Understanding_Cryptography_Chptr_6---Intro_to_Public_Key

Understanding_Cryptography_Chptr_6---Intro_to_Public_Key -...

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Unformatted text preview: Understanding Cryptography – A Textbook for Students and Practitioners by Christof Paar and Jan Pelzl www.crypto-textbook.com Chapter 6 – Introduction to Public-Key Cryptography ver. November 18, 2010 These slides were prepared by Timo Kasper and Christof Paar 2/29 Some legal stuff (sorry): Terms of Use • The slides can used free of charge. All copyrights for the slides remain with Christof Paar and Jan Pelzl. • The title of the accompanying book “Understanding Cryptography” by Springer and the author’s names must remain on each slide. • If the slides are modified, appropriate credits to the book authors and the book title must remain within the slides. • It is not permitted to reproduce parts or all of the slides in printed form whatsoever without written consent by the authors. Chapter 6 of Understanding Cryptography by Christof Paar and Jan Pelzl 3/29 Content of this Chapter • Symmetric Cryptography Revisited • Principles of Asymmetric Cryptography • Practical Aspects of Public-Key Cryptography • Important Public-Key Algorithms • Essential Number Theory for Public-Key Algorithms Chapter 6 of Understanding Cryptography by Christof Paar and Jan Pelzl 4/29 Content of this Chapter • Symmetric Cryptography Revisited • Principles of Asymmetric Cryptography • Practical Aspects of Public-Key Cryptography • Important Public-Key Algorithms • Essential Number Theory for Public-Key Algorithms Chapter 6 of Understanding Cryptography by Christof Paar and Jan Pelzl 5/29 Two properties of symmetric (secret-key) crypto-systems: • The same secret key K is used for encryption and decryption • Encryption and Decryption are very similar (or even identical) functions U Symmetric Cryptography revisited e K (x) d K (y) x y x K K Alice Bob Chapter 6 of Understanding Cryptography by Christof Paar and Jan Pelzl 6/29 U Symmetric Cryptography: Analogy Chapter 6 of Understanding Cryptography by Christof Paar and Jan Pelzl K K Safe with a strong lock, only Alice and Bob have a copy of the key • Alice encrypts b locks message in the safe with her key • Bob decrypts b uses his copy of the key to open the safe • Symmetric algorithms, e.g., AES or 3DES, are very secure, fast & widespread but : • Key distribution problem: The secret key must be transported securely • Number of keys: In a network, each pair of users requires an individual key b n users in the network require keys, each user stores (n-1) keys • Alice or Bob can cheat each other , because they have identical keys. Example : Alice can claim that she never ordered a TV on-line from Bob (he could have fabricated her order). To prevent this: „non-repudiation“ 7/29 U Symmetric Cryptography: Shortcomings Example: 6 users (nodes) keys (edges) Chapter 6 of Understanding Cryptography by Christof Paar and Jan Pelzl 15 2 5 6 = ⋅ 8/29 Content of this Chapter • Symmetric Cryptography Revisited • Principles of Asymmetric Cryptography • Practical Aspects of Public-Key Cryptography...
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Understanding_Cryptography_Chptr_6---Intro_to_Public_Key -...

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