SignDigest and VerifyDigest traits

Support for signing and verifying prehashed message `Digest`s, for use
with signature algorithms that support Initialize-Update-Finalize usage.

signature-crate/Cargo.toml

@@ -12,8 +12,9 @@ keywords      = ["crypto", "ecdsa", "ed25519", "signature", "signing"]
 categories    = ["cryptography", "no-std"]
 
 [dependencies]
+digest = { version = "0.8", optional = true, default-features = false }
 
 [features]
-default = ["std"]
+default = ["digest", "std"]
 alloc   = []
 std     = ["alloc"]

signature-crate/src/lib.rs

@@ -14,13 +14,17 @@
     unused_qualifications
 )]
 
+#[cfg(feature = "digest")]
+pub extern crate digest;
+
 #[cfg(any(feature = "std", test))]
 #[macro_use]
 extern crate std;
 
 mod error;
 mod prelude;
-mod sign;
+pub mod sign;
 mod signature;
+pub mod verify;
 
-pub use crate::{error::Error, sign::Sign, signature::Signature};
+pub use crate::{error::Error, sign::Sign, signature::Signature, verify::Verify};

signature-crate/src/sign/digest.rs

@@ -0,0 +1,18 @@
+//! Support for signing messages which have been prehashed messages using
+//! the `Digest` trait.
+//!
+//! For use signature algorithms that support an Initialize-Update-Finalize
+//! (IUF) API, such as ECDSA or Ed25519ph.
+
+use crate::{error::Error, Signature};
+use digest::Digest;
+
+/// Sign the given prehashed message `Digest` using `Self`.
+pub trait SignDigest<D, S>: Send + Sync
+where
+    D: Digest,
+    S: Signature,
+{
+    /// Sign the given prehashed message `Digest`, returning a signature.
+    fn sign(&self, digest: D) -> Result<S, Error>;
+}

signature-crate/src/sign.rs → signature-crate/src/sign/mod.rs

@@ -1,8 +1,13 @@
-//! Trait for generating digital signatures of message bytestrings
+//! Traits for generating digital signatures
 
+#[cfg(feature = "digest")]
+pub(crate) mod digest;
+
+#[cfg(feature = "digest")]
+pub use self::digest::SignDigest;
 use crate::{error::Error, Signature};
 
-/// Sign the provided bytestring message using `Self` (e.g. a cryptographic key
+/// Sign the provided message bytestring using `Self` (e.g. a cryptographic key
 /// or connection to an HSM), returning a digital signature.
 pub trait Sign<S: Signature>: Send + Sync {
     /// Sign the given message and return a digital signature

signature-crate/src/verify/digest.rs

@@ -0,0 +1,19 @@
+//! Support for verifying messages which have been prehashed messages using
+//! the `Digest` trait.
+//!
+//! For use signature algorithms that support an Initialize-Update-Finalize
+//! (IUF) API, such as ECDSA or Ed25519ph.
+
+use crate::{error::Error, Signature};
+use digest::Digest;
+
+/// Verify the provided signature for the given prehashed message `Digest`
+/// is authentic.
+pub trait VerifyDigest<D, S>: Send + Sync
+where
+    D: Digest,
+    S: Signature,
+{
+    /// Verify the signature against the given `Digest`
+    fn verify(&self, digest: D, signature: &S) -> Result<(), Error>;
+}

signature-crate/src/verify.rs → signature-crate/src/verify/mod.rs

@@ -1,5 +1,10 @@
-//! Trait for verifying digital signatures of message bytestrings
+//! Trait for verifying digital signatures
 
+#[cfg(feature = "digest")]
+pub(crate) mod digest;
+
+#[cfg(feature = "digest")]
+pub use self::digest::VerifyDigest;
 use crate::{error::Error, Signature};
 
 /// Verify the provided message bytestring using `Self` (e.g. a public key)