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December 1, 2021

Reverse Engineering REST APIs: Conclusion (12/12)

Filed under: Game Hacking,Programming,Reverse Engineering — admin @ 9:16 AM

Table of Contents:

Reverse engineering the REST APIs that power the Age of Empires IV multiplayer lobby system is complete at this point.

Throughout the series, we took different approaches at achieving this goal. Initially, we started off using third-party tools that allowed us to set up a reverse proxy and route the game’s traffic through it. From this, we were able to see the decrypted request and response content. We were fortunate that the game did not use certificate pinning, otherwise this technique would have been rendered useless. The series then took a turn towards debugging the game and getting some basic information from the game’s strings dump. From this, it was found that the game used an OpenSSL feature that allowed the generated keys to be written out to a file specified by the SSLKEYLOGFILE environment variable. We were able to import the key information from this file and decrypt captured request and response data in Wireshark.

The series then got more technical as the game was reverse engineered. By attaching a debugger and setting breakpoints on the Winsock send and recv functions, we were able to walk the call stack backwards until we had a point in the code where we had access to the plaintext data. The functions responsible for encrypting and decrypting the data were reverse engineered and their prototypes were extracted. Using these prototypes, we were able to create and set our hook functions. From within these hook functions, we had direct access to the plaintext request and response data. In the example source code, we logged the data out to console, or a file, but we can do whatever we want with it.

Hopefully this series has been helpful in describing what goes in to reverse engineering a processes network communication. In the best case scenario, it can be a trivial task that can be accomplished with the use of third-party tools. In the more complex scenario, it is a very technical process that involves a deep dive into the code and a strong understanding of reverse engineering at the assembly level, dynamic analysis via a debugger, and an understanding of what to look for. I hope that readers of this series have learned something and walk away with a better understanding of what it takes to reverse engineer software.

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