voprf-vx/src/ciphersuite.rs

// Copyright (c) Meta Platforms, Inc. and affiliates.
//
// This source code is dual-licensed under either the MIT license found in the
// LICENSE-MIT file in the root directory of this source tree or the Apache
// License, Version 2.0 found in the LICENSE-APACHE file in the root directory
// of this source tree. You may select, at your option, one of the above-listed
// licenses.

//! Defines the CipherSuite trait to specify the underlying primitives for VOPRF

use crate::Group;
use core::ops::Mul;
use digest::block_api::BlockSizeUser;
use digest::typenum::{IsLess, IsLessOrEqual, U256};
use digest::{Digest, FixedOutput, HashMarker, OutputSizeUser};
use hash2curve::OprfParameters;
use hybrid_array::ArraySize;
use hybrid_array::typenum::{IsGreaterOrEqual, Prod, True, U2};

/// Configures the underlying primitives used in VOPRF
pub trait CipherSuite
where
    <Self::Group as Group>::SecurityLevel: Mul<U2>,
    <Self::Hash as OutputSizeUser>::OutputSize: ArraySize
        + IsLess<U256>
        + IsLessOrEqual<<Self::Hash as BlockSizeUser>::BlockSize, Output = True>
        + IsGreaterOrEqual<Prod<<Self::Group as Group>::SecurityLevel, U2>, Output = True>,
{
    /// The ciphersuite identifier as dictated by
    /// <https://www.rfc-editor.org/rfc/rfc9497>
    const ID: &'static [u8];

    /// A finite cyclic group along with a point representation that allows some
    /// customization on how to hash an input to a curve point. See [`Group`].
    type Group: Group;

    /// The main hash function to use (for HKDF computations and hashing
    /// transcripts).
    type Hash: Digest + BlockSizeUser + Default + FixedOutput + HashMarker;
}

/// A generic [`CipherSuite`] implementation for any compatible (Group, Hash) pair
#[allow(dead_code)]
#[derive(Debug)]
pub struct Suite<G, H>(core::marker::PhantomData<(G, H)>);

impl<G, H> CipherSuite for Suite<G, H>
where
    G: Group + OprfParameters,
    H: BlockSizeUser + Default + FixedOutput + HashMarker + OutputSizeUser,
    <G as Group>::SecurityLevel: Mul<U2>,
    <H as OutputSizeUser>::OutputSize: ArraySize
        + IsLess<U256>
        + IsLessOrEqual<<H as BlockSizeUser>::BlockSize, Output = True>
        + IsGreaterOrEqual<Prod<<G as Group>::SecurityLevel, U2>, Output = True>,
{
    const ID: &'static [u8] = G::ID;
    type Group = G;
    type Hash = H;
}