The Code Workbook - Cryptography through Excel Macros

by Bhuwan Singh

This book is totally in debt to Simon Singh. I read his Code Book a few months ago, and was absolutely fascinated by his description of ciphers. It took little time to realize that actually programming the various ciphers that Simon Singh had described in his book would be an incredible amount of fun. Hence this book on Excel Macro implementation of Ciphers.While the Code Book by Simon Singh covers vast scope and is hugely entertaining and informative, in The Code Workbook we cover just the basics of ciphers – the simplest monoalphabetic substitution cipher is the best place to start. It is easily implemented, easily breakable and is great insight into how ciphers may be created and broken. Following the monoalphabetic substitution cipher, we have the more formidable polyalphabetic substitution cipher. This is much harder to break, but has been broken.One specific form of the polyalphabetic cipher is the one time pad. While this is at heart a polyalphabetic substitution, it has certain unique properties that make it unbreakable – even in theory. Someone using a one-time pad is guaranteed perfect secrecy. So there is, inside this book, simple code and instructions to encode messages in a manner that would be unbreakable even against attack from the most sophisticated spies and hackers in the world.This book stops at the creation of one time pad ciphers. There are weaknesses that make the one time pad difficult to implement. These weaknesses are in the areas of random number generation – a formidable mathematical task that is way beyond the scope of this book – and in key exchange – the weakest security link. Asymmetric Ciphers and key exchange are not implemented in this book because implementation requires the use of arbitrary precision arithmetic, which is difficult, but not impossible, in Excel. There is a way to implement arbitrary precision arithmetic using matrix functions or excel add ins, but I have nothing to say on that.The book is for enthusiasts. For someone who has already read Simon Singh’s incomparable Code Book, it is an indispensable companion to now go and actually do it. Anyone from 10 to 100 years of age who likes programming will enjoy this book.As always, all programs in this book are available via email to anyonemacro@gmail.comHave Fun!

50 pages, Kindle Edition

First published April 13, 2013