OpenSSL certificates and key sizes

[Chris Ball]

>> On Fri, 14 Apr 2006 15:29:34 -0400, John Abreau <jabr at blu.org> said:

   > Are there any problems with making the keys, particularly the CA
   > key, something like 4096 bits long?  How about 8192 bits long?

Either is fine, but I personally find 8192 bits a little distasteful;
most CA keys are 4096 bits long, and have an expiry of around fifteen
years.  

4096-bit keys have been conjectured "safe", against the best-known 
algorithms, for 45 years[1].  So, it makes sense to take that, plan 
for dramatic but conventional advances (since you can't plan for 
unconventional ones) and set an expiry of a decade or two.  I think
it makes less sense to go with an 8192-bit key and be attempting to 
plan hundreds of years into the future.

(But IANACryptographer.)

Footnotes:
 [1]:  <http://www.win.tue.nl/~klenstra/key.pdf>, p.32.

-- 
Chris Ball   <cjb at mrao.cam.ac.uk>    <http://blog.printf.net/>