Phantom

Inspired by encryption techniques used in the Phantom malware family, this challenge implements a cipher algorithm to protect its secrets.

You are provided with a compiled Linux binary that prompts for a decryption key. The encrypted data is stored as hex strings and split into two parts. Analyze the binary to understand the encryption mechanism and recover the flag.

Binary Information:

Filename: phantom
Size:     23,000 bytes (23 KB)
MD5:      063fba451464a936516f10ee8d56106e
SHA1:     653d9e50dd054f0a8544c8eadaae078ab88b0722
SHA256:   64c413ce73667f18b39ceb5aace803834f71fb373d2206b5b6b938e44915cc04

Verify integrity after download:

md5sum phantom
sha1sum phantom
sha256sum phantom