AF-3DFB-CR · Kriptanaliz
Layered XOR Cipher
DOWNLOADABLE encrypted file. The real flag is base64 + single-byte XOR encrypted (crack with a 256-key brute force). The base64-only blob is a decoy.
Scenario
A file with two encoded blobs. One is ONLY base64 and decodes directly but yields a plausible-looking FAKE flag (decoy). The other is base64 + single-byte XOR encrypted; its base64 decode is unreadable, so brute-force the 256 possible XOR keys (or frequency analysis) to get the readable text and the real flag. Provide the real flag and the XOR key; do not fall for the base64 decoy.
Anti-forensics techniques
- Multi-layer encoding (base64 + XOR)
- Single-byte XOR brute force
- Base64-only fake blob (red herring)
Provided artifacts
- Encrypted text file (base64 + XOR layers)
Sample questions
- q1: What is the real flag after decrypting the XOR layer?
- q2: What is the single-byte XOR key? (e.g. 0x5a)
- trap1: Do NOT report the fake flag from the base64-only blob as the answer.
Soundness trap
The base64-only blob decodes directly but is FAKE; presenting it as the answer is heavily penalized. The real flag appears after cracking the XOR.
Scoring
XOR brute-force solve + base64-decoy resistance (soundness).
DOWNLOADABLE
Download and solve
The answer key is hidden (scored set); the flag is encrypted, you must decrypt it.