signature: add MultipartSigner and MultipartVerifier

signature/src/signer.rs

@@ -24,6 +24,18 @@ pub trait Signer<S> {
     fn try_sign(&self, msg: &[u8]) -> Result<S, Error>;
 }
 
+/// Equivalent of [`Signer`] but the message is provided in non-contiguous byte slices.
+pub trait MultiPartSigner<S> {
+    /// See [`Signer::sign()`].
+    fn multi_part_sign(&self, msg: &[&[u8]]) -> S {
+        self.try_multi_part_sign(msg)
+            .expect("signature operation failed")
+    }
+
+    /// See [`Signer::try_sign()`].
+    fn try_multi_part_sign(&self, msg: &[&[u8]]) -> Result<S, Error>;
+}
+
 /// Sign the provided message bytestring using `&mut Self` (e.g. an evolving
 /// cryptographic key such as a stateful hash-based signature), returning a
 /// digital signature.
@@ -103,6 +115,23 @@ pub trait RandomizedSigner<S> {
     ) -> Result<S, Error>;
 }
 
+/// Equivalent of [`RandomizedSigner`] but the message is provided in non-contiguous byte slices.
+#[cfg(feature = "rand_core")]
+pub trait RandomizedMultiPartSigner<S> {
+    /// See [`RandomizedSigner::sign_with_rng()`].
+    fn multi_part_sign_with_rng<R: CryptoRng + ?Sized>(&self, rng: &mut R, msg: &[&[u8]]) -> S {
+        self.try_multi_part_sign_with_rng(rng, msg)
+            .expect("signature operation failed")
+    }
+
+    /// See [`RandomizedSigner::try_sign_with_rng()`].
+    fn try_multi_part_sign_with_rng<R: TryCryptoRng + ?Sized>(
+        &self,
+        rng: &mut R,
+        msg: &[&[u8]],
+    ) -> Result<S, Error>;
+}
+
 /// Combination of [`DigestSigner`] and [`RandomizedSigner`] with support for
 /// computing a signature over a digest which requires entropy from an RNG.
 #[cfg(all(feature = "digest", feature = "rand_core"))]

signature/src/verifier.rs

@@ -14,6 +14,12 @@ pub trait Verifier<S> {
     fn verify(&self, msg: &[u8], signature: &S) -> Result<(), Error>;
 }
 
+/// Equivalent of [`Verifier`] but the message is provided in non-contiguous byte slices.
+pub trait MultiPartVerifier<S> {
+    /// See [`Verifier::verify()`].
+    fn multi_part_verify(&self, msg: &[&[u8]], signature: &S) -> Result<(), Error>;
+}
+
 /// Verify the provided signature for the given prehashed message [`Digest`]
 /// is authentic.
 ///