Cryptography Essay

In this era when the Internet provides essential communication between tens of millions of people and is being increasingly used as a tool for security becomes a tremendously important issue to deal with, So it is important to deal with it. There are many aspects to security and many applications, ranging from secure commerce and payments to private communications and protecting passwords. One essential aspect for secure communications is that of cryptography. But it is important to note that while cryptography is necessary for secure communications, it is not by itself sufficient. Cryptography is the science of writing in secret code and is an ancient art; In the old age people use to send encoded message which can be understand by the receiver only who know the symbolic and relative meaning of that encoded message .The first documented use of cryptography in writing dates back to circa 1900 B.C. Egyptian scribe used non-standard hieroglyphs in an inscription. After writing was invented cryptography appeared spontaneously 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. In telecommunications and data cryptography is necessary when communicating in any untrusted medium, which includes any network, particularly the Internet [1].Within the context of any application-to-application communication, there are some security requirements, including:

• Authentication: The process of proving one's identity. (The primary forms of host-to-host authentication on the Internet today are name-based or address-based, both of which are notoriously weak.)

• Privacy/confidentiality: Ensuring that ...

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...different cipher text in a stream cipher [20].

Stream ciphers come in many flavors but two are worth mentioning here. Self-synchronizing stream ciphers calculate each bit in the keystream as a function of the previous n bits in the keystream. It is termed as "self-synchronizing" because the decryption process can be synchronized with the encryption process merely by knowing how far into the n-bit key stream it is. One problem is error propagation in the self-synchronizing, a garbled bit in transmission will result in n garbled bits at the receiving side. Synchronous stream ciphers generate the key stream in a fashion independent from the message stream but by using the same key stream generation function at sender and receiver. While stream ciphers do not propagate transmission errors, they are, by their nature, periodic so that the key stream will eventually repeat