csrp-gmp

csrp-gmp is a minimal C implementation of the Secure Remote Password protocol, originally written by Tom Cocagne to depend on OpenSSL, ported to LibGMP by est31. The project is intended for direct inclusion into utilizing programs. It's only dependency is LibGMP.

SRP Overview

SRP is a cryptographically strong authentication protocol for password-based, mutual authentication over an insecure network connection.

Unlike other common challenge-response autentication protocols, such as Kereros and SSL, SRP does not rely on an external infrastructure of trusted key servers or certificate management. Instead, SRP server applications use verification keys derived from each user's password to determine the authenticity of a network connection.

SRP provides mutual-authentication in that successful authentication requires both sides of the connection to have knowledge of the user's password. If the client side lacks the user's password or the server side lacks the proper verification key, the authentication will fail.

Unlike SSL, SRP does not directly encrypt all data flowing through the authenticated connection. However, successful authentication does result in a cryptographically strong shared key that can be used for symmetric-key encryption.

Porter's notes

Compared with csrp, some things have changed for the outside. As LibGMP doesn't ship with a cryptographically strong PRNG, strong PRNGs provided (and seeded) by the OS are used instead. On non-Windows operating systems, you should ensure that /dev/urandom is readable, or customize random generation in fill_buff. The call srp_random_seed has been removed.

The call srp_user_new has a new parameter, username_for_verifier, allowing to use different usernames for verifier and srp login.

Added option for srp_create_salted_verification_key call to specify a salt.

We ship with OpenSSL's implementation of the SHA256 hash algorithm. Support for other hash algoritms was dropped (but re-introducing is fairly easy, just copy from an OpenSSL source distribution).

Usage Example

For an usage example, see test_srp.c