feat: separate sign() and sign_with_rng()

src/dsa/rpo_falcon512/keys/mod.rs

@@ -35,7 +35,7 @@ mod tests {
 
         // sign a random message
         let message: Word = [ONE; 4];
-        let signature = sk.sign(message, &mut rng);
+        let signature = sk.sign_with_rng(message, &mut rng);
 
         // make sure the signature verifies correctly
         assert!(pk.verify(message, &signature));

src/dsa/rpo_falcon512/keys/secret_key.rs

@@ -109,13 +109,17 @@ impl SecretKey {
     // SIGNATURE GENERATION
     // --------------------------------------------------------------------------------------------
 
-    /// Signs a message with the secret key.
-    ///
-    /// Takes a randomness generator implementing `Rng` and outputs a signature `Signature`.
-    ///
-    /// # Errors
-    /// Returns an error of signature generation fails.
-    pub fn sign<R: Rng>(&self, message: Word, rng: &mut R) -> Signature {
+    /// Signs a message with this secret key.
+    #[cfg(feature = "std")]
+    pub fn sign(&self, message: Word) -> Signature {
+        use rand::{rngs::StdRng, SeedableRng};
+
+        let mut rng = StdRng::from_entropy();
+        self.sign_with_rng(message, &mut rng)
+    }
+
+    /// Signs a message with the secret key relying on the provided randomness generator.
+    pub fn sign_with_rng<R: Rng>(&self, message: Word, rng: &mut R) -> Signature {
         let mut nonce_bytes = [0u8; SIG_NONCE_LEN];
         rng.fill_bytes(&mut nonce_bytes);
         let nonce = Nonce::new(nonce_bytes);

src/dsa/rpo_falcon512/signature.rs

@@ -364,7 +364,7 @@ mod tests {
         let mut rng = RpoRandomCoin::new(seed);
 
         let sk = SecretKey::with_rng(&mut rng);
-        let signature = sk.sign(Word::default(), &mut rng);
+        let signature = sk.sign_with_rng(Word::default(), &mut rng);
         let serialized = signature.to_bytes();
         let deserialized = Signature::read_from_bytes(&serialized).unwrap();
         assert_eq!(signature.sig_poly(), deserialized.sig_poly());