Chapter 8

Chapter 8 - Learning Objectives Upon completion of this...

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Principles of Information Security, 3rd edition 2 Learning Objectives Upon completion of this material, you should be able to: Chronicle the most significant events and discoveries in the history of cryptology Explain the basic principles of cryptography Describe the operating principles of the most popular tools in the area of cryptography List and explicate the major protocols used for secure communications Discuss the nature and execution of the dominant methods of attack used against cryptosystems
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Principles of Information Security, 3rd edition 3 Introduction Cryptography: process of making and using codes to secure transmission of information Encryption: converting original message into a form unreadable by unauthorized individuals Cryptanalysis: process of obtaining original message from encrypted message without knowing algorithms Cryptology: science of encryption; combines cryptography and cryptanalysis
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Principles of Information Security, 3rd edition 4 Foundations of Cryptology With emergence of technology, need for encryption in information technology environment greatly increased All popular Web browsers use built-in encryption features for secure e-commerce applications
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Principles of Information Security, 3rd edition 5 Cipher Methods Plaintext can be encrypted through bit stream or block cipher method Bit stream: each plaintext bit transformed into cipher bit one bit at a time Block cipher: message divided into blocks (e.g., sets of 8- or 16-bit blocks) and each is transformed into encrypted block of cipher bits using algorithm and key
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Principles of Information Security, 3rd edition 6 Cipher Methods (continued) Cryptosystems typically made up of algorithms, data handling techniques, and procedures Substitution cipher: substitute one value for another Monoalphabetic substitution: uses only one alphabet Polyalphabetic substitution: more advanced; uses two or more alphabets Vigenère cipher: advanced cipher type that uses simple polyalphabetic code; made up of 26 distinct cipher alphabets
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Principles of Information Security, 3rd edition 7
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Principles of Information Security, 3rd edition 8 Cipher Methods (continued) Transposition cipher: rearranges values within a block to create ciphertext Exclusive OR (XOR): function of Boolean algebra; two bits are compared If two bits are identical, result is binary 0 If two bits not identical, result is binary 1
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Principles of Information Security, 3rd edition 9 Table 8-1 Exclusive OR Operations
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Principles of Information Security, 3rd edition 10 Cipher Methods (continued) Vernam cipher: developed at AT&T; uses set of characters once per encryption process Book (running key) cipher: uses text in book as key to decrypt a message; ciphertext contains codes representing page, line and word numbers
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Principles of Information Security, 3rd edition 11 Hash Functions Mathematical algorithms that generate message
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Chapter 8 - Learning Objectives Upon completion of this...

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