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Make copy_key optional in fastcrypto-pq #1008

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f1f0e43
Make copy_key optional in fastcrypto-pq
jonas-lj Aug 24, 2026
71f524a
[chore] Drop the forced copy_key feature from fastcrypto-cli
mahdi-mysten Sep 3, 2026
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8 changes: 6 additions & 2 deletions fastcrypto-pq/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,7 @@ repository = "https://github.com/MystenLabs/fastcrypto"
publish = false

[dependencies]
# copy_key is not optional here
fastcrypto = { path = "../fastcrypto", features = ["copy_key"] }
fastcrypto = { path = "../fastcrypto" }

@mahdi-mysten mahdi-mysten Aug 26, 2026

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cargo check --workspace fails on

fastcrypto/fastcrypto-pq/src/mldsa65/mod.rs

Line 167 in f1f0e43

impl KeyPair for MLDSA65KeyPair {

with error:

error[E0046]: not all trait items implemented, missing: `copy`
   --> fastcrypto-pq/src/mldsa65/mod.rs:179:1

the core issue I think is:

fastcrypto/fastcrypto-cli/Cargo.toml

Line 13 in f1f0e43

fastcrypto = { path = "../fastcrypto", features = ["copy_key"] }

hardcodes features = ["copy_key"], so feature unification turns it on for the shared fastcrypto build.

fastcrypto-derive = { path = "../fastcrypto-derive", version = "0.1.4" }
# The C backend (mldsa-native, pinned as a submodule inside the wrapper)
mysten-mldsa-native-rs = { git = "https://github.com/MystenLabs/mysten-mldsa-native-rs.git", rev = "ea1a9794c7ad0c68b9410121964b7439540826bc", version = "0.1.0" }
Expand All @@ -23,6 +22,11 @@ bincode.workspace = true
zeroize.workspace = true

[features]
# Forwards to fastcrypto's copy_key, which gates KeyPair::copy for every scheme. Optional
# here so that depending on this crate does not turn private key copying on for the rest of
# the dependency graph through feature unification.
copy_key = ["fastcrypto/copy_key"]

# Forwards to the wrapper's verified assembly backends: NEON on aarch64, AVX2 on x86_64
# behind a runtime CPU probe. Identical signatures either way, roughly 2.5x faster.
native = ["mysten-mldsa-native-rs/native"]
Expand Down
2 changes: 1 addition & 1 deletion fastcrypto-pq/README.md
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Expand Up @@ -55,7 +55,7 @@ smart-contract vaults rather than the native transaction path.

```bash
# everything, both schemes
cargo test -p fastcrypto-pq --features native
cargo test -p fastcrypto-pq --all-features

# only the SLH-DSA building blocks
cargo test -p fastcrypto-pq sphincs
Expand Down
2 changes: 1 addition & 1 deletion fastcrypto-pq/src/mldsa65/mod.rs
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Expand Up @@ -177,7 +177,7 @@ impl KeyPair for MLDSA65KeyPair {
self.private
}

// Not cfg-gated on copy_key; this crate always enables fastcrypto/copy_key
#[cfg(feature = "copy_key")]
fn copy(&self) -> Self {
MLDSA65KeyPair {
public: self.public.clone(),
Expand Down
5 changes: 3 additions & 2 deletions fastcrypto-pq/src/tests/mldsa65_tests.rs
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Expand Up @@ -180,7 +180,7 @@ fn serialize_deserialize() {
verify_serialization(&signature, Some(signature.as_ref()));

// The secret side serializes as the 32-byte seed
let private = keypair.copy().private();
let private = MLDSA65PrivateKey::from_bytes(keypair.as_ref()).unwrap();
verify_serialization(&private, Some(private.as_ref()));
let kp_bytes = bincode::serialize(&keypair).unwrap();
assert_eq!(kp_bytes, keypair.as_ref());
Expand Down Expand Up @@ -241,6 +241,7 @@ fn keypair_from_str_roundtrip() {
}

#[test]
#[cfg(feature = "copy_key")]
fn copy_key_pair_preserves_identity() {
let keypair = keys().pop().unwrap();
let copied = keypair.copy();
Expand Down Expand Up @@ -290,7 +291,7 @@ fn debug_output_is_redacted_for_secrets() {
let keypair = keys().pop().unwrap();

// Secret material must never appear in formatted output.
let private = keypair.copy().private();
let private = MLDSA65PrivateKey::from_bytes(keypair.as_ref()).unwrap();
assert!(!format!("{private:?}").contains(&Base64::encode(keypair.as_ref())));

// Public types print their base64 form, which assertion failures rely on.
Expand Down
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