Challenge / Quantum

Global Hyperlink Zone

By Jennofrie Daguil · Cybersecurity and Red Team Operator

The challenge provides a Qiskit-based server that accepts quantum gate instructions for five qubits. It measures the circuit 256 times and compares the resulting bitstreams. The server splits the measured results into five 256-bit shares and checks: It also...

Very EasyPublished 2025-05-14Sanitized local writeup

Scenario

Global Hyperlink Zone attack path

Objective

Challenge walkthrough focused on Quantum evidence, validation, and reusable operator lessons.

Global Hyperlink Zone sanitized attack graph

Walkthrough flow

Circuit constraints

State manipulation

Measurement strategy

Proof captured

Source coverage

Moderate source coverage

Status: partial. This article is generated from 4 sanitized Markdown sources and keeps raw flags, credentials, keys, cookies, and reusable secrets out of the rendered blog.

71% coverage

Evidence verdict

Moderate confidence: the page is useful for review, but it should be treated as partial because the available source material is thinner or less narrative-complete.

Quantum/Global_Hyperlink_Zone/writeup.md
htb-challenge/Quantum/Global_Hyperlink_Zone/notes.md
htb-challenge/Quantum/Global_Hyperlink_Zone/memory-summary.md
htb-challenge/Quantum/Global_Hyperlink_Zone/hypothesis-board.md

Technical Walkthrough

Global Hyperlink Zone - Writeup

Summary

The challenge provides a Qiskit-based server that accepts quantum gate instructions for five qubits. It measures the circuit 256 times and compares the resulting bitstreams.

Key Logic

The server splits the measured results into five 256-bit shares and checks:

python

shares[0] == shares[1] and
shares[1] == shares[3] and
shares[2] == shares[4] and
shares[4] != shares[0]

It also rejects deterministic all-zero or all-one streams.

Solve

We need two independently random but internally correlated groups:

qubits 0, 1, 3: 3-qubit GHZ state
qubits 2, 4: Bell pair

The required instructions are:

text

H:0;CX:0,1;CX:0,3;H:2;CX:2,4

Run:

bash

python3 solve/solve.py <TARGET> 30428

The flag is saved in loot/flag.txt.

Source-Backed Dossier

The sections below are merged from companion Markdown notes for the same case. They are rendered after sanitization so the article stays precise without publishing raw flags, credentials, or target-specific secrets.

Notes

Scope

Challenge: Global Hyperlink Zone
Category: Quantum
Difficulty: Very Easy
Remote: <TARGET>:30428
Download: <local workspace>
Workspace: <local workspace>

File Inventory

File	SHA256	Type
`files/Global_Hyperlink_Zone.zip`	`<hash redacted>`	Zip archive
`files/extracted/quantum_global_hyperlink_zone/server.py`	`<hash redacted>`	Python script

Evidence Ledger

Timestamp	Action	Output File	Finding	Next Step
2026-05-07	Unzipped challenge	`files/extracted/quantum_global_hyperlink_zone/server.py`	Only source file is `server.py`	Read validation logic
2026-05-07	Reviewed `server.py`	terminal output	Server builds a 5-qubit Qiskit circuit from instructions and measures 256 shots	Derive required correlations
2026-05-07	Tested remote reachability	`analysis/remote-reachability.txt`	TCP connection to `<TARGET>:30428` succeeded	Send derived sequence
2026-05-07	Sent sequence	`analysis/remote-solve.txt`	`H:0;CX:0,1;CX:0,3;H:2;CX:2,4` initialized the hyperlink	Save flag
2026-05-07	Verified flag	`loot/flag.txt`	Flag format matches `<flag stored in loot/flag.txt>`	Write solve script

Reasoning

The server stores one 256-bit measurement stream per qubit. It accepts only if:

qubits 0, 1, and 3 produce identical streams
qubits 2 and 4 produce identical streams
the two groups differ from each other
no stream is all-zero or all-one

This is exactly achieved by creating:

a 3-qubit GHZ state across 0,1,3
a Bell pair across 2,4

Sequence:

text

H:0;CX:0,1;CX:0,3;H:2;CX:2,4

Memory Summary

Metadata

Platform: HackTheBox Challenges
Category:
Challenge:
Difficulty:
Source workspace:

Validated Solve Chain

Concepts only. Do not include raw flags, reusable credentials, tokens, cookies, private keys, or live secrets.

Reusable Lessons

Dead Ends

Tool Quirks

Evidence Paths

Ingestion Decision

Proposed for LightRAG: yes/no
Requires user approval before ingestion: yes

Hypothesis Board

Rank	Path	Evidence	Missing Proof	Cheapest Validation	Confidence	Status

Closed Branches

Branch	Evidence Tested	Failure Output	Reason Closed	Revisit Condition

Technical analogy

How to remember this solve

Think of the quantum circuit like a fragile sequence of switches. The solve is about arranging the switches so the final measurement lands in the one state that unlocks the flag.

For Global Hyperlink Zone, keep the mental model simple: identify the trusted assumption, prove it with the smallest safe test, then automate or repeat only the part that directly leads to the flag.