Operation Orchid picoCTF 2022 Solution

Description

1. Step 1Find files and inspect bash history
   Use fls -r to find the bash history inode, then icat to extract it. The history shows exactly how flag.txt was encrypted, including the password. That is all you need to undo the process.
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   Bash history (~/.bash_history) records every command typed in a terminal session and persists across reboots. It is one of the first places a forensic investigator examines when analyzing a disk image, because it shows exactly what commands a user ran - including commands with sensitive arguments like passwords, API keys, and file paths.

   The critical mistake here is passing the password directly on the command line with -k password. This exposes the password in at least three places: the shell history file, the process list (readable by other users while the command is running via ps aux), and potentially shell log files. The safer approach is to use -pass file:keyfile or let OpenSSL prompt interactively, which keeps the password out of both history and process listings.

   In real forensics, bash history often reveals attacker tooling, downloaded scripts, data exfiltration commands, and privilege escalation attempts. Attackers sometimes try to clear history with history -c or by setting HISTSIZE=0, but the on-disk .bash_history file may still contain entries if the session wasn't terminated cleanly.

2. Step 2Decrypt the file
   Run the inverse openssl command (-d) on flag.txt.enc to produce flag.txt and read the picoCTF flag.
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   AES-256 (Advanced Encryption Standard with a 256-bit key) is the current gold standard for symmetric encryption. It is used by governments, militaries, and commercial software worldwide. Unlike DES or 3DES, AES has no practical known attacks against the algorithm itself when used correctly - the weakness demonstrated here is entirely in key management, not the cipher.

   OpenSSL's aes256 subcommand uses AES in CBC mode by default with a password-based key derivation function (EVP_BytesToKey) and a random salt (when -salt is specified). The salt is prepended to the ciphertext so that decryption can derive the same key. The -d flag switches from encryption to decryption mode.

   The irony of naming a password unbreakablepassword1234567 while storing it in bash history illustrates the real-world principle that the strength of encryption is only as good as the security of the key. AES-256 is mathematically unbreakable with a good key, but a key stored in plaintext in a recoverable file provides no protection at all.

Flag

Sister challenge to Operation Oni - same disk-image methodology, different artifact. Oni rewards you with an SSH key; here the bash history hands you the password to a locally encrypted file. Verify the encrypted blob actually decrypts (the openssl `-d` exit code is 0) before assuming you've grabbed the right file from the image.