCodeAt(0)));     // ciphertext as Uint8Array

See also https://stackoverflow.com/questions/1068280/javascript-regex-multiline-flag-doesnt-work

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