network security chapter 8 12/13/20151. cryptography introduction to cryptography substitution...
TRANSCRIPT
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Network Security
Chapter 8
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Cryptography
• Introduction to Cryptography
• Substitution Ciphers
• Transposition Ciphers
• One-Time Pads
• Two Fundamental Cryptographic Principles
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Need for Security
Some people who cause security problems and why.04/21/23 www.ishuchita.com 3
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An Introduction to Cryptography
The encryption model (for a symmetric-key cipher).04/21/23 www.ishuchita.com 4
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Transposition Ciphers
A transposition cipher.04/21/23 www.ishuchita.com 5
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One-Time Pads
The use of a one-time pad for encryption and the possibility of getting any possible plaintext from
the ciphertext by the use of some other pad.
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Quantum Cryptography
An example of quantum cryptography.04/21/23 www.ishuchita.com 7
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Symmetric-Key Algorithms
• DES – The Data Encryption Standard
• AES – The Advanced Encryption Standard
• Cipher Modes
• Other Ciphers
• Cryptanalysis
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Product Ciphers
Basic elements of product ciphers. (a) P-box. (b) S-box. (c) Product.04/21/23 www.ishuchita.com 9
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Data Encryption Standard
The data encryption standard. (a) General outline.(b) Detail of one iteration. The circled + means exclusive OR.04/21/23 www.ishuchita.com 10
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Triple DES
(a) Triple encryption using DES. (b) Decryption.04/21/23 www.ishuchita.com 11
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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.
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AES (2)
An outline of Rijndael.
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AES (3)
Creating of the state and rk arrays.04/21/23 www.ishuchita.com 14
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Electronic Code Book Mode
The plaintext of a file encrypted as 16 DES blocks.04/21/23 www.ishuchita.com 15
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Cipher Block Chaining Mode
Cipher block chaining. (a) Encryption. (b) Decryption.04/21/23 www.ishuchita.com 16
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Cipher Feedback Mode
(a) Encryption. (c) Decryption.04/21/23 www.ishuchita.com 17
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Stream Cipher Mode
A stream cipher. (a) Encryption. (b) Decryption.04/21/23 www.ishuchita.com 18
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Counter Mode
Encryption using counter mode.04/21/23 www.ishuchita.com 19
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Cryptanalysis
Some common symmetric-key cryptographic algorithms.04/21/23 www.ishuchita.com 20
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Public-Key Algorithms
• RSA
• Other Public-Key Algorithms
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RSA
An example of the RSA algorithm.04/21/23 www.ishuchita.com 22
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Digital Signatures
• Symmetric-Key Signatures
• Public-Key Signatures
• Message Digests
• The Birthday Attack
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Symmetric-Key Signatures
Digital signatures with Big Brother.04/21/23 www.ishuchita.com 24
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Public-Key Signatures
Digital signatures using public-key cryptography.04/21/23 www.ishuchita.com 25
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Message Digests
Digital signatures using message digests.04/21/23 www.ishuchita.com 26
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SHA-1
Use of SHA-1 and RSA for signing nonsecret messages.04/21/23 www.ishuchita.com 27
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SHA-1 (2)
(a) A message padded out to a multiple of 512 bits.
(b) The output variables. (c) The word array.04/21/23 www.ishuchita.com 28
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Management of Public Keys
• Certificates
• X.509
• Public Key Infrastructures
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Problems with Public-Key Encryption
A way for Trudy to subvert public-key encryption.04/21/23 www.ishuchita.com 30
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Certificates
A possible certificate and its signed hash.04/21/23 www.ishuchita.com 31
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X.509
The basic fields of an X.509 certificate.04/21/23 www.ishuchita.com 32
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Public-Key Infrastructures
(a) A hierarchical PKI. (b) A chain of certificates.04/21/23 www.ishuchita.com 33
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Communication Security
• IPsec
• Firewalls
• Virtual Private Networks
• Wireless Security
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IPsec
The IPsec authentication header in transport mode for IPv4.04/21/23 www.ishuchita.com 35
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IPsec (2)
(a) ESP in transport mode. (b) ESP in tunnel mode.04/21/23 www.ishuchita.com 36
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Firewalls
A firewall consisting of two packet filters and an application gateway.04/21/23 www.ishuchita.com 37
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Virtual Private Networks
(a) A leased-line private network. (b) A virtual private network.04/21/23 www.ishuchita.com 38
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802.11 Security
Packet encryption using WEP.04/21/23 www.ishuchita.com 39
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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
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Authentication Based on a Shared Secret Key
Two-way authentication using a challenge-response protocol.04/21/23 www.ishuchita.com 41
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Authentication Based on a Shared Secret Key (2)
A shortened two-way authentication protocol.04/21/23 www.ishuchita.com 42
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Authentication Based on a Shared Secret Key (3)
The reflection attack.04/21/23 www.ishuchita.com 43
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Authentication Based on a Shared Secret Key (4)
A reflection attack on the protocol of Fig. 8-32.04/21/23 www.ishuchita.com 44
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Authentication Based on a Shared Secret Key (5)
Authentication using HMACs.04/21/23 www.ishuchita.com 45
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Establishing a Shared Key:The Diffie-Hellman Key Exchange
The Diffie-Hellman key exchange.04/21/23 www.ishuchita.com 46
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Establishing a Shared Key:The Diffie-Hellman Key Exchange
The bucket brigade or man-in-the-middle attack.04/21/23 www.ishuchita.com 47
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Authentication Using a Key Distribution Center
A first attempt at an authentication protocol using a KDC.04/21/23 www.ishuchita.com 48
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Authentication Using a Key Distribution Center (2)
The Needham-Schroeder authentication protocol.04/21/23 www.ishuchita.com 49
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Authentication Using a Key Distribution Center (3)
The Otway-Rees authentication protocol (slightly simplified).04/21/23 www.ishuchita.com 50
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Authentication Using Kerberos
The operation of Kerberos V4.04/21/23 www.ishuchita.com 51
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Authentication Using Public-Key Cryptography
Mutual authentication using public-key cryptography.04/21/23 www.ishuchita.com 52
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E-Mail Security
• PGP – Pretty Good Privacy
• PEM – Privacy Enhanced Mail
• S/MIME
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PGP – Pretty Good Privacy
PGP in operation for sending a message.04/21/23 www.ishuchita.com 54
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PGP – Pretty Good Privacy (2)
A PGP message.04/21/23 www.ishuchita.com 55
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Web Security
• Threats
• Secure Naming
• SSL – The Secure Sockets Layer
• Mobile Code Security
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Secure Naming
(a) Normal situation. (b) An attack based on breaking into DNS and modifying Bob's record.04/21/23 www.ishuchita.com 57
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Secure Naming (2)
How Trudy spoofs Alice's ISP.04/21/23 www.ishuchita.com 58
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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 has of the A and KEY records to verify their authenticity.04/21/23 www.ishuchita.com 59
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Self-Certifying Names
A self-certifying URL containing a hash of server's name and public key.
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SSL—The Secure Sockets Layer
Layers (and protocols) for a home user browsing with SSL.04/21/23 www.ishuchita.com 61
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SSL (2)
A simplified version of the SSL connection establishment subprotocol.04/21/23 www.ishuchita.com 62
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SSL (3)
Data transmission using SSL.04/21/23 www.ishuchita.com 63
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Java Applet Security
Applets inserted into a Java Virtual Machine interpreter inside the browser.04/21/23 www.ishuchita.com 64
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Social Issues
• Privacy
• Freedom of Speech
• Copyright
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Anonymous Remailers
Users who wish anonymity chain requests through multiple anonymous remailers.04/21/23 www.ishuchita.com 66
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Freedom of Speech
Possibly banned material:
1. Material inappropriate for children or teenagers.
2. Hate aimed at various ethnic, religious, sexual, or other groups.
3. Information about democracy and democratic values.
4. Accounts of historical events contradicting the government's version.
5. Manuals for picking locks, building weapons, encrypting messages, etc.
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Steganography
(a) Three zebras and a tree. (b) Three zebras, a tree, and the complete text of five plays by William Shakespeare.04/21/23 www.ishuchita.com 68