cryptography & network security forouzan pdf

It's known as the Caesar cipher, because Julius Caesar used it for his confidential correspondence as his biographer Suetonius described it, 'if he had anything confidential to say, he wrote it in cipher, that is, by so changing the order of the letters of the alphabet. This is all very abstract, and a good way to understand the specifics of what we're talking about is to look at one of the earliest known forms of cryptography. Keep algorithms and keys in your mind, because they'll be important as we move on. In a secure cryptographic system, even if you know the method by which some message is encrypted, it should be difficult or impossible to decrypt without that key. A key is just another piece of information, almost always a number, that specifies how the algorithm is applied to the plaintext in order to encrypt it. One important aspect of the encryption process is that it almost always involves both an algorithm and a key. Encryption-'making secret'-is what we call the process of turning plaintext into ciphertext Encryption is an important part of cryptography, but doesn't encompass the entire science.

The syllable crypt may make you think of tombs, but it comes from a Greek word that means 'hidden' or 'secret.' Cryptography literally means 'secret writing.' Cryptology, meanwhile, means something like 'knowledge of secrecy' if cryptography is the practice of writing secret messages, then cryptology is the theory, although the two words are often used interchangeably. encryptionīefore we move into the meat of this article, let's define a couple terms related to cryptography.

In cryptography, an original human readable message, referred to as plaintext, is changed by means of an algorithm, or series of mathematical operations, into something that to an uninformed observer would look like gibberish this gibberish is called ciphertext.Ĭryptographic systems require some method for the intended recipient to be able to make use of the encrypted message-usually, though not always, by transforming the ciphertext back into plaintext. Cryptography is the art of keeping information secure by transforming it into form that unintended recipients cannot understand.

Cryptography & network security forouzan pdf