Slide an toàn và hệ thống bảo mật thông tin chapter 3 cryptography symmetric classical

.c om cu u du o ng th an co ng Cryptography CuuDuongThanCong.com https://fb.com/tailieudientucntt Basic Terminology of cryptography 2) History of cryptography 3) Symmetric Cipher 4) Asymmetric Cipher 5) Hashing algorithms cu u du o ng th an co ng 1) c om Contents CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om cu u du o ng th an co ng Basic Terminology CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Basic Terminology co  Ciphertext: the crypted message ng  Plaintext: The original message Ciphertext du o Plaintext ng th an  Encryption: the process of converting plaintext into ciphertext u  Decryption: the process of recovering ciphertext into plaintext cu Ciphertext Plaintext  Cipher: is an algorithm to encrypt or decrypt information CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Basic Terminology  Cryptosystem: The algorithms, or ciphers, used to encrypt and decrypt co ng data cu u du o ng th an Cryptosystem = encryption + decryption algorithms  Key: info used in cipher known only to sender/receiver CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Cryptology ng  Cryptography: is the Science of Writing in Secret Code co  Cryptanalysis: science of studying attacks against cryptographic systems du o cu CRYPTOGRAPHY u CRYPTOLOGY ng th an  Cryptology = Cryptography + Cryptanalysis CRYPTANALYSIS CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Cryptography co  Type of encryption operations used ng Cryptographic systems are characterized along three independent dimensions th an  Substitution: replacing each element of the plaintext with another element ng  Transposition: rearranging the order of the elements of the plaintext cu u du o  Product: using multiple stages of substitutions and transpositions CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Cryptography th an  Asymmetric: two-key, public-key co  Symmetric: single-key, private-key ng  Number of keys used: ng  way in which the plaintext is processed du o  Block cipher: processes the input one block of elements at a time cu u  Stream cipher: processes the input elements continuously CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Cryptanalysis  Objective: to recover the key in use rather than simply to recover the co ng plaintext of a single ciphertext th an  Two general approaches: ng  Brute-force attack: try every key to decipher the ciphertext du o  Cryptanalysis attack: exploit the characteristics of the algorithm to attempt to cu u deduce a specific plaintext or to deduce the key being used CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Cryptanalysis  Brute-force attack: On average, half of all possible keys must be tried to cu u du o ng th an co ng achieve success CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Hill Cipher cu u du o ng th an co ng  Decryption CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om e) Polyalphabetic Ciphers  Another way to improve on the simple monoalphabetic technique is to use co ng different monoalphabetic substitutions as one proceeds through the ng  The features in common: th an plaintext message du o  A set of related monoalphabetic substitution rules is used cu u  A key determines which particular rule is chosen for a given transformation CuuDuongThanCong.com https://fb.com/tailieudientucntt .c om Vigenere Cipher ng  Simplest polyalphabetic substitution cipher co  Plaintext: cu u  ciphertext letters m