dsa: implement Signer and Verifier using SHA-256 as default

dsa/src/signing_key.rs

@@ -14,7 +14,7 @@ use pkcs8::{
 use rand::{CryptoRng, RngCore};
 use signature::{
     hazmat::{PrehashSigner, RandomizedPrehashSigner},
-    DigestSigner, RandomizedDigestSigner,
+    DigestSigner, RandomizedDigestSigner, Signer,
 };
 use zeroize::{Zeroize, Zeroizing};
 
@@ -95,6 +95,13 @@ impl SigningKey {
     }
 }
 
+impl Signer<Signature> for SigningKey {
+    fn try_sign(&self, msg: &[u8]) -> Result<Signature, signature::Error> {
+        let digest = sha2::Sha256::new_with_prefix(msg);
+        self.try_sign_digest(digest)
+    }
+}
+
 impl PrehashSigner<Signature> for SigningKey {
     fn sign_prehash(&self, prehash: &[u8]) -> Result<Signature, signature::Error> {
         let k_kinv = crate::generate::secret_number_rfc6979::<sha2::Sha256>(self, prehash);

dsa/src/verifying_key.rs

@@ -11,7 +11,7 @@ use pkcs8::{
     der::{asn1::UIntRef, AnyRef, Decode, Encode},
     spki, AlgorithmIdentifier, DecodePublicKey, EncodePublicKey, SubjectPublicKeyInfo,
 };
-use signature::{hazmat::PrehashVerifier, DigestVerifier};
+use signature::{hazmat::PrehashVerifier, DigestVerifier, Verifier};
 
 /// DSA public key.
 #[derive(Clone, PartialEq, PartialOrd)]
@@ -75,6 +75,12 @@ impl VerifyingKey {
     }
 }
 
+impl Verifier<Signature> for VerifyingKey {
+    fn verify(&self, msg: &[u8], signature: &Signature) -> Result<(), signature::Error> {
+        self.verify_digest(sha2::Sha256::new_with_prefix(msg), signature)
+    }
+}
+
 impl PrehashVerifier<Signature> for VerifyingKey {
     fn verify_prehash(
         &self,

dsa/tests/signature.rs

@@ -6,7 +6,10 @@ use pkcs8::der::{Decode, Encode};
 use rand::{CryptoRng, RngCore, SeedableRng};
 use rand_chacha::ChaCha8Rng;
 use sha2::Sha256;
-use signature::{DigestVerifier, RandomizedDigestSigner};
+use signature::{
+    hazmat::{PrehashSigner, PrehashVerifier},
+    DigestVerifier, RandomizedDigestSigner, Signer, Verifier,
+};
 
 /// Seed used for the ChaCha8 RNG
 const SEED: u64 = 0x2103_1949;
@@ -87,3 +90,28 @@ fn verify_signature() {
         .verify_digest(Sha256::new().chain_update(MESSAGE), &signature)
         .is_ok());
 }
+
+#[test]
+fn signer_verifier_signature() {
+    let signing_key = generate_deterministic_keypair();
+    let verifying_key = signing_key.verifying_key();
+    let message = b"Hello world! This is the message signed as part of the testing process.";
+
+    // construct signature manually and by `Signer` defaults. Ensure results are identical.
+    let manual_digest = Sha256::new_with_prefix(message).finalize();
+    let manual_signature = signing_key.sign_prehash(&manual_digest).unwrap();
+    let signer_signature = signing_key.sign(message);
+    verifying_key.verify(message, &manual_signature).unwrap();
+    verifying_key.verify(message, &signer_signature).unwrap();
+    assert_eq!(manual_signature, signer_signature);
+
+    // verify signature manually and by `Verifier` defaults. Ensure signatures can be applied interchangeably.
+    verifying_key
+        .verify_prehash(&manual_digest, &manual_signature)
+        .unwrap();
+    verifying_key
+        .verify_prehash(&manual_digest, &signer_signature)
+        .unwrap();
+    verifying_key.verify(message, &manual_signature).unwrap();
+    verifying_key.verify(message, &signer_signature).unwrap();
+}