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STORY2 — Wiki

"Hack our STORY" — JuCrypt

STORY2 is a symmetric block cipher that uses a shared narrative passphrase as its key. Two people who know the same story can encrypt and decrypt messages without exchanging random key bytes.

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Quick navigation

Page	Contents
Installation & Setup	Requirements, C extension build
API Reference	encrypt, decrypt, decrypt_str
Architecture & Design	Round structure, MDS construction, key schedule
Security & Cryptography	Differential/linear bounds, attack boundaries, threat model
Performance & Benchmarks	Throughput numbers, C extension optimisations
Custom S-box Pool	customju/sboxes.json format, pool loading rules
Changelog	Version history

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Thirty-second example

from story2 import STORY2
 
story = "The summer we found the tide pool near the lighthouse"
 
# Encrypt
ct, nonce, tag = STORY2.encrypt("Hello, world", story)
 
# Decrypt
pt = STORY2.decrypt_str(ct, story, nonce, tag)
print(pt)  # Hello, world

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Core properties

Property	Value
Block size	16 bytes (128-bit)
Derived key	256-bit, HMAC-SHA256 from story passphrase
Rounds	5 (fixed)
MDS matrix	16×16 Cauchy over GF(2⁸), branch number 17
Permutation	None — full diffusion from MDS alone
Authentication	HMAC-SHA256 over nonce ‖ ciphertext
Mode	CTR with 8-byte random nonce
S-box	Key-dependent, pool of 255 bijections
Whitening	Final ARK, independently derived key

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Paper

S-NAB-035, LOVELACE Brigade. Author: I., Nabil.