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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
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
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 systems3
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
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
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
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