use u16 for number of signers (#156)

* use Identifier instead of index

* remove pub(crate) from the Identifier index

* Refreshed Identifier newtype of Scalar with traits

* Remove commented out lines

* add test vectors with indices larger than 1 byte

* add little_endian_serialize to implement Ord for Identifier

* use u16 for number of signers

* fix variable use

Co-authored-by: Deirdre Connolly <durumcrustulum@gmail.com>

frost-core/src/frost/keys.rs

@@ -306,8 +306,8 @@ where
 ///
 /// [`trusted_dealer_keygen`]: https://www.ietf.org/archive/id/draft-irtf-cfrg-frost-11.html#appendix-C
 pub fn keygen_with_dealer<C: Ciphersuite, R: RngCore + CryptoRng>(
-    num_signers: u8,
-    threshold: u8,
+    num_signers: u16,
+    threshold: u16,
     mut rng: R,
 ) -> Result<(Vec<SecretShare<C>>, PublicKeyPackage<C>), &'static str> {
     let mut bytes = [0; 64];
@@ -466,8 +466,8 @@ pub struct PublicKeyPackage<C: Ciphersuite> {
 /// Returns an error if the parameters (num_signers, threshold) are inconsistent.
 pub(crate) fn generate_secret_polynomial<C: Ciphersuite>(
     secret: &SharedSecret<C>,
-    num_signers: u8,
-    threshold: u8,
+    num_signers: u16,
+    threshold: u16,
     mut coefficients: Vec<Scalar<C>>,
 ) -> Result<(Vec<Scalar<C>>, VerifiableSecretSharingCommitment<C>), &'static str> {
     if threshold < 2 {
@@ -521,8 +521,8 @@ pub(crate) fn generate_secret_polynomial<C: Ciphersuite>(
 /// [`secret_share_shard`]: https://www.ietf.org/archive/id/draft-irtf-cfrg-frost-11.html#appendix-C.1
 pub(crate) fn generate_secret_shares<C: Ciphersuite>(
     secret: &SharedSecret<C>,
-    numshares: u8,
-    threshold: u8,
+    numshares: u16,
+    threshold: u16,
     coefficients: Vec<Scalar<C>>,
 ) -> Result<Vec<SecretShare<C>>, &'static str> {
     let mut secret_shares: Vec<SecretShare<C>> = Vec::with_capacity(numshares as usize);

frost-core/src/frost/keys/dkg.rs

@@ -43,7 +43,7 @@ pub struct Round1SecretPackage<C: Ciphersuite> {
     /// The public commitment for the participant (C_i)
     pub commitment: VerifiableSecretSharingCommitment<C>,
     /// The total number of signers.
-    pub num_signers: u8,
+    pub num_signers: u16,
 }
 
 /// A package that must be sent by each participant to some other participants
@@ -77,7 +77,7 @@ pub struct Round2SecretPackage<C: Ciphersuite> {
     /// The participant's own secret share (f_i(i)).
     pub secret_share: Scalar<C>,
     /// The total number of signers.
-    pub num_signers: u8,
+    pub num_signers: u16,
 }
 
 /// Performs the first part of the distributed key generation protocol
@@ -88,8 +88,8 @@ pub struct Round2SecretPackage<C: Ciphersuite> {
 /// must be sent to other participants.
 pub fn keygen_part1<C: Ciphersuite, R: RngCore + CryptoRng>(
     identifier: Identifier<C>,
-    num_signers: u8,
-    threshold: u8,
+    num_signers: u16,
+    threshold: u16,
     mut rng: R,
 ) -> Result<(Round1SecretPackage<C>, Round1Package<C>), &'static str> {
     let secret: SharedSecret<C> = SharedSecret::random(&mut rng);

frost-core/src/tests.rs

@@ -58,7 +58,7 @@ pub fn check_sign_with_dealer<C: Ciphersuite, R: RngCore + CryptoRng>(mut rng: R
 }
 
 fn check_sign<C: Ciphersuite + PartialEq, R: RngCore + CryptoRng>(
-    threshold: u8,
+    threshold: u16,
     key_packages: HashMap<frost::Identifier<C>, frost::keys::KeyPackage<C>>,
     mut rng: R,
     pubkeys: frost::keys::PublicKeyPackage<C>,
@@ -173,13 +173,9 @@ where
     // In practice, each participant will perform this on their own environments.
     for participant_index in 1..=numsigners {
         let participant_identifier = participant_index.try_into().expect("should be nonzero");
-        let (secret_package, round1_package) = frost::keys::dkg::keygen_part1(
-            participant_identifier,
-            numsigners as u8,
-            threshold,
-            &mut rng,
-        )
-        .unwrap();
+        let (secret_package, round1_package) =
+            frost::keys::dkg::keygen_part1(participant_identifier, numsigners, threshold, &mut rng)
+                .unwrap();
 
         // Store the participant's secret package for later use.
         // In practice each participant will store it in their own environment.

frost-core/src/tests/vectors.rs

@@ -210,8 +210,8 @@ pub fn check_sign_with_test_vectors<C: Ciphersuite>(json_vectors: &Value) {
     let threshold = share_polynomial_coefficients.len() + 1;
     let secret_shares = generate_secret_shares(
         &secret_key,
-        numshares as u8,
-        threshold as u8,
+        numshares as u16,
+        threshold as u16,
         share_polynomial_coefficients,
     )
     .unwrap();

frost-p256/src/lib.rs

@@ -250,8 +250,8 @@ pub mod keys {
     /// Allows all participants' keys to be generated using a central, trusted
     /// dealer.
     pub fn keygen_with_dealer<RNG: RngCore + CryptoRng>(
-        num_signers: u8,
-        threshold: u8,
+        num_signers: u16,
+        threshold: u16,
         mut rng: RNG,
     ) -> Result<(Vec<SecretShare>, PublicKeyPackage), &'static str> {
         frost::keys::keygen_with_dealer(num_signers, threshold, &mut rng)

frost-ristretto255/src/lib.rs

@@ -228,8 +228,8 @@ pub mod keys {
     /// Allows all participants' keys to be generated using a central, trusted
     /// dealer.
     pub fn keygen_with_dealer<RNG: RngCore + CryptoRng>(
-        num_signers: u8,
-        threshold: u8,
+        num_signers: u16,
+        threshold: u16,
         mut rng: RNG,
     ) -> Result<(Vec<SecretShare>, PublicKeyPackage), &'static str> {
         frost::keys::keygen_with_dealer(num_signers, threshold, &mut rng)