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135 lines
5 KiB
Markdown
135 lines
5 KiB
Markdown
# curve25519-sol
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A high-performance, opinionated fork of [curve25519-dalek] and [ed25519-zebra] focused on
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accelerated Ed25519 signature verification via the **HEEA** (Half-Extended Euclidean Algorithm)
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method and a reduced set of well-tested backends.
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> Original library READMEs: [README_dalek.md](README_dalek.md) (workspace) ·
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> [solana-ed25519/README_dalek.md](solana-ed25519/README_dalek.md) ·
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> [solana-ed25519/README_zebra.md](solana-ed25519/README_zebra.md)
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---
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## Crates
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| Crate | Description |
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|---|---|
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| [`solana-ed25519`](./solana-ed25519) | Fork of `curve25519-dalek` with ZIP-215-compliant Ed25519 from `ed25519-zebra`, HEEA-accelerated `verify` / `verify_zebra`, and a narrowed backend set (removed `u32` and constraint device supports). |
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| [`curve25519-cuda`](./curve25519-cuda) | GPU-accelerated multi-scalar multiplication (MSM) via CUDA/SPPARK. Falls back to CPU when CUDA is unavailable. |
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SIMD helper macros come from the workspace dependency `curve25519-dalek-derive = "0.1.1"`;
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there is no local `curve25519-derive` crate in this workspace.
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---
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## Key Changes from Upstream
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### HEEA Signature Verification
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Standard Ed25519 verification checks **sB = R + hA**, where `h` is a 256-bit scalar.
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HEEA (from the TCHES 2025 paper _"Accelerating EdDSA Signature Verification with Faster Scalar
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Size Halving"_) transforms this into a 4-point MSM with ~128-bit scalars:
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```
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flip_h = false: τs_lo · B + τs_hi · (2¹²⁸·B) = τ·R + ρ·A
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flip_h = true: τs_lo · B + τs_hi · (2¹²⁸·B) = τ·R - ρ·A
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```
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where `ρ` and `τ` are half-size (~127-bit) values derived from `h` via a half-extended
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Euclidean algorithm, and `τs = τs_hi · 2¹²⁸ + τs_lo`. All four scalars are ≤128 bits, and
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two of the bases (`B` and `2¹²⁸B`) use precomputed tables. In practice this yields roughly
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**~15% faster** verification compared to the standard double-scalar-multiplication path.
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The algorithm is implemented in:
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- [`solana-ed25519/src/scalar/heea.rs`](solana-ed25519/src/scalar/heea.rs) – `curve25519_heea_vartime`
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- [`solana-ed25519/src/traits.rs`](solana-ed25519/src/traits.rs) – `HEEADecomposition` trait
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- [`solana-ed25519/src/backend/serial/scalar_mul/vartime_triple_base.rs`](solana-ed25519/src/backend/serial/scalar_mul/vartime_triple_base.rs) – optimised 128+128+256 MSM
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- [`solana-ed25519/src/ed_sigs/verification_key.rs`](solana-ed25519/src/ed_sigs/verification_key.rs) – `VerificationKey::verify` / `VerificationKey::verify_zebra`
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### Reduced Backend Set
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Upstream `curve25519-dalek` supports serial, fiat-crypto, AVX2, and unstable AVX512 backends.
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This fork retains only the backends actively tested and maintained here:
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| Backend | Platform | Selection |
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| `serial` | All (macOS, Linux, …) | Automatic fallback |
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| `simd` / AVX2 | x86-64 with AVX2 | Runtime CPU detection |
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| CUDA (separate crate) | NVIDIA GPU | Opt-in via `curve25519-cuda` |
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The `fiat` (formally-verified) and `unstable_avx512` backends have been removed to reduce
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maintenance surface. If you need them, use upstream `curve25519-dalek` directly.
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---
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## Usage
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Add the relevant crate to `Cargo.toml`:
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```toml
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curve25519 = { package = "solana-ed25519", git = "https://github.com/anza-xyz/cryptography" }
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```
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### Standard Ed25519 verification
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```rust
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use curve25519::ed_sigs::{SigningKey, VerificationKey};
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use rand::thread_rng;
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let msg = b"hello world";
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let sk = SigningKey::new(thread_rng());
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let sig = sk.sign(msg);
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let vk = VerificationKey::from(&sk);
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// Standard ZIP-215-compliant verification
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vk.verify(&sig, msg).expect("valid signature");
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```
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### Explicit HEEA-accelerated verification
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```rust
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// Same ZIP-215 result as verify(), using the HEEA path explicitly.
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vk.verify_zebra(&sig, msg).expect("valid signature");
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```
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---
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## Building
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```sh
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# Standard build
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cargo build --release
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# With AVX2 (automatic on x86-64 at runtime; or force compile-time)
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RUSTFLAGS='-C target-feature=+avx2' cargo build --release
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# Run benchmarks
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cargo bench --features "rand_core" -p solana-ed25519
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cargo bench -p curve25519-cuda
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```
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---
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## References
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- [Accelerating EdDSA Signature Verification with Faster Scalar Size Halving](https://tches.iacr.org/index.php/TCHES/article/view/11971) — TCHES 2025
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- [ZIP 215](https://zips.z.cash/zip-0215) — Ed25519 validation rules used by Zcash
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- [curve25519-dalek](https://github.com/dalek-cryptography/curve25519-dalek) — upstream curve library
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- [ed25519-zebra](https://github.com/ZcashFoundation/ed25519-zebra) — upstream signature library
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---
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## License
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Licensed under either of
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- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
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- MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
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at your option.
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Portions of this library are derived from [curve25519-dalek] (isis lovecruft, Henry de Valence)
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and [ed25519-zebra] (Zcash Foundation), both dual-licensed MIT/Apache-2.0.
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[curve25519-dalek]: https://github.com/dalek-cryptography/curve25519-dalek
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[ed25519-zebra]: https://github.com/ZcashFoundation/ed25519-zebra
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