cookie ready

internal/prestashop/cookie/codec.go

@@ -74,6 +74,9 @@ func (c *nativeCodec) Decode(raw string) (*SessionContext, error) {
 	if err != nil {
 		return nil, err
 	}
+	if err := validatePlaintextChecksum(string(plaintext), c.cfg.CookieIV); err != nil {
+		return nil, err
+	}
 
 	values, orderedKeys := parsePlaintext(string(plaintext))
 	return &SessionContext{
@@ -129,12 +132,10 @@ func (c *nativeCodec) decryptInternal(ciphertextHex string) ([]byte, error) {
 		return nil, err
 	}
 
-	message := append(append(append([]byte{}, salt...), iv...), encrypted...)
-	if len(expectedHMAC) == macSize && !verifyHMAC(expectedHMAC, message, keys.akey) {
-		// Some existing shop cookies decrypt correctly but fail MAC verification with
-		// the same behavior observed in the reference implementation this codec ports.
-		// Keep decryption permissive for compatibility, but still compute the MAC so
-		// the encode path emits a complete payload.
+	message := append(append(append([]byte{}, header...), salt...), iv...)
+	message = append(message, encrypted...)
+	if len(expectedHMAC) != macSize || !verifyHMAC(expectedHMAC, message, keys.akey) {
+		return nil, errors.New("integrity check failed")
 	}
 
 	return aesCTR(encrypted, keys.ekey, iv)
@@ -161,7 +162,8 @@ func (c *nativeCodec) encryptInternal(plaintext string) (string, error) {
 		return "", err
 	}
 
-	message := append(append(append([]byte{}, salt...), iv...), encrypted...)
+	message := append(append(append([]byte{}, []byte(currentVersion)...), salt...), iv...)
+	message = append(message, encrypted...)
 	h := hmac.New(sha256.New, keys.akey)
 	h.Write(message)
 	mac := h.Sum(nil)
@@ -269,6 +271,34 @@ func verifyHMAC(expected, message, key []byte) bool {
 	return hmac.Equal(h.Sum(nil), expected)
 }
 
+func validatePlaintextChecksum(plaintext, cookieIV string) error {
+	pairs := strings.Split(plaintext, fieldSeparator)
+	if len(pairs) == 0 {
+		return errors.New("missing cookie checksum")
+	}
+
+	bodyPairs := pairs[:len(pairs)-1]
+	body := strings.Join(bodyPairs, fieldSeparator)
+	if body != "" {
+		body += fieldSeparator
+	}
+
+	lastPair := pairs[len(pairs)-1]
+	checksumParts := strings.SplitN(lastPair, pairSeparator, 2)
+	if len(checksumParts) != 2 || checksumParts[0] != "checksum" {
+		return errors.New("missing cookie checksum")
+	}
+	if cookieIV == "" {
+		return errors.New("cookie iv is required for checksum validation")
+	}
+
+	want := fmt.Sprintf("%d", crc32.ChecksumIEEE([]byte(cookieIV+body)))
+	if checksumParts[1] != want {
+		return errors.New("cookie checksum mismatch")
+	}
+	return nil
+}
+
 func decodeHex(input string) ([]byte, error) {
 	if len(input)%2 != 0 {
 		return nil, errors.New("odd length hex")