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

Dec 25, 2015

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Corey Harris
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Page 1: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Network Security

Page 2: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

An Introduction to Cryptography

The encryption model (for a symmetric-key cipher).

Page 3: 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

Page 4: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Data Encryption Standard

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

Page 5: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Triple DES

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

Page 6: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

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.

Page 7: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

AES

An outline of Rijndael.

Page 8: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

AES

Creating of the state and rk arrays.

Page 9: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Electronic Code Book Mode

The plaintext of a file encrypted as 16 DES blocks.

Page 10: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Cipher Block Chaining Mode

Cipher block chaining. (a) Encryption. (b) Decryption.

Page 11: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Cipher Feedback Mode

(a) Encryption. (c) Decryption.

Page 12: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Stream Cipher Mode

A stream cipher. (a) Encryption. (b) Decryption.

Page 13: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Counter Mode

Encryption using counter mode.

Page 14: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

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=Pemod n

7. Decryption is P=Cd mod n

Page 15: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

RSA

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

Page 16: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Digital Signatures

• Symmetric-Key Signatures

• Public-Key Signatures

• Message Digests

Page 17: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Symmetric-Key Signatures

Digital signatures with Big Brother.

Page 18: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Public-Key Signatures

Digital signatures using public-key cryptography.

Page 19: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Message Digests (MD5, SHA-1)

Digital signatures using message digests.

Page 20: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Management of Public Keys

• Certificates

• X.509

• Public Key Infrastructures

Page 21: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Problems with Public-Key Encryption

A way for Trudy to subvert public-key encryption.

Page 22: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Certificates

A possible certificate and its signed hash.

Page 23: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

X.509

The basic fields of an X.509 certificate.

Page 24: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Public-Key Infrastructures

(a) A hierarchical PKI. (b) A chain of certificates.

Page 25: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Communication Security

• IPsec

• Firewalls

• Virtual Private Networks

• Wireless Security

Page 26: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

IPsec

The IPsec authentication header in transport mode for IPv4.

Page 27: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

IPsec

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

Page 28: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Firewalls

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

Page 29: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Virtual Private Networks

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

Page 30: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

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

Page 31: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Authentication Based on a Shared Secret Key

Authentication using HMACs.

Page 32: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Authentication Using a Key Distribution Center

A first attempt at an authentication protocol using a KDC.

Page 33: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Authentication Using a Key Distribution Center

The Needham-Schroeder authentication protocol.

Page 34: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Authentication Using Kerberos

The operation of Kerberos V4.

Page 35: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Authentication Using Public-Key Cryptography

Mutual authentication using public-key cryptography.

Page 36: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

E-mail SecurityPGP – Pretty Good Privacy

PGP in operation for sending a message.

Page 37: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

PGP – Pretty Good Privacy

A PGP message.

Page 38: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

Web Security

• Secure Naming

• SSL – The Secure Sockets Layer

Page 39: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

DNS Spoofing

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

Page 40: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

DNS Spoofing

How Trudy spoofs Alice's ISP.

Page 41: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

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.

Page 42: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

SSL—The Secure Sockets Layer

Layers (and protocols) for a home user browsing with SSL.

Page 43: Network Security. An Introduction to Cryptography The encryption model (for a symmetric-key cipher).

SSL

A simplified version of the SSL connection establishment subprotocol.