Add `no-std` support (#11)

* Add no_std support

* Update CHANGELOG

* Remove unused alloc feature flag

* Remove a forgotten comment

Co-authored-by: str4d <thestr4d@gmail.com>

* Make zeroize dependency optional

* Add alloc feature flag

* Clean the code by outer attributes

* use 2021 edition

Co-authored-by: str4d <thestr4d@gmail.com>
Co-authored-by: Conrado Gouvea <conradoplg@gmail.com>

CHANGELOG.md

@@ -5,6 +5,9 @@ Entries are listed in reverse chronological order.
 ## Unreleased
 
 * Migrate to `group` 0.12, `jubjub` 0.9, `pasta_curves` 0.4
+* Added support for `no-std` builds, via new (default-enabled) `std` and `alloc`
+  feature flags. Module `batch` is supported on `alloc` feature only. Module
+  `frost` is supported on `std` feature only.
 
 ## 0.2.0
 

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "reddsa"
-edition = "2018"
+edition = "2021"
 # When releasing to crates.io:
 # - Update html_root_url
 # - Update CHANGELOG.md
@@ -23,15 +23,19 @@ description = "A standalone implementation of the RedDSA signature scheme."
 features = ["nightly"]
 
 [dependencies]
-blake2b_simd = "1"
-byteorder = "1.4"
-group = "0.12"
-jubjub = "0.9"
-pasta_curves = "0.4"
-rand_core = "0.6"
+blake2b_simd = { version = "1", default-features = false }
+byteorder = { version = "1.4", default-features = false }
+group = { version = "0.12", default-features = false }
+jubjub = { version = "0.9", default-features = false }
+pasta_curves = { version = "0.4", default-features = false, features = ["alloc"] }
+rand_core = { version = "0.6", default-features = false }
 serde = { version = "1", optional = true, features = ["derive"] }
-thiserror = "1.0"
-zeroize = { version = "1", default-features = false, features = ["zeroize_derive"] }
+thiserror = { version = "1.0", optional = true }
+
+[dependencies.zeroize]
+version = "1"
+features = ["zeroize_derive"]
+optional = true
 
 [dev-dependencies]
 bincode = "1"
@@ -44,8 +48,11 @@ rand_chacha = "0.3"
 serde_json = "1.0"
 
 [features]
+std = ["blake2b_simd/std", "thiserror", "zeroize", "alloc",
+       "serde"] # conditional compilation for serde not complete (issue #9)
+alloc = []
 nightly = []
-default = ["serde"]
+default = ["std"]
 
 [[bench]]
 name = "bench"

src/batch.rs

@@ -18,7 +18,8 @@
 //! and loss of the ability to easily pinpoint failing signatures.
 //!
 
-use std::convert::TryFrom;
+use alloc::vec::Vec;
+use core::convert::TryFrom;
 
 use group::{
     cofactor::CofactorGroup,
@@ -246,7 +247,7 @@ impl<S: SpendAuth, B: Binding<Scalar = S::Scalar, Point = S::Point>> Verifier<S,
             VKs.push(VK);
         }
 
-        use std::iter::once;
+        use core::iter::once;
 
         let scalars = once(&P_spendauth_coeff)
             .chain(once(&P_binding_coeff))

src/error.rs

@@ -8,18 +8,28 @@
 // - Deirdre Connolly <deirdre@zfnd.org>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
-use thiserror::Error;
+use core::fmt;
 
 /// An error related to RedDSA signatures.
-#[derive(Error, Debug, Copy, Clone, Eq, PartialEq)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub enum Error {
     /// The encoding of a signing key was malformed.
-    #[error("Malformed signing key encoding.")]
     MalformedSigningKey,
     /// The encoding of a verification key was malformed.
-    #[error("Malformed verification key encoding.")]
     MalformedVerificationKey,
     /// Signature verification failed.
-    #[error("Invalid signature.")]
     InvalidSignature,
 }
+
+#[cfg(feature = "std")]
+impl std::error::Error for Error {}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::MalformedSigningKey => write!(f, "Malformed signing key encoding."),
+            Self::MalformedVerificationKey => write!(f, "Malformed verification key encoding."),
+            Self::InvalidSignature => write!(f, "Invalid signature."),
+        }
+    }
+}

src/frost.rs

@@ -23,6 +23,7 @@
 //! Internally, keygen_with_dealer generates keys using Verifiable Secret
 //! Sharing,  where shares are generated using Shamir Secret Sharing.
 
+use alloc::vec::Vec;
 use std::{
     collections::HashMap,
     convert::{TryFrom, TryInto},

src/hash.rs

@@ -8,7 +8,7 @@
 // - Deirdre Connolly <deirdre@zfnd.org>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
-use std::marker::PhantomData;
+use core::marker::PhantomData;
 
 use blake2b_simd::{Params, State};
 

src/lib.rs

@@ -8,19 +8,30 @@
 // - Deirdre Connolly <deirdre@zfnd.org>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
+#![no_std]
 #![deny(missing_docs)]
 #![doc = include_str!("../README.md")]
 
 //! Docs require the `nightly` feature until RFC 1990 lands.
 
+#[cfg(feature = "alloc")]
+#[macro_use]
+extern crate alloc;
+#[cfg(feature = "std")]
+extern crate std;
+
+#[cfg(feature = "alloc")]
 pub mod batch;
 mod constants;
 mod error;
+#[cfg(feature = "std")]
 pub mod frost;
 mod hash;
+#[cfg(feature = "std")]
 mod messages;
 pub mod orchard;
 pub mod sapling;
+#[cfg(feature = "alloc")]
 mod scalar_mul;
 pub(crate) mod signature;
 mod signing_key;
@@ -74,12 +85,18 @@ pub(crate) mod private {
     }
 
     pub trait Sealed<T: SigType>:
-        Copy + Clone + Default + Eq + PartialEq + std::fmt::Debug
+        Copy + Clone + Default + Eq + PartialEq + core::fmt::Debug
     {
         const H_STAR_PERSONALIZATION: &'static [u8; 16];
         type Scalar: group::ff::PrimeField + SealedScalar;
+
+        // `Point: VartimeMultiscalarMul` is conditioned by `alloc` feature flag
+        // This is fine because `Sealed` is an internal trait.
+        #[cfg(feature = "alloc")]
         type Point: group::cofactor::CofactorCurve<Scalar = Self::Scalar>
             + scalar_mul::VartimeMultiscalarMul<Scalar = Self::Scalar, Point = Self::Point>;
+        #[cfg(not(feature = "alloc"))]
+        type Point: group::cofactor::CofactorCurve<Scalar = Self::Scalar>;
 
         fn basepoint() -> T::Point;
     }

src/messages.rs

@@ -6,6 +6,7 @@ use crate::{frost, signature, verification_key, SpendAuth};
 use group::GroupEncoding;
 use serde::{Deserialize, Serialize};
 
+use alloc::vec::Vec;
 use std::{collections::BTreeMap, convert::TryInto};
 
 #[cfg(test)]

src/orchard.rs

@@ -1,15 +1,19 @@
 //! Signature types for the Orchard protocol.
 
-use std::borrow::Borrow;
+#[cfg(feature = "alloc")]
+use alloc::vec::Vec;
+#[cfg(feature = "alloc")]
+use core::borrow::Borrow;
 
-use group::{ff::PrimeField, Group, GroupEncoding};
+use group::GroupEncoding;
+#[cfg(feature = "alloc")]
+use group::{ff::PrimeField, Group};
 use pasta_curves::pallas;
 
-use crate::{
-    private,
-    scalar_mul::{LookupTable5, NonAdjacentForm, VartimeMultiscalarMul},
-    SigType,
-};
+use crate::{private, SigType};
+
+#[cfg(feature = "alloc")]
+use crate::scalar_mul::{LookupTable5, NonAdjacentForm, VartimeMultiscalarMul};
 
 /// The byte-encoding of the basepoint for `OrchardSpendAuthSig`.
 const ORCHARD_SPENDAUTHSIG_BASEPOINT_BYTES: [u8; 32] = [
@@ -74,6 +78,7 @@ impl private::Sealed<Binding> for Binding {
     }
 }
 
+#[cfg(feature = "alloc")]
 impl NonAdjacentForm for pallas::Scalar {
     /// Compute a width-\\(w\\) "Non-Adjacent Form" of this scalar.
     ///
@@ -136,6 +141,7 @@ impl NonAdjacentForm for pallas::Scalar {
     }
 }
 
+#[cfg(feature = "alloc")]
 impl<'a> From<&'a pallas::Point> for LookupTable5<pallas::Point> {
     #[allow(non_snake_case)]
     fn from(A: &'a pallas::Point) -> Self {
@@ -149,6 +155,7 @@ impl<'a> From<&'a pallas::Point> for LookupTable5<pallas::Point> {
     }
 }
 
+#[cfg(feature = "alloc")]
 impl VartimeMultiscalarMul for pallas::Point {
     type Scalar = pallas::Scalar;
     type Point = pallas::Point;

src/scalar_mul.rs

@@ -10,7 +10,8 @@
 // - Henry de Valence <hdevalence@hdevalence.ca>
 // - Deirdre Connolly <deirdre@zfnd.org>
 
-use std::{borrow::Borrow, fmt::Debug};
+use alloc::vec::Vec;
+use core::{borrow::Borrow, fmt::Debug};
 
 use jubjub::{ExtendedNielsPoint, ExtendedPoint};
 

src/signature.rs

@@ -8,7 +8,7 @@
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
 //! RedDSA Signatures
-use std::marker::PhantomData;
+use core::marker::PhantomData;
 
 use crate::SigType;
 

src/signing_key.rs

@@ -8,7 +8,7 @@
 // - Deirdre Connolly <deirdre@zfnd.org>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
-use std::{
+use core::{
     convert::{TryFrom, TryInto},
     marker::PhantomData,
 };

src/verification_key.rs

@@ -8,7 +8,7 @@
 // - Deirdre Connolly <deirdre@zfnd.org>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
-use std::{
+use core::{
     convert::{TryFrom, TryInto},
     hash::{Hash, Hasher},
     marker::PhantomData,

tests/batch.rs

@@ -1,3 +1,5 @@
+#![cfg(feature = "alloc")]
+
 use rand::thread_rng;
 
 use reddsa::*;

tests/bincode.rs

@@ -1,8 +1,8 @@
-use std::convert::TryFrom;
+#![cfg(feature = "std")]
 
 use proptest::prelude::*;
-
 use reddsa::*;
+use std::convert::TryFrom;
 
 proptest! {
     #[test]

tests/frost.rs

@@ -1,3 +1,5 @@
+#![cfg(all(feature = "std", feature = "serde"))]
+
 use rand::thread_rng;
 use std::collections::HashMap;
 

tests/librustzcash_vectors.rs

@@ -1,4 +1,4 @@
-use std::convert::TryFrom;
+use core::convert::TryFrom;
 
 #[macro_use]
 extern crate lazy_static;

tests/proptests.rs

@@ -1,4 +1,4 @@
-use std::convert::TryFrom;
+use core::convert::TryFrom;
 
 use proptest::prelude::*;
 use rand_core::{CryptoRng, RngCore};

tests/smallorder.rs

@@ -1,4 +1,4 @@
-use std::convert::TryFrom;
+use core::convert::TryFrom;
 
 use jubjub::{AffinePoint, Fq};