Module proj_crypto::asymmetric::commitments

Implementation of Pedersen's Commitment scheme http://download.springer.com/static/pdf/357/chp%253A10.1007%252F3-540-46766-1_9.pdf

The implementation here is likely to be particularly sketchy as I really do not understand the maths behind the discrete logarithm problem. The advice not to use this for anything important holds particularly strongly here.

Example - Homomorphic Commitments

This example demonstrates the homorphic properties of Pedersen Commitments.

use proj_crypto::asymmetric::commitments::*;
use gmp::mpz::Mpz;

sodiumoxide::init();

let co_eff1 = Mpz::from(rand_u64());
let co_eff2 = Mpz::from(rand_u64());
let data1 = Mpz::from(rand_u64());
let data2 = Mpz::from(rand_u64());
let result = data1.clone()*co_eff1.clone() + data2.clone()*co_eff2.clone(); // assume this does not become greater than p

let params = gen_dh_params().unwrap(); // this step can take a long time
let a = random_a(&params.1);
let a_result = (a.clone()*co_eff1.clone() + a.clone()*co_eff2.clone()).modulus(&params.0);

let context1 = CommitmentContext::from_opening((data1, a.clone()), params.clone()).unwrap();
let context2 = CommitmentContext::from_opening((data2, a.clone()), params.clone()).unwrap();
let context_result = CommitmentContext::from_opening((result, a_result), params.clone()).unwrap();

let commit1 = context1.to_commitment();
let commit2 = context2.to_commitment();
let commit_result = context_result.to_commitment();

let commit_blind_result = (commit1 * co_eff1) + (commit2 * co_eff2);

assert!(commit_result == commit_blind_result);

Structs

Commitment	The commitment its self as one would share along a wire
CommitmentContext	A structure containing all the data relating to a commitment. This contains secrets. Drop has been implemented for Mpz to clear the memory when it goes out of scope.

Functions

gen_dh_params	Generates diffie-hellman parameters appropriate for use with the commitments.
random_a	Return a suitable value for a to use in an opening
read_dhparams	Reads and validates DHParams from a file
verify_dh_params	Verify a DHParameters instance
write_dhparams	Writes DHParams to a file

Type Definitions

DHParams	(p, q, g, h) where g and h are the bases suitable to be raised to a power forming the discrete logarithm problem, q is the subgroup in Z_p in which we will perform computations and p is the large prime which forms the large group. Calculations are done modulo p.
Opening	The data required to open a commitment: the data committed to and the random integer a