Bug 34

Summary:	Incorrect claim about Commercial SSH's key length
Product:	Portable OpenSSH	Reporter:	D. Hugh Redelmeier <hugh>
Component:	Documentation	Assignee:	OpenSSH Bugzilla mailing list <openssh-bugs>
Status:	CLOSED FIXED
Severity:	trivial	CC:	hugh
Priority:	P2
Version:	-current
Hardware:	All
OS:	All
URL:	http://www.openssh.com/faq.html#2.6

Description D. Hugh Redelmeier 2001-12-10 18:54:59 AEDT

The FAQ says "Such keys were advertised as being full-length, but are actually,
half the time, half as long as advertised".  This would only be true in base 1. 
In binary, the keys are only 1 bit shorter.  Well, I guess that a quarter of the
time they would be 2 bits shorter, etc. -- I haven't checked.

On the other hand, OpenSSH keys always have the high bit on, actually making a
naive brute force attack easier than against SSH's SSH keys (half as many
possible keys).  This cannot matter very much.

Comment 1 Damien Miller 2001-12-12 12:25:59 AEDT

I agree "half as long" is a little misleading, "half as large" is closer to the
truth.

wrt the brute force argument, forcing the high-bit on would make the brute force
attack harder as there would be more potential factors for a given number
(remember these are RSA keys). Though I don't know the scaling for state of the
art sieving.

Comment 2 Niels Provos 2001-12-13 07:21:18 AEDT

I do not see anything wrong there.  A 1023-bit RSA key is a 1023-bit key, and
 not a 1024-bit key.

Comment 3 D. Hugh Redelmeier 2001-12-13 07:34:41 AEDT

A 1023-bit key is not a 512-bit key.  Saying that it is "half as long as
advertised" is saying that it is a 512-bit key.  Not true.

Comment 4 Ben Lindstrom 2002-04-06 14:35:32 AEST


*** This bug has been marked as a duplicate of 132 ***

Comment 5 D. Hugh Redelmeier 2002-04-12 16:10:31 AEST

This is not the same bug as 132.  This is a bug in the FAQ.  132 is a
bug/feature of real code.  They are related, but not the same.

Comment 6 Niels Provos 2002-04-13 00:59:28 AEST

the language has been modified to just say smaller than advertised.  they are still half the size, its the base two logarithm that is one shorter.

Comment 7 Damien Miller 2004-04-14 12:24:17 AEST

Mass change of RESOLVED bugs to CLOSED