Freeze catalog signature vectors (T-614)

core/catalog/verifier.go

@@ -66,17 +66,9 @@ func (verifier Verifier) Verify(document []byte) (VerifiedDocument, error) {
 	if err != nil {
 		return VerifiedDocument{}, err
 	}
-	signature, err := base64.StdEncoding.Strict().DecodeString(signatureText)
+	signature, err := decodeCanonicalSignature(signatureText)
 	if err != nil {
-		return VerifiedDocument{}, fmt.Errorf("%w: base64: %v", ErrSignatureInvalid, err)
-	}
-	if len(signature) != ed25519.SignatureSize {
-		return VerifiedDocument{}, fmt.Errorf(
-			"%w: got %d signature bytes, want %d",
-			ErrSignatureInvalid,
-			len(signature),
-			ed25519.SignatureSize,
-		)
+		return VerifiedDocument{}, fmt.Errorf("%w: %v", ErrSignatureInvalid, err)
 	}
 	if !ed25519.Verify(verifier.publicKey, signedPayload, signature) {
 		return VerifiedDocument{}, ErrSignatureInvalid
@@ -87,3 +79,21 @@ func (verifier Verifier) Verify(document []byte) (VerifiedDocument, error) {
 		SignedPayload: append([]byte(nil), signedPayload...),
 	}, nil
 }
+
+func decodeCanonicalSignature(value string) ([]byte, error) {
+	signature, err := base64.StdEncoding.Strict().DecodeString(value)
+	if err != nil {
+		return nil, fmt.Errorf("invalid standard Base64: %w", err)
+	}
+	if base64.StdEncoding.EncodeToString(signature) != value {
+		return nil, errors.New("signature must use canonical padded Base64")
+	}
+	if len(signature) != ed25519.SignatureSize {
+		return nil, fmt.Errorf(
+			"got %d signature bytes, want %d",
+			len(signature),
+			ed25519.SignatureSize,
+		)
+	}
+	return signature, nil
+}