Global Hyperlink Zone

Author: 0xIDA
Platform: HTB · Category: web · Difficulty: Very Easy

Platform: HTB | Category: Web | Difficulty: Very Easy
Target: 154.57.164.67:32358

Solvers

solve.py

Summary

A Qiskit-based quantum circuit challenge where you must construct a 5-qubit gate sequence that produces specific measurement correlations across qubits to "initialize the hyperlink" and receive the flag.

Analysis

The server (server.py) accepts a semicolon-delimited string of quantum gate instructions in <gate>:<params> format, builds a 5-qubit circuit, runs 256 shots on the qasm_simulator, and checks the measurement outcomes ("shares"):

Condition 1: shares[0] == shares[1] == shares[3] — qubits 0, 1, and 3 must measure identically across all 256 shots
Condition 2: shares[2] == shares[4] — qubits 2 and 4 must measure identically
Condition 3: shares[4] != shares[0] — the two groups must produce different 256-bit strings
Condition 4: No share can be all-0x00 or all-0xFF bytes (rejects trivial all-|0⟩ or all-|1⟩ states)

Solution

Use H (Hadamard) gates to create superposition and CX (CNOT) gates to entangle/duplicate measurement outcomes:

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

How it works:

H:0 — puts qubit 0 into superposition (50% |0⟩, 50% |1⟩) — avoids all-0/all-255 trap
CX:0,1 — CNOT copies qubit 0's state to qubit 1 (they always measure the same)
CX:0,3 — CNOT copies qubit 0's state to qubit 3 (all three match)
H:2 — puts qubit 2 into independent superposition
CX:2,4 — copies qubit 2's state to qubit 4

Group A (0,1,3) and Group B (2,4) each have consistent in-group measurement patterns but differ from each other because their Hadamard gates produce independent random sequences.

Flag

HTB{4_57r4ng3_gr33nb3rg3r_h0rn3_z31L1ng3r_57473_1n1714L1z35_7h3_hyp3rL1nk!}

Tools Used

netcat — raw TCP to target
curl — download challenge files

Key Takeaways

CNOT entanglement = measurement correlation between control and target qubits
H gate creates superposition → avoids all-0/all-255 byte traps
The "shares" are the accumulated measurement bitstrings converted to bytes
Chain of CX gates lets you broadcast one qubit's outcome to many qubits