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

Cargo.toml

@@ -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" }

src/builder.rs

@@ -1,7 +1,8 @@
 //! Types and functions for building Sapling transaction components.
 
-use core::fmt;
-use std::{collections::BTreeMap, iter, marker::PhantomData};
+use alloc::collections::BTreeMap;
+use alloc::vec::Vec;
+use core::{fmt, iter, marker::PhantomData};
 
 use group::ff::Field;
 use incrementalmerkletree::Position;
@@ -11,24 +12,27 @@ use redjubjub::{Binding, SpendAuth};
 use zcash_note_encryption::EphemeralKeyBytes;
 
 use crate::{
-    bundle::{
-        Authorization, Authorized, Bundle, GrothProofBytes, OutputDescription, SpendDescription,
-    },
-    circuit,
+    bundle::{Authorization, Authorized, Bundle, GrothProofBytes},
     keys::{
         EphemeralSecretKey, ExpandedSpendingKey, FullViewingKey, OutgoingViewingKey,
         SpendAuthorizingKey, SpendValidatingKey,
     },
     note::ExtractedNoteCommitment,
     note_encryption::{sapling_note_encryption, Zip212Enforcement},
-    prover::{OutputProver, SpendProver},
     util::generate_random_rseed_internal,
-    value::{
-        CommitmentSum, NoteValue, TrapdoorSum, ValueCommitTrapdoor, ValueCommitment, ValueSum,
-    },
+    value::{NoteValue, ValueCommitTrapdoor, ValueCommitment, ValueSum},
+    Anchor, Diversifier, MerklePath, Node, Note, Nullifier, PaymentAddress, SaplingIvk,
+    NOTE_COMMITMENT_TREE_DEPTH,
+};
+
+#[cfg(feature = "circuit")]
+use crate::{
+    bundle::{OutputDescription, SpendDescription},
+    circuit,
+    prover::{OutputProver, SpendProver},
+    value::{CommitmentSum, TrapdoorSum},
     zip32::ExtendedSpendingKey,
-    Anchor, Diversifier, MerklePath, Node, Note, Nullifier, PaymentAddress, ProofGenerationKey,
-    SaplingIvk, NOTE_COMMITMENT_TREE_DEPTH,
+    ProofGenerationKey,
 };
 
 /// If there are any shielded inputs, always have at least two shielded outputs, padding
@@ -268,6 +272,7 @@ impl PreparedSpendInfo {
         (cv, nullifier, rk, alpha)
     }
 
+    #[cfg(feature = "circuit")]
     fn build<Pr: SpendProver, R: RngCore>(
         self,
         proof_generation_key: Option<ProofGenerationKey>,
@@ -464,6 +469,7 @@ impl PreparedOutputInfo {
         )
     }
 
+    #[cfg(feature = "circuit")]
     fn build<Pr: OutputProver, R: RngCore>(
         self,
         rng: &mut R,
@@ -664,6 +670,7 @@ impl Builder {
     }
 
     /// Constructs the Sapling bundle from the builder's accumulated state.
+    #[cfg(feature = "circuit")]
     pub fn build<SP: SpendProver, OP: OutputProver, R: RngCore, V: TryFrom<i64>>(
         self,
         extsks: &[ExtendedSpendingKey],
@@ -726,6 +733,7 @@ impl Builder {
 
 /// Constructs a new Sapling transaction bundle of the given type from the specified set of spends
 /// and outputs.
+#[cfg(feature = "circuit")]
 pub fn bundle<SP: SpendProver, OP: OutputProver, R: RngCore, V: TryFrom<i64>>(
     rng: R,
     bundle_type: BundleType,
@@ -917,6 +925,7 @@ fn build_bundle<B, SP, OP, R: RngCore>(
 /// Type alias for an in-progress bundle that has no proofs or signatures.
 ///
 /// This is returned by [`Builder::build`].
+#[cfg(feature = "circuit")]
 pub type UnauthorizedBundle<V> = Bundle<InProgress<Unproven, Unsigned>, V>;
 
 /// Marker trait representing bundle proofs in the process of being created.
@@ -951,9 +960,11 @@ impl<P: InProgressProofs, S: InProgressSignatures> Authorization for InProgress<
 ///
 /// The [`SpendDescription`]s and [`OutputDescription`]s within the bundle contain the
 /// private data needed to create proofs.
+#[cfg(feature = "circuit")]
 #[derive(Clone, Copy, Debug)]
 pub struct Unproven;
 
+#[cfg(feature = "circuit")]
 impl InProgressProofs for Unproven {
     type SpendProof = circuit::Spend;
     type OutputProof = circuit::Output;
@@ -969,29 +980,34 @@ impl InProgressProofs for Proven {
 }
 
 /// Reports on the progress made towards creating proofs for a bundle.
+#[cfg(feature = "circuit")]
 pub trait ProverProgress {
     /// Updates the progress instance with the number of steps completed and the total
     /// number of steps.
     fn update(&mut self, cur: u32, end: u32);
 }
 
+#[cfg(feature = "circuit")]
 impl ProverProgress for () {
     fn update(&mut self, _: u32, _: u32) {}
 }
 
+#[cfg(feature = "circuit")]
 impl<U: From<(u32, u32)>> ProverProgress for std::sync::mpsc::Sender<U> {
     fn update(&mut self, cur: u32, end: u32) {
         // If the send fails, we should ignore the error, not crash.
         self.send(U::from((cur, end))).unwrap_or(());
     }
 }
 
+#[cfg(feature = "circuit")]
 impl<U: ProverProgress> ProverProgress for &mut U {
     fn update(&mut self, cur: u32, end: u32) {
         (*self).update(cur, end);
     }
 }
 
+#[cfg(feature = "circuit")]
 struct CreateProofs<'a, SP: SpendProver, OP: OutputProver, R: RngCore, U: ProverProgress> {
     spend_prover: &'a SP,
     output_prover: &'a OP,
@@ -1001,6 +1017,7 @@ struct CreateProofs<'a, SP: SpendProver, OP: OutputProver, R: RngCore, U: Prover
     progress: u32,
 }
 
+#[cfg(feature = "circuit")]
 impl<'a, SP: SpendProver, OP: OutputProver, R: RngCore, U: ProverProgress>
     CreateProofs<'a, SP, OP, R, U>
 {
@@ -1041,6 +1058,7 @@ impl<'a, SP: SpendProver, OP: OutputProver, R: RngCore, U: ProverProgress>
         OP::encode_proof(proof)
     }
 
+    #[cfg(feature = "circuit")]
     fn map_authorization<S: InProgressSignatures>(
         &mut self,
         a: InProgress<Unproven, S>,
@@ -1052,6 +1070,7 @@ impl<'a, SP: SpendProver, OP: OutputProver, R: RngCore, U: ProverProgress>
     }
 }
 
+#[cfg(feature = "circuit")]
 impl<S: InProgressSignatures, V> Bundle<InProgress<Unproven, S>, V> {
     /// Creates the proofs for this bundle.
     pub fn create_proofs<SP: SpendProver, OP: OutputProver>(