anza-cryptography-source/ed25519-heea/README.md

ed25519-heea

ZIP-215-compliant Ed25519 signatures with HEEA-accelerated verification, forked from ed25519-zebra.

For the original ed25519-zebra documentation see README_zebra.md.

This crate is part of the curve25519-sol workspace.

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Changes from ed25519-zebra

verify_heea: fast-path signature verification

A new method VerificationKey::verify_heea has been added alongside the existing verify. Both methods accept the same arguments and produce identical results — verify_heea is a drop-in accelerated replacement for verify.

The HEEA method (from the TCHES 2025 paper "Accelerating EdDSA Signature Verification with Faster Scalar Size Halving") transforms the standard 2-point MSM:

[8][s]B = [8]R + [8][h]A     (standard)

into a 4-point MSM over half-size (~128-bit) scalars:

τs_lo·B + τs_hi·(2¹²⁸·B) = τ·R + ρ·A     (HEEA)

where ρ ≡ ±τ·h (mod ℓ) and τs = τs_hi·2¹²⁸ + τs_lo. All four scalars are ≤128 bits, and the two basepoints (B and 2¹²⁸B) use precomputed lookup tables, giving approximately ~15% faster verification compared to the standard path.

Dependencies

ed25519-zebra was updated to depend on this fork's curve25519 crate instead of curve25519-dalek, in order to access HEEADecomposition and vartime_triple_scalar_mul_basepoint.

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ZIP 215

ZIP-215-compliant Ed25519 validation rules are fully preserved from ed25519-zebra:

• Non-canonical point encodings are accepted for A and R.
• s must be a canonical integer less than the group order ℓ.
• The cofactor-cleared equation [8][s]B = [8]R + [8][h]A is used (not the RFC 8032 variant).

See README_zebra.md and ZIP 215 for full details.

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Usage

[dependencies]
ed25519-heea = { git = "https://github.com/zz-sol/ed25519-sol", package = "ed25519-heea" }

Example

use core::convert::TryFrom;
use rand::thread_rng;
use ed25519_heea::{SigningKey, VerificationKey};

let msg = b"curve25519-sol";

// Generate key and sign
let sk = SigningKey::new(thread_rng());
let sig = sk.sign(msg);
let vk = VerificationKey::from(&sk);

// Standard ZIP-215 verification (from ed25519-zebra)
vk.verify(&sig, msg).expect("valid signature");

// HEEA-accelerated verification (same result, ~15% faster)
vk.verify_heea(&sig, msg).expect("valid signature");

Batch verification

Batch verification is unchanged from ed25519-zebra and uses a randomised linear combination to check multiple signatures in one pass:

#[cfg(feature = "alloc")]
{
    use ed25519_heea::batch;

    let mut verifier = batch::Verifier::new();
    for (vk_bytes, sig, msg) in items {
        verifier.queue((vk_bytes, sig, msg));
    }
    verifier.verify(thread_rng()).expect("all valid");
}

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Features

Feature	Default?	Description
std	✓	Enables std; without it the crate is no_std + alloc.
alloc	✓	Enables batch verification.
serde		Serialization for key and signature types.
pkcs8		PKCS#8 DER encoding/decoding for VerificationKey.

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MSRV

Rust 1.85.0 (Edition 2024).

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References

• TCHES 2025 paper – Accelerating EdDSA Signature Verification with Faster Scalar Size Halving
• ed25519-zebra – upstream library (Zcash Foundation)
• ZIP 215 – Ed25519 validation rules for Zcash
• Original ed25519-zebra README

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT license (LICENSE-MIT)

at your option.