pakery-spake2

pakery-spake2

SPAKE2 balanced PAKE protocol implementation (RFC 9382).

Part of the pakery workspace.

SPAKE2 is a balanced (symmetric) PAKE with mutual explicit key confirmation. Both parties share a password-derived scalar and agree on a session key with provable security.

Usage

[dependencies]
pakery-spake2 = "0.1"
pakery-crypto = { version = "0.1", features = ["ristretto255"] }

Example

use pakery_spake2::{Spake2Ciphersuite, PartyA, PartyB};
use pakery_crypto::{Ristretto255Group, Sha512Hash, HkdfSha512, HmacSha512};
use pakery_crypto::{SPAKE2_M_COMPRESSED, SPAKE2_N_COMPRESSED};
use pakery_core::crypto::Hash;

struct MySpake2Suite;

impl Spake2Ciphersuite for MySpake2Suite {
    type Group = Ristretto255Group;
    type Hash = Sha512Hash;
    type Kdf = HkdfSha512;
    type Mac = HmacSha512;
    const NH: usize = 64;
    const M_BYTES: &'static [u8] = &SPAKE2_M_COMPRESSED;
    const N_BYTES: &'static [u8] = &SPAKE2_N_COMPRESSED;
}

// Requires the `os_rng` crate feature. In rand_core 0.9 `OsRng` only
// implements `TryRngCore`; `UnwrapErr` adapts it to the `CryptoRng`
// bound used by pakery's API (panics on RNG failure, which never
// happens on a real OS).
let mut rng = rand_core::UnwrapErr(rand_core::OsRng);

// Derive password scalar
let hash = Sha512Hash::digest(b"password");
let w = Ristretto255Group::scalar_from_wide_bytes(&hash).unwrap();

// Both parties exchange shares and derive keys
let (pa, state_a) = PartyA::<MySpake2Suite>::start(
    &w, b"alice", b"bob", b"aad", &mut rng,
).unwrap();

let (pb, state_b) = PartyB::<MySpake2Suite>::start(
    &w, b"alice", b"bob", b"aad", &mut rng,
).unwrap();

let out_a = state_a.finish(&pb).unwrap();
let out_b = state_b.finish(&pa).unwrap();

// Session keys match
assert_eq!(out_a.session_key.as_bytes(), out_b.session_key.as_bytes());

// Verify mutual confirmation MACs
out_a.verify_peer_confirmation(&out_b.confirmation_mac).unwrap();
out_b.verify_peer_confirmation(&out_a.confirmation_mac).unwrap();

Features

Feature	Description
std (default)	Enable std support
getrandom	Enable OS-backed RNG via rand_core/getrandom
test-utils	Expose deterministic constructors for testing

Security

• #![forbid(unsafe_code)]
• Constant-time comparisons via subtle
• Secret values zeroized on drop via zeroize
• Validated against RFC 9382 test vectors

MSRV

The minimum supported Rust version is 1.79.

License

Licensed under either of Apache License, Version 2.0 or MIT License at your option.