browserid-crypto

JavaScript implementation of JSON Web Signatures and JSON Web Tokens as needed by BrowserID.


- libs contains third-party libraries that need to be included. See
libs/dependencies.txt and libs/package.txt

- This is written as CommonJS modules for node and
such. Browserify is used to bundle it all up.

NOTE: this is written as future documentation of v0.2 APIs, which will not
be backwards compatible with v0.1.

Overview
===

JSON Web Tokens (JWTs) look like:

eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

(line breaks are for readability)

JWTs are made up of three components, each base64url-encoded, joined by a period character. A JWT can be either a JWS (JSON Web Signature) or a JWE (JSON Web Encryption). In this library, we only consider JWS. Because JWT is effectively the abstract superclass of both JWS and JWE, we don't expose JWT APIs directly (as of v0.2.0). We simply expose a JWS API.

We use JWK (JSON Web Keys) to specify keys:
http://tools.ietf.org/html/draft-ietf-jose-json-web-key-00

We use JWA (JSON Web Algorithms) to specify algorithms:
http://tools.ietf.org/html/draft-ietf-jose-json-web-algorithms-00
(we add algorithm "DSA" to indicate DSA, with DS160 the standard DSA 1024/160.)

Usage
=====

1. for Node 4+ ensure that you are using g++ 4.8 (use CXX=g++-4.8 to force that version)
2. npm install browserid-crypto
3. in javascript: require('browserid-crypto')

Basic API
=========
``javascript
var jwcrypto = require("browserid-crypto");
require("browserid-crypto/lib/algs/ds");

// random number generation is taken care of automatically
// with auto-seeding that is optimized for server or browser
// setup

// more entropy can be added as follows
// this can be useful to incorporate server-provided entropy
// on clients that don't have any good entropy of their own
// entropy should be either a 32 bit int, an array of ints, or a string
jwcrypto.addEntropy('entropy');

// generate a key
// we use DSA, which is "DS" in JSON Web Algorithm parlance
// we use keysize 160, which has a specific interpretation based
// on the algorithm, in this case DSA 1024/160, standard DSA.
jwcrypto.generateKeypair({
algorithm: 'DSA',
keysize: 160
}, function(err, keypair) {
// error in err?

// serialize the public key
console.log(keypair.publicKey.serialize());

// just the JSON object to embed in another structure
console.log(JSON.stringify({stuff: keypair.publicKey.toSimpleObject()}));

// replace this with the key to sign
var publicKeyToCertify = keypair.publicKey.serialize();

// create and sign a JWS
var payload = {principal: {email: 'some@dude.domain'},
pubkey: jwcrypto.loadPublicKey(publicKeyToCertify)};

jwcrypto.sign(payload, keypair.secretKey, function(err, jws) {
// error in err?

// serialize it
console.log(jws.toString());

// replace with things to verify
var signedObject = jws;
var publicKey = keypair.publicKey;

// verify it
jwcrypto.verify(signedObject, publicKey, function(err, payload) {
// if verification fails, then err tells you why
// if verification succeeds, err is null, and payload is
// the signed JS object.
});
});

// replace this with the key to load
var storedSecretKey = keypair.secretKey.serialize();

// also, if loading a secret key from somewhere
var otherSecretKey = jwcrypto.loadSecretKey(storedSecretKey);
});
`

Assertions
====

Sometimes the JSON object to sign should be a standard assertion with pre-defined fields.

`javascript
var assertion = require("browserid-crypto").assertion;

// payload of the assertion
var payload = {principal: {email: 'some@dude.domain'}};

// add special fields which will be encoded properly
// payload cannot contain reserved fields
assertion.sign(payload, {issuer: "foo.com", expiresAt: new Date(new Date().valueOf() + 5000),
issuedAt: new Date().valueOf(), audience: "https://example.com"},
keypair.secretKey,
function(err, signedAssertion) {
// a normal signedObject, much like above
// can be verified with jwcrypto.verify

// or verified specifically for jwt, with expiration verification
var now = new Date();
assertion.verify(signedObject, keypair.publicKey, now, function(err, payload, assertionParams) {
// payload is the original payload
// assertionParams contains issuedAt, expiresAt as dates
// and issuer and audience as strings.
});
});
`

Note that timestamps (for issuedAt and expiresAt) are integers containing the standard JS milliseconds-since-epoch, or objects with methods named .valueOf() which will return such an integer. The assertion format currently serializes these integers verbatim; a future version may serialize them as seconds (instead of milliseconds) to conform with the JWT specifications.

Certs
=======

Sometimes the JSON objects to sign are certificates

`javascript
var cert = require("browserid-crypto").cert;

var keyToCertify = keypairToCertify.publicKey;
var principal = {email: "someone@example.com"};

var assertionParams = {issuer: "foo.com", issuedAt: new Date(),
expiresAt: new Date()};

// cert params, kid is optional, others are required
var certParams = {kid: "key-2012-08-11",
publicKey: keyToCertify,
principal: principal};

var additionalPayload = {};

// payload cannot contain reserved fields
cert.sign(certParams,
assertionParams, additionalPayload,
keypair.secretKey,
function(err, signedObject) {
// normal signedObject
// can be verified with jwcrypto.verify

// or verified specifically for certification
// include a date that is considered the "now"
cert.verify(signedObject, keypair.publicKey, now, function(err, payload, assertionParams, certParams) {
// the extra payload
// the assertionParams specifics
// the certParams include publicKey being certified, and principal bound to it.
});
});

// bundle a cert chain and an assertion
var bundle = cert.bundle([certs], assertion);

function getPK(issuer, next) {
// function to get a public key for an issuer
}

var now = new Date();

// verify just the chain of certs
cert.verifyChain([certs], now, getPK, function(err, certParamsArray) {
// err is an error or null
// if no error:
// certParamsArray is the array of individual cert params from each verification
// including specifically the publicKey and principal parameters
});

// verify a chain of certs and assertion
cert.verifyBundle(bundle, now, getPK, function(err, certParamsArray, payload, assertionParams) {
// err is an error or null
// if no error:
// certParamsArray is the array of individual cert params from each verification
// payload is the assertion payload, and assertionParams is the assertion params.
});
``