Introduction

This module asks you to specify the Route transposition cipher, in which a message is “routed” around a grid in a spiral pattern. This cipher is very simple on paper, but might be more of a challenge to specify in Cryptol.

Prerequisites

Before working through this lab, you’ll need

You’ll also need experience with

For a background on Route, we recommend perusing the Wikipedia entries on transposition ciphers in general and Route in particular.

Skills You’ll Learn

This is an independent exercise. Who knows what you’ll learn?

Load This Module

This lab is a literate Cryptol document — that is, it can be loaded directly into the Cryptol interpreter. Load this module from within the Cryptol interpreter running in the cryptol-course directory with:

Cryptol> :m labs::Transposition::Route
Loading module Cryptol
Loading module specs::Primitive::Symmetric::Cipher::Block::Cipher
Loading module specs::Primitive::Symmetric::Cipher::Block::DES
Loading module labs::CryptoProofs::CryptoProofs
Loading module labs::Transposition::CommonProperties
Loading module labs::Transposition::Transposition
Loading module labs::Transposition::Route

Start by defining the module for this lab:

module labs::Transposition::Route where

You should import your common definitions for transposition ciphers:

import labs::Transposition::Transposition

Route

EXERCISE: Define pi and pi_test. The aforementioned Wikipedia article presents an example. pi_test should include it.

Conclusion

This lab asked you to specify the Route transposition cipher. Now you have at least one independently written spec under your belt. Go forth and do good!

Solicitation

How was your experience with this lab? Suggestions are welcome in the form of a ticket on the course GitHub page: https://github.com/weaversa/cryptol-course/issues

From here, you can go somewhere!

     
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