Cryptography: Part ii

One of the earliest poly-alphabetic cipher is the Vigenere Cipher developed in the 16^th century which was very simple because the key was just a word. This was easy to crack for smaller codes but for the longer texts which is crack able a type of frequency analysis  developed in the 19^th century by cryptographer Charles Babbage. 

Babbage realized that in a long enough message some patterns still show up. Like your key has 7 letters which means there are only 7 ways to encrypt the word ‘the’ but if your message uses ‘the’ 8 times there are definitely going to be repeats. So he counted how many letters separated those repeated patterns if they were separated by 7, 14 or 21 letters he knew the key would be probably 7 letters long there he would use the frequency analysis to decode the 7 scrambled alphabets. 

Babbage‘s method is just one example why it is so hard to create an unbreakable cipher. Your key creates a pattern with the encrypted message and with the word it uncovers that pattern.

It turns out that to really have an unbreakable cipher is to use what is known as “One-time Pad Encryption” which uses the key that is as long as the message itself that means there are not any patterns in the encrypted text there is nothing to analyse there is nothing to go backwards. The sender and the recipient contains the same Pad. A sheet containing list of Roman letters which is used as the key. Once a sheet is used to decode a message, you destroy it. Then you use the next sheet for the next message. So you never repeat a key. As long as you keep the pad same the message can't be de-crypted by anyone else.

But you can’t always use one type Pad encryption. Let us say you want to give a message half way across the earth whom you will never meet you won’t be able to give them a matching pad. In warfare that is the situation that comes up a lot. In 20^th century there were better ways to decrypt a code. Remote communication like the usage of telegraph was incredibly valuable during war time, it was essential as only your alias would understand what you are saying.

The Germans experimented with a new more complicated mono-alphabetic cipher during world war-1. But eventually the French managed to crack it. But again in world war-2 the Germans came up with a new cipher and this time its security seemed perfect may be you have heard of it, the Enigma Machine. The machine used the poly alphabetic cipher that used scrambled the alphabet a different way each time you type the new letter. As far as the Germans knew the only way to de-cipher the code is to have your own enigma machine which is set up using a key that changes everyday.

The machine was meant to work like a one-time pad as the alphabet was re-scrambled for every letter of the word. But it too had few flaws, like no letter could be encoded as “Itself” that doesn’t seem to be a big deal ending up as fatal weakness.

British mathematician Alan Turing along with rest of his team designed a machine of their own that could crack the enigma code. Cracking a enigma code was a huge a advantage for alias.

These days encryption is mostly important in Digital Computing and that is not perfect either because now a day hackers know everything about you it’s because the encryption methods are breakable. Companies that store your data take a lot into consideration like how you can complete billions of operations per second brute force suddenly becomes a lot more practical.

But how could they be stopped is a story for another day. Till then Happy Reading.