caesar

1
Caesar

Shift letters by a fixed amount — the classic Roman cipher

xor

2
XOR

Bitwise XOR encryption with a repeating key byte

base64

3
Base64

Binary-to-text encoding hiding plaintext messages

vigenere

4
Vigenere

Polyalphabetic cipher with a keyword — unbreakable for centuries

hex

5
Hex

Hexadecimal encoded plaintext — decode hex to ASCII

hash-prefix

6
Hash Prefix

Find a string whose SHA-256 starts with a given prefix

lattice

7
Lattice

Map grid coordinates to letters — geometry-based cipher

eigenvector

8
Eigenvector

Compute eigenvectors to reveal hidden ASCII passwords

scytale

9
Scytale

Ancient Spartan transposition cipher — wrap text around a rod

enigma

10
Enigma

Simulated 3-rotor Enigma with reflector — WWII cipher

compression

11
Compression

Zlib-compressed payload — decompress to reveal the message

oracle

12
Oracle

Future-event key using real-world BTC price data

fft

13
FFT

Frequency domain — DFT-transformed message, decode with iDFT

bezier

14
Bezier

Parametric curve through a letter grid — De Casteljau decoding

terrain

15
Terrain

3D elevation grid — hidden bitmap in Z-axis displacement

lensing

16
Lensing

Compound diff-7: NURBS + gravitational lens + XOR payload

mirror

17
Mirror

Two-agent co-op: each decrypts half, combine for full message

nurms

18
NURMS

Subdivide a 5x5 control mesh — sample heights to recover letters

quantum

19
Quantum

Single-qubit states rotated through quantum gates — invert to decode

elliptical

20
Elliptical

Gravitational masses warp a grid — strongest deflection wins each cell

elastic

21
Elastic Path

XOR-ciphered curve weights — decrypt, reconstruct the spline, read the word

plumb

22
Plumb

A pipe network — simulate water flow through the correct inlet to reveal a hidden word

flux

23
Flux

Magnetic poles hidden in inverse-square flux — solve A.x = b

galton

24
Galton Board

Pin densities from a Galton board — cluster to separate ON from OFF

cylinder

25
Cylinder

Text on a rotating cylinder — find the circumference that reveals the message

lwe

26
LWE

Post-quantum lattice crypto — recover s from A.s + e = b (mod Q)

shamir

27
Shamir SS

Reconstruct a secret from k polynomial shares via Lagrange interpolation over GF(p)

merkle

28
Merkle Proof

Verify a leaf belongs in a Merkle tree by reconstructing the root from a proof path

elliptic-curve

29
EC DLog

Find k from Q = k.G on a small elliptic curve over GF(p) — brute force to BSGS

spore

30
Spore

Radial hyphae grow toward a character ring. Simulate the growth — the touch sequence spells the hidden word.

boolean-matrix

31
Boolean Matrix

Voxel CSG cipher — shuffled Z-slice mask tiles. The grouping is the cipher.

parallax

32
Parallax

A 3D point cloud hides a word that only appears from a specific camera position, target, and FOV.

scrollfall

33
ScrollFall

A ball drops through scrolling columns of text. Physics determines capture timing. The grid appears random — only N chars carry signal.

prism-refraction

34
Prism

A laser fires through a prism. Snell's law refracts the beam toward a letter on the inner wall. Laser position x prism geometry x refractive index = nonlinear cipher.

chime

35
Chime

Faceted flying objects with Helmholtz resonator cavities. An interrogation pulse rings each cavity at its resonant frequency — a musical note on the 12-TET scale. Frequency to note to character.

spectral-glass

36
Spectral Glass

A doped glass filter absorbs at specific wavelengths. Match absorption dips to a reference table to read characters in wavelength order.

logic-gate

37
Logic Gate

A digital logic circuit — simulate gates forward through the DAG. Output bits encode the answer in 5-bit binary.

newtons-cradle

38
Newton's Cradle

Simulate pendulum physics across multiple cradles with varying materials and gravity. Collision counts encode the answer.

wave-superposition

39
Wave Superposition

A sampled audio waveform — sum of sine waves at consonant intervals. FFT the signal, identify peak frequencies, compute semitone ratios, map to letters.

spacetime-causality

40
Spacetime Causality

Einstein's special relativity: events in spacetime with timelike separation (|x| ≤ ct) can causally affect you. Filter spacelike noise, sort causally connected events by time — the labels spell the message. Same physics GPS satellites use.

reed-solomon

41
Reed-Solomon

Polynomial error correction — recover a message from shares. The same math that lets QR codes and Voyager survive corruption.

viterbi

42
Viterbi

Maximum-likelihood decoding of convolutional codes. Used in NASA deep space links, digital TV, and GSM phones.

bb84

43
BB84

Quantum key distribution — recover a sifted key from qubit bases and measurements. The world's first quantum cryptographic protocol.

ligo

44
LIGO

Interferometer phase shifts from gravitational waves. Detect ripples in spacetime — the same physics that won the 2017 Nobel Prize.

heat-equation

45
Heat Equation

1D thermal diffusion — initial temperatures encode a message. Used in CPU cooling, steel tempering, and climate modeling.

watershed

46
Watershed

D8 hydrological flow model — elevation grid values encode ASCII. Used by USGS for flood prediction and dam placement.

pagerank

47
PageRank

Rank web pages by link importance — the algorithm that launched Google. The ranked pages spell the answer.

dna-sequencing

48
DNA Sequencing

Overlap-layout-consensus genome assembly from short reads. The same bioinformatics used to sequence COVID-19.

protein-folding

49
HP Protein Folding

Hydrophobic-polar model of protein folding on a 2D grid. The core insight behind AlphaFold's Nobel Prize.

gravitational-warp

50
Gravitational Warp

General relativity: a photon's path bends as it passes near massive objects. Simulate gravitational deflection to trace the curved trajectory through a letter grid.

hydraulic

51
Hydraulic Cipher

Water taps fill buckets of different sizes. Handle angles control flow rates. The water levels spell a word when you find the common open duration.

eulers-formula

52
Euler's Formula

Complex rotations on the unit circle - compute e^(iθ) = cos θ + i sin θ to find landing positions that spell a hidden word. The most beautiful equation in mathematics.

handshake-lemma

53
Handshake Lemma

In any graph, sum of degrees = 2 × edges. Given a degree sequence, compute total handshakes and map to a letter.

basel-problem

54
Basel Problem

Euler proved the sum of 1/n² from 1 to ∞ equals π²/6. Compute a partial sum and extract its fractional digits to find the answer letter.

birthday-paradox

55
Birthday Paradox

What's the probability that two people in a group share a birthday? Compute it iteratively — the percentage maps to a letter.

logistic-map

56
Logistic Map

Iterate the famous chaos equation x → r×x×(1−x). After N steps, the value encodes a letter — a glimpse into chaos theory.

euclidean-algorithm

57
Euclidean Algorithm

The oldest algorithm still in use. Count the division steps in Euclid's GCD method — steps mod 26 gives you the letter.

mandelbrot

58
Mandelbrot

Compute Mandelbrot set iteration counts for points on the complex plane. Each count maps to a letter — the grid spells a hidden word.

game-of-life

59
Game of Life

Conway's cellular automaton — simulate N generations on a 6x6 grid. The final pattern's rows, read as binary, map to letters.

eulerian-path

60
Eulerian Path

A graph where an Eulerian path visits every edge exactly once. The vertex labels along that path spell the secret word.

monty-hall

61
Monty Hall

The classic probability paradox: three doors, one car. Compute the probability of winning by switching — the answer maps to a letter.

tower-of-hanoi

62
Tower of Hanoi

The classic recursive puzzle. Compute the minimum number of moves for N disks — 2^N - 1 mod 26 gives the answer letter.

pigeonhole

63
Pigeonhole

N+1 points in an N×N grid — by the pigeonhole principle, two share a row or column. The shared index maps to a letter.

chinese-remainder

64
Chinese Remainder

Solve a system of two congruences with coprime moduli. The unique solution modulo M mod 26 gives the answer letter.

hamming

65
Hamming (7,4)

The simplest algebraic error correction code. Each 7-bit block corrects 1 bit flip using syndrome decoding via a parity-check matrix. Used in ECC RAM and Voyager.

fhss

66
FHSS

Frequency Hopping Spread Spectrum -- invented by Hedy Lamarr in 1942 for torpedo guidance. Hop across frequencies to survive jamming. The basis of Bluetooth, WiFi, satellite TV, and Link 16.

ldpc

67
LDPC

Sparse parity-check codes decoded by iterative belief propagation on a Tanner graph. The state of the art in error correction -- used in 5G, WiFi 6, DVB-S2, and SpaceX Starlink.

bombe

68
Bombe

Turing's electromechanical Enigma codebreaker -- deduce Enigma rotor positions from a known plaintext (crib). The machine that broke the Nazi cipher at Bletchley Park.

rsa

69
RSA

The first public-key cryptosystem. Factor a small RSA modulus n=p*q, compute the private key d, and decrypt the message. Foundational to HTTPS, SSH, and digital signatures.

des

70
DES

Simplified Feistel network cipher — the Data Encryption Standard that secured banking for 20+ years. Trace rounds through XOR, S-boxes, and swap operations.

aes

71
AES

The Advanced Encryption Standard — Rijndael cipher. Trace one round of SubBytes, ShiftRows, MixColumns, and AddRoundKey. The most widely deployed cipher in history.

diffie-hellman

72
Diffie-Hellman

The key exchange that made public-key crypto possible. Given g, p, and two public values, compute the shared secret. Used in every TLS handshake.

tls-handshake

73
TLS Handshake

Simulate the TLS 1.2 handshake: ClientHello, ServerHello, certificate exchange, and key derivation via SHA256. The protocol that secures every HTTPS connection.

wireguard

74
WireGuard

The modern VPN protocol — 4,000 lines of code replacing 400,000. Noise protocol key exchange with Curve25519. Built into the Linux kernel since 5.6.

pem-certificate

75
PEM Certificate

Decode an X.509 certificate in PEM format. Extract the subject, issuer, and public key from a base64-encoded DER structure. Used in every HTTPS connection.

collatz

76
Collatz Conjecture

Take any number. If even, halve it. If odd, triple and add one. The conjecture says you always reach 1. Count the steps.

goldbach

77
Goldbach's Conjecture

Every even number greater than 2 is the sum of two primes. Find the Goldbach partition for a given even integer.

four-color

78
Four Color Theorem

Color any planar map with 4 colors so adjacent regions never share the same color. One of the first major computer-assisted proofs in mathematics.

shannon-entropy

79
Shannon Entropy

Compute the Shannon entropy of a message: H = -Σ p_i log₂(p_i). The mathematical foundation of information theory and data compression.

luhn

80
Luhn Algorithm

The mod-10 check digit algorithm behind every credit card PAN. Invented by Hans Peter Luhn at IBM in 1954. Double every second digit from the right and sum.

crypto1

81
Crypto-1 RFID

The 48-bit LFSR stream cipher in billions of Mifare Classic transit cards and access badges. Broken by chip reverse-engineering in 2008. Now a cautionary tale in security-by-obscurity.

emv

82
EMV Chip-and-Pin

The protocol behind 10 billion payment cards. Each chip transaction generates a unique ARQC cryptogram from dynamic session keys derived via the Application Transaction Counter.

fingerprint

83
Fingerprint

Match minutiae sets — ridge endings and bifurcations — against a template database. Sir Francis Galton's 1892 system still underpins AFIS (Automated Fingerprint Identification System) worldwide.

iris

84
IrisCode

Decode a 256-byte IrisCode via Gabor wavelet demodulation. John Daugman's 1993 algorithm powers border control at 300+ airports. The iris is more stable than any fingerprint.

runes

85
Elder Futhark

Decipher the 24-rune Elder Futhark alphabet used by Germanic tribes from ~150 CE. The word 'rune' means 'secret' or 'mystery' — each symbol carries a poetic meaning from Fehu (wealth) to Dagaz (dawn).

gabor-wavelet

86
Gabor Wavelet

A sine wave localised by a Gaussian window — Dennis Gabor's 1946 idea gives you time-frequency analysis. The mathematical basis of Daugman's IrisCode, fingerprint enhancement, and JPEG 2000.

phone-tone

87
Phone Tone

Decode DTMF frequency pairs — the tones that dial the world. Each key on a phone keypad produces two simultaneous frequencies. Blue box hackers used this to command the phone network. Now it's your puzzle.

atbash

88
Atbash

Mirror the alphabet — A becomes Z, B becomes Y. The oldest known substitution cipher, used in the Hebrew Bible.

columnar

89
Columnar

Write in a grid row by row, read column by column — the transposition cipher that armed the Allied forces in WWI.

resonant-cascade

90
Resonant Cascade

Drive a harmonic oscillator at its natural frequency — compute the collapse pattern to decode the cipher.

plain-sight

91
Plain Sight

A secret word hidden in the first letters of sentences in normal-looking text — steganography in plain sight.

pgp

92
PGP RSA

Pretty Good Privacy — factor an RSA modulus, derive the private key, and decrypt a PGP-style ciphertext. Phil Zimmermann's 1991 crypto system.