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Secret%20Key%20Cryptography - CSC405 Introduction to...

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CSC405 Introduction to Computer Security Fall 2007 Introduction to Cryptography and Secret Key Cryptography Portions of the material for this lecture are taken from “Designing Network Security, 2 nd Ed by Merike Kaeo, Cisco System” *Material for this lecture has been borrowed from the class textbook Network Security and from Dr. Khaled Harfoush, DES Spring 2005 lecture notes. Keywords: symmetric key encryption, asymmetric encryption, hash functions, digital signatures, authentication & authorization, key management, key escrow Cryptography is the basis for secure communications; it is; therefore, important that you understand three basic cryptographic functions: symmetric encryption, asymmetric encryption, and one-way hash functions. Most current authentication, integrity, and confidentiality technologies derive from these three cryptographic functions. Terminology Cryptography is the science of writing or reading codes messages; it is the basic building block that enables the mechanisms of authentication, integrity, and confidentiality. Confidentiality ensures that no one except the sender and receiver of the data can actually understand the data. Integrity ensures that the data has not been altered in transit Authentication establishes the identity of either the sender or the receiver of information or both. In some communication instances, it is not always a requirement to have mutual authentication of both parties. plaintext/cleartext – a message’s original form that is not encrypted ciphertext – the mangled information encryption -- the process for producing ciphertext from plaintext decryption -- the process for production plaintext from ciphertext A cryptographic key is a digital object that you can use to encrypt, decrypt, and sign information. To Publish or Not to Publish Common practice today is for most commercial cryptosystems to be published and for military cryptosystems to be kept secret. Background / History Hieroglyphics Egyptians 3,000 BC A Spartan Scytale 1 1 Krutz, Ronald; Vines, Russell Dean; The CISSP Prep Guide: Mastering the CISSP and ISSEP Exams, Second Edition, p. 208
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CSC405 Introduction to Computer Security Fall 2007 Spartans 400 BC Military cryptography was employed by the Spartans in the form of a strip of papyrus or parchment wrapped around a wooden rod. This system was called a Scytale. The message to be encoded was written lengthwise down (or up) the rod on the wrapped material. Then, the material was unwrapped and carried to the recipient. In its unwrapped form, the writing appeared to be random characters. When the material we rewound on the rod of the same diameter, d, and minimum length, l, the message could be read. Caesar Cipher 2 Julius Caesar 50 B.C. ABCDEFGHIJKLMNOPQRSTUVXYZ (shifting three places for C3) DEFGHIJKLMNOPQRSTUVXYZABC Cipher Disks 3 Italy, Leon Battista Alberti 1460 Two Concentric disks. Each disk had an alphabet around its periphery, and by rotating one disk with respect to the other, a letter in one alphabet could be transformed to a letter in another alphabet.
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Secret%20Key%20Cryptography - CSC405 Introduction to...

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