Update EncryptedMultisigDescriptor.java

Replaced broken code relying on non-existent Java methods (getAuthenticationTag() and setAuthenticationTag()), causing compilation errors.
Correctly implemented AES-GCM encryption and decryption:
Removed manual extraction/injection of authentication tags.
Encrypted blobs now properly combine IV and ciphertext (with embedded tag).
Decryption validates integrity via Cipher.doFinal().
Ensured secure key derivation using SHA-256 on sorted zpubs.

src/main/java/com/sparrowwallet/sparrow/wallet/EncryptedMultisigDescriptor.java

@@ -34,26 +34,28 @@ public class EncryptedMultisigDescriptor {
         GCMParameterSpec spec = new GCMParameterSpec(TAG_LENGTH * 8, iv); // Create GCM spec with IV and tag bits
         cipher.init(Cipher.ENCRYPT_MODE, skey, spec); // Initialize cipher for encryption
         byte[] ct = cipher.doFinal(descriptor.getBytes(StandardCharsets.UTF_8)); // Encrypt descriptor to ciphertext
-        byte[] tag = cipher.getAuthenticationTag();  // Get authentication tag (unused here, but typically from doFinal)
-        byte[] blob = new byte[IV_LENGTH + TAG_LENGTH + ct.length];  // Create output blob array
+
+        // Build encryption blob: IV + Ciphertext (tag included in ciphertext)
+        byte[] blob = new byte[IV_LENGTH + ct.length]; // IV + Ciphertext (which includes tag)
         System.arraycopy(iv, 0, blob, 0, IV_LENGTH); // Copy IV to start of blob
-        System.arraycopy(tag, 0, blob, IV_LENGTH, TAG_LENGTH);  // Copy tag after IV
-        System.arraycopy(ct, 0, blob, IV_LENGTH + TAG_LENGTH, ct.length);  // Copy ciphertext after tag
+        System.arraycopy(ct, 0, blob, IV_LENGTH, ct.length); // Copy entire ciphertext (tag included) after IV
+
         return Base64.getEncoder().encodeToString(blob); // Base64 encode blob and return as string
     }
 
     // Method to decrypt an encrypted blob string using AES-GCM with the given key
     public static String decrypt(String blobStr, byte[] key) throws Exception {
         byte[] blob = Base64.getDecoder().decode(blobStr); // Decode Base64 blob to bytes
-        if (blob.length < IV_LENGTH + TAG_LENGTH) throw new IllegalArgumentException();  // Check minimum length
+        if (blob.length < IV_LENGTH) throw new IllegalArgumentException("Invalid blob length"); // Check minimum length
+
         byte[] iv = Arrays.copyOfRange(blob, 0, IV_LENGTH); // Extract IV from blob
-        byte[] tag = Arrays.copyOfRange(blob, IV_LENGTH, IV_LENGTH + TAG_LENGTH);  // Extract tag
-        byte[] ct = Arrays.copyOfRange(blob, IV_LENGTH + TAG_LENGTH, blob.length);  // Extract ciphertext
+        byte[] ct = Arrays.copyOfRange(blob, IV_LENGTH, blob.length); // Extract ciphertext (tag included)
+
         SecretKeySpec skey = new SecretKeySpec(key, "AES"); // Create AES key
         Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding"); // Get cipher instance
         GCMParameterSpec spec = new GCMParameterSpec(TAG_LENGTH * 8, iv); // Create GCM spec
         cipher.init(Cipher.DECRYPT_MODE, skey, spec); // Initialize for decryption
-        cipher.setAuthenticationTag(tag);  // Set expected tag for verification (GCM-specific)
+
         try {
             return new String(cipher.doFinal(ct), StandardCharsets.UTF_8); // Decrypt and return string
         } catch (AEADBadTagException e) {