Base64

Platform HASBL CTF 2026 Difficulty Mixed (Easy → Medium) OS Jeopardy — Forensics (Linux toolchain) Tags QR-code decoding with Reed-Solomon tolerance, JPEG metadata extraction (EXIF, COM, XMP), base64/base32 encoding fingerprints, bit-stream-to-JPEG reconstruction, magic-byte surgical repair, file-header recognition HASBL CTF 2026 is a multi-category jeopardy event with Reverse Engineering, Pwn, Web, and Forensics tracks. This writeup is dedicated to the Forensics track — the five forensics challenges (Quick Response, Logo, Digits, our sweet cat, Pamuk, and The Magic of "Magic Numbers") were all solved, and each one teaches a different file-forensics primitive: QR-code decoding despite a visual overlay, JPEG metadata extraction across EXIF and COM segments, bit-stream-to-JPEG byte reconstruction, base64-wrapped JPEG with hex content, and surgical magic-byte repair plus XMP metadata walking. ...

Platform BKISC CTF 2026 Difficulty Easy OS Encoding Points 50 Tags JDK source reading, custom Base64 alphabet, UTF-16 BE Cryptografie is a 50-point crypto challenge from BKISC CTF 2026 that hangs off a single, very specific hint: FileSystemPreferences.dirName(). If you’ve never had to look at the OpenJDK source before, this challenge is a tour of an internal Base64-like helper that almost nobody outside the JDK uses — and the decoder only takes about ten lines once you know where to look. ...