CodeBash

Establish Your Cover Identity

Before any operation begins, you need a codename. Enter your real name below. Your codename will be generated deterministically using a multi-step cryptographic algorithm. The same name will always produce the same codename.

Your real name

Your name is not stored at this stage.

Your Classified Codename

■ How Your Codename Was Generated

Step 1: Normalisation

Strip non-alphabetic characters and convert to uppercase

Step 2: Vigenère Cipher (Key: GCHQ)

Each letter is shifted by the corresponding key letter, cycling every 4 characters

Step 3: ASCII Extraction

The first 4 encoded characters are converted to their ASCII integer values

Step 4: XOR Pairing

Pairs of ASCII values are XOR’d together, then combined into a 16-bit seed

Step 5: Polynomial Hash

The seed is fed through a polynomial hash (base 31) over the remaining encoded characters, the same algorithm used in Java’s String.hashCode()

Step 6: Index Derivation

Modulo arithmetic maps the final hash to two word lists of 64 entries each

Why does the same name always give the same codename?
Because the algorithm is deterministic: no randomness is involved. This is how hash functions work. It also means that anyone who knows the algorithm could reverse-engineer your identity from your codename alone. This is why real systems add a salt, a unique random value mixed in before hashing, so that identical inputs produce different outputs. Without a salt, a codename database like this one is vulnerable to a precomputation attack.

Mission Briefing

Select an Operation, Agent

Operations are classified by difficulty. Complete Recruit-level missions before advancing. Each operation tests different areas of your computer science knowledge.

Recruit Single-step puzzles · Hints available · Beginner to GCSE level

Operation LOCKDOWN

5 stages · Ciphers · Number bases · Algorithms · Logic · Hashing

ENTER →

Leaderboard →

Operation SWITCHBACK

5 stages · Queues · Hex · Selection Sort · Logic · Compression

ENTER →

Leaderboard →

Operation CLEARWATER

5 stages · ROT-13 · Binary · Loops · Boolean · Networking

ENTER →

Leaderboard →

Analyst Multi-step puzzles · No hints · Tools not named · A-Level difficulty

Operation BLACKOUT

5 stages · Binary Search · Two’s Complement · Merge Sort · Big O · Hashing

ENTER →

Leaderboard →

Operation NIGHTFALL

5 stages · Recursion · IEEE 754 · Call Trees · De Morgan’s · ASCII

ENTER →

Leaderboard →

Operation IRONVEIL

5 stages · LMC · Regex · Bubble Sort · Dijkstra’s · Compression

ENTER →

Leaderboard →

Specialist Chained answers · No hints · Theory of Computation · Advanced A-Level and beyond

Operation DEEPCOVER

5 stages · LMC · Automata · Turing Machines · Big O · Chained

ENTER →

Leaderboard →

Operation PHANTOM NET

5 stages · RSA · Modular Arithmetic · Hashing · IPv6 · Chained

ENTER →

Leaderboard →

Operation ZERO DAY

5 stages · Graph Theory · SHA-256 · Quicksort · Network Flow · Chained

ENTER →

Leaderboard →

Stage 01 / 05 - Operation LOCKDOWN

The Intercepted Transmission

A rogue process has encrypted the school server and locked out all staff. You have been brought in to restore access.

The first layer of security was changed this morning. Our signals team intercepted a transmission sent between two unknown parties shortly before the lockdown:

DFFHVV FRGH: IRXU

The transmission appears garbled. Analysts believe it contains the access code for Layer 1. Decode it and enter the code below.

Enter access code

Not all interceptions require a complex key. This looks like a classical substitution method, one of the oldest tricks in cryptography. Each letter has been shifted by a fixed amount through the alphabet.

Try it yourself: Encryption & Ciphers tool

✓ ACCESS GRANTED - LAYER 1 CLEARED

Caesar shift 3 → ACCESS CODE: FOUR. Layer 2 uses a different system entirely.

Stage 02 / 05 - Operation LOCKDOWN

The Technician’s Log

Layer 1 is down. The system has routed you to the memory management module.

A maintenance log was found on the compromised machine. One entry stands out:

[09:17:32] WARN: Suspicious read at address 0b01001010
[09:17:33] INFO: Flagged for review

The security audit form requires the address in decimal. The log uses a notation engineers sometimes prefer when working directly with hardware.

Enter the decimal address

The prefix 0b is a standard programming convention that indicates which number system is being used. Once you identify the system, converting to decimal is straightforward.

Try it yourself: Number Base Converter

✓ ACCESS GRANTED - LAYER 2 CLEARED

0b01001010 = 74 decimal. Address verified. Layer 3 requires you to understand a program’s exact behaviour.

Stage 03 / 05 - Operation LOCKDOWN

The Challenge-Response Protocol

You are through to the authentication layer. This system does not use a static password.

Every session, the server runs the following program against a challenge sequence. Your response must exactly match the value held in result when the program finishes.

Today’s challenge sequence: [3, 1, 4, 1, 5]

def authenticate(arr):

    result = 0

    for i in range(len(arr)):

        if arr[i] > result:

            result = arr[i]

    return result

What value does the program return?

Enter the response value

Work through the program manually. Set up columns for i, arr[i], and result. Update each column at every iteration. The condition on line 4 controls when result changes.

Try it yourself: Trace Table tool

✓ ACCESS GRANTED - LAYER 3 CLEARED

Correct response: 5. The algorithm finds the maximum value. Authentication accepted.

Stage 04 / 05 - Operation LOCKDOWN

The Electronic Lock

Almost there. The final physical barrier is an electronically controlled door with three input switches: A, B, and C.

The door release circuit uses the following Boolean expression:

(A AND NOT B) OR (B AND C)

Today’s switch configuration, set by the intruder to block access:

A = 1 B = 0 C = 1

Does the circuit output 1 (door opens) or 0 (door stays locked)?

Enter circuit output (1 or 0)

Evaluate the expression in order of precedence. Resolve NOT first, then each AND expression separately, then combine the two results with OR.

Try it yourself: Logic Gates tool

✓ ACCESS GRANTED - LAYER 4 CLEARED

(1 AND NOT 0) OR (0 AND 1) = (1 AND 1) OR 0 = 1 OR 0 = 1. Door open. One layer remains.

Stage 05 / 05 - Operation LOCKDOWN

The Stolen Credentials

Final layer. The intruder stored their backdoor credentials inside a hash table before locking the system. You need to locate and wipe them.

The database uses a hash table with 11 slots (numbered 0 to 10). Hash function:

slot = (sum of ASCII values of key) mod 11

Forensics have identified the backdoor username as DOG. Which slot holds these credentials?

ASCII reference: D = 68, O = 79, G = 71

Enter slot number (0–10)

Sum the three ASCII values. Then find the remainder when that sum is divided by 11. The remainder is the slot number.

Try it yourself: Hash Table tool

✓ ALL LAYERS CLEARED

68 + 79 + 71 = 218 → 218 mod 11 = 9. Slot 9 located. Credentials wiped.

✓ OPERATION COMPLETE

Server Restored

All five security layers have been bypassed. The rogue process has been terminated and administrator access has been restored.

Ciphers

Number Bases

Algorithms

Logic Gates

Hash Tables

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Time

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Hints used

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Wrong answers

CodeBash Escape Room

Establish Your Cover Identity

Server Restored