Support no_std for ed25519-consensus.

This moves the `std::error::Error` impl for `Error` and the `batch` module behind the `std` feature flag.

.github/workflows/main.yml

@@ -1,21 +1,64 @@
-name: CI
+on: [push, pull_request]
 
-on: [push]
+name: Continuous integration
 
 jobs:
-  test_nightly:
-    name: test on nightly
+  check:
+    name: Check
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
-    # Because we use nightly features for building docs,
-    # using --all-features will fail without nightly toolchain.
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: nightly
-        override: true
-    - uses: actions-rs/cargo@v1
-      with:
-        command: test
-        args: --all-features
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: check
 
+  test:
+    name: Test Suite
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+
+  fmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+      - run: rustup component add rustfmt
+      - uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check
+
+  nostd:
+    name: Build on no_std
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          target: thumbv7em-none-eabihf
+          override: true
+      - uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: --no-default-features --target thumbv7em-none-eabihf

Cargo.toml

@@ -9,15 +9,16 @@ license = "MIT OR Apache-2.0"
 edition = "2018"
 repository = "https://github.com/penumbra-zone/ed25519-consensus"
 description = "Ed25519 suitable for use in consensus-critical contexts."
+resolver = "2"
 
 [dependencies]
-hex = "0.4"
-sha2 = "0.9"
-rand_core = "0.6"
-thiserror = "1"
-curve25519-dalek = { package = "curve25519-dalek-ng", version = "4.1" }
+hex = { version = "0.4", default-features = false, features = ["alloc"] }
+sha2 = { version = "0.9", default-features = false }
+rand_core = { version = "0.6", default-features = false }
+curve25519-dalek = { package = "curve25519-dalek-ng", version = "4.1", default-features = false, features = ["u64_backend", "alloc"] }
 serde = { version = "1", optional = true, features = ["derive"] }
-zeroize = "1.1"
+zeroize = { version = "1.1", default-features = false }
+thiserror = { version = "1", optional = true }
 
 [dev-dependencies]
 rand = "0.8"
@@ -28,8 +29,8 @@ color-eyre = "0.5"
 once_cell = "1.4"
 
 [features]
-nightly = []
-default = ["serde"]
+std = ["thiserror"]
+default = ["serde", "std"]
 
 [[test]]
 name = "rfc8032"

src/batch.rs

@@ -202,8 +202,8 @@ impl Verifier {
             A_coeffs.push(A_coeff);
         }
 
+        use core::iter::once;
         use curve25519_dalek::constants::ED25519_BASEPOINT_POINT as B;
-        use std::iter::once;
         let check = EdwardsPoint::vartime_multiscalar_mul(
             once(&B_coeff).chain(A_coeffs.iter()).chain(R_coeffs.iter()),
             once(&B).chain(As.iter()).chain(Rs.iter()),

src/error.rs

@@ -1,18 +1,20 @@
+#[cfg(feature = "std")]
 use thiserror::Error;
 
 /// An error related to Ed25519 signatures.
-#[derive(Error, Debug, Copy, Clone, Eq, PartialEq)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[cfg_attr(feature = "std", derive(Error))]
 pub enum Error {
     /// The encoding of a secret key was malformed.
-    #[error("Malformed secret key encoding.")]
+    #[cfg_attr(feature = "std", error("Malformed secret key encoding."))]
     MalformedSecretKey,
     /// The encoding of a public key was malformed.
-    #[error("Malformed public key encoding.")]
+    #[cfg_attr(feature = "std", error("Malformed public key encoding."))]
     MalformedPublicKey,
     /// Signature verification failed.
-    #[error("Invalid signature.")]
+    #[cfg_attr(feature = "std", error("Invalid signature."))]
     InvalidSignature,
     /// A byte slice of the wrong length was supplied during parsing.
-    #[error("Invalid length when parsing byte slice.")]
+    #[cfg_attr(feature = "std", error("Invalid length when parsing byte slice."))]
     InvalidSliceLength,
 }

src/lib.rs

@@ -1,7 +1,9 @@
 #![doc(html_root_url = "https://docs.rs/ed25519-consensus/1.0.0")]
 #![doc = include_str!("../README.md")]
 #![deny(missing_docs)]
+#![cfg_attr(not(feature = "std"), no_std)]
 
+#[cfg(feature = "std")]
 pub mod batch;
 mod error;
 mod signature;

src/signature.rs

@@ -1,5 +1,5 @@
 use crate::Error;
-use std::convert::TryFrom;
+use core::convert::TryFrom;
 
 /// An Ed25519 signature.
 #[derive(Copy, Clone, Eq, PartialEq)]

src/signing_key.rs

@@ -1,4 +1,4 @@
-use std::convert::TryFrom;
+use core::convert::TryFrom;
 
 use curve25519_dalek::{constants, scalar::Scalar};
 use rand_core::{CryptoRng, RngCore};

src/verification_key.rs

@@ -1,4 +1,4 @@
-use std::convert::{TryFrom, TryInto};
+use core::convert::{TryFrom, TryInto};
 
 use curve25519_dalek::{
     edwards::{CompressedEdwardsY, EdwardsPoint},
@@ -19,7 +19,7 @@ use crate::{Error, Signature};
 /// A `VerificationKeyBytes` can be used to verify a single signature using the
 /// following idiom:
 /// ```
-/// use std::convert::TryFrom;
+/// use core::convert::TryFrom;
 /// # use rand::thread_rng;
 /// # use ed25519_consensus::*;
 /// # let msg = b"ed25519-consensus";