deuterium Himanshu Sheoran's blog on tech, security, CTFs and cryptography
2023.03.18Blog on CTFs

Challenge archive: HTB Cyber Apocalypse 2023 - Blokechain

Hack The Box 2023 - Cryptography.

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By deuterium.

Summary

Mine blocks against a private hash function and earn enough to destroy the vessels.

Read this challenge as plain text or JSON.

Browser practice

Blokechain terminal

Practice only. Rewards are public dummy values, not event flags. Completion is saved separately on this device when storage is available. Nothing runs until you choose Start.

Browser practice needs JavaScript and module Worker support.

Enter sends; Shift+Enter adds a line. Input is not echoed in program output. Stop interrupts computation; Reset clears the session without starting another.

Browser limits and console API

Limits use UTF-8 bytes: 2 MiB per input line, 4 MiB and 4096 lines per batch (including separators), 8 MiB output per operation, and a 1 MiB visible transcript. Earlier output is replaced with a truncation notice. Setup progress is separate, capped at 1024 characters and four updates per second. Original challenge deadlines still apply after setup; there is no extra setup deadline.

The console API is window.challengePractice: start(), send(stringOrLines), stop(), and reset(). Select the version above before starting. Start and Send resolve at the next input prompt or program exit with {output, state, solved}; output contains only that operation's program text. Concurrent operations are rejected. Stop, Reset, deadlines and Worker failures reject in-flight operations; terminal errors carry partial output in error.result.

Strings accept LF or CRLF; a final newline ends the last line without adding another blank line. An empty string sends one blank line. Arrays contain literal lines without LF. Unused lines are discarded if the program exits. Reset keeps saved completion. Public dummy rewards do not unlock the original answer checker.

Files

These files describe the original interactive service. The browser practice above is local; no TCP endpoint or retired remote service is connected.

The handout contains server.py and prints a placeholder when you win; it does not include the event flag.

This copy comes from Cyberkarta’s community archive, not an official HTB repository. The original remote service is retired; browser practice runs locally with a public dummy reward.

Download

Sh 
mkdir -p cyber-apocalypse-2023-blokechain
cd cyber-apocalypse-2023-blokechain
curl --fail --location --output challenge.txt \
  "https://deut-erium.github.io/challenges/cyber-apocalypse-2023/blokechain/challenge.txt"
curl --fail --location --output challenge.json \
  "https://deut-erium.github.io/challenges/cyber-apocalypse-2023/blokechain/challenge.json"
curl --fail --location --output crypto_blokechain.zip \
  "https://deut-erium.github.io/assets/challenges/cyber-apocalypse-2023-blokechain/crypto_blokechain.zip"

Sources and solutions (spoilers)

All challenges · CTF tutorials