{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

lec-03-des - CSE565 Computer Security Lectures 3 4 Block...

Info icon This preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
9/07/10 UB Fall 2010 CSE565: S. Upadhyaya Lec 3.1 CSE565: Computer Security Lectures 3 & 4 Block Ciphers and Data Encryption Standard Shambhu Upadhyaya Computer Science & Eng. University at Buffalo Buffalo, New York 14260
Image of page 1

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

View Full Document Right Arrow Icon
9/07/10 UB Fall 2010 CSE565: S. Upadhyaya Lec 3.2 Overview Block Ciphers – 10 minutes Description of DES – 55 minutes Encryption Algorithm (Initial Permutation, Key Transformation, Expansion Permutation, S-Box, P- Box, Final Permutation) Decryption Algorithm Security of DES – 10 minutes Cryptanalysis – Linear, Differential & Related key– 10 minutes DES Variants – 5 minutes (some slides adapted from Lawrie Brown)
Image of page 2
9/07/10 UB Fall 2010 CSE565: S. Upadhyaya Lec 3.3 Modern Block Ciphers Study of modern block ciphers One of the most widely used types of cryptographic algorithms In particular will introduce DES (Data Encryption Standard) We will study AES later
Image of page 3

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

View Full Document Right Arrow Icon
9/07/10 UB Fall 2010 CSE565: S. Upadhyaya Lec 3.4 S-Permutation Ciphers Shannon observed that two weak but complementary ciphers can be made more secure by applying them together Product cipher (Apply E1 and then E2) In 1949 Shannon introduced idea of substitution-permutation (S- P) networks modern substitution-transposition product cipher This forms the basis of modern block ciphers S-P networks are based on the two primitive cryptographic operations we have seen before: substitution (S-box) permutation (P-box) Provide confusion and diffusion of message
Image of page 4
9/07/10 UB Fall 2010 CSE565: S. Upadhyaya Lec 3.5 Confusion and Diffusion Cipher needs to completely obscure statistical properties of original message A one-time pad does this More practically Shannon suggested combining elements to obtain: Diffusion – dissipates statistical structure of plaintext over bulk of ciphertext Confusion – makes relationship between ciphertext and key as complex as possible
Image of page 5

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

View Full Document Right Arrow Icon
9/07/10 UB Fall 2010 CSE565: S. Upadhyaya Lec 3.6 Feistel Cipher Structure Horst Feistel devised the Feistel cipher based on concept of invertible product cipher Partitions input block into two halves process through multiple rounds perform a substitution on left data half this is based on applying a round function to the right half & subkey and take the Ex-OR then have permutation swapping halves Implements Shannon’s substitution-permutation network concept
Image of page 6
9/07/10 UB Fall 2010 CSE565: S. Upadhyaya Lec 3.7 Feistel Cipher Structure
Image of page 7

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

View Full Document Right Arrow Icon
9/07/10 UB Fall 2010 CSE565: S. Upadhyaya Lec 3.8 Feistel Cipher Design Principles Block size increasing size improves security, but slows cipher Key size increasing size improves security, makes exhaustive key searching harder, but may slow cipher Number of rounds increasing number improves security, but slows cipher Subkey generation greater complexity can make analysis harder, but slows cipher Round function greater complexity can make analysis harder, but slows cipher Fast software en/decryption & ease of analysis are more recent concerns for practical use and testing
Image of page 8
9/07/10 UB Fall 2010 CSE565: S. Upadhyaya Lec 3.9 Feistel Cipher Decryption
Image of page 9

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

View Full Document Right Arrow Icon
Image of page 10
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