Random Bit Generation with Full Entropy and Configurable Prediction Resistance in a Node.js Application

This is the fourth and last post of a series describing a proof-of-concept web app that implements cryptographic authentication using Node.js with a MongoDB back-end. Part 1 described the login process. Part 2 described the registration process. Part 3 described login session maintenance. The proof-of-concept app, called app-mongodb.js, or simply app-mongodb, can be found in a zip file downloadable from the cryptographic authentication page.

In app-mongodb, random bits are used on the server side for generating registration and login challenges to be signed by the browser, and for generating login session IDs. On the client side, they are used for generating key pairs and computing randomized signatures on server challenges.

In quest of full entropy

There are established methods for obtaining random bits to be used in web apps. On the client side, random bits can be obtained from crypto.getRandomValues, which is part of the W3C Web Crypto API. On the server side, /dev/urandom can be used in Linux, MacOS and most flavors of Unix. However, neither of these methods guarantees full entropy.

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Login Session Maintenance in Node.js using Express and Handlebars

This is part 3 of a series of posts describing a proof-of-concept web app that implements cryptographic authentication using Node.js with a MongoDB back-end. Part 1 described the login process. Part 2 described the registration process. This Part 3 is concerned with login session maintenance in a broader scope than cryptographic authentication. Part 4, concerned with random bit generation, is now available. The proof-of-concept app, called app-mongodb.js, can be found in a zip file downloadable from the cryptographic authentication page.

Update. The name of the constant securityStrength has been changed to rbgSecurityStrength as noted in the last post of the series and reflected in one of the snippets below.

At first glance it may seem that there is no need for login session maintenance in a web app that implements cryptographic authentication with a key pair. Every HTTP request can be authenticated on its own without linking it to a session, by sending the public key to the back-end and proving possession of the private key, as in the login process described in Part 1. That login process relied on the user supplying the username in order to locate the user record, but this is not essential, since the user record could be located in the database by searching for the public key, which is unique with overwhelming probability.

But login sessions provide important login/logout functionality, allowing the user to choose whether to authenticate or not. A member of a site accessible to both members and non-members, for example, may choose to visit the site without authenticating in order to see what information is made available by the site to non-members. Also, the proof of possession of the private key has a latency cost for the user due to the need to retrieve the challenge from the server, and a computational cost for the server and the browser. These costs are insignificant if incurred once per session, but may not be insignificant if incurred for every HTTP request.

The app discussed in this series, app-mongodb.js, implements login sessions in the traditional way using session cookies. Having said that I could stop here. But the Express framework used in the app provides interesting ways of implementing traditional login sessions, which are worth discussing.

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Credential Registration for Cryptographic Authentication with Node.js and MongoDB

This is part 2 of a series of posts describing a proof-of-concept web app that implements cryptographic authentication using Node.js, Express, Handlebars, MongoDB and Mongoose. All parts are now available. Part 1 describes the login process. This Part 2 describes the registration process. Part 3 describes login session maintenance. Part 4 is concerned with random bit generation.

Update. The name of the constant securityStrength has been changed to rbgSecurityStrength as noted in the last post of the series and reflected in the snippets below.

Part 1 of this series described the login process of a proof-of-concept Node.js application that implements cryptographic authentication using a MongoDB database back-end. The app, called app-mongodb.js, can be found in a zip file downloadable from the cryptographic authentication page, where it is bundled together with a simpler app that has the same functionality and the same front-end but emulates the database using JavaScript objects, provided for comparison.

This post describes the registration process of app-mongodb.js. The app has a registration page reachable from a link found under a top-of-page login form in the public pages of the app. The registration page has a form where the user enters a username, a first name and a last name, but no password. The first and last names are representative of any info that the user may be asked to provide in a full-fledged application.

The registration process of app-mongodb.js has a structure similar to that of the login process described in Part 1. The browser sends an HTTP POST request to the /register-username endpoint of the server, conveying the username, first name and last name. The server creates a user record, called a “user document” in MongoDB terminology, and responds with a JavaScript POST redirection. The JavaScript POST redirection consists of downloading a script that generates a key pair, signs a server challenge with the private key, and sends the public key and the signature to the /register-public-key endpoint in a second HTTP POST request. The server cryptographically validates the public key, verifies the signature, and adds the public key to the user document.

The following code snippet shows how the server processes the first HTTP POST request, received at the /register-username endpoint.

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Cryptographic authentication with Node.js and MongoDB

This is part 1 of a series of posts describing a proof-of-concept web app that implements cryptographic authentication using Node.js, Express, Handlebars, MongoDB and Mongoose. All parts are now available. Part 2 describes the registration process. Part 3 describes login session maintenance. Part 4 is concerned with random bit generation.

Update. The name of the constant securityStrength has been changed to rbgSecurityStrength as noted in the last post of the series and reflected the snippets below.

The PJCL library allows full-stack web developers to use the same cryptographic API on a browser front-end and a Node.js back-end, as explained here. At the last IIW we demoed a web app, implemented using Node.js and Express, that featured cryptographic authentication with a DSA key pair, using PJCL both in the browser to sign a challenge and in the Node.js server to verify the signature. Initial implementations of the app were complicated by having to work around a Firefox bug, which we reported and was confirmed. But eventually we found a simple way of bypassing that bug.

The IIW demo app was very simple. It only had a public “home page” and a private “welcome page”, and it emulated the back-end database using JavaScript objects. We are now releasing a more substantial proof of concept of cryptographic authentication that again uses Node.js and Express, but this time uses a MongoDB database, accessed via a Mongoose driver. Besides using an actual rather than emulated database, the new proof-of-concept app includes features such as on-the-fly login and garbage collection of incomplete user registrations. It also shows how to implement random bit generation with full initial entropy and configurable prediction resistance, which I plan to discuss in another blog post of this series.

The new app is available in a new cryptographic authentication page of the Pomcor site. It is bundled together in a zip file with a simpler app that has the same functionality and the same front-end, but emulates the database using JavaScript objects. The two apps, called app-mongodb.js and app-nodb.js, share the same static files and views. Comparing the two apps may help with understanding the code of the more complex app-mongodb.js. The apps may be run in any Node.js server with access to a MongoDB database and a /dev/random device file, as explained in a README file included in the zip archive.

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Second Release of PJCL Expands Functionality Following NIST Cryptographic Specifications

Today we have released version 0.9.1 of the Pomcor JavaScript Crytpographic Library (PJCL). The initial public release provided digital signature functionality, which we had been using internally for our own research on authentication and identity proofing. This release adds key agreement and key derivation functionality. The next release will provide symmetric and asymmetric encryption primitives, including AES and RSA. To be notified of future releases you may sign up for the user forum, subscribe to the feed of this blog, or follow me on Twitter (@fcorella). (Update: The PJCL user forum has been discontinued as of May 27, 2018.)

PJCL can be used in any JavaScript environment, both client-side (e.g. in a browser) and server-side (e.g. under Node.js). It comes with extensive documentation on the functionality that it provides, which includes:

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Pomcor Releases JavaScript Cryptographic and Big Integer Library

We have just released a beta version of a JavaScript cryptographic library usable in any JavaScript environment and based on very fast big integer arithmetic functionality that may be of interest in its own right.

The Pomcor JavaScript Cryptographic Library (PJCL) is available free of charge for any kind of use, but not under a traditional open source license. The traditional open source paradigm encourages contributions by the developer community at large, but we believe that this paradigm is not well suited to cryptography. To protect the integrity of the cryptographic code, the license prohibits modification of the cryptographic functions.

We have been using the library internally for our own research on authentication and identity proofing, and this first release includes symmetric and asymmetric digital signature functionality, including HMAC, DSA, and ECDSA with NIST curves. Future releases will provide broader cryptographic functionality, including encryption and key exchange. We believe that the library provides the only available JavaScript implementation of DSA, which is important to those wary of the opportunities for hiding backdoors that might be provided by elliptic curve technology.

The underlying big integer functionality includes Karatsuba multiplication. Continue reading “Pomcor Releases JavaScript Cryptographic and Big Integer Library”