A tale of Phobos - how we almost cracked a ransomware using CUDA

This report analyzes the Phobos ransomware's weak key-schedule, demonstrates how that weakness can be exploited to recover keys, and documents a high-performance CUDA-based proof-of-concept decryptor (with source code). It explains the entropy analysis, brute-force optimizations, performance tuning (SHA-256 and AES on GPU), required assumptions (precise time, PID/TID knowledge), practical limitations, and includes the sample hash and repository for the PoC.