This library provides data structures representing Diffie-Hellman Groups stated in RFC3526. The data structures are useful in implementing cryptographic protocols such as Internet Key Exchange (IKE).

It provides constants of the primes in typed BigUint given by dependency num-bigint. For example, you can get the value by calling a method in provided structs that implements the trait MODPGroup.

MODPGroup5::prime_modulus();

The struct Element represents an element in the MODP Group, which implements traits in std::ops for arithmetic operations.

It is an example to illustrate the secret sharing in Diffie-Hellman Key Exchange.

// A = g^a mod p
let a = BigUint::from_str("2").unwrap();
let A = Element::<MODPGroup5>::from_biguint(a.clone());
// B = g^b mod p
let b = BigUint::from_str("3").unwrap();
let B = Element::<MODPGroup5>::from_biguint(b.clone());

// shared secret = B^a = A^b mod p
let s = B.pow(&a);
let z = A.pow(&b);

assert_eq!(s, z)

The library can provide a so-called Prime Group when enabling the feature primegroup. Tit is the struct PrimeGroup that represents a MODP Group such that:

p is prime modulus, which is a safe prime.
q is also a prime s.t. p = 2q+1 mod p
g is a generator s.t. g^q mod p = 1

See Wiki for details about p and q.

The provided MODP Groups are having safe primes as modulus. You can create a group from them, for example,

PrimeGroup::new::<MODPGroup5>(128); // a 128-bit generator