Communication: Fix encryption issue in push notifications

[PaRangger]

Checklist

General

• I tested all changes and their related features with all corresponding user types on a test server.
• This is a small issue that I tested locally and was confirmed by another developer on a test server.
• Language: I followed the guidelines for inclusive, diversity-sensitive, and appreciative language.
• I chose a title conforming to the naming conventions for pull requests.

Server

• Important: I implemented the changes with a very good performance and prevented too many (unnecessary) and too complex database calls.
• I strictly followed the server coding and design guidelines.

Motivation and Context

Currently there is an issue that causes notifications to be encrypted wrongly. This is due to a race condition where multiple threads access the same instance of a cipher object and overwrite its initialization vector while others are still encrypting. This leads to notification payloads like this:

{"notificationPlaceholders":["Patterns in Software Engineering (WS24/25)","Test reserveFittingPEV requries us to use the @Spy annotation for stubbing the ReservationManager. However Mockito requires a no args constructor to be able to use the @Spy annotati?��2�?���ۂGP��&"���5Ɩ��˓)h�r�J��n|8��ǁ�ب��b�ߔ

Description

Instead of having a static reference to a single cipher, the cipher instance is now initialized per-notification removing the possibility of overlaps.

Steps for Testing

Prerequisites:

• 2 Students/Tutors/Instructors in the same course
• 1 Android or iOS Device with Push Notifications enabled
• 1 Course with communication enabled

1. Log in to Artemis on the webclient with user 1 and on the native app with user 2
2. Navigate to the course
3. Navigate to the communication tab
4. Write a post with user 2
5. Answer to that post with user 1
6. Wait until you get a notification on the native device
7. Verify that the notification displays the proper text

Testserver States

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Review Progress

Code Review

• Code Review 1
• Code Review 2

Manual Tests

• Test 1
• Test 2

Test Coverage

TBD

Summary by CodeRabbit

• Bug Fixes
  • Improved error handling in the encryption process for push notifications.
  • Addressed potential race conditions by creating a new instance of Cipher for each encryption operation.

[coderabbitai]

Warning

There were issues while running some tools. Please review the errors and either fix the tool’s configuration or disable the tool if it’s a critical failure.

🔧 pmd (7.8.0)

src/main/java/de/tum/cit/aet/artemis/communication/service/notifications/push_notifications/PushNotificationService.java

The following rules are missing or misspelled in your ruleset file category/vm/bestpractices.xml: BooleanInstantiation, DontImportJavaLang, DuplicateImports, EmptyFinallyBlock, EmptyIfStmt, EmptyInitializer, EmptyStatementBlock, EmptyStatementNotInLoop, EmptySwitchStatements, EmptySynchronizedBlock, EmptyTryBlock, EmptyWhileStmt, ExcessiveClassLength, ExcessiveMethodLength, ImportFromSamePackage, MissingBreakInSwitch, SimplifyBooleanAssertion. Please check your ruleset configuration.

Walkthrough

The pull request modifies the PushNotificationService class, specifically addressing the encryption mechanism for push notifications. The primary change involves removing a static Cipher field and creating a new Cipher instance within the encrypt method for each encryption operation. This approach mitigates potential race conditions by ensuring thread-safe encryption. The error handling has been enhanced by expanding the catch block to include additional exception types related to cryptographic operations.

Changes

File	Change Summary
src/main/java/de/tum/cit/aet/artemis/communication/service/notifications/push_notifications/PushNotificationService.java	- Removed static Cipher field - Modified encrypt method to create a new Cipher instance per encryption - Expanded error handling with additional exception catches

Suggested labels

bugfix, ready to merge, component:Communication

Suggested reviewers

• sachmii
• cremertim
• HawKhiem
• asliayk
• Cathy0123456789

Possibly related PRs

• Communication: Fix mentioned users recieving notifications in conversations they are not part of #9814: Changes in SingleUserNotificationService class related to notification handling, potentially intersecting with encryption processes in PushNotificationService

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[coderabbitai]

Actionable comments posted: 1

♻️ Duplicate comments (1)

src/main/java/de/tum/cit/aet/artemis/communication/service/notifications/push_notifications/PushNotificationService.java (1)

197-197: ⚠️ Potential issue

Security: Replace CBC mode with GCM for better security

The current encryption algorithm (AES/CBC/PKCS5Padding) has known vulnerabilities:

• CBC mode is vulnerable to padding oracle attacks
• Requires careful IV handling to prevent chosen-plaintext attacks

Recommend switching to AES/GCM/NoPadding which provides:

• Authenticated encryption
• Protection against tampering
• No padding oracle vulnerabilities

Here's how to implement the change:

- var cipher = Cipher.getInstance(Constants.PUSH_NOTIFICATION_ENCRYPTION_ALGORITHM);
+ // Update the constant to use "AES/GCM/NoPadding"
+ var cipher = Cipher.getInstance("AES/GCM/NoPadding");
+ // GCM requires a 12-byte nonce instead of IV
+ byte[] nonce = new byte[12];
+ random.nextBytes(nonce);
+ GCMParameterSpec spec = new GCMParameterSpec(128, nonce);
+ cipher.init(Cipher.ENCRYPT_MODE, key, spec);

Note: This change requires updating the decryption logic on the client side and handling the nonce similar to how the IV is currently handled.

🧹 Nitpick comments (1)

src/main/java/de/tum/cit/aet/artemis/communication/service/notifications/push_notifications/PushNotificationService.java (1)

203-205: Enhance error logging for better debugging

While the error handling is comprehensive, the error message could be more specific to help with debugging encryption issues.

- log.error("Error encrypting push notification payload!", e);
+ log.error("Failed to encrypt push notification: {} (Key algorithm: {}, Key length: {} bits)", 
+     e.getMessage(), 
+     key.getAlgorithm(), 
+     key.getEncoded().length * 8, 
+     e);

📜 Review details

Configuration used: .coderabbit.yaml
Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 50adb94 and b101c6f.

📒 Files selected for processing (1)

• src/main/java/de/tum/cit/aet/artemis/communication/service/notifications/push_notifications/PushNotificationService.java (1 hunks)

🧰 Additional context used

📓 Path-based instructions (1)

src/main/java/de/tum/cit/aet/artemis/communication/service/notifications/push_notifications/PushNotificationService.java (1)

Pattern src/main/java/**/*.java: naming:CamelCase; principles:{single_responsibility,small_methods,no_duplication}; db:{perf_queries,datetime_not_timestamp}; rest:{stateless,singleton,delegate_logic,http_only,minimal_dtos}; dtos:{java_records,no_entities,min_data,single_resp}; di:constructor_injection; kiss:simple_code; file_handling:os_indep_paths; practices:{least_access,avoid_transactions,code_reuse,static_member_ref,prefer_primitives}; sql:{param_annotation,uppercase,avoid_subqueries};java:avoid_star_imports