Crack the Leaked XOR Keystream

XOR Encryption — Symmetric and Fragile

XOR (exclusive-OR) is one of the simplest symmetric cipher primitives: each byte of plaintext is combined with a corresponding byte of the key using the ^ operator. Because XOR is its own inverse, the same operation encrypts and decrypts — just XOR the ciphertext with the same key again.

Why Short, Static Keys Are Dangerous

When the key is shorter than the message it is repeated (a technique known as Vigenère-style key repetition). If an attacker discovers the key — through source-code leaks, firmware dumps, or simple guessing — the entire ciphertext collapses instantly. This lab simulates exactly that scenario: the key was found hard-coded in a public Git repository.

Your Mission

You are given a hex-encoded XOR-encrypted blob and the leaked key s3cr3tK3y. Decode the hex to raw bytes, then XOR every byte with the repeating key to recover the plaintext flag.

Recommended Tools

• Python one-liner: python3 -c "import binascii; ct=bytes.fromhex('BLOB'); key=b's3cr3tK3y'; print(bytes(c^key[i%len(key)] for i,c in enumerate(ct)).decode())"
• CyberChef: pipe From Hex → XOR (key s3cr3tK3y, UTF-8, Standard)
• openssl / xxd can help inspect raw bytes if you prefer shell tools