Computer Security Cryptography Chapter 1 Symmetricⅰ phers··· ●●。●● COMP4690. HKBU
COMP4690, HKBU 1 Computer Security -- Cryptography Chapter 1 Symmetric Ciphers
●●●●● ●●●● ●●0 Outline ●●● ●●●● Overview of Cryptography Classical Encryption Techniques Substitution Transposition ● Block Ciphers DES AES COMP4690. HKBU
COMP4690, HKBU 2 Outline ⚫ Overview of Cryptography ⚫ Classical Encryption Techniques ⚫ Substitution ⚫ Transposition ⚫ Block Ciphers ⚫ DES ⚫ AES
●●●●● ●●●● ●●0 Basic Terminology ●●● ●●●● plaintext -the original intelligible message ciphertext- the coded message that depends on the plaintext and the secret key cipher-algorithm for transforming plaintext to ciphertext key -info used in cipher, known only to sender/recipient encipher(encrypt)-converting plaintext to ciphertext decipher (decry pt)-recovering ciphertext from plaintext cryptography -study of encryption principles/methods cry ptanalysis( codebreaking)-the study of principles/methods of deciphering ciphertext without knowing key cryptology-the field of both cryptography and cryptanalysis COMP4690. HKBU
COMP4690, HKBU 3 Basic Terminology ⚫ plaintext - the original intelligible message ⚫ ciphertext - the coded message that depends on the plaintext and the secret key ⚫ cipher - algorithm for transforming plaintext to ciphertext ⚫ key - info used in cipher, known only to sender/recipient ⚫ encipher (encrypt) - converting plaintext to ciphertext ⚫ decipher (decrypt) - recovering ciphertext from plaintext ⚫ cryptography - study of encryption principles/methods ⚫ cryptanalysis (codebreaking) - the study of principles/ methods of deciphering ciphertext without knowing key ⚫ cryptology - the field of both cryptography and cryptanalysis
●●●●● ●●●● ●●0 Symmetric Encryption ●●● ●●●● e Also called conventional private-key single-key sender and recipient share a common key o all classical encryption algorithms are private- key o was the only type prior to the invention of public-key in 1970S COMP4690. HKBU
COMP4690, HKBU 4 Symmetric Encryption ⚫ Also called conventional / private-key / single-key ⚫ sender and recipient share a common key ⚫ all classical encryption algorithms are privatekey ⚫ was the only type prior to the invention of public-key in 1970’s
●●●●● ●●●● ●●0 Symmetric Cipher Model ●●● ●●●● Secret key shared by Secret key shared by sender and recipient sender and recipient Transmitted ciphertext Plaintext Plaintext Input Encryption algorithm Decryption algorithm output (e. g, DES) (reverse of encryption algorithm) COMP4690. HKBU
COMP4690, HKBU 5 Symmetric Cipher Model