Update unit test file

Update existing tests and ensure they work as expected and add a unit test case
to check for public key mismatch.

Signed-off-by: Jang <hjjang501@gmail.com>

pkg/util/checkpoint_test.go

@@ -355,6 +355,8 @@ func TestSigningRoundtripCheckpoint(t *testing.T) {
 
 func TestInvalidSigVerification(t *testing.T) {
 	ecdsaKey, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	pubKeyHash, _ := GetPublicKeyHash(ecdsaKey.Public())
+
 	for _, test := range []struct {
 		checkpoint     Checkpoint
 		s              []note.Signature
@@ -382,12 +384,27 @@ func TestInvalidSigVerification(t *testing.T) {
 			s: []note.Signature{
 				{
 					Name:   "something",
-					Hash:   1234,
+					Hash:   pubKeyHash,
 					Base64: "not_base 64 string",
 				},
 			},
 			expectedResult: false,
 		},
+		{
+			checkpoint: Checkpoint{
+				Origin: "Log Checkpoint v0 public key mismatch",
+				Size:   123,
+				Hash:   []byte("bananas"),
+			},
+			pubKey: ecdsaKey.Public(),
+			s: []note.Signature{
+				{
+					Name:   "something",
+					Hash:   123,
+					Base64: "bm90IGEgc2ln", // not a valid signature; public key mismatch happens first
+				},
+			},
+		},
 		{
 			checkpoint: Checkpoint{
 				Origin: "Log Checkpoint v0 invalid signature",
@@ -398,7 +415,7 @@ func TestInvalidSigVerification(t *testing.T) {
 			s: []note.Signature{
 				{
 					Name:   "someone",
-					Hash:   142,
+					Hash:   pubKeyHash,
 					Base64: "bm90IGEgc2ln", // valid base64, not a valid signature
 				},
 			},

pkg/util/signed_note.go

@@ -54,7 +54,7 @@ func (s *SignedNote) Sign(identity string, signer signature.Signer, opts signatu
 	if err != nil {
 		return nil, fmt.Errorf("retrieving public key: %w", err)
 	}
-	pkHash, err := getPublicKeyHash(pk)
+	pkHash, err := GetPublicKeyHash(pk)
 	if err != nil {
 		return nil, err
 	}
@@ -79,21 +79,11 @@ func (s SignedNote) Verify(verifier signature.Verifier) bool {
 	msg := []byte(s.Note)
 	digest := sha256.Sum256(msg)
 
-	/*
-		Clarifications required:
-		0. Am I understanding this correctly? calculate the hash of the public key in every loop? Isn't the PK constant throughout this function call?
-		1. Would it still suffice to still only return `false` upon error?
-		2. Should I write a function to reuse the logic for generating hash of the PK?
-		3. How can I test this?
-			- unit tests
-			- end-to-end behavior test
-	*/
-
 	pk, err := verifier.PublicKey()
 	if err != nil {
 		return false
 	}
-	verifierPkHash, err := getPublicKeyHash(pk)
+	verifierPkHash, err := GetPublicKeyHash(pk)
 	if err != nil {
 		return false
 	}
@@ -210,7 +200,7 @@ func SignedNoteValidator(strToValidate string) bool {
 	return s.UnmarshalText([]byte(strToValidate)) == nil
 }
 
-func getPublicKeyHash(publicKey crypto.PublicKey) (uint32, error) {
+func GetPublicKeyHash(publicKey crypto.PublicKey) (uint32, error) {
 	pubKeyBytes, err := x509.MarshalPKIXPublicKey(publicKey)
 	if err != nil {
 		return 0, fmt.Errorf("marshalling public key: %w", err)