斗 长 Secure communication ￥斗 ★★ s How to achieve secure communication?
11 Secure Communication How to achieve secure communication?
斗 长 Cryptography ￥斗 ★★ o Cryptographyis one of the main tools used to provide data security, both staticand dynamic What otherways for secure communication? s Basic idea encrypt(cleartext, e-key)=ciphertext decrypt(ciphertext, d-key)=cleartext
12 Cryptography Cryptography is one of the main tools used to provide data security, both static and dynamic – What other ways for secure communication? Basic idea – encrypt (clear text, e-key) = cipher text – decrypt (cipher text, d-key) = clear text
★ “长 Basics of Cryptography ￥斗 ★★ Encryption ke Decryption key E Encryption C=E(P, KU Decryption/ P=D(C, KDI Plaintext In [Algorithm Ciphertext Algorithm Plaintext Out Encryption Decryption Relationship between plaintext and ciphertext
13 Basics of Cryptography Relationship between plaintext and ciphertext Encryption Algorithm Decryption Algorithm P KE Ciphertext C=E(P, K P=D(C, KD) E ) Plaintext In Plaintext Out Encryption key Decryption key KD Encryption Decryption
斗 长 Cryptography ￥斗 ★★ o Encrypt and decrypt algorithms are usually public o Shouldn't be able to deduce d-key from (cleartext, cipher text) pairs
14 Cryptography Encrypt and decrypt algorithms are usually public Shouldn’t be able to deduce d-key from (clear text, cipher text) pairs
斗 长 One-Way Functions ￥斗 ★★ o Encryption function should be selected such that given formula for f(x) easy to evaluate= f(x) o But given y computationally infeasible to find x
15 One-Way Functions Encryption function should be selected such that – given formula for f(x) – easy to evaluate y = f(x) But given y – computationally infeasible to find x