Lecture "On safety and security of information systems: Cryptography" provide students with knowledge about: Basic terminology of cryptography; History of cryptography; Symmetric cipher; . Please refer to the detailed content of the lecture! | Cryptography Contents 1 Basic Terminology of cryptography 2 History of cryptography 3 Symmetric Cipher 4 Asymmetric Cipher 5 Hashing algorithms 1. Basic Terminology Basic Terminology Plaintext The original message Ciphertext the crypted message Encryption the process of converting plaintext into ciphertext Plaintext Ciphertext Decryption the process of recovering ciphertext into plaintext Ciphertext Plaintext Cipher is an algorithm to encrypt or decrypt information. Basic Terminology Cryptosystem The algorithms or ciphers used to encrypt and decrypt data Cryptosystem encryption decryption algorithms. Key info used in cipher known only to sender receiver Cryptology Cryptography is the Science of Writing in Secret Code Cryptanalysis science of studying attacks against cryptographic systems Cryptology Cryptography Cryptanalysis CRYPTOLOGY CRYPTOGRAPHY CRYPTANALYSIS Cryptography Cryptographic systems are characterized along three independent dimensions Type of encryption operations used Substitution replacing each element of the plaintext with another element Transposition rearranging the order of the elements of the plaintext. Product using multiple stages of substitutions and transpositions Cryptography Number of keys used Symmetric single-key private-key Asymmetric two-key public-key way in which the plaintext is processed Block cipher processes the input one block of elements at a time Stream cipher processes the input elements continuously Cryptanalysis Objective to recover the key in use rather than simply to recover the plaintext of a single ciphertext. Two general approaches Brute-force attack try every key to decipher the ciphertext Cryptanalysis attack exploit the characteristics of the algorithm to attempt to deduce a specific plaintext or to deduce the key being used Cryptanalysis Brute-force attack On average half of all possible keys must be tried to achieve success. Cryptology CRYPTOLOGY CRYPTOGRAPHY CRYPTANALYSIS SYMMETRIC ASYMMETRIC CLASSICAL MODERN .
