Good Stanford Javascript Crypto Library (SJCL) examples? (JS cryptography)

Question

I am looking at a way to do client-side cryptography in Javascript (keeping http://www.matasano.com/articles/javascript-cryptography/ in mind) and have found SJCL. But I seem unable to find good code examples for it. Any pointers?

Answer 1

I did a presentation last year titled Developer's Guide to JavaScript and Web Cryptography and have the demo site online at https://jswebcrypto.azurewebsites.net/

This includes simple Hash, HMAC, PBKDF2 and AES examples for OpenSSL command line (as a baseline) SJCL, CryptoJS, Node.js Crypto, and even W3C Web Cryptography API

Here are the SJCL examples:

Hash

var out = sjcl.hash.sha1.hash("The quick brown fox jumps over the lazy dog");
var hash = sjcl.codec.hex.fromBits(out)
// "2fd4e1c67a2d28fced849ee1bb76e7391b93eb12"

HMAC

var key = sjcl.codec.utf8String.toBits("key");
var out = (new sjcl.misc.hmac(key, sjcl.hash.sha256)).mac("The quick brown fox jumps over the lazy dog");
var hmac = sjcl.codec.hex.fromBits(out)
// "f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8"

PBKDF2

var hmacSHA1 = function (key) {
    var hasher = new sjcl.misc.hmac( key, sjcl.hash.sha1 );
    this.encrypt = function () {
        return hasher.encrypt.apply( hasher, arguments );
    };
};

var passwordSalt = sjcl.codec.hex.toBits( "cf7488cd1e48e84990f51b3f121e161318ba2098aa6c993ded1012c955d5a3e8" );
var derivedKey = sjcl.misc.pbkdf2( "password", passwordSalt, 100, 256, hmacSHA1 );
var hexKey = sjcl.codec.hex.fromBits( derivedKey );
// c12b2e03a08f3f0d23f3c4429c248c275a728814053a093835e803bc8e695b4e

Note: This requires you in include sha1.js in addition to sjcl.js.

Answer 2

This might be a bit late, but I too have recently been looking into how to do client-side cryptographic hashing, and the answer by Kevin Hakanson was very helpful, the demo site is very useful too! It shows how to use a custom PseudoRandom Function with PBKDF2 (the HMAC and SHA1), but I figured out that if one is not passed in, SJCL has defaults and I just wanted to show how to do that, along with generating a random salt.

I also found the sjcl docs quite helpful.

To generate a random salt and use PBKDF2 on the password "password", you could do this, which ends up being just 3 lines:

// Each random "word" is 4 bytes, so 8 would be 32 bytes
var saltBits = sjcl.random.randomWords(8);
// eg. [588300265, -1755622410, -533744668, 1408647727, -876578935, 12500664, 179736681, 1321878387]

// I left out the 5th argument, which defaults to HMAC which in turn defaults to use SHA256
var derivedKey = sjcl.misc.pbkdf2("password", saltBits, 1000, 256);
// eg. [-605875851, 757263041, -993332615, 465335420, 1306210159, -1270931768, -1185781663, -477369628]

// Storing the key is probably easier encoded and not as a bitArray
// I choose base64 just because the output is shorter, but you could use sjcl.codec.hex.fromBits
var key = sjcl.codec.base64.fromBits(derivedKey);
// eg. "2+MRdS0i6sHEyvJ5G7x0fE3bL2+0Px7IuVJoYeOL6uQ="

If you wanted to store the salt, you probably want to encode it

var salt = sjcl.codec.base64.fromBits(saltBits);
// eg. "IxC/6ZdbU/bgL7PkU/ZCL8vAd4kAvr64CraQaU7KQ3M="
// Again I just used base64 because it's shorter, but you could use hex

// And to get the bitArray back, you would do the exact opposite
var saltBits = sjcl.codec.base64.toBits(salt);