Don't recompute H when verifying positive reports

src/positive_report.rs

@@ -3,12 +3,11 @@
 
 use crate::{get_date, CONFIG, COUNTRY_CODES};
 
-use curve25519_dalek::{RistrettoPoint, Scalar};
+use curve25519_dalek::{ristretto::RistrettoBasepointTable, Scalar};
 use ed25519_dalek::{Signature, Signer, SigningKey, Verifier, VerifyingKey};
 use lox_library::{cred::Lox, proto::positive_report as lox_pr, IssuerPubKey};
 use serde::{Deserialize, Serialize};
 use sha1::{Digest, Sha1};
-use sha2::Sha512;
 use std::option::Option;
 
 #[derive(Debug)]
@@ -106,12 +105,14 @@ impl PositiveReport {
     /// Verify everything except the Lox proof.
     /// Parameters:
     ///   - The bucket ID for the bucket containing this bridge
+    ///   - A basepoint table for computing multiples of H
     ///   - The bridge verifying key for this bridge (if bridge token is required)
     /// These parameters are assumed to be correct and are NOT checked against
     /// the fingerprint listed in the report.
     pub fn verify_excluding_lox_proof(
         self,
         bucket: Scalar,
+        Htable: &RistrettoBasepointTable,
         bridge_key: Option<VerifyingKey>,
     ) -> bool {
         // Verify bridge token
@@ -132,11 +133,8 @@ impl PositiveReport {
             }
         }
         // Verify knowledge of bucket ID
-        let H = RistrettoPoint::hash_from_bytes::<Sha512>(
-            format!("{}{}", lox_pr::H_GENERATOR_STRING, self.lox_proof.date).as_bytes(),
-        );
         let BP = self.lox_proof.BP;
-        if bucket * H != BP {
+        if &bucket * Htable != BP {
             return false;
         }
         true