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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. In data and telecommunications, cryptography is necessary when communicating over any untrusted medium, which includes just about any network, particularly the Internet.

Within the context of any application-to-application communication, there are some specific 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 no one can read the message except the intended receiver.

• Integrity: Assuring the receiver that the received message has not been altered in any way from the original.

• Non-repudiation: A mechanism to prove that the sender really sent this message.

Cryptography, then, not only protects data from theft or alteration, but can also be used for user authentication. There are, in general, three types of cryptographic schemes typically used to accomplish these goals: secret key (or symmetric) cryptography, public-key (or asymmetric) cryptography, and hash functions, each of which is described below. In all cases, the initial unencrypted data is referred to asplaintext. It is encrypted into ciphertext, which will in turn (usually) be decrypted into usable plaintext.

In many of the

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...Symmetric Cryptography Secret writings have been found in many civilizations dating back to thousands of years where wide spread writings were adopted. Some of these civilizations included the Egyptians with their use of hieroglyphics, the Greeks and Spartan and the use of Scytale, and the Romans with the use of the Caesar Cipher. All these encryption methods could be thought of as symmetric encryption, which uses the same key to encrypt and decrypt the ciphertext. With a more contemporary look at symmetric key encryption with computer data, we can classify it into two categories called block ciphers and stream ciphers. The data in a block cipher would be broken down into specific sizes, for example 64-bit blocks or 128-bit blocks, which then the blocks would be encrypted separately. In stream ciphers, data would be encrypted in a stream of bits as oppose to dividing the data into blocks of bits. The decryption process for these two classification of symmetric encryption, of course, would be to use the same encryption key. Differences and Similarities with Symmetric and Asymmetric The fundamental difference between symmetric and asymmetric cryptography would be that asymmetric uses two keys, a public and private key, for encryption and decryption. If a private key is used to encrypt, then a related public key would be used to decrypt. This could also work the other way around when a public key is used to encrypt, then a related private key would be used to decrypt. Unlike...

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...In the 20th- century cryptography was adopted by international government to protect private and sensitive information and for communication purposes. Cryptography is known as the science of secret writing that enables storage and transfer of information that is hidden from everyone, but only can read by those who are authorized. The concept of cryptography is to protect confidential information and to assure the identity of people who send electronic messages and conduct electronic transactions are who they say they are. There are also various types of cryptography for example symmetric keys or shared- secret cryptography, is when you use the same key to both encrypt and decrypt a message. The most common form of symmetric key cryptography is the data Encryption standard. The second type of cryptography is asymmetric key cryptography, two keys are needed. A message encrypted using one key can only be decrypted using the other and vice versa. One key is called public key and the other is called the private key. Cryptosystem disguises messages, allowing only selected people to see though the disguise. The mechanisms that make up a strong cryptosystem is the size and means used to protect cryptographic keys. The longer the key the harder it is to break the encryption. A cryptosystem is considered strong only until it’s cracked. Strong cryptosystems produce cipher text that always appears random to standard statistical test. They also resist all known attacks on cryptosystem. The...

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...History of Cryptography Developments in cryptography | Period | Development | 2000 BC | In Egypt, hieroglyphics were used in inscriptions. | 500-600 BC | Hebrews used the atbash method for encryption. In this method, each letter of the alphabet mapped to a different letter to hide the true meaning of a word. | 487 BC | The Spartans used the scytale for encryption – messages were written on paper wrapped around a wooden rod. The paper was then unwrapped and sent. The recipient could read the message only by wrapping this paper on a rod of the same length and diameter. | 100-44 BC | Julius Caesar used an encryption method similar to the atbash method. He shifted each letter of the alphabet by a fixed number of places to send encrypted messages. | 1379 | Gabrieli di Lavinde developed the nomenclator. | 1466-1467 | The first polyalphabetic cipher was invented, which was much stronger than the nomenclator. | 1518 | Johannes Trithemius invented a steganographic cipher in which each letter was represented as a word taken from a succession of columns. | 1553 | Giovan Batista Belaso introduced the use of a passphrase as the key for a repeated polyalphabetic cipher. In 1563, Giovanni Battista Porta introduced the digraphic cipher and classified ciphers as transposition, substitution, and symbol substitution. | 1585 | Blaise de Vigenere developed the polyalphabetic substitution cipher. William Frederick Friedman published a book on cryptography, and is known as the...

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...Prologue: Cryptography is an excellent art/science of protecting data from unwanted intruders by transforming the data to an unreadable format which can be brought back to the original form only by those who are authenticated to do so. This system depends vastly on a principle of key usage and is the basic underlying principle of network security. A detailed technical discussion of cryptography ,particularly from a network’s stand point provides a compelling and an up to date examination of the political and the social issues that are now inextricably intertwined with cryptography. A complete discussion of cryptography itself requires a complete book and so we touch on only the essential aspects of cryptography. It is now high time to introduce Alice and Bob who are essentially the widely accepted persons for a discussion on networks as communicators. Also ,the third party Trudy ,the intruder also has a wide role to play in hacking the discussion of the two. So the whole thread would hang about these three and the ways there adhere to secure and hack the data that is transmitted. A First look on Terminologies Now its high time to know the basic terminologies of Cryptography. Firstly the text that we type in the human understandable format is called as the Plain Text. The plain text is then converted to a generally incomprehensive form called as the Cipher text using a technique called Encryption which usually does this, and the cipher is transmitted. Precisely...

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