Hi there, I recently noticed the following problem:
<quote> I'm running a (Debian stable) server of my own with a free cert from cacert.org. I've imported the root CA to Opera, and https is fine -- no warnings whatsoever. I'm also running an IMAP server (Courier) with TLS, no problems here either. BUT there is a problem with SMTP using Exim 4.50. Opera keeps complaining that my server was using a short public key which is unsafe. Why is this??? I'm using 4096 bit RSA. [...] If I force Opera to accept the certificate anyway (I can't "install" it by any means, but have to click "accept" each time I try to send a message), Opera is able to connect to the mail server. Exim logs "TLS-1.0:RSA_AES_256_CBC_SHA:32" as the crypto suite used. </quote> I posted about this problem into the Opera forum (see http://my.opera.com/community/forums/topic.dml?id=167205), and received the following reply from one of the Opera developers: <quote> The server selected an encryption method that uses RSA combined with Ephermal (dynamic) Diffie-Hellman (DHE), a method which uses short-lived (temporary) Diffie-Hellman keys authenticated by a signature from the RSA key. I have seen a couple of servers that uses a default DHE length of 512 bit or less (I once saw one sending a 256(!) bit key). Such keylengths (<900 bits) are far too short to provide any significant security. I suggest that you check the DHE key-generation configuration of the SMTP server. IMO the length of that key should match the keylength of the certificate, but to get level 3 encryption it must be at least 1024 bits long. </quote> The binary has been built by the Debian guys with GnuTLS support. Unfortunately I'm not deep enough into crypto programming to have a look at the source myself, but what the Opera developer wrote sounds reasonable to me. Can anyone comment on this? Thanks, Ralf -- ## List details at http://www.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://www.exim.org/eximwiki/
