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interpreting or uncovering the deciphered codes without the sender’s consentor authorization).Cryptology is an area of special difficulty for readers and studentsbecause many good techniques and analyses are available but remain theproperty of organizations whose main business is secrecy. As such, we discussthe fundamental technique of cryptography in this section without making anyspecific recommendations.1.4.1 Basic Cryptographic FunctionsBasic cryptography comprises encryption, decryption, and key managementunit, as shown in Fig. 1.3. Encryption (enciphering) is the process ofconverting messages, information, or data into a form unreadable by anyoneexcept the intended recipient. The encrypted (enciphered) text is called acryptogram. Encrypted data must be deciphered (unlocked, or decrypted)before the recipient can read it. Decryption is the unlocking of the lockedmessage—that is, the reverse of encryption. ‘‘Key’’simply means ‘‘password’’.Key management refers to the generation, distribution, recognition, andreception of the cryptographic keys. Cryptographic key management is themost important element of any cryptographic system (simply called cryptosystem)design.Encryption uses a special system called an algorithm to convert the textof the original message (plaintext) into an encrypted form of the message(ciphertext or cryptogram). Algorithms are step-by-step procedures for solvingproblems in the case of encryption, for enciphering and deciphering a plaintextmessage. Cryptographic algorithms (like key and transformation functions)equate individual characters in the plaintext with one or more different keys,numbers, or strings of characters. In Fig. 1.3, the encryption algorithm E ytransforms the transmitted message M T into a cryptogram C y by the cryptographickey K E algorithm. The received message M R is obtained through theFIGURE 1.3General cryptographic functions.Copyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.