lecture_4 - Introduction to Cryptography CS 136 Computer...

Info icon This preview shows pages 1–14. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture 4 Page 1 CS 136, Winter 2010 Introduction to Cryptography CS 136 Computer Security Peter Reiher January 14, 2010
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lecture 4 Page 2 CS 136, Winter 2010 Outline What is data encryption? Cryptanalysis Basic encryption methods Substitution ciphers Permutation ciphers
Image of page 2
Lecture 4 Page 3 CS 136, Winter 2010 Introduction to Encryption Much of computer security is about keeping secrets One method is to make the secret hard for others to read While (usually) making it simple for authorized parties to read
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lecture 4 Page 4 CS 136, Winter 2010 Encryption Encryption is the process of hiding information in plain sight Transform the secret data into something else Even if the attacker can see the transformed data, he can’t understand the underlying secret
Image of page 4
Lecture 4 Page 5 CS 136, Winter 2010 Encryption and Data Transformations Encryption is all about transforming the data One bit or byte pattern is transformed to another bit or byte pattern Usually in a reversible way
Image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lecture 4 Page 6 CS 136, Winter 2010 Encryption Terminology Encryption is typically described in terms of sending a message Though it’s used for many other purposes The sender is S The receiver is R The transmission medium is T And the attacker is O
Image of page 6
Lecture 4 Page 7 CS 136, Winter 2010 More Terminology Encryption is the process of making message unreadable/unalterable by O Decryption is the process of making the encrypted message readable by R A system performing these transformations is a cryptosystem Rules for transformation sometimes called a cipher
Image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lecture 4 Page 8 CS 136, Winter 2010 Plaintext and Ciphertext Plaintext is the original form of the message (often referred to as P ) Transfer $100 to my savings account Ciphertext is the encrypted form of the message (often referred to as C ) Sqzmredq #099 sn lx rzuhmfr zbbntms
Image of page 8
Lecture 4 Page 9 CS 136, Winter 2010 Very Basics of Encryption Algorithms Most algorithms use a key to perform encryption and decryption Referred to as K The key is a secret Without the key, decryption is hard With the key, decryption is easy
Image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lecture 4 Page 10 CS 136, Winter 2010 Terminology for Encryption Algorithms The encryption algorithm is referred to as E() C = E(K,P) The decryption algorithm is referred to as D() Sometimes the same algorithm as E() The decryption algorithm also has a key
Image of page 10
Lecture 4 Page 11 CS 136, Winter 2010 Symmetric and Asymmetric Encryption Systems Symmetric systems use the same keys for E and D : P = D(K, C) Expanding, P = D(K, E(K,P)) Asymmetric systems use different keys for E and D: C = E(K E ,P) P = D(K D ,C)
Image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lecture 4 Page 12 CS 136, Winter 2010 Characteristics of Keyed Encryption Systems If you change only the key, a given plaintext encrypts to a different ciphertext Same applies to decryption Decryption should be hard without knowing the key
Image of page 12
Lecture 4 Page 13 CS 136, Winter 2010 Cryptanalysis The process of trying to break a cryptosystem Finding the meaning of an encrypted message without being given the key
Image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 14
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern