The Secure Remote Password Protocol lets you authenticate password secured logins without having to transmit the plain text password by establishing a cryptographic key (Password-Authenticated Key-Agreement = PAKE).
SRP is a standard defined in RFC 2945 and originally developed by Tom Wu, who also developed the BigInteger library used by this project. This software implements version 6 of the SRP protocol using HTML5/JavaScript technology on client and server side.
Client requires a HTML5 capable web browser. WebSockets are utilized to exchange messages in order to establish a cryptographic key. Node.js is required on server side with WebSocket module installed (npm -g install ws). Static pages may be delivered via standard http server (e.g. Apache or Nginx).
Run prototype implementation:
- Server: node server.js
- Client: open "index.html", enter "root" and "1234" as user/pass and submit
- Shortly after, a message showing "Authentication successful!" should appear
The actual SRP implementation is located in shared/lib/srp.js whereas client/client.js and server/server.js orchestrate the communication flow over WebSockets and the SRP steps.
Feel free to adjust parameters or client/server logic to your needs, since this is only a prototype implementation. You may also exchange cryptographic hashing algorithm and key derivation function by algorithms of your choice. Currently SHA256 is used for cryptographic hashing and scrypt with N=16384, r=8, p=1 and L=64 is used for iterative key derivation. For productive use you may also generate your own large safe prime as modulus (N) for arithmetic operations. However, the provided N (AC6B...FF73) will work out of the box. It is taken from [RFC5054 Appendix A (SRP Group Parameters)](http://tools.ietf.org/html/ rfc5054#appendix-A) and a proven safe prime of 2048 bit length with a generator (g) of 2. Please note, that you will have to reset all user passwords if you modify hash or key derivation algorithms or the modulus.
The current implementation of the software is not specifically optimized for performance or load balancing, which may result in weakness for denial of service attacks in the worst case.
Another problem which may arise under heavy load is to provide enough entropy for the cryptographic strong random number generators to work. If not enough entropy is available then an exception will be thrown and the authentication process will immediately abort. You may modify the computeRandom function to supply more entropy sources if needed or to not abort and instead wait until enough entropy is available.
Although because of the nature of the protocol it is not necessary to secure the connection with SSL/TLS during key exchange, it is recommended to always use WebSocketSecure to prevent firewall issues with plain WebSocket traffic.
This software is free and open source. See LICENSE for details.