A Good Encryption Algorithm

Abstract

A message that is sent over an insecure channel needs to be protected. This is where a good encryption algorithm is needed. There are generally two transformations that take place. The sender will encrypt the message and the receiver will then decrypt it. To ensure that you have a strong encryption that can’t be broken by unwanted people, you must test your encryption. In this paper, I look at different ciphers and how they operate. I was motivated to do this study as I found it fascinating how complex the encryptions used are and the length of time people will spend to break them.

Introduction

Encryption has been around for many years. From using cryptography to encrypt pen and paper messages to today where it is a necessity for

These blocks are of a fixed size. It encrypts each block independently. This differs from a stream cipher which would encrypt every individual bit of data. So, in a text file, a stream cipher would encrypt every letter. It would do this by using a random piece of text. It would pair the message letters with the random letters and covert both to numbers. So, a = 0, b = 1 etc. It would then sum the paired numbers. So, if the message letter was ‘b’ and the random text letter was ‘f’ you would get 6. Next convert it back to a letter which would give you ‘g’. By doing this with every letter you get your encrypted text. This could then only be decrypted by having the random letters (the key).

A block cipher would divide it into blocks and encrypt each block. While a stream cipher is faster than a block cipher, it wouldn’t be as secure. So, block ciphers are more secure but they also need more memory while a stream cipher would have low memory requirement. Some block ciphers can also have integrity protection or use authentication.

A disadvantage to a block cipher is that they can be susceptible to noise in transmission. If this happens and even one bit of data gets corrupt/changed, it will make the message unrecoverable. If this was to happen to a stream cipher, it would mean that only a small part of the message would be unreadable.

So, what exactly is a block

DES was developed by IBM in the 70s. It started when the U.S. National Bureau of Standards (NBS) sent out an open call for an encryption system as sending electronic data would have security risks. The only real contender was IBM who produced a block cipher called Lucifer. After IBM and NBS collaborated about it, the product was DES

(CANNIÈRE, n.d.)

DES works by splitting the plain text message into blocks of 64 bits. It uses an algorithm to scramble the text. Then it applies a 56-bit key to it for several steps then scrambles it again. The image below shows how the scramble works. It basically changes each letter to a random different letter.

(DATA Encryption Standard, n.d.)

So, what happens when we apply the key?

There are 16 rounds that the text goes through. DES only uses 56 bits of the cipher key as 8 of the bits are not used. These are used as parity bits. It splits the message in two and takes one side. It encrypts this side with the key and then applies xor with the other side. This result is then used for input into the next round and it’s repeated for 16 rounds. The below diagram shows a clear working of