Cryptography and Network Security

Transcription

1 Cryptography and Network Security Spring Lecture 14: Folklore, Course summary, Exam requirements Ion Petre Department of IT, Åbo Akademi University 1

2 Folklore on cryptography and network security Change keys periodically Use different keys for encryption, for authentication, and for signing Use different keys for different purposes Have both sides contribute to the master key Both sides have to be broken to find the key Do not let one side to determine the key Hash in a constant when hashing a password Randomly chosen IVs Random is good but what one really needs is very different IVs; hashing a sequence count will work Do not let encrypted data start with a constant or a predictable value Compress data before encrypting it Less data to handle, compressed data may look more random than the original plaintext, careful with fixed headers Overestimate the size of the key rather than following official default values Timing attacks useful for smart card-based systems, less useful for network-based applications 2

3 Summary of the course Exam requirements 3

4 Overview of the course I. CRYPTOGRAPHY Secret-key cryptography Classical encryption techniques DES, AES, RC5, RC4 Public-key cryptography RSA Key management II. AUTHENTICATION MAC Hashes and message digests Digital signatures Kerberos III. NETWORK SECURITY security Web security (SSL, secure electronic transactions) IP security Firewalls Wireless security Viruses 4

5 Symmetric-key cryptosystems Classical systems DES Caesar cipher encryption/decryption, attack Monoalphabetic ciphers frequency attack Playfair cipher encryption/decryption Polyalphabetic ciphers (Vigenere) encryption/decryption, cryptanalysis One-time pad Transpositions: rail-fence, row-transpositions Enigma: description Structure of a Feistel cipher, encryption, decryption DES scheme: key length, input/output length, structure of the algorithm, main ingredients (S-boxes, permutations, subkey generation), cipher modes of operations and their purposes 5

6 Symmetric-key cryptosystems AES AES scheme: key length, input/output length, structure of the algorithm, main ingredients (byte substitution, shift rows, mix columns, add round key), key expansion AES decryption using the same algorithm 2DES: meet-in-the-middle attack 3DES scheme RC5 RC4 Parameters, key expansion, encryption/decryption scheme Principle of stream ciphers RC4 scheme 6

7 Public-key cryptography Principle of public-key systems keys, encryption/decryption, authentication RSA RSA scheme Fast modular exponentiation Miller-Rabin primality test Pseudo-random number generators 7

8 Key management and authentication Distribution of public keys Public key authority and the distribution protocol Certificate authority and the distribution protocol Public-key infrastructures principle Distribution of secret keys Using public-key cryptosystems the protocol Diffie-Hellman key exchange protocol and the man-in-the-middle attack Using key distribution centers the protocol Authentication using Kerberos Protocol 8

9 Digital signatures Arbitrated digital signatures Protocol Direct digital signatures Principle, weaknesses 9

10 Message authentication Message authentication code (MAC) Principle DES-based MAC Hash functions HMAC Principle Birthday attack MD5 scheme, main ingredients SHA-1 scheme, main ingredients Principle Scheme 10

11 Network security security PGP: scheme, key management S/MIME: scheme, key management Web security Secure naming: cracking DNS, DNSsec, self-certifying names Secure connections: SSL (protocol), TLS Secure electronic transactions: overview, dual signatures IP security Tunnel mode Transport mode Firewalls generalities Wireless security generalities 11

12 System security generalities Intruder detection techniques Password management Malicious software 12