Privacy: freedom from unauthorized intrusion observation

1
Introduction

• Privacy freedom from unauthorized intrusion
  (observation)
• Security freedom from danger

2
Introduction

• Known Information
• Software Complexity
• Encryption Schemes
• Secure Web Documents
• Digital Signatures
• Firewalls

3
Known Information
May affects privacy

• Information Published by Others
• Volunteered Information
• Information Collection

4
Known Information
Information Published by Others

• Telephone listings
• Public events
• Company profile

5
Known Information
Volunteered Information
Filling out a form on Web site
Information Collection

• Internet simplifies information collection
• Search engines

6
Software Complexity
Contributing Factors

• Program size (browser75,000 lines. textbook
  35,000)
• Software interface
• Market forces
• Team development

May affects privacy and security
Browsers, Networks, Operating Systems, and
Servers
Patches
7
Encryption Schemes

• Basic Concepts
• Prime Numbers
• Private Key Cryptography
• Public Key Cryptography
• Hashing Algorithms

8
Encryption Schemes
Basic Concepts

• Method of encoding information
• Plaintext
• Ciphertext
• Cipher (verbencrypt info or noun encryption
  scheme)
• Encryption key
• Decrypt (decipher)

9
Encryption Schemes
Basic Concepts
10
Encryption Schemes
Prime Numbers

• Whole-number factors are 1 and itself
• Composite numbers
• 11822333323240847502768634087507457208740207458647
  848740204071. (62 digits) Is this number prime?
• Large numbers are used in public key cryptography.

11
Encryption Schemes
Private Key Cryptography

• Sender and receiver share same private key
• Key used to encrypt plaintext and decrypt
  Ciphertext

12
Private Key Cryptography
A simple cypher - encryption
Alice and Bob share a private key 5 Alice wants
to send meet me at the roadhouse at noon
urgent meetm eatth eroad house atnoo nurge nt
Alice encrypts the message using the key, and
sends it meehannearotutetounrttasogmhdeoe
13
Private Key Cryptography
A simple cypher - decryption

• meehannearotutetounrttasogmhdeoe
• Bob uses his key 5 and sees that he has received
  32 characters, which means 6 complete rows and
  the 7 row has only 2 letters.
• This means he has to build 2 columns with 7
  letters and another 3 columns with six letters.

14
Encryption Schemes
Public Key Cryptography

• There are two keys, a private and a public key.
• Any message encrypted with one of the key can be
  decrypted with the other.

15
Encryption Schemes
Public Key Cryptography - Authentication

• Every sender has its own private key
• Everybody else has the corresponding public key

16
Encryption Schemes
Public Key Cryptography - Encryption

• A receiver (bank) has its own private key.
• Everybody else has the corresponding public key
  (because it is published by the bank)

17
Encryption Schemes
Hashing Algorithms Verify Message Integrity

• Alice writes a message to Bob.
• It computes a hash value based on the message.
• It sends along both the message and the hash
  value.
• Bob receives the message, it computes the has h
  value and it compares it with the hash value
  received.

18
Secure Web Documents

• A website is secure if you see a key or a lock in
  the status bar of the browser.
• It needs
• Secure server
• https
• Sniffing

19
Digital Signatures

• Introduction
• Digital Signature Example
• Pretty Good Privacy

20
Digital Signatures
Introduction

• Mechanism used to officially sign electronic
  documents
• Verify sender and content of message

21
Digital Signatures
Digital Signature Example
22
Digital Signatures
Digital Signature Example

• Sender computes hash of plaintext
• Sender encrypts hash with public key cryptography
• Sender encrypts plaintext with private key
  cryptography
• Sender sends private-key-encrypted ciphertext
• Sender sends public-key-encrypted hash
• Receiver reverses the steps

23
Digital Signatures
Pretty Good Privacy

• 1995
• Phil Zimmermann
• Authentication
• Compression
• Digital signature
• Privacy capabilities
• Used by Computer Emergency Response Team (CERT)

On Linux computers you have GPG.
24
Firewalls
25
Firewalls

• Security mechanism
• Protects LANs from Internet
• Two kinds of firewalls
• Uses filters at network layer
• Proxy servers