Make SigningKey::from use Self::new()

This matches #472.

Author: marshallpierce

CHANGELOG.md

@@ -4,6 +4,8 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 
+
 ## 0.9.6 (2023-12-01)
 ### Added
 - expose a `pss::get_default_pss_signature_algo_id` helper ([#393])

src/pkcs1v15/signing_key.rs

@@ -197,10 +197,10 @@ where
 
 impl<D> From<RsaPrivateKey> for SigningKey<D>
 where
-    D: Digest,
+    D: Digest + AssociatedOid,
 {
     fn from(key: RsaPrivateKey) -> Self {
-        Self::new_unprefixed(key)
+        Self::new(key)
     }
 }
 

tests/pkcs1v15.rs

@@ -1,3 +1,7 @@
+use pkcs1::DecodeRsaPrivateKey;
+use rsa::RsaPrivateKey;
+use signature::Signer;
+
 // simple but prevent regression - see https://github.com/RustCrypto/RSA/issues/329
 #[cfg(feature = "pem")]
 #[test]
@@ -21,3 +25,43 @@ fn signature_stringify() {
     assert_eq!(format!("{:X}", signature), expected);
     assert_eq!(signature.to_string(), expected);
 }
+
+#[test]
+fn new_vs_from() {
+    let priv_key = RsaPrivateKey::from_pkcs1_pem(PRIV_KEY_PKCS1_PEM).unwrap();
+
+    let msg = b"1234";
+
+    let sig_via_new = rsa::pkcs1v15::SigningKey::<sha2::Sha256>::new(priv_key.clone()).sign(msg);
+    let sig_via_from = rsa::pkcs1v15::SigningKey::<sha2::Sha256>::from(priv_key.clone()).sign(msg);
+    assert_eq!(sig_via_new, sig_via_from);
+}
+
+// randomly generated key, hardcoded for test repeatability
+const PRIV_KEY_PKCS1_PEM: &str = "-----BEGIN RSA PRIVATE KEY-----
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+Rmb665iB5fwpqmbE/hYKIn7asYQE+V0dkgt8M3qvlJJ5JJbCrJx3
+-----END RSA PRIVATE KEY-----";