On Sat, 12 Feb 2011 14:16:00 +0100, Ludolf Holzheid lholzheid@bihl-wiedemann.de wrote:
On Fri, 2011-02-11 23:40:10 +0100, Jean-Yves F. Barbier wrote:
Hi list,
I'm using stunnel between two machines only, so is there a risk to reuse the server stunnel.pem on the client? (and if it's risky, why?)
I wouldn't want to have our server's private key on a windows netbook of one of our sales people, but if the two machines are in a trusted environment and the file permissions are set properly, I don' see any reason why this could be a problem.
Fortunately we only use real OS :)
Though I think I understood the concept of PKI, I don't know the first thing about the mathematics used for asymmetric encryption -- maybe using the same key on both ends is a strange corner case I'm not aware of. I don't expect this to be the cases, but I don't know.
As far as I understood, the private key is used at session setup only (for negotiating the session key, which is newly created for each session). This is to reduce the amount of data that could be used to 'guess' the private key. If you use the same key pair on both ends, this doubles this data. However, I don't think this raises the chances of success for guessing the private key to a real-world likelihood.
Hmmm, so it looks like may the entropy may be higher with 2 different keys.
If I had to set up an SSL-secured point-to-point tunnel, my first idea would be to use different key pairs on both sides (thinking of the point-to-point tunnel as a special case of multi-client tunnels), but I'm not aware of any real reason not to do so.
HTH,
Thanks Ludolf, you made me reconsider and I think I'll use 2 différent keys (that was pure lazyness: on an athlonXP-2600+ a dhparam of 4096 bytes is *very* long to calculate.)
JY