Change to better distinguish signature schemes

It is currently possible to call `APK::verify` or `PublicKey::verify` on
the same signature type, leading to situations where even if a user is
technically *allowed* to call the function, verification is in principle
impossible, since the signature schemes used to produce a signature are
different. Furthermore, the `sign_vulnerable` function is arguably
misnamed, since it is only actually vulnerable to a rogue key attack
*when used in a multi-signature context*.

In the interest of fixing this, this commit introduces a couple of changes
to the API of the crate, designed to better distinguish and clarify the
usage of the two different signature schemes it provides.

First and foremost, a new signature type - `MultisigSignature` is added,
representing a signature produced using the multi-signature scheme.
Conversely, the already existing `Signature` type is taken to mean the a
signature produced using the single-key scheme.
The functions under `SecretKey`, `sign_vulnerable` and `sign`, are
respectively renamed into `sign` and `sign_multisig`, and the latter is
changed to return the new `MultisigSignature` type.
The "aggregated public key" type is renamed from `APK` into
`MultisigPublicKey`, to better denote its use and to be in line with the
kind signature it can now verify using the `verify` function - which is
changed to take a `MultisigSignature`.

On a more subtle note, the `From<&PublicKey>` and `From<&SecretKey>`
implementations for `MultisigPublicKey`, formerly `APK` are removed and
the API of `MultisigPublicKey::aggregate` is changed to *not* take
`&self`, and only take a slice of `PublicKey`. This is designed to
promote the intended usage of the struct - aggregating a collection of
public keys, as opposed to just "aggregating" one.

Resolves: #18

CHANGELOG.md

@@ -7,6 +7,23 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Add `MultisigSignature` struct [#18]
+- Add `Error::NoKeysProvided` variant [#18]
+
+### Changed
+
+- Rename `SecretKey::sign` to `sign_multisig` and change return to `MultisigSignature` [#18]
+- Rename `SecretKey::sign_vulnerable` to `sign` [#18]
+- Rename `APK` to `MultisigPublicKey` [#18]
+- Change `APK::verify` to take a `MultisigSignature` [#18]
+
+### Removed
+
+- Remove `impl From<&PublicKey> for APK` [#18]
+- Remove `impl From<&SecretKey> for APK` [#18]
+
 ## [0.3.1] - 2024-06-27
 
 ### Changed
@@ -48,6 +65,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add initial commit, this package continues the development of [dusk-bls12_381-sign](https://github.com/dusk-network/bls12_381-sign/) at version `0.6.0` under the new name: `bls12_381-bls` and without the go related code.
 
 <!-- ISSUES -->
+[#18]: https://github.com/dusk-network/bls12_381-bls/issues/18
 [#8]: https://github.com/dusk-network/bls12_381-bls/issues/8
 [#7]: https://github.com/dusk-network/bls12_381-bls/issues/7
 [#5]: https://github.com/dusk-network/bls12_381-bls/issues/5

Cargo.toml

@@ -25,7 +25,7 @@ bytecheck = { version = "0.6", optional = true, default-features = false }
 rayon = { version = "1.8", optional = true }
 
 [dev-dependencies]
-rand = { version = "0.8", default-features = false, features = ["std_rng"] }
+rand = "0.8"
 
 [features]
 rkyv-impl = [

benches/signature_bench.rs

@@ -9,79 +9,61 @@
 extern crate test;
 
 mod benches {
-    use bls12_381_bls::{PublicKey, SecretKey, APK};
+    use bls12_381_bls::{MultisigPublicKey, PublicKey, SecretKey};
     use dusk_bytes::Serializable;
-    use rand_core::{OsRng, RngCore};
+    use rand::rngs::OsRng;
+    use rand::RngCore;
     use test::Bencher;
 
     #[bench]
-    fn bench_sign_vulnerable(b: &mut Bencher) {
+    fn bench_sign(b: &mut Bencher) {
         let sk = SecretKey::random(&mut OsRng);
         let msg = random_message();
-        b.iter(|| sk.sign_vulnerable(&msg));
+        b.iter(|| sk.sign(&msg));
     }
 
     #[bench]
-    fn bench_sign(b: &mut Bencher) {
+    fn bench_multisig_sign(b: &mut Bencher) {
         let sk = SecretKey::random(&mut OsRng);
         let pk = PublicKey::from(&sk);
         let msg = random_message();
-        b.iter(|| sk.sign(&pk, &msg));
+        b.iter(|| sk.sign_multisig(&pk, &msg));
     }
 
     #[bench]
     fn bench_verify(b: &mut Bencher) {
         let sk = SecretKey::random(&mut OsRng);
         let pk = PublicKey::from(&sk);
         let msg = random_message();
-        let sig = sk.sign_vulnerable(&msg);
+        let sig = sk.sign(&msg);
         b.iter(|| pk.verify(&sig, &msg));
     }
 
     #[bench]
-    fn bench_aggregate_sig(b: &mut Bencher) {
+    fn bench_multisig_aggregate_sig(b: &mut Bencher) {
         let sk = SecretKey::random(&mut OsRng);
+        let pk = PublicKey::from(&sk);
         let msg = random_message();
-        let sig = sk.sign_vulnerable(&msg);
+        let sig = sk.sign_multisig(&pk, &msg);
         b.iter(|| sig.aggregate(&[sig]));
     }
 
     #[bench]
-    fn bench_aggregate_pk(b: &mut Bencher) {
-        let sk = SecretKey::random(&mut OsRng);
-        let pk = PublicKey::from(&sk);
-        let mut apk = APK::from(&pk);
-        b.iter(|| apk.aggregate(&[pk]));
-    }
-
-    #[bench]
-    fn bench_aggregate_pk_64_bulk(b: &mut Bencher) {
+    fn bench_multisig_aggregate_pk(b: &mut Bencher) {
         let sk = SecretKey::random(&mut OsRng);
         let pk = PublicKey::from(&sk);
-        let mut apk = APK::from(&pk);
-        let mut pks = vec![];
-        for _ in 0..64 {
-            let sk = SecretKey::random(&mut OsRng);
-            let pk = PublicKey::from(&sk);
-            pks.push(pk)
-        }
-        let pks = &pks[..];
-        b.iter(|| apk.aggregate(pks));
+        b.iter(|| MultisigPublicKey::aggregate(&[pk]));
     }
 
     #[bench]
-    fn bench_aggregate_pk_64_each(b: &mut Bencher) {
-        let sk = SecretKey::random(&mut OsRng);
-        let pk = PublicKey::from(&sk);
-        let mut apk = APK::from(&pk);
+    fn bench_multisig_aggregate_pk_64_bulk(b: &mut Bencher) {
         let mut pks = vec![];
         for _ in 0..64 {
             let sk = SecretKey::random(&mut OsRng);
             let pk = PublicKey::from(&sk);
             pks.push(pk)
         }
-        let pks = &pks[..];
-        b.iter(|| pks.iter().for_each(|&p| apk.aggregate(&[p])));
+        b.iter(|| MultisigPublicKey::aggregate(&pks[..]));
     }
 
     fn random_message() -> [u8; 100] {

src/error.rs

@@ -17,6 +17,8 @@ pub enum Error {
     InvalidSignature,
     /// Invalid Point
     InvalidPoint,
+    /// Tried to aggregate an empty list of public keys
+    NoKeysProvided,
 }
 
 impl From<DuskBytesError> for Error {
@@ -35,6 +37,9 @@ impl fmt::Display for Error {
             Self::InvalidPoint => {
                 write!(f, "Invalid Point")
             }
+            Self::NoKeysProvided => {
+                write!(f, "No keys provided")
+            }
         }
     }
 }

src/keys.rs

@@ -4,6 +4,5 @@
 //
 // Copyright (c) DUSK NETWORK. All rights reserved.
 
-pub mod apk;
 pub mod public;
 pub mod secret;