Monday, April 13, 2020

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Insecurities Of WhatsApp's, Signal's, And Threema's Group Chats

Posted: 13 Apr 2020 11:01 PM PDT

Recently, the theoretical and practical analysis of secure instant messenger protocols received much attention, but the focus of prior evaluations mostly lay in one-to-one communication. In this blog post we want to presents the results of our work that focuses on group chat protocols of three major instant messenger applications; namely Signal, WhatsApp, and Threema.

In this blog post, we aim to focus on the practical impact and the found weaknesses identified by our analysis. The interested reader may also look into our paper for more details.


Our Aim and What We Were Looking For

End-to-end encryption protects the confidentiality of communication that is forwarded via central servers to the designated receivers. As a consequence, neither parties on the network route of the messages, nor the provider of the central server (e.g. the WhatsApp server) should be able to read any information out of the observation of the communication. In particular, no other user of the application should have access to the communication. Further it might be desirable to require that also the messages' integrity is end-to-end protected and that a sender is informed about the delivery state of sent messages.
Delivery state information in Signal (upper screenshot) and WhatsApp (lower screenshot)

In a two party scenario, this analysis is rather fixed to two components of the protocol: the key establishment between both parties and the communication channel protection using the established key (mostly consisting of an encryption algorithm and a scheme for providing integrity like MACs or signature schemes).

Regarded attackers


In a group setting, the same attackers apply (network, provider, other users). However the requirements for secure communication differ. It is further necessary that only group members can write to and read content from the group. Additionally, only administrators of the group are able to add new members.

In addition to these standard requirements, we also evaluated the protocols' security guarantees if the client's secrets were revealed (forward secrecy and future secrecy).

Our Approach

We analyzed the mentioned protocols by reading the source code and debugging the apps. We also used alternative open source implementations of Threema and WhatsApp as a help and we traced the network traffic. When using alternative implementations, we only took incoming traffic into account, which was generated by official applications. Thereby we extracted the protocol descriptions and evaluated them regarding the defined requirements.

Our Findings

In WhatsApp and Threema, the provider was able to manipulate the set of members. Threema only allowed the provider to rewind the set of members to a previous state. As a consequence previously removed members could have been added to the group again. The WhatsApp provider is able to arbitrarily manipulate the member set. Thereby further members and administrators can be added to the group. Since the authenticity of group manipulation is not protected, the WhatsApp provider can set the real group administrator as the source of manipulation even though this administrator was not active.

Since Signal's key exchange protocol provides future secrecy, we also evaluated the protocol's ability to recover into a secure group state after a member's state was compromised. The essential weakness here is that a sender only needs to know the static group ID to send a message to the group. If a group member receives a message with the correct group ID, no verification regarding the current member set takes place but the message is directly added to the group communication. Consequently it is sufficient to retrieve the group ID in order to send messages to the group. Since Signal treats content messages the same way as messages for the manipulation of the group set, an attacker who knows the group ID can add herself to the group and thereby read the subsequent group communication.

In addition to this, in all cases the delivery state of sent messages was not securely provided. Threema's group chats do not inform the sender about the delivery state while Signal and WhatsApp do not protect the delivery information on the end-to-end layer. Therefore the central provider can forge this information and drop messages without letting the communicating parties detect this.

Also the order of messages was manipulable for the providers of the applications such that the provider is able to deliver the messages in a different order than they were sent. Threema's weakness of rewinding a group state results from missing replay attack protection.

Impact of Weaknesses

Even though end-to-end encryption is implemented in all analyzed applications, the central providers can largely manipulate the communication in groups and partially also read it.
In all applications, the provider can undetectably drop and reorder messages during the delivery and thereby manipulate the view of the communication such that further attacks can be obfuscated.
The central servers of WhatsApp can be used to add arbitrary users to groups and thereby receive their communication.
To achieve the same result for Signal, it suffices to retrieve the group ID. An earlier member who left the group once still knows this ID since it is static. However, in contrast to WhatsApp, the origin of the manipulation is correctly displayed in the Signal application (which was not the fact when we started our analysis).

As a result, the end-to-end protection of WhatsApp is not sufficient to reach confidentiality in groups. For Signal no future secrecy is reached in groups and Threema was vulnerable to replay attacks which resulted in further weaknesses.

Responsible Disclosure

We disclosed our findings to the developers and received varying response. Threema updated their protocol in version 3.14 such that our attacks are not feasible anymore. Moxie Marlinspike responded that Signal is "working on an entirely new group mechanism that we should be deploying soon". WhatsApp did not hold out the prospect of fixing the described vulnerabilities (Update 01/18: According to Facebook's Security Head, the invite links make a fix more difficult [1]; we proposed a way to solve this issue [2]).

[1] https://twitter.com/alexstamos/status/951169036947107840
[2] https://web-in-security.blogspot.de/2018/01/group-instant-messaging-why-baming.html

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Hacking Freemium Games - The Evolution Of PC Game Cheating

Posted: 13 Apr 2020 10:48 PM PDT

This post is going to be a rather strange post compared to previous ones. But bear with me, in the middle of the post you will see why this post fits the IT security topic.

I'm also terribly sorry for not posting recently, but I was busy with my SPSE and SLAE certification. Both are recommended for Python and Assembly noobs like me. But back to this post.

A little bit of history

Cheating in games started as help for game testers. By using invincibility or infinite ammo testers were able to test the game quicker, which meant less money spent on testing. I personally use cheat codes in games, depending on my mood. Sometimes it feels good to slash all the opponents while I'm invincible, sometimes it is more fun to play the game without cheats. One can argue whether cheating in games is OK or not, but I believe it depends, there is no black or white. But one thing is for sure, it is part of the gaming industry. There is huge demand for cheats. There were even cheat books printed on paper...


The different types of cheats (on PC)

There are different types of cheats in PC gaming. Following is a noncomplete list of these cheats:

Cheat codes

The good old IDDQD type of cheats. These are left in the game by the developers intentionally. Nothing interesting here.

Edit memory

This is my favorite. I will talk about this at the end of the post. Whenever a user launches a new program, the program's whole memory is accessible (read/write) to every other program launched by the user. And since the memory stores the current game state (health, ammo, armor, etc.), these values can be changed easily. In the good old times, there were POKE commands to do this cheats, and the memory address to write into was published by people who found where the game stores the most critical states about the game.

Code injection

This is like patching the game code. For example, one can change the "DEC (pointer to your current health)" instruction with NOP (do nothing), thus becoming invincible. In multi-player cheats, there is the aimbot to help you aim at enemies, wallhack to see through the wall, increase hitbox of the enemy for smoother hit, or in MMORPGs, one can write macros to collect items while the player is not online. I would say the so-called "trainers" more or less fit into this category and the previous one.

Saved game editor

The first time a kid meets a hex-editor (just like the co-author of this blog did with SIM City when he was 10 years old - David). It can teach a lot about file structures, the hexadecimal numeral system, etc. Fun times. 

Hacking game server

Not very common, but even more fun. Warning: endless trolling possibilities in multi-player games ahead :) How to hack a game server? Well, I think this might deserve another full blog post ...

Network traffic hacking

One last necessary type of cheating is to modify network traffic between the client and the game server. AFAIK SSL is not universal in gaming, so stunnel is not needed for this hack, but ettercap can help in changing the communication.

Why cheating becomes more critical (and challenging)?

Now in the age of in-app-payments, the game creators are no longer thinking about cheats as funny things but something to be destroyed to the ground. Because cheating decreases its revenue. Or not. At least they think it does. To quote Wikipedia here, "cheating in such games is nonetheless a legal grey area because there are no laws against modifying software which is already owned, as detailed in the Digital Millennium Copyright Act." 

A lot of online games include anti-cheating components like PunkBuster, nProtect GameGuard, or Valve Anti-Cheat. This whole cheating/anti-cheating industry is the same as the virus/anti-virus industry. A cat and mouse game.

Freemium games

If you have not played with "freemium" games, you should watch South Park season 18, episode 6. - "Freemium Isn't Free." If you did play with freemium games, you definitely have to watch it :) There are many problems with freemium games. It is free to install, free to play. The first 3-4 hours might be fun to play. But after that, it turns out it is impossible to advance in the game without paying money for it. And by spending cash, I mean spending a LOT! Let's have a look at today's example, an arcade racing video game.


For 99.99 USD, you can get 3 000 000 credit. For almost double the price of a new PC game, you can get these credits. In this particular game, I estimate one have to play ~6-24 hours constantly to get this amount of credit. But by playing ~6 hours, I mean 6 hours without progress in the game! Kind of boring. And what do you get from 3 000 000 credit? You can buy one of the most expensive cars, but can't tune them fully. You have to play more (without progress) or buy more. But guess what, there are more cars you can't buy by only playing the game. Those are only available via in-app-purchase.


Even though the player has 58 765 533 credits, it is not possible to buy this car. Only available through real money.


So, what are your possibilities? You are either Richie Rich, and can afford the money to buy these. Or you can be insane, and try to play the game without in-app-purchase. Or give up the game and try another freemium ... Or, you can try to hack the game!

Hack all the freemium games!

Although I was not playing this racing game from day one, I was able to witness the evolution of the cheats against this game. The cheats which worked in one day was not working one month later. The game is continuously updated to defeat the newly published cheats.

Noob start

So, I want to hack this game, what is the first thing a noob like me does? Bing it! Google it! 
From the first page result, let's check this tool:


While trying to download that, I just have to give my email address to spammers, or my mobile number will be subscribed to premium rate text messages. What fun.


Another "cheat" program will install malware/adware on your computer. Never ever try these programs. They are fake 99% of the time and after installing those you will have another problem, not just how to hack freemium games.

Beginners start - Cheat engine

When I first heard about hacking games in memory, I visualized hours of OllyDBG/ImmunityDBG/(insert your favorite Windows debugger here). It turned out, there are some specialized tools to help you with cheating the game. No assembly knowledge required. My favourite tool is CheatEngine. I highly recommend to download it and spend 10 minutes to get past the built-in tutorial levels to get a feeling about this tool. It's super duper awesome.



When I first tried to hack this game myself, I scanned the memory for my actual credit and tried to change that, no luck. Keep reading, you will see what happened.

The second cheat I tried with cheat engine was something like this
  1. Start the game, play the first level, and check how many credits is paid for winning the race. Pro tip: use dual display for full-screen game cheating.
  2. Restart the same level, attach Cheat Engine to the game's process
  3. Scan the memory for the same value at the beginning of the race
  4. Scan the memory for the same value at the end of the game. The intersect of the first and second scan includes the real value where the credit is stored for winning the race.
  5. Change the values (both the real one and some false positives) to something big
  6. Watch the game to crash
  7. Be amazed at the money you received
Nowadays, most of the cheats on YouTube does not work. Except for these kind of cheats. I don't want to recreate that tutorial, so you should watch it first then come back.



Are you back? Great. Do you have any idea what have you just seen? No? Well, in this case, don't try this at home. Copy-pasting assembly code from random internet posts and running on your computer is always a bad idea. It is precisely as risky as downloading free programs from random internet sites.

Although I have not seen people trolling others with this cheat engine type of shellcode, I think the time will come when these will be turned into something terrible. These shellcodes might work, or might harm your computer. The good news is, we can have a look at the code and analyze it. 

When you open CheatEngine and try to define a new custom type, you are greeted with a skeleton assembly code. I don't want to detail what all the skeleton code does, let's just focus on the difference between the skeleton code and the code used in the video. This is the "decrypt function":

xor eax, 0baadf00d
rol eax, 0e

What does it mean? The actual credit is encrypted in memory. If you want to scan it in memory, you won't be able to find it. But! The encryption is rotating the value to the right (ROR) with 0xE (14 in decimal), and after that, it is XOR-ed with 0xbaadf00d. Decrypting it is the inverse of the functions in reverse order (in this particular case, the order does not matter, but that's not the point). The inverse function of XOR is XOR, and the inverse function of ROR (rotate right) is ROL (rotate left). Now that we analyzed the assembly code, we can be sure that it is safe to execute. Just follow the video and see your coins falling from the sky. For free. In a freemium game. Have fun!

Encrypt memory - applications at financial institutions

Another exciting thing is that I don't recall any thick client applications in the financial industry encrypting the values in memory. And I agree, there are more significant problems with thick client applications than not encrypting the essential values in memory. But still, some thick client applications are regularly updated, maintained. Maybe it is a good idea to encrypt the values in memory. It will make attackers' life harder. Not impossible, but harder. Perhaps the developers of these applications should learn from the gaming industry (or from malware developers for that matter) because it is a shame that an arcade racing game or an FPS is protected better than an application responsible for transacting millions of dollars. Just think about the RAM scraping malware stealing millions of credit card data ...

Moral of the story

Cheating is part of the gaming history, and the freemium games are trying to take away the cheats from the gamers because they want money. Thanks to CheatEngine and some clever hacks, these programs can be still beaten. And guess what, there is CheatEngine for Android - although it did not work for me on the latest Android. And sometimes, hacking all kinds of applications can be more comfortable with CheatEngine, compared to traditional debuggers.

Also, always check the code before executing it! And when you find something cool, publish it, so everyone could enjoy the games!


More info

« Confinement strict jusqu’au 11 mai »

Posted: 13 Apr 2020 10:38 PM PDT

mardi 14 avril 2020 - Le Parisien
logo Le Parisien L'ESSENTIEL
DE L'ACTU
Bonjour, au lendemain de la très attendue allocution d'Emmanuel Macron, nous faisons le point ce mardi 14 avril sur ses annonces et les réactions qu'elles suscitent. D'abord bien sûr, sur le prolongement du confinement « strict » jusqu'au 11 mai. Le président a détaillé qu'à cette date, les écoles et les crèches devraient rouvrir, ainsi que les collèges et lycées, mais pas les facs. Les bars, restaurants et musées resteront eux fermés, en attendant la mise en place d'un grand plan de déconfinement. Celui-ci nécessitera du dépistage à grande échelle et la fourniture de masques « grand public », a assuré le chef de l'Etat. « On espère qu'il a ouvert les yeux », nous confient des soignants après ce discours. Retrouvez également les réactions de parents, de l'opposition, de chefs d'entreprises ou encore des organisateurs de festivals, interdits jusqu'à mi-juillet. A lire enfin, ces footballeurs qui n'échappent pas à la déprime du confiné. Côté météo, quelques nuages bas le matin, en provenance de la mer du Nord, contrarieront le soleil de la Somme aux Flandres. Il en sera de même du Pays basque à l'Occitanie, en remontant à Auvergne-Rhône-Alpes et PACA. Mais le temps sera globalement sec et ensoleillé. Bonne lecture et bonne fête aux Maxime !
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Networking | Routing And Switching | Tutorial 4 | 2018

Posted: 13 Apr 2020 10:25 PM PDT


Welcome to my 4th new tutorial of the series of networking. In this blog you'll the content about network switches. You'll learn about how to make a communication successful and secure in the same network (LAN) by using STP. As Spanning tree protocol (STP) we used in multi-switched networks. Why we use this protocol in multi-switched network etc.

What is Switch? 

A switch is an intelligent device used to connect multiple devices within the same network. The intelligence of is that it requires Media Access Control (MAC) address for communication and doesn't allow broadcast.  Let's understand the whole thing by a little example, consider there is a network having 3 end devices name Device-A, Device-B,Device-C connected with each other respectively with the help of switch. When a Device-A sends data to Device-C so that data will only forwarded by switch to Device-C not to Device-B.

What is Media Access Control (MAC) address?

A Media Access Control (MAC) address is 48-bit unique physical address given to network interface controller (NIC) or network adapter, for communication within the same network which is given by its manufacturer. It is made up of hexadecimal numbers like a1:b1:cc:ac:2e:f1.

What is STP?


STP stands for Spanning tree protocol which is basically used in bridge and switches to prevent loops when you have a redundant links in the Ethernet networks. If the loop is present in the Ethernet network so the whole network will suffer because there will MAC instability in the MAC table,  duplicate frames generation and so on. Let's move to the video for further detail.

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