FAQ 5/23/00 11:21 AM Page 1 FAQ v e rsion 4.1 - May 2000 Frequently A s ked Questions about To d ay ’s Cry p t o g ra p h y L A B O R AT O R I E S ™ - 1 Copyright c 1992-2000 RSA Security Inc. All rights reserved. RSA BSAFE Crypto-C, RSA BSAFE Crypto-J, Keon Desktop, MD2, MD4, MD5, RC2, RC4, RC5, RC6, RSA, and SecurID are trademarks or registered trademarks of RSA Security Inc. Other products and names are trademarks or registered trademarks of their respective owners. For permission to reprint or redistribute in part or in whole, send e-mail to [email protected] or contact your RSA Security representative. How to cite this document: Author: RSA Laboratories Title: RSA Laboratories' Frequently Asked Questions About Today's Cryptography, Version 4.1 Year: 2000 Publisher: RSA Security Inc. Frequently Asked Questions About Today's Cryptography 2 Contents Foreword 8 1 Introduction 9 1.1 What is RSA Laboratories' Frequently Asked Questions About Today's Cryptography? 9 1.2 What is cryptography? . 10 1.3 What are some of the more popular techniques in cryptography? . 12 1.4 How is cryptography applied? . 13 1.5 What are cryptography standards? . 16 1.6 What is the role of the United States government in cryptography? . 17 1.7 Why is cryptography important? . 18 2 Cryptography 20 2.1 Cryptographic Tools . 20 2.1.1 What is public-key cryptography? . 20 2.1.2 What is secret-key cryptography? . 22 2.1.3 What are the advantages and disadvantages of public-key cryptography compared with secret-key cryptography? . 23 2.1.4 What is a block cipher? . 25 2.1.4.1 What is an iterated block cipher? . 26 2.1.4.2 What is Electronic Code Book Mode? . 27 2.1.4.3 What is Cipher Block Chaining Mode? . 28 2.1.4.4 What is Cipher Feedback Mode? . 30 2.1.4.5 What is Output Feedback Mode? . 31 2.1.5 What is a stream cipher? . 32 2.1.5.1 What is a Linear Feedback Shift Register? . 33 2.1.6 What is a hash function? . 34 2.1.7 What are Message Authentication Codes? . 36 2.1.8 What are interactive proofs and zero-knowledge proofs? . 37 2.1.9 What are secret sharing schemes? . 39 2.2 Simple Applications of Cryptography . 40 2.2.1 What is privacy? . 40 2.2.2 What is a digital signature and what is authentication? . 41 2.2.3 What is a key agreement protocol? . 43 2.2.4 What is a digital envelope? . 44 2.2.5 What is identification? . 45 - 3 2.3 Hard Problems . 46 2.3.1 What is a hard problem? . 46 2.3.2 What is a one-way function? . 47 2.3.3 What is the factoring problem? . 48 2.3.4 What are the best factoring methods in use today? . 49 2.3.5 What improvements are likely in factoring capability? . 50 2.3.6 What is the RSA Factoring Challenge? . 52 2.3.7 What is the discrete logarithm problem? . 54 2.3.8 What are the best discrete logarithm methods in use today? . 55 2.3.9 What are the prospects for a theoretical breakthrough in the discrete logarithm problem? . 56 2.3.10 What are elliptic curves? . 57 2.3.11 What are lattice-based cryptosystems? . 58 2.3.12 What are some other hard problems? . 59 2.4 Cryptanalysis . 60 2.4.1 What is cryptanalysis? . 60 2.4.2 What are some of the basic types of cryptanalytic attack? . 61 2.4.3 What is exhaustive key search? . 62 2.4.4 What is the RSA Secret Key Challenge? . 63 2.4.5 What are the most important attacks on symmetric block ciphers? . 64 2.4.6 What are some techniques against hash functions? . 66 2.4.7 What are the most important attacks on stream ciphers? . 67 2.4.8 What are the most important attacks on MACs? . 69 2.4.9 At what point does an attack become practical? . 70 2.5 Supporting Tools in Cryptography . 71 2.5.1 What is primality testing? . 71 2.5.2 What is random number generation? . 72 3 Techniques in Cryptography 73 3.1 RSA . 73 3.1.1 What is the RSA cryptosystem? . 73 3.1.2 How fast is the RSA algorithm? . 75 3.1.3 What would it take to break the RSA cryptosystem? . 76 3.1.4 What are strong primes and are they necessary for the RSA system? . 78 3.1.5 How large a key should be used in the RSA cryptosystem? . 79 3.1.6 Could users of the RSA system run out of distinct primes? . 81 3.1.7 How is the RSA algorithm used for privacy in practice? . 82 3.1.8 How is the RSA algorithm used for authentication and digital signatures in practice? . 83 3.1.9 Is the RSA cryptosystem currently in use? . 84 3.1.10 Is the RSA system an official standard today? . 85 3.1.11 Is the RSA system a de facto standard? . 86 3.2 DES . 87 3.2.1 What is DES? . 87 3.2.2 Has DES been broken? . 88 Frequently Asked Questions About Today's Cryptography 4 3.2.3 How does one use DES securely? . 89 3.2.4 Should one test for weak keys in DES? . 90 3.2.5 Is DES a group? . 91 3.2.6 What is triple-DES? . 92 3.2.7 What is DESX? . 93 3.2.8 What are some other DES variants? . 94 3.3 AES . 95 3.3.1 What is the AES? . 95 3.3.2 What are some candidates for the AES? . 96 3.3.3 What is the schedule for the AES? . 98 3.4 DSA . 99 3.4.1 What are DSA and DSS? . 99 3.4.2 Is DSA secure? . 100 3.5 Elliptic Curve Cryptosystems . 101 3.5.1 What are elliptic curve cryptosystems? . 101 3.5.2 Are elliptic curve cryptosystems secure? . 102 3.5.3 Are elliptic curve cryptosystems widely used? . 103 3.5.4 How do elliptic curve cryptosystems compare with other cryptosystems? . 104 3.5.5 What is the Certicom ECC Challenge? . 105 3.6 Other Cryptographic Techniques . 106 3.6.1 What is Diffie-Hellman? . 106 3.6.2 What is RC2? . 108 3.6.3 What is RC4? . 109 3.6.4 What are RC5 and RC6? . 110 3.6.5 What are SHA and SHA-1? . 111 3.6.6 What are MD2, MD4, and MD5? . 112 3.6.7 What are some other block ciphers? . 113 3.6.8 What are some other public-key cryptosystems? . 116 3.6.9 What are some other signature schemes? . 118 3.6.10 What are some other stream ciphers? . 119 3.6.11 What other hash functions are there? . 120 3.6.12 What are some secret sharing schemes? . 121 4 Applications of Cryptography 123 4.1 Key Management . 123 4.1.1 What is key management? . 123 4.1.2 General . 124 4.1.2.1 What key size should be used? 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