Create key's over 4096 bit ????

Aleksandar Milivojevic alex at
Wed Dec 21 19:02:14 CET 2005

Quoting Holger Schuettel <holger.schuettel at>:

> I've any questions. How can i generate a keypair with size  more than
> 4096 bits? I've a RSA key from my friend in my keyring with 16384 bits.
> How is that possible?

Your friend probably used some hacked code that has limit removed.  Anyhow,
generating such a long key isn't going to buy you anything (other than people
making jokes about you).  The 2048 bit keys are more than sufficiently 
long. If you *really* want long key, use 4096 (you are not going to be 
any more
secure, but if it will make you feel better go for it).  I've one 4096 bit key
that I almost never used (the ones that I did use we all at most 2048 bits
long).  This includes both PGP and S/MIME keys.

It would take *very* long time to generate 16k key.  On my 2.8GHz Pentium D it
is very slow.  All operations on such a long key would also take a lot of CPU
cycles.  See for yourself:

$ openssl genrsa -out looong.key 16384

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