Revert "signature: replace signature_derive with blanket impls (#1827)" (#1840)

This reverts commit bf47748.

Per #1831 this change breaks inference when there is a single explicit
impl of the `Signer` trait.

It also wasn't possible to add corresponding blanket impls to the
`Async*` traits, e.g. `AsyncSigner` for `AsyncDigestSigner`, because of
the existing blanket impl of `AsyncSigner` for `Signer` which we
definitely want to preserve.

As a general rule of thumb, blanket impls only make sense if they work
100% of the time, which doesn't seem to be happening here.

Closes #1831

Author: tarcieri

.github/workflows/signature.yml

@@ -37,8 +37,9 @@ jobs:
           toolchain: ${{ matrix.rust }}
           targets: ${{ matrix.target }}
       - run: cargo build --target ${{ matrix.target }} --release --no-default-features
-      - run: cargo build --target ${{ matrix.target }} --release --no-default-features --features digest
+      - run: cargo build --target ${{ matrix.target }} --release --no-default-features --features derive
       - run: cargo build --target ${{ matrix.target }} --release --no-default-features --features rand_core
+      - run: cargo build --target ${{ matrix.target }} --release --no-default-features --features derive,rand_core
 
   minimal-versions:
     if: false # disabled until we stop using pre-releases
@@ -51,7 +52,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.85.0 # MSRV
+          - 1.85.0 # Minimum Rust version the tests pass on
           - stable
     steps:
       - uses: actions/checkout@v4
@@ -62,3 +63,19 @@ jobs:
       - run: cargo test --release --no-default-features
       - run: cargo test --release
       - run: cargo test --release --all-features
+
+  derive:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - 1.85.0 # MSRV
+          - stable
+    steps:
+      - uses: actions/checkout@v4
+      - uses: RustCrypto/actions/cargo-cache@master
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust }}
+      - run: cargo test --release
+        working-directory: signature_derive

Cargo.lock

@@ -10,6 +10,7 @@ members = [
     "elliptic-curve",
     "kem",
     "password-hash",
+    "signature_derive",
     "universal-hash",
     "signature",
 ]

Cargo.toml

@@ -13,11 +13,11 @@ categories = ["cryptography", "no-std"]
 description = "Traits for cryptographic signature algorithms (e.g. ECDSA, Ed25519)"
 
 [dependencies]
-signature = "=2.3.0-pre.7"
+signature = "=3.0.0-pre"
 
 [features]
 digest = ["signature/digest"]
-std = ["signature/std"]
+std = []
 rand_core = ["signature/rand_core"]
 
 [package.metadata.docs.rs]

async-signature/Cargo.toml

@@ -21,7 +21,7 @@ cipher = { version = "0.5.0-pre.7", path = "../cipher", optional = true }
 digest = { version = "0.11.0-pre.9", path = "../digest", optional = true, features = ["mac"] }
 elliptic-curve = { version = "0.14.0-rc.1", path = "../elliptic-curve", optional = true }
 password-hash = { version = "0.6.0-rc.0", path = "../password-hash", optional = true }
-signature = { version = "3.0.0-pre", path = "../signature", optional = true, default-features = false }
+signature = { version = "=3.0.0-pre", path = "../signature", optional = true, default-features = false }
 universal-hash = { version = "0.6.0-rc.0", path = "../universal-hash", optional = true }
 
 [features]

crypto/Cargo.toml

@@ -13,6 +13,7 @@ categories = ["cryptography", "no-std"]
 description = "Traits for cryptographic signature algorithms (e.g. ECDSA, Ed25519)"
 
 [dependencies]
+derive = { package = "signature_derive", version = "2", optional = true, path = "../signature_derive" }
 digest = { version = "=0.11.0-pre.10", optional = true, default-features = false }
 rand_core = { version = "0.9", optional = true, default-features = false }
 

signature/Cargo.toml

@@ -145,6 +145,12 @@ mod prehash_signature;
 
 pub use crate::{encoding::*, error::*, keypair::*, signer::*, verifier::*};
 
+#[cfg(feature = "derive")]
+pub use derive::{Signer, Verifier};
+
+#[cfg(all(feature = "derive", feature = "digest"))]
+pub use derive::{DigestSigner, DigestVerifier};
+
 #[cfg(feature = "digest")]
 pub use {crate::prehash_signature::*, digest};
 

signature/src/lib.rs

@@ -19,8 +19,9 @@ use crate::{
 /// This approach is relatively common in signature schemes based on the
 /// [Fiat-Shamir heuristic].
 ///
-/// For signature types that implement this trait, a blanket impl of the [`Signer`] trait is
-/// available for any types that impl [`DigestSigner`], and likewise for the [`Verifier`] for
+/// For signature types that implement this trait, when the `derive` crate
+/// feature is enabled a custom derive for [`Signer`] is available for any
+/// types that impl [`DigestSigner`], and likewise for deriving [`Verifier`] for
 /// types which impl [`DigestVerifier`].
 ///
 /// [Fiat-Shamir heuristic]: https://en.wikipedia.org/wiki/Fiat%E2%80%93Shamir_heuristic

signature/src/prehash_signature.rs

@@ -3,7 +3,7 @@
 use crate::error::Error;
 
 #[cfg(feature = "digest")]
-use crate::{PrehashSignature, digest::Digest};
+use crate::digest::Digest;
 
 #[cfg(feature = "rand_core")]
 use crate::rand_core::{CryptoRng, TryCryptoRng};
@@ -82,17 +82,6 @@ pub trait DigestSigner<D: Digest, S> {
     fn try_sign_digest(&self, digest: D) -> Result<S, Error>;
 }
 
-#[cfg(feature = "digest")]
-impl<S, T> Signer<S> for T
-where
-    S: PrehashSignature,
-    T: DigestSigner<S::Digest, S>,
-{
-    fn try_sign(&self, msg: &[u8]) -> Result<S, Error> {
-        self.try_sign_digest(S::Digest::new_with_prefix(msg))
-    }
-}
-
 /// Sign the given message using the provided external randomness source.
 #[cfg(feature = "rand_core")]
 pub trait RandomizedSigner<S> {
@@ -135,21 +124,6 @@ pub trait RandomizedDigestSigner<D: Digest, S> {
     ) -> Result<S, Error>;
 }
 
-#[cfg(all(feature = "digest", feature = "rand_core"))]
-impl<S, T> RandomizedSigner<S> for T
-where
-    S: PrehashSignature,
-    T: RandomizedDigestSigner<S::Digest, S>,
-{
-    fn try_sign_with_rng<R: TryCryptoRng + ?Sized>(
-        &self,
-        rng: &mut R,
-        msg: &[u8],
-    ) -> Result<S, Error> {
-        self.try_sign_digest_with_rng(rng, S::Digest::new_with_prefix(msg))
-    }
-}
-
 /// Sign the provided message bytestring using `&mut Self` (e.g. an evolving
 /// cryptographic key such as a stateful hash-based signature), and a per-signature
 /// randomizer, returning a digital signature.

signature/src/signer.rs

@@ -3,7 +3,7 @@
 use crate::error::Error;
 
 #[cfg(feature = "digest")]
-use crate::{PrehashSignature, digest::Digest};
+use crate::digest::Digest;
 
 /// Verify the provided message bytestring using `Self` (e.g. a public key)
 pub trait Verifier<S> {
@@ -39,14 +39,3 @@ pub trait DigestVerifier<D: Digest, S> {
     /// Verify the signature against the given [`Digest`] output.
     fn verify_digest(&self, digest: D, signature: &S) -> Result<(), Error>;
 }
-
-#[cfg(feature = "digest")]
-impl<S, T> Verifier<S> for T
-where
-    S: PrehashSignature,
-    T: DigestVerifier<S::Digest, S>,
-{
-    fn verify(&self, msg: &[u8], signature: &S) -> Result<(), Error> {
-        self.verify_digest(S::Digest::new_with_prefix(msg), signature)
-    }
-}