Challenge Overview

Disaster! One of the workstations on the network seems to have been compromised. Users are reporting that their important files are inaccessible, replaced with.locked extensions. A menacing ransom note (displayed by Challenge1.exe) has appeared on the screen, demanding Bitcoin for the recovery key. Luckily, our intrusion detection system was active during the incident and managed to capture the network traffic (traffice.pcapng) generated by the malware. Furthermore, due to a temporary debug setting left active on the compromised machine, the TLS session keys were logged (sslkeylog.log). Your mission, should you choose to accept it, is to play digital forensics investigator. Dive into the captured network data, figure out how the ransomware operated, and see if you can recover the decryption key the attackers used. The original flag is locked away in C: \Users\User\Documents\CTF_Vault\Flag.txt.locked. Analyze the provided network capture file (traffice.pcapng) using the supplied TLS key log file (sslkeylog.log) to decrypt the communication between the infected host and the attacker's command-and-control server. Identify how the encryption key was handled or transmitted. Extract the correct decryption key and use it (potentially with the ransomware's own interface) to decrypt Flag.txt.locked and recover the flag.

What You Will Learn

  • Analyzing network traffic captures to investigate ransomware activity.
  • Decrypting TLS-encrypted communications using a provided key log file.
  • Identifying command-and-control (C2) communication within packet data.
  • Extracting encryption or decryption keys from network analysis.
  • Recovering locked files by applying the discovered decryption key.

Program Curriculum

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