Crate srp

Secure Remote Password (SRP) protocol implementation.

This implementation is generic over hash functions using Digest trait, so you will need to choose a hash function, e.g. Sha256 from sha2 crate. Additionally this crate allows to use a specialized password hashing algorithm for private key computation instead of method described in the SRP literature.

Compatibility with over implementations was not yet tested.

Usage

Add srp dependecy to your Cargo.toml:

[dependencies]
rand = "0.3"

and this to your crate root:

extern crate srp;

Next read documentation for client and server modules.

Algorithm description

Here we briefly describe implemented algroithm. For additionall information refer to SRP literature. All arithmetic is done modulo N, where N is a large safe prime (N = 2q+1, where q is prime). Additionally g MUST be a generator modulo N. It’s STRONGLY recommended to use SRP parameters provided by this crate in the groups module.

Client	Data transfer	Server
a_pub = g^a	— a_pub, I —>	(lookup s, v for given I)
x = PH(P, s)	<— b_pub, s —	b_pub = k*v + g^b
u = H(a_pub ‖ b_pub)		u = H(a_pub ‖ b_pub)
s = (b_pub - k*g^x)^(a+u*x)		S = (b_pub - k*g^x)^(a+u*x)
K = H(s)		K = H(s)
M1 = H(A ‖ B ‖ K)	— M1 —>	(verify M1)
(verify M2)	<— M2 —	M2 = H(A ‖ M1 ‖ K)

Variables and notations have the following meaning:

• I — user identity (username)
• P — user password
• H — one-way hash function
• PH — password hashing algroithm, in the RFC 5054 described as H(s ‖ H(I ‖ ":" ‖ P))
• ^ — (modular) exponentiation
• ‖ — concatenation
• x — user private key
• s — salt generated by user and stored on the server
• v — password verifier equal to g^x and stored on the server
• a, b — secret ephemeral values (at least 256 bits in length)
• A, B — Public ephemeral values
• u — scrambling parameter
• k — multiplier parameter (k = H(N || g) in SRP-6a)

Modules

client

SRP client implementation.

groups

Groups from RFC 5054

server

SRP server implementation

types

Additional SRP types.