Implement Hash trait for VerifyingKey (#265)

* Added and cleaned up some verification docs

Co-authored-by: Michael Rosenberg <michael@mrosenberg.pub>

src/verifying.rs

@@ -11,6 +11,7 @@
 
 use core::convert::TryFrom;
 use core::fmt::Debug;
+use core::hash::{Hash, Hasher};
 
 use curve25519_dalek::digest::generic_array::typenum::U64;
 use curve25519_dalek::digest::Digest;
@@ -38,8 +39,19 @@ use crate::signature::*;
 use crate::signing::*;
 
 /// An ed25519 public key.
+///
+/// # Note
+///
+/// The `Eq` and `Hash` impls here use the compressed Edwards y encoding, _not_ the algebraic
+/// representation. This means if this `VerifyingKey` is non-canonically encoded, it will be
+/// considered unequal to the other equivalent encoding, despite the two representing the same
+/// point. More encoding details can be found
+/// [here](https://hdevalence.ca/blog/2020-10-04-its-25519am).
+///
+/// If you don't care and/or don't want to deal with this, just make sure to use the
+/// [`VerifyingKey::verify_strict`] function.
 // Invariant: VerifyingKey.1 is always the decompression of VerifyingKey.0
-#[derive(Copy, Clone, Default, Eq, PartialEq)]
+#[derive(Copy, Clone, Default, Eq)]
 pub struct VerifyingKey(pub(crate) CompressedEdwardsY, pub(crate) EdwardsPoint);
 
 impl Debug for VerifyingKey {
@@ -54,6 +66,18 @@ impl AsRef<[u8]> for VerifyingKey {
     }
 }
 
+impl Hash for VerifyingKey {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.as_bytes().hash(state);
+    }
+}
+
+impl PartialEq<VerifyingKey> for VerifyingKey {
+    fn eq(&self, other: &VerifyingKey) -> bool {
+        self.as_bytes() == other.as_bytes()
+    }
+}
+
 impl From<&ExpandedSecretKey> for VerifyingKey {
     /// Derive this public key from its corresponding `ExpandedSecretKey`.
     fn from(expanded_secret_key: &ExpandedSecretKey) -> VerifyingKey {
@@ -114,7 +138,7 @@ impl VerifyingKey {
     /// # Returns
     ///
     /// A `Result` whose okay value is an EdDSA `VerifyingKey` or whose error value
-    /// is an `SignatureError` describing the error that occurred.
+    /// is a `SignatureError` describing the error that occurred.
     #[inline]
     pub fn from_bytes(bytes: &[u8; PUBLIC_KEY_LENGTH]) -> Result<VerifyingKey, SignatureError> {
         let compressed = CompressedEdwardsY(*bytes);
@@ -176,14 +200,12 @@ impl VerifyingKey {
     /// * `context` is an optional context string, up to 255 bytes inclusive,
     ///   which may be used to provide additional domain separation.  If not
     ///   set, this will default to an empty string.
-    /// * `signature` is a purported Ed25519ph [`Signature`] on the `prehashed_message`.
+    /// * `signature` is a purported Ed25519ph signature on the `prehashed_message`.
     ///
     /// # Returns
     ///
     /// Returns `true` if the `signature` was a valid signature created by this
     /// `Keypair` on the `prehashed_message`.
-    ///
-    /// [rfc8032]: https://tools.ietf.org/html/rfc8032#section-5.1
     #[allow(non_snake_case)]
     pub fn verify_prehashed<D>(
         &self,
@@ -229,7 +251,7 @@ impl VerifyingKey {
     /// 1. Scalar Malleability
     ///
     /// The authors of the RFC explicitly stated that verification of an ed25519
-    /// signature must fail if the scalar `s` is not properly reduced mod \ell:
+    /// signature must fail if the scalar `s` is not properly reduced mod $\ell$:
     ///
     /// > To verify a signature on a message M using public key A, with F
     /// > being 0 for Ed25519ctx, 1 for Ed25519ph, and if Ed25519ctx or
@@ -322,7 +344,7 @@ impl VerifyingKey {
     /// * `context` is an optional context string, up to 255 bytes inclusive,
     ///   which may be used to provide additional domain separation.  If not
     ///   set, this will default to an empty string.
-    /// * `signature` is a purported Ed25519ph [`Signature`] on the `prehashed_message`.
+    /// * `signature` is a purported Ed25519ph signature on the `prehashed_message`.
     ///
     /// # Returns
     ///

tests/ed25519.rs

@@ -283,6 +283,7 @@ mod integrations {
     use super::*;
     use rand::rngs::OsRng;
     use sha2::Sha512;
+    use std::collections::HashMap;
 
     #[test]
     fn sign_verify() {
@@ -427,6 +428,33 @@ mod integrations {
 
         assert!(result.is_ok());
     }
+
+    #[test]
+    fn public_key_hash_trait_check() {
+        let mut csprng = OsRng {};
+        let secret: SigningKey = SigningKey::generate(&mut csprng);
+        let public_from_secret: VerifyingKey = (&secret).into();
+
+        let mut m = HashMap::new();
+        m.insert(public_from_secret, "Example_Public_Key");
+
+        m.insert(public_from_secret, "Updated Value");
+
+        let (k, v) = m.get_key_value(&public_from_secret).unwrap();
+        assert_eq!(k, &public_from_secret);
+        assert_eq!(v.clone(), "Updated Value");
+        assert_eq!(m.len(), 1usize);
+
+        let second_secret: SigningKey = SigningKey::generate(&mut csprng);
+        let public_from_second_secret: VerifyingKey = (&second_secret).into();
+        assert_ne!(public_from_secret, public_from_second_secret);
+        m.insert(public_from_second_secret, "Second public key");
+
+        let (k, v) = m.get_key_value(&public_from_second_secret).unwrap();
+        assert_eq!(k, &public_from_second_secret);
+        assert_eq!(v.clone(), "Second public key");
+        assert_eq!(m.len(), 2usize);
+    }
 }
 
 #[cfg(all(test, feature = "serde"))]