lec-08 - CSE565: Computer Security Lecture 8 Public Key...

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1 9/24/09 UB Fall 2009 CSE565: S. Upadhyaya Lec 8.1 CSE565: Computer Security Lecture 8 Public Key Cryptography and RSA Shambhu Upadhyaya Computer Science & Eng. University at Buffalo Buffalo, New York 14260 09/24/09 UB Fall 2009 CSE565: S. Upadhyaya Lec 8.2 Acknowledgments Material for some slides is drawn from Lawrie Brown’s slides
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2 09/24/09 UB Fall 2009 CSE565: S. Upadhyaya Lec 8.3 Motivation (1) Public Key Cryptography Perhaps the only true revolution in the history of cryptography Based on mathematical functions unlike conventional ones DES is a significant advance by IBM, but based on substitution and permutation PKEs are asymmetric techniques -- use two separate keys Enhance confidentiality, key distribution and authentication 09/24/09 UB Fall 2009 CSE565: S. Upadhyaya Lec 8.4 Motivation (2) Addresses two key issues: Key distribution – how to have secure communications in general without having to trust a KDC with your key Digital signatures – how to verify a message comes intact from the claimed sender Public invention due to Whitfield Diffie & Martin Hellman at Stanford in 1976 Known earlier in classified community
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3 09/24/09 UB Fall 2009 CSE565: S. Upadhyaya Lec 8.5 Advantages Advantages of PKE Anyone can send a secret message to a user with fewer keys Conventional systems require a separate key for every pair of users Illustration A,B,C want to set up communication channels in pairs Keys needed -- kAB, kAC, kBC n user system requires n(n-1)/2 keys 09/24/09 UB Fall 2009 CSE565: S. Upadhyaya Lec 8.6 Public-Key Characteristics (1) Public-Key algorithms rely on two keys with the characteristics that it is: Computationally infeasible to find decryption key knowing only algorithm & encryption key Computationally easy to en/decrypt messages when the relevant (en/decrypt) key is known Either of the two related keys can be used for encryption, with the other used for decryption (in some schemes)
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4 09/24/09 UB Fall 2009 CSE565: S. Upadhyaya Lec 8.7 PKE Characteristics (2) Each user has two keys A public key and a private key Public key may be published freely - like a
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lec-08 - CSE565: Computer Security Lecture 8 Public Key...

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