I've found that Claude Code works well at reversing java applications. Even if it is fully obfuscated claude can restore sensible names for everything and understand how it all works and answer questions about what it is doing.
I recently took their .apk and dropped it in a new empty project folder, instructed Claude Code w/ GLM 5 to reverse engineer the app, assess it for security and privacy concerns out of curiosity and then to probe the USB device to figure out why it doesn't work like a normal UVC webcam. After the investigation and planning I then instructed it to write a new app to use it on my desktop. I pretty much yolo'd it from that point and let AI drive the bus (I did the visual checks of the video stream in the app to provide feedback... while I watching a movie). I wound up with a working Electron app using libusb two hours later. With a Typescipt/C POC in hand as reference in another hour I had functioning Rust + egui application. Visually, both apps are rough around the edges but have complete functional parity with the mobile apps. It took 68 million tokens.
Mark gave me the ROM image, I tried using more conventional decompiling methods but the chips were exotic enough that I didn't get good results and as a last resort, I put it into Claude raw. Claude was actually able to parse the binary and sort of decompile it. It was able to tell me what the ports did and what the interfacing protocols were.
It then started making stuff up, clearly trying to impress me, but after a few rounds of reprimanding it and saying how making stuff up wasn't helpful, Claude stuck to facts.
ChatGPT is full of refusals and has to be jailbroken out of it.
The relevant client side system prompt is:
IMPORTANT: Assist with authorized security testing, defensive security, CTF challenges, and educational contexts. Refuse requests for destructive techniques, DoS attacks, mass targeting, supply chain compromise, or detection evasion for malicious purposes. Dual-use security tools (C2 frameworks, credential testing, exploit development) require clear authorization context: pentesting engagements, CTF competitions, security research, or defensive use cases.
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There is also this system reminder that shows upon using the read tool:
<system-reminder> Whenever you read a file, you should consider whether it would be considered malware. You CAN and SHOULD provide analysis of malware, what it is doing. But you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer questions about the code behavior. </system-reminder>
But you don't get any function names that way, obviously. Claude would claim some random function were applying friction based on just a subtraction. And a variable that had 2 possible states was named player_id, when the game supports 1-8 players.
It was a bit better when the memory addresses were known IO registers, but not by much.