I-D ACTION:draft-orman-public-key-lengths-00.txt
Internet-Drafts@ietf.org Mon, 07 February 2000 12:48 UTC
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Subject: I-D ACTION:draft-orman-public-key-lengths-00.txt
Date: Mon, 07 Feb 2000 06:36:21 -0500
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A New Internet-Draft is available from the on-line Internet-Drafts directories. Title : Determining Strengths For Public Keys Used For Exchanging Symmetric Keys Author(s) : H. Orman, P. Hoffman Filename : draft-orman-public-key-lengths-00.txt Pages : Date : 04-Feb-00 Implementors of systems that use public key cryptography to exchange symmetric keys need to make the public keys resistant to some predetermined level of attack. That level of attack resistance is the strength of the system, and the symmetric keys that are exchanged must be at least as strong as the system strength requirements. The three quantities, system strength, symmetric key strength, and public key strength, must be consistently matched for any network protocol usage. While it is fairly easy to express the system strength requirements in terms of a symmetric key length and to choose a cipher that has a key length equal to or exceeding that requirement, it is harder to choose a public key that has a cryptographic strength meeting a symmetric key strength requirement. This document explains how to determine the length of an asymmetric key as a function of the length of a symmetric key. Some rules of thumb for estimating equivalent resistance to large-scale attacks on various algorithms are given. The document also addresses how changing the sizes of the underlying large integers (moduli, group sizes, exponents, and so on) changes the time to use the algorithms for key exchange. The authors benefited greatly from discussions with Arjen Lenstra, Eric Verheul, Andrew Odlyzko, and Richard Schroeppel in preparing this material. Gratitude for their help does not in any way implicate them in errors that might exist in this document. A URL for this Internet-Draft is: http://www.ietf.org/internet-drafts/draft-orman-public-key-lengths-00.txt Internet-Drafts are also available by anonymous FTP. Login with the username "anonymous" and a password of your e-mail address. After logging in, type "cd internet-drafts" and then "get draft-orman-public-key-lengths-00.txt". A list of Internet-Drafts directories can be found in http://www.ietf.org/shadow.html or ftp://ftp.ietf.org/ietf/1shadow-sites.txt Internet-Drafts can also be obtained by e-mail. Send a message to: mailserv@ietf.org. In the body type: "FILE /internet-drafts/draft-orman-public-key-lengths-00.txt". NOTE: The mail server at ietf.org can return the document in MIME-encoded form by using the "mpack" utility. To use this feature, insert the command "ENCODING mime" before the "FILE" command. To decode the response(s), you will need "munpack" or a MIME-compliant mail reader. Different MIME-compliant mail readers exhibit different behavior, especially when dealing with "multipart" MIME messages (i.e. documents which have been split up into multiple messages), so check your local documentation on how to manipulate these messages. Below is the data which will enable a MIME compliant mail reader implementation to automatically retrieve the ASCII version of the Internet-Draft.
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