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More Concepts of Cryptography and Cryptanalysis. Reference William Stallings, Cryptography and Network Security, 3rd Edition, Prentice Hall. Characterization of Cryptographic Systems. 1. Type of Operations Used Subsittution Transposition
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More Concepts of Cryptography and Cryptanalysis • Reference • William Stallings, Cryptography and Network Security, 3rd Edition, Prentice Hall. More Concepts of Cryptography and Cryptanalysis
Characterization of Cryptographic Systems • 1. Type of Operations Used • Subsittution • Transposition • Product Systems--Multiple Stages of Substituion and Transposition More Concepts of Cryptography and Cryptanalysis
Characterization of Cryptographic Systems • 2. Number of Keys • Same single or secret key • Different keys for sender and receiver • 3. Processing Technique • Block cipher--one block at a time. • Stream cipher--processes elements continuously, one element at a time. More Concepts of Cryptography and Cryptanalysis
Code Breaking Techniques • Cryptanalysis • Relies on the nature of the algorithm and perhaps some knowledge of the characteristics of the plaintext. • Attempts to discover the ciphertext or the key. • Brute-force Attacks • Attacker tries all possible keys. • On average, half of all possible keys must be tried. More Concepts of Cryptography and Cryptanalysis
Definitions of Security • An encryption scheme is unconditionally secure if the ciphertext generated by the scheme does not contain enough information to determine the corresponding plaintext, no matter the amount of ciphertext available. • Besides the one-time pad, there is no algorithm that is unconditionally secure. More Concepts of Cryptography and Cryptanalysis
Definitions of Security (p.2) • An encryption algorithm is said to be computationally secure if: • The cost of breaking the cipher exceeds the value of the encrypted information. • The time required to break the cipher exceeds the useful lifetime of the information. More Concepts of Cryptography and Cryptanalysis