Cryptography Basics

The word cryptography may not ring a bell with someone who has only rudimentary knowledge of Information Technology. But unknowingly he/she enjoys the benefits that cryptography provides every day. For those who deal in the business of protecting information using Information Technology, cryptography is akin to the Holy Grail. Initially it was only used by the military for decoding enemy messages but today it is being used in things more mundane such as email. Cryptography deals with all aspects of secure messaging, authentication, digital signatures, electronic money, and other applications.

Cryptography protects a message or file from being read by an eavesdropper who has no other means of access to either the original text of what is protected, or the key with which it is encrypted. When a message is sent to someone, it is converted into undecipherable code, so that no one other than the intended reader would know what is written. Once the message reaches the intended recipient he will require the program that decrypts it. Julius Caesar was a master of a primitive form of cryptography. When Caesar sent messages to his trusted acquaintances, he had to ensure that the messengers would not read the message. So he replaced every A by a D, every B by a E, and continued through the alphabet. Only someone who knew the ``shift by 3'' rule could decipher his messages. Cryptography can be used to encrypt your entire hard disk. Cryptography grew extremely complex during World War II when Germany exploited to the hilt. They created Enigma machines that would use multiple rounds of alphanumeric random encryption to pass messages from one submarine to the other. For years the allied forces tried to crack the code using countless permutations and combinations, they were only successful when they managed to capture a submarine that had an Enigma machine on board.

Cryptography wasn't always complicated. But the arrival of that beast called the Internet destroyed all accepted conventions. The game had changed drastically. Cryptography was rendered practically useless because there is no technology that is widely available today that prevents the Internet Service Provider from seeing what web sites that the user visits. Routing thorough another server has been used but this is not a cryptography technique and by no means foolproof.

Cryptography has a lot of jargon which scares of most first time readers. Demystifying the jargon is half the battle won for elementary cryptologists. The initial message that is sent is called plaintext. This is then encrypted and converted into something called ciphertext. Cryptanalysis is the art of breaking cryptosystems without knowing the decryption key. Cryptology is the study of both cryptography and cryptanalysis. A cryptosystem is usually a whole collection of algorithms. The algorithms are labeled; the labels are called keys. In order to decrypt the message it is important that the proper key is known. When someone gets access to the message without knowing the key he is called cryptanalyst. The benchmark of great cryptography is that it appears random when confronted with any form of statistical testing. But even when statistics fail to unravel the mystery of cryptography, it is possible that it could be caught out by an ingenious cryptoanalyst.

There are two types of key-based encryption algorithms, symmetric and asymmetric algorithms. The difference is that symmetric algorithms use the same key for encryption and decryption, whereas asymmetric algorithms use a different key for encryption and decryption. The decryption key cannot be derived from the encryption key. Symmetric algorithms can be divided into stream ciphers and block ciphers. Stream ciphers can encrypt a single bit of plaintext at a time, whereas block ciphers take a number of bits.

A digital signature is a small amount of data that was created using some secret key, and there is a public key that can be used to verify that the signature was really generated using the corresponding private key. Digital signatures are used to verify that a message really comes from the claimed sender.

Cryptography is here to stay; it will evolve to fulfill the ever-increasing security needs of computer users all over the world. The next frontier is the Internet. Algorithms have been developed to counter the all-pervasive influence of the Internet Service Providers but they are confined to the realm of hackers. Cryptography will ensure that this is the norm of tomorrow.