Implement no_std support via a default-enabled std feature flag.

.github/workflows/ci.yml

@@ -41,12 +41,36 @@ jobs:
       matrix:
         target:
           - wasm32-wasi
+          - thumbv7em-none-eabihf
     steps:
       - uses: actions/checkout@v4
+        with:
+          path: crate_root
+      # We use a synthetic crate to ensure no dev-dependencies are enabled, which can
+      # be incompatible with some of these targets.
+      - name: Create synthetic crate for testing
+        run: cargo init --lib ci-build
+      - name: Copy Rust version into synthetic crate
+        run: cp crate_root/rust-toolchain.toml ci-build/
+      - name: Copy patch directives into synthetic crate
+        run: |
+          echo "[patch.crates-io]" >> ./ci-build/Cargo.toml
+          cat ./crate_root/Cargo.toml | sed "0,/.\+\(patch.crates.\+\)/d" >> ./ci-build/Cargo.toml
+      - name: Add no_std pragma to lib.rs
+        run: |
+          echo "#![no_std]" > ./ci-build/src/lib.rs
+      - name: Add sapling-crypto as a dependency of the synthetic crate
+        working-directory: ./ci-build
+        run: cargo add --no-default-features --path ../crate_root
+      - name: Add lazy_static with the spin_no_std feature
+        working-directory: ./ci-build
+        run: cargo add lazy_static --features "spin_no_std"
       - name: Add target
+        working-directory: ./ci-build
         run: rustup target add ${{ matrix.target }}
-      - name: Build crate
-        run: cargo build --no-default-features --verbose --target ${{ matrix.target }}
+      - name: Build for target
+        working-directory: ./ci-build
+        run: cargo build --verbose --target ${{ matrix.target }}
 
   bitrot:
     name: Bitrot check

CHANGELOG.md

@@ -9,6 +9,13 @@ and this library adheres to Rust's notion of
 
 ### Added
 - `sapling_crypto::pczt::Zip32Derivation::extract_account_index`
+- `no_std` compatibility has been introduced by means of a default-enabled
+  `std` feature flag.
+- A default-enabled `circuit` is now provided to enable downstream users to
+  avoid the need to depend upon the `bellman` crate.
+
+### Changed
+- MSRV is now 1.66
 
 ## [0.4.0] - 2024-12-16
 

Cargo.toml

@@ -7,7 +7,7 @@ authors = [
     "Kris Nuttycombe <[email protected]>",
 ]
 edition = "2021"
-rust-version = "1.65"
+rust-version = "1.66"
 description = "Cryptographic library for Zcash Sapling"
 homepage = "https://github.com/zcash/sapling-crypto"
 repository = "https://github.com/zcash/sapling-crypto"
@@ -18,48 +18,50 @@ features = ["test-dependencies"]
 rustdoc-args = ["--cfg", "docsrs"]
 
 [dependencies]
-ff = "0.13"
-group = { version = "0.13", features = ["wnaf-memuse"] }
+ff = { version = "0.13", default-features = false }
+group = "0.13"
 
-bls12_381 = "0.8"
-jubjub = "0.10"
-redjubjub = "0.7"
+bls12_381 = { version = "0.8", default-features = false, features = ["alloc"] }
+jubjub = { version = "0.10", default-features = false, features = ["alloc"] }
+redjubjub = { version = "0.7", default-features = false }
 zcash_spec = "0.1"
 
 # Boilerplate
 getset = "0.1"
 
+# No-std support
+core2 = { version = "0.3", default-features = false, features = ["alloc"] }
+
 # Circuits
-bellman = { version = "0.14", default-features = false, features = ["groth16"] }
+bellman = { version = "0.14", features = ["groth16"], optional = true }
 
 # CSPRNG
-rand = "0.8"
-rand_core = "0.6"
+rand = { version = "0.8", default-features = false }
+rand_core = { version = "0.6", default-features = false }
 
 # Digests
-blake2b_simd = "1"
-blake2s_simd = "1"
+blake2b_simd = { version = "1", default-features = false }
+blake2s_simd = { version = "1", default-features = false }
 
 # Documentation
-document-features = "0.2"
+document-features = { version = "0.2", optional = true }
 
 # Encodings
-byteorder = "1"
-hex = "0.4"
+hex = { version = "0.4", default-features = false, features = ["alloc"] }
 
 # Logging and metrics
-memuse = "0.2.1"
-tracing = "0.1"
+memuse = { version = "0.2.2", default-features = false }
+tracing = { version = "0.1", default-features = false }
 
 # Note Commitment Trees
-bitvec = "1"
-incrementalmerkletree = { version = "0.7", features = ["legacy-api"] }
+bitvec = { version = "1", default-features = false }
+incrementalmerkletree = { version = "0.7", default-features = false, features = ["legacy-api"] }
 
 # Note encryption
 zcash_note_encryption = { version = "0.4", features = ["pre-zip-212"] }
 
 # Secret management
-subtle = "2.2.3"
+subtle = { version = "2.2.3", default-features = false }
 
 # Static constants
 lazy_static = "1"
@@ -69,8 +71,9 @@ proptest = { version = "1", optional = true }
 
 # ZIP 32
 aes = "0.8"
-fpe = "0.6"
-zip32 = "0.1"
+fpe = { version = "0.6", default-features = false, features = ["alloc"] }
+zip32 = { version = "0.1.1", default-features = false }
+
 
 [dev-dependencies]
 chacha20poly1305 = "0.10"
@@ -83,10 +86,26 @@ rand_xorshift = "0.3"
 pprof = { version = "0.11", features = ["criterion", "flamegraph"] } # MSRV 1.56
 
 [features]
-default = ["multicore"]
+default = ["multicore", "std"]
+std = [
+  "core2/std",
+  "document-features",
+  "group/wnaf-memuse",
+  "redjubjub/std",
+  "circuit",
+]
+
+## Enables creation of Sapling proofs
+circuit = [
+  "bellman",
+  "bls12_381/bits",
+  "bls12_381/groups",
+  "bls12_381/pairings",
+  "jubjub/bits",
+]
 
 ## Enables multithreading support for creating proofs.
-multicore = ["bellman/multicore"]
+multicore = ["circuit", "bellman/multicore"]
 
 ### A temporary feature flag that exposes granular APIs needed by `zcashd`. These APIs
 ### should not be relied upon and will be removed in a future release.
@@ -105,3 +124,6 @@ harness = false
 [[bench]]
 name = "pedersen_hash"
 harness = false
+
+[patch.crates-io]
+redjubjub = { git = "https://github.com/nuttycom/redjubjub", rev = "e413019904400f4caa3550df7c4040befadfbb14" }

README.md

@@ -1,6 +1,13 @@
 # sapling-crypto
 
-This repository contains a (work-in-progress) implementation of Zcash's "Sapling" cryptography.
+This repository contains an implementation of Zcash's "Sapling" cryptography.
+
+## `no_std` compatibility
+
+Downstream users of this crate must enable the `spin_no_std` feature of the
+`lazy_static` crate in order to take advantage of `no_std` builds; this is due
+to the fact that `--no-default-features` builds of `lazy_static` still rely on
+`std`.
 
 ## License
 

rust-toolchain.toml

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "1.65.0"
+channel = "1.66.0"
 components = ["clippy", "rustfmt"]