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.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
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