26-05-2012, 05:17 PM
DESIGN OF AES(ADVANCED ENCRYPTION STANDARD) ENCRYPTION AND DECRYPTION ALGORITHM WITH 128-BITS KEY LENGTH
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INTRODUCTION
Data that can be read and understood without any special measures is called plaintext or cleartext. The method of disguising plaintext in such a way as to hide its substance is called encryption. Encrypting plaintext results in unreadable gibberish called ciphertext. You use encryption to ensure that information is hidden from anyone for whom it is not intended, even those who can see the encrypted data. The process of reverting ciphertext to its original plaintext is called decryption. Figure 1.1 illustrates this process.
WHAT IS CRYPTOGRAPHY
To enhance the security of the data, code language for writing messages were used. The branch of mathematics that investigates the code languages and methods is called cryptology. Cryptology consists of two streams namely cryptography and cryptanalysis. Cryptography is a science of coding message secretly while cryptanalysis is a science of breaking codes.
HOW DOES CRYPTOGRAPHY WORK
A cryptographic algorithm, or cipher, is a mathematical function used in the encryption and decryption process. A cryptographic algorithm works in combination with a key—a word, number, or phrase—to encrypt the plaintext. The same plaintext encrypts to different ciphertext with different keys.
The security of encrypted data is entirely dependent on two things: the strength of the cryptographic algorithm and the secrecy of the key.
THE PURPOSE OF CRYPTOGRAPHY
Cryptography is the science of writing in secret code and is an ancient art; the first documented use of cryptography in writing dates back to circa 1900 B.C. when an Egyptian scribe used non-standard hieroglyphs in an inscription. Some experts argue that cryptography appeared spontaneously sometime after writing was invented, with applications ranging from diplomatic missives to war-time battle plans. It is no surprise, then, that new forms of cryptography came soon after the widespread development of computer communications.
METHODS OF ENCRYPTION
Although there can be several pieces to an encryption method, the two main pieces are the algorithms and the keys. As stated earlier, algorithms are usually complex mathematical formulas that dictate the rules of how the plaintext will be turned into cipher text. A key is a string of random bits that will be inserted into the algorithm. For two entities to be able to communicate via encryption, they must use the same algorithm and, many times, the same key. In some encryption methods, the receiver and the sender use the same key and in other encryption methods, they must use different keys for encryption and decryption purposes. The following sections explain the difference between these two types of encryption methods.