From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.io/gmane.emacs.gnus.general/83422 Path: news.gmane.org!not-for-mail From: Ted Zlatanov Newsgroups: gmane.emacs.gnus.general Subject: Re: gnutls.c warning Date: Thu, 27 Jun 2013 13:43:34 -0400 Organization: =?utf-8?B?0KLQtdC+0LTQvtGAINCX0LvQsNGC0LDQvdC+0LI=?= @ Cienfuegos Message-ID: <874ncjqwjd.fsf@lifelogs.com> References: <87fvw57tx5.wl%hskuhra@eumx.net> <87li5x5qxp.fsf@thinkpad.tsdh.de> Reply-To: ding@gnus.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1372355152 6691 80.91.229.3 (27 Jun 2013 17:45:52 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 27 Jun 2013 17:45:52 +0000 (UTC) To: ding@gnus.org Original-X-From: ding-owner+M31682@lists.math.uh.edu Thu Jun 27 19:45:50 2013 Return-path: Envelope-to: ding-account@gmane.org Original-Received: from util0.math.uh.edu ([129.7.128.18]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UsGGU-0006bi-7F for ding-account@gmane.org; Thu, 27 Jun 2013 19:45:50 +0200 Original-Received: from localhost ([127.0.0.1] helo=lists.math.uh.edu) by util0.math.uh.edu with smtp (Exim 4.63) (envelope-from ) id 1UsGEc-000576-3J; Thu, 27 Jun 2013 12:43:54 -0500 Original-Received: from mx2.math.uh.edu ([129.7.128.33]) by util0.math.uh.edu with esmtps (TLSv1:AES256-SHA:256) (Exim 4.63) (envelope-from ) id 1UsGEZ-00056t-Ax for ding@lists.math.uh.edu; Thu, 27 Jun 2013 12:43:51 -0500 Original-Received: from quimby.gnus.org ([80.91.231.51]) by mx2.math.uh.edu with esmtps (TLSv1:AES256-SHA:256) (Exim 4.76) (envelope-from ) id 1UsGEW-0001oJ-RP for ding@lists.math.uh.edu; Thu, 27 Jun 2013 12:43:50 -0500 Original-Received: from plane.gmane.org ([80.91.229.3]) by quimby.gnus.org with esmtp (Exim 4.72) (envelope-from ) id 1UsGEU-0006Ff-TV for ding@gnus.org; Thu, 27 Jun 2013 19:43:46 +0200 Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1UsGET-0004bo-L3 for ding@gnus.org; Thu, 27 Jun 2013 19:43:45 +0200 Original-Received: from pool-72-93-34-251.bstnma.east.verizon.net ([72.93.34.251]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 27 Jun 2013 19:43:45 +0200 Original-Received: from tzz by pool-72-93-34-251.bstnma.east.verizon.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 27 Jun 2013 19:43:45 +0200 X-Injected-Via-Gmane: http://gmane.org/ Mail-Followup-To: ding@gnus.org Original-Lines: 56 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: pool-72-93-34-251.bstnma.east.verizon.net X-Face: bd.DQ~'29fIs`T_%O%C\g%6jW)yi[zuz6;d4V0`@y-~$#3P_Ng{@m+e4o<4P'#(_GJQ%TT= D}[Ep*b!\e,fBZ'j_+#"Ps?s2!4H2-Y"sx" Mail-Copies-To: never User-Agent: Gnus/5.130008 (Ma Gnus v0.8) Emacs/24.3.50 (gnu/linux) Cancel-Lock: sha1:Qw9p6xocCO4EsHeakJT1eDgB9YM= X-Spam-Score: -3.2 (---) List-ID: Precedence: bulk Xref: news.gmane.org gmane.emacs.gnus.general:83422 Archived-At: On Wed, 26 Jun 2013 08:25:38 +0200 Tassilo Horn wrote: TH> "Herbert J. Skuhra" writes: >>> I keep getting this warning, and can't find any way to turn it off. >>> >>> gnutls.c: [1] Note that the security level of the Diffie-Hellman key exchange >>> has been lowered to 256 bits and this may allow decryption of the session data TH> Ditto. This is not coming from Emacs, actually. Shutting it up requires lowering the gnutls.el verbosity level altogether. But the warning is very important and should not be ignored. >>> Is there some setting to say ok, I understand, quit nagging me? >> >> After setting gnutls-min-prime-bits to 1024 I no longer get this >> warning. TH> ,----[ C-h v gnutls-min-prime-bits RET ] TH> | gnutls-min-prime-bits is a variable defined in `gnutls.el'. TH> | Its value is 1024 TH> | Original value was 256 TH> | TH> | Documentation: TH> | Minimum number of prime bits accepted by GnuTLS for key exchange. TH> | During a Diffie-Hellman handshake, if the server sends a prime TH> | number with fewer than this number of bits, the handshake is TH> | rejected. (The smaller the prime number, the less secure the TH> | key exchange is against man-in-the-middle attacks.) TH> | TH> | A value of nil says to use the default GnuTLS value. TH> `---- TH> Hm, what happens if the value is higher than what the server wants to TH> provide? Connection error (fine)? Drop to an insecured connection TH> (please no!)? Or do the servers automatically increase the bit number TH> if a client rejects a handshake? (The below is AFAIK and please forgive any inaccuracies.) We rely on GnuTLS to DTRT. The DH handshake does not affect the security of the session after it's established, so it would not create an insecure connection. Its only purpose is to shake hands and exchange identities. When the client (Emacs) and the server negotiate to 1024, for instance, everything is kosher. They will try for the highest number. For GMail, for instance, I never get the warning you saw. So maybe this is a problem with a specific TLS implementation? I don't know, sorry. We had plenty of discussion about this. Lowering the minimum to 256 is actually very strongly discouraged but many Emacs users asked for it and I feel the warning is a viable compromise. Ted