I-D ACTION:draft-orman-public-key-lengths-01.txt

[[e-mail]]

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-01.txt
	Pages		: 13
	Date		: 10-Aug-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.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-orman-public-key-lengths-01.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-01.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:
	[e-mail].
In the body type:
	"FILE /internet-drafts/draft-orman-public-key-lengths-01.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.

ftp://ftp.ietf.org/internet-drafts/draft-orman-public-key-lengths-01.txt"><ftp://ftp.ietf.org/internet-drafts/draft-orman-public-key-lengths-01.txt>