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

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Presentation transcript:

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

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

AES – The Advanced Encryption Standard Rules for AES proposals 1.The algorithm must be a symmetric block cipher. 2.The full design must be public. 3.Key lengths of 128, 192, and 256 bits supported. 4.Both software and hardware implementations required 5.The algorithm must be public or licensed on nondiscriminatory terms.

AES An outline of Rijndael.

AES Creating of the state and rk arrays.

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

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

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

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

Counter Mode Encryption using counter mode.

Public-Key Algorithms RSA (Rivest,Shamir, Adleman) 1.Choose two large prime numbers p and q (typically 1024 bits) 2.Compute n=pxq and z=(p-1)x(q-1) 3.Choose a number relatively prime to z and call it d. 4.Find e such that exd=1mod z 5.Public key is (n,e), private key is (n,d) 6.Encryption is C=P e mod n 7.Decryption is P=C d mod n

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

Digital Signatures Symmetric-Key Signatures Public-Key Signatures Message Digests

Symmetric-Key Signatures Digital signatures with Big Brother.

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

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

Management of Public Keys Certificates X.509 Public Key Infrastructures

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

Certificates A possible certificate and its signed hash.

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

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

Communication Security IPsec Firewalls Virtual Private Networks Wireless Security

IPsec The IPsec authentication header in transport mode for IPv4.

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

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

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

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

Authentication Based on a Shared Secret Key Authentication using HMACs.

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

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

Authentication Using Kerberos The operation of Kerberos V4.

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

Security PGP – Pretty Good Privacy PGP in operation for sending a message.

PGP – Pretty Good Privacy A PGP message.

Web Security Secure Naming SSL – The Secure Sockets Layer

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

DNS Spoofing How Trudy spoofs Alice's ISP.

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.

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

SSL A simplified version of the SSL connection establishment subprotocol.