Change answer hash algorithm to SHA1₄

CHANGELOG.md

@@ -6,8 +6,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [v4.6.0] - unreleased
 ### Changed
-- We are now using djb2xor instead of sha256 to hash puzzle answers
-- Lots of work on the built-in theme
+- Answer hashes are now the first 4 characters of the hex-encoded SHA1 digest
+- Reworked the built-in theme
 - [moth.mjs](theme/moth.mjs) is now the standard MOTH library for ECMAScript
 - Devel mode no longer accepts an empty team ID
 

pkg/transpile/puzzle.go

@@ -4,7 +4,7 @@ import (
 	"bufio"
 	"bytes"
 	"context"
-	"crypto/sha256"
+	"crypto/sha1"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -85,9 +85,9 @@ func (puzzle *Puzzle) computeAnswerHashes() {
 	}
 	puzzle.AnswerHashes = make([]string, len(puzzle.Answers))
 	for i, answer := range puzzle.Answers {
-		sum := sha256.Sum256([]byte(answer))
+		sum := sha1.Sum([]byte(answer))
 		hexsum := fmt.Sprintf("%x", sum)
-		puzzle.AnswerHashes[i] = hexsum
+		puzzle.AnswerHashes[i] = hexsum[:4]
 	}
 }
 

pkg/transpile/puzzle_test.go

@@ -23,6 +23,12 @@ func TestPuzzle(t *testing.T) {
 		if (len(p.Answers) == 0) || (p.Answers[0] != "YAML answer") {
 			t.Error("Answers are wrong", p.Answers)
 		}
+		if len(p.Answers) != len(p.AnswerHashes) {
+			t.Error("Answer hashes length does not match answers length")
+		}
+		if len(p.AnswerHashes[0]) != 4 {
+			t.Error("Answer hash is wrong length")
+		}
 		if (len(p.Authors) != 3) || (p.Authors[1] != "Buster") {
 			t.Error("Authors are wrong", p.Authors)
 		}