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Lecture notes on Computer and network security: Lecture 13 - Avinash Kak

Lecture 13 - Certificates, digital signatures, and the diffie-hellman key exchange algorithm. The goals of this chapter are: Authenticating users and their public keys with certificates signed by Certificate Authorities (CA), exchanging session keys with public-key cryptography, X.509 certificates, Perl and Python code for harvesting RSA moduli from X.509 certificates, the Diffie-Hellman algorithm for exchanging session keys. | Lecture 13: Certificates, Digital Signatures, and the Diffie-Hellman Key Exchange Algorithm Lecture Notes on “Computer and Network Security” by Avi Kak (kak@purdue.edu) February 29, 2016 6:16pm c 2016 Avinash Kak, Purdue University Goals: • Authenticating users and their public keys with certificates signed by Certificate Authorities (CA) • Exchanging session keys with public-key cryptography • X.509 certificates • Perl and Python code for harvesting RSA moduli from X.509 certificates • The Diffie-Hellman algorithm for exchanging session keys • The ElGamal digital signature algorithm • Can the certificates issued by CAs be forged? CONTENTS Section Title Page 13.1 Using Public Keys to Exchange Secret Session Keys 3 13.2 A Direct Key Exchange Protocol 5 13.3 Certificate Authorities for Authenticating Your Public Key 8 13.3.1 13.4 13.4.1 Using Authenticated Public Keys to Exchange a Secret Session Key 14 The X.509 Certificate Format Standard for Public-Key Infrastructure (PKI) 16 Harvesting RSA Moduli from X.509 Certificates — Perl and Python code 29 13.5 The Diffie-Hellman Algorithm for Generating a Shared Secret Session Key 37 13.6 The ElGamal Algorithm for Digital Signatures 46 13.7 On Solving the Discrete Logarithm Problem 51 13.8 Can the Certificates Issued by a CA be Forged? 55 13.9 Homework Problems 58 2 Computer and Network Security by Avi Kak Lecture 13 13.1: USING PUBLIC KEYS TO EXCHANGE SECRET SESSION KEYS • From the presentation on RSA cryptography in Lecture 12, you saw that public key cryptography, at least when using the RSA algorithm, is not suitable for the encryption of the actual message content. • However, public key cryptography fulfills an extremely important role in the overall design and operation of secure computer networks because it leads to superior protocols for managing and distributing secret session keys that can subsequently be used for the encryption of actual message content using symmetric-key algorithms .