async-signature: move to AFIT; MSRV 1.75 (#1428)

`AFIT` was stabilized in Rust 1.75.

`#[allow(async_fn_in_trait)]` is required until a solution to RPITIT is
merged in rust.

This put responsability on the implementor of `async_signature::AsyncSigner`
to make sure their future is `Send`able.
see rust-lang/rust#115822 (comment)
for more context.

Also introduces an `AsyncRandomizedSigner` trait.

Co-authored-by: Arthur Gautier <arthur.gautier@arista.com>

.github/workflows/async-signature.yml

@@ -23,7 +23,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - 1.60.0 # MSRV
+          - 1.75.0 # MSRV
           - stable
     steps:
       - uses: actions/checkout@v4

async-signature/Cargo.toml

@@ -10,14 +10,14 @@ readme        = "README.md"
 keywords      = ["crypto", "ecdsa", "ed25519", "signature", "signing"]
 categories    = ["cryptography", "no-std"]
 edition       = "2021"
-rust-version  = "1.60"
+rust-version  = "1.75"
 
 [dependencies]
-async-trait = "0.1.9"
 signature = ">= 2.0, <2.3"
 
 [features]
 digest = ["signature/digest"]
+rand_core = ["signature/rand_core"]
 
 [package.metadata.docs.rs]
 all-features = true

async-signature/README.md

@@ -9,7 +9,7 @@
 
 ## Minimum Supported Rust Version
 
-Rust **1.60** or higher.
+Rust **1.75** or higher.
 
 Minimum supported Rust version can be changed in the future, but it will be
 done with a minor version bump.
@@ -36,7 +36,7 @@ dual licensed as above, without any additional terms or conditions.
 [docs-image]: https://docs.rs/async-signature/badge.svg
 [docs-link]: https://docs.rs/async-signature/
 [license-image]: https://img.shields.io/badge/license-Apache2.0/MIT-blue.svg
-[rustc-image]: https://img.shields.io/badge/rustc-1.60+-blue.svg
+[rustc-image]: https://img.shields.io/badge/rustc-1.75+-blue.svg
 [chat-image]: https://img.shields.io/badge/zulip-join_chat-blue.svg
 [chat-link]: https://rustcrypto.zulipchat.com/#narrow/stream/260048-signatures
 [build-image]: https://github.com/RustCrypto/traits/workflows/async-signature/badge.svg?branch=master&event=push

async-signature/src/lib.rs

@@ -17,13 +17,14 @@ pub use signature::{self, Error};
 #[cfg(feature = "digest")]
 pub use signature::digest::{self, Digest};
 
-use async_trait::async_trait;
+#[cfg(feature = "rand_core")]
+use signature::rand_core::CryptoRngCore;
 
 /// Asynchronously sign the provided message bytestring using `Self`
 /// (e.g. client for a Cloud KMS or HSM), returning a digital signature.
 ///
 /// This trait is an async equivalent of the [`signature::Signer`] trait.
-#[async_trait(?Send)]
+#[allow(async_fn_in_trait)]
 pub trait AsyncSigner<S: 'static> {
     /// Attempt to sign the given message, returning a digital signature on
     /// success, or an error if something went wrong.
@@ -33,7 +34,6 @@ pub trait AsyncSigner<S: 'static> {
     async fn sign_async(&self, msg: &[u8]) -> Result<S, Error>;
 }
 
-#[async_trait(?Send)]
 impl<S, T> AsyncSigner<S> for T
 where
     S: 'static,
@@ -48,7 +48,7 @@ where
 ///
 /// This trait is an async equivalent of the [`signature::DigestSigner`] trait.
 #[cfg(feature = "digest")]
-#[async_trait(?Send)]
+#[allow(async_fn_in_trait)]
 pub trait AsyncDigestSigner<D, S>
 where
     D: Digest + 'static,
@@ -60,7 +60,6 @@ where
 }
 
 #[cfg(feature = "digest")]
-#[async_trait(?Send)]
 impl<D, S, T> AsyncDigestSigner<D, S> for T
 where
     D: Digest + 'static,
@@ -71,3 +70,41 @@ where
         self.try_sign_digest(digest)
     }
 }
+
+/// Sign the given message using the provided external randomness source.
+#[cfg(feature = "rand_core")]
+#[allow(async_fn_in_trait)]
+pub trait AsyncRandomizedSigner<S> {
+    /// Sign the given message and return a digital signature
+    async fn sign_with_rng_async(&self, rng: &mut impl CryptoRngCore, msg: &[u8]) -> S {
+        self.try_sign_with_rng_async(rng, msg)
+            .await
+            .expect("signature operation failed")
+    }
+
+    /// Attempt to sign the given message, returning a digital signature on
+    /// success, or an error if something went wrong.
+    ///
+    /// The main intended use case for signing errors is when communicating
+    /// with external signers, e.g. cloud KMS, HSMs, or other hardware tokens.
+    async fn try_sign_with_rng_async(
+        &self,
+        rng: &mut impl CryptoRngCore,
+        msg: &[u8],
+    ) -> Result<S, Error>;
+}
+
+#[cfg(feature = "rand_core")]
+impl<S, T> AsyncRandomizedSigner<S> for T
+where
+    S: 'static,
+    T: signature::RandomizedSigner<S>,
+{
+    async fn try_sign_with_rng_async(
+        &self,
+        rng: &mut impl CryptoRngCore,
+        msg: &[u8],
+    ) -> Result<S, Error> {
+        self.try_sign_with_rng(rng, msg)
+    }
+}