Binary Decoder Reconstruction in C
Recreated a decoder from supplied binary artifacts and validated its behavior through iterative compilation and debugging.
Publication context. This article summarizes an independently completed technical interview exercise using original commentary. The challenge was provided by a third party; the exercise is not represented as my own product, a public vulnerability, or a commissioned professional engagement. Original company branding, challenge assets, flags, and step-by-step solution details have been omitted.
The problem
The assessment supplied binary artifacts and a decoder behavior to recover. Initial execution tracing gave partial insight but did not provide a complete, reusable decoding algorithm.
Research methodology
- Inspected the artifacts and experimented with Unicorn Engine to understand how the decoding logic ran.
- Used binary inspection and Ghidra pseudocode to identify data transformations and control flow.
- Translated the observed algorithm into C, fixed early runtime errors, and reran tests against the provided data.
Tools & techniques
Unicorn EngineCyberChefGhidraCLinux
Result
The reconstructed C program successfully decoded the intended challenge output. The result was a working local reproduction of program behavior, not a newly discovered security vulnerability.
What I practiced
Emulation, decompilation, C reconstruction, iterative debugging, and validation of reverse-engineered logic.
A summary of a completed controlled assessment, not a disclosure of a third-party vulnerability. Results refer only to the exercise materials described.