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Network Security

Network Security. An Introduction to Cryptography. The encryption model (for a symmetric-key cipher). Symmetric-Key Algorithms. DES – The Data Encryption Standard AES – The Advanced Encryption Standard Cipher Modes. Data Encryption Standard.

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Network Security

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  1. Network Security

  2. An Introduction to Cryptography • The encryption model (for a symmetric-key cipher).

  3. Symmetric-Key Algorithms • DES – The Data Encryption Standard • AES – The Advanced Encryption Standard • Cipher Modes

  4. Data Encryption Standard • The data encryption standard. (a) General outline.(b) Detail of one iteration. The circled + means exclusive OR.

  5. Triple DES • (a) Triple encryption using DES. (b) Decryption.

  6. AES – The Advanced Encryption Standard • Rules for AES proposals • The algorithm must be a symmetric block cipher. • The full design must be public. • Key lengths of 128, 192, and 256 bits supported. • Both software and hardware implementations required • The algorithm must be public or licensed on nondiscriminatory terms.

  7. AES • An outline of Rijndael.

  8. AES • Creating of the state and rk arrays.

  9. Electronic Code Book Mode • The plaintext of a file encrypted as 16 DES blocks.

  10. Cipher Block Chaining Mode • Cipher block chaining. (a) Encryption. (b) Decryption.

  11. Cipher Feedback Mode • (a) Encryption. (c) Decryption.

  12. Stream Cipher Mode • A stream cipher. (a) Encryption. (b) Decryption.

  13. Counter Mode • Encryption using counter mode.

  14. Public-Key Algorithms • RSA (Rivest,Shamir, Adleman) • Choose two large prime numbers p and q (typically 1024 bits) • Compute n=pxq and z=(p-1)x(q-1) • Choose a number relatively prime to z and call it d. • Find e such that exd=1mod z • Public key is (n,e), private key is (n,d) • Encryption is C=Pemod n • Decryption is P=Cd mod n

  15. RSA • An example of the RSA algorithm • n=33,z=20,e=3,d=7

  16. Digital Signatures • Symmetric-Key Signatures • Public-Key Signatures • Message Digests

  17. Symmetric-Key Signatures • Digital signatures with Big Brother.

  18. Public-Key Signatures • Digital signatures using public-key cryptography.

  19. Message Digests (MD5, SHA-1) • Digital signatures using message digests.

  20. Management of Public Keys • Certificates • X.509 • Public Key Infrastructures

  21. Problems with Public-Key Encryption • A way for Trudy to subvert public-key encryption.

  22. Certificates • A possible certificate and its signed hash.

  23. X.509 • The basic fields of an X.509 certificate.

  24. Public-Key Infrastructures • (a) A hierarchical PKI. (b) A chain of certificates.

  25. Communication Security • IPsec • Firewalls • Virtual Private Networks • Wireless Security

  26. IPsec • The IPsec authentication header in transport mode for IPv4.

  27. IPsec • (a) ESP in transport mode. (b) ESP in tunnel mode.

  28. Firewalls • A firewall consisting of two packet filters and an application gateway.

  29. Virtual Private Networks • (a) A leased-line private network. (b) A virtual private network.

  30. Authentication Protocols • Authentication Based on a Shared Secret Key • Establishing a Shared Key: Diffie-Hellman • Authentication Using a Key Distribution Center • Authentication Using Kerberos • Authentication Using Public-Key Cryptography

  31. Authentication Based on a Shared Secret Key • Authentication using HMACs.

  32. Authentication Using a Key Distribution Center • A first attempt at an authentication protocol using a KDC.

  33. Authentication Using a Key Distribution Center • The Needham-Schroeder authentication protocol.

  34. Authentication Using Kerberos • The operation of Kerberos V4.

  35. Authentication Using Public-Key Cryptography • Mutual authentication using public-key cryptography.

  36. E-mail SecurityPGP – Pretty Good Privacy • PGP in operation for sending a message.

  37. PGP – Pretty Good Privacy • A PGP message.

  38. Web Security • Secure Naming • SSL – The Secure Sockets Layer

  39. DNS Spoofing • (a) Normal situation. (b) An attack based on breaking into DNS and modifying Bob's record.

  40. DNS Spoofing • How Trudy spoofs Alice's ISP.

  41. Secure DNS An example RRSet for bob.com. The KEY record is Bob's public key. The SIG record is the top-level com server's signed A and KEY records to verify their authenticity.

  42. SSL—The Secure Sockets Layer • Layers (and protocols) for a home user browsing with SSL.

  43. SSL • A simplified version of the SSL connection establishment subprotocol.

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