The writeup archive

A hardened Merkle-Hellman knapsack: 96 public weights generated as a_i = r·b_i mod q from a tight superincreasing sequence, at density ≈ 0.91 — deliberately just under the 0.9408 CJLOS…

A stego challenge built on visual secret sharing: two images (share1.png, share2.png) from a lighthouse keeper's apprentices. Individually they look like noise; XOR them back together…

A stream cipher built on an LCG, leaking only the high 16 bits of each 64-bit state. The flag is XORed with the low bytes of the state sequence — so recovering the hidden low bits…

Total Recall (SunshineCTF 2026) is a statically linked, stripped x86-64 binary with essentially no code to reuse — but it leaks its own stack address and offers two full-chunk reads,…

The two APKs cooperate to reconstruct an encrypted DEX payload. Each contains a 32,768-byte asset named half.bin. Their native libraries publish their own half through a memory-backed…

It is a stripped, statically linked, 64-bit x86-64 ELF executable. This means there are no helpful function symbols, so the validation logic must be located by inspecting its control…

The challenge provides chall.py and output.json. A trusted setup samples a secret integer tau and builds a structured reference string (SRS) containing successive powers of the secret in…

The archive the_shape_of_silence.zip contains:

Recover the note and its attachment record as they existed immediately after the operation committed for export export-07abca69cd99. The evidence consists of four ASCII strings, in order:

Recover the incident token belonging to the container instance serving dispatch-ac1af5608a at 2026-08-14 10:10:08.555 +05:30. The input archive contains:

Files provided:** chall (3).py, output (3).json

The challenge asks us to identify the derivative matching the constraints in case.json, reconstruct its manifest ancestry all the way back to the original capture, and use six exact…

PHANTOM-15 was declared permanently offline during an industrial pressure incident. Although the gateway delivered a low-priority continuity report, it did not deliver the subsequent…

An unrecognized device was observed on a Lumeta smart-lighting mesh, sending a periodic diagnostic report. The challenge supplies:

We are given a single executable named chall and must find the 32-byte input that causes it to accept our answer. Unlike a simple strcmp checker, this program transforms the input before…

The challenge required identifying a location from an image and submitting the associated market name as the flag.

We are provided with a network packet capture file challenge2.pcap. Using tshark, we inspect the HTTP requests and responses contained within the capture:

The challenge pointed participants toward the CRYOVAULT 2026 competition rules. The clue was in Rule 2 — Flag Format, which appeared to show an ordinary example of the flag syntax.

chall (1).py — the challenge generator, including the polynomial construction and encryption scheme. output (1).json — 512 shuffled shares, finite-field parameters, and the AES-GCM…

FP02CF4.SHD — Windows print-job shadow/metadata file FP02CF4.SPL — spooled print data scan.png — scanned printed page with a faint tracking-dot pattern Tools: file, strings (including…

The archive includes a registry.fvr volume, fvrctl, an SDK header, documentation, and daemon logs. The daemon uses fvregd 1.4.2 / on-disk format v1. In v1, the 16-byte cell descriptor…

Service:** nc 0.cloud.chals.io 15036 — fresh process per connection.

The edge proxy enforces its restricted-header rules only while decoding the primary HEADERS frame. By padding the header block so the sensitive headers fall into CONTINUATION frames, the…

The instance is a "Capability Broker" (auth-gw, Node/Express) that mills Ed25519-signed CBOR capability tokens, plus a secret vault (vault-api, Python/Flask) that enforces role + caps…