Bug#446036: exim4: please compile against openssl instead of gnutls

[Sam Morris]

I can't speak for whether GnuTLS' historical interoperability issues
are still a problem.

I think it is worth noting that OpenSSL 3.0 is available under the
Apache License v2. As such it should now be compatible with GPL'd
software excepting that which is GPLv2-only.

I would like to refer to the blog post "Crytographic Right Answers" <
https://latacora.micro.blog/2018/04/03/cryptographic-right-answers.html
>, which makes the following recommendation regarding web site security
(I am generalizing this to apply to TLS in general, yes):

   Use AWS ALB/ELB or OpenSSL, with LetsEncrypt

   [...]

   Otherwise, there was a dark period between 2010 and 2016 where
   OpenSSL might not have been the right answer, but that time has
   passed. OpenSSL has gotten better, and, more importantly, OpenSSL is
   on-the-ball with vulnerability disclosure and response.

   Using anything besides OpenSSL will drastically complicate your
   system for little, no, or even negative security benefit. So just
   keep it simple.

   [...]

   Avoid: offbeat TLS libraries like PolarSSL, GnuTLS, and MatrixSSL.

OpenSSL is also recommended by previous 'cryptographic right answers' 
posts from others over the years (Tomas Ptacek in 2015 and Colin
Percival in 2009). On the other hand, Latacora opens with:

   We’re less interested in empowering developers and a lot more
   pessimistic about the prospects of getting this stuff right.

Which does indicate bias towards secure secure and correct
implementations over user freedom (after all, they recommend paying
Amazon to do to TLS termination for you rather than even trying to do
it yourself with OpenSSL!)

In 2020, I think it's worth revisiting whether sticking with GnuTLS is
the best choice for Debian's users. Perhaps OpenSSL's relicensing makes
the political reason to stay with GnuTLS less important (I'll of course
defer to the opinions of the maintainers here!)

Anyway, if the maintainers would reconsider switching to OpenSSL once
3.0 enters Debian then I'd like to help!

-- 
Sam Morris 

Bug#446036: exim4: please compile against openssl instead of gnutls

[Simon Josefsson]

Stephen Gran sg...@debian.org writes:

 This one time, at band camp, Simon Josefsson said:
 Hi!  I'm commenting one thing only in this post, prompted by
 http://lists.gnu.org/archive/html/gnutls-devel/2008-01/msg4.html.
 
  and most importantly for me, openssl actually supports full
  certificate chain lookups, so you can be guaranteed that this cert was
  signed was signed by that ca.  gnutls does not, to the best of my
  knowledge.
 
 That is not true.  GnuTLS can verify that the client certificate chains
 back to the CA, and has been doing so for a long time (before I became
 GnuTLS maintainer).  Naturally, the application needs to do the right
 thing to trigger that feature, but there are examples and documentation
 on how to do it.  I looked in the source for exim4 in src/tls-gnu.c
 which contains:

 I spoke imprecisely, and for that I'm sorry.  I meant that when exim is 
 compiled against openssl, it can be pointed to a directory of hashed
 certs and it will perform validation against certs found there.  gnutls
 does not seem to have this ability, to the best of my knowledge, and you
 have to instead manually include the ca.crts you are interested in a
 file.

Right.

 This may be a limitation of the parts of the gnutls API that exim
 exposes, but I was under the impression this is a limitation of
 gnutls.

It is intentional, not a limitation.  The method to use a directory with
hashed certs is specific to OpenSSL.  The GnuTLS APIs allows you to
implement that model, if you really want to: use readdir to list the
files in the directory, and decide whether to parse and trust each file
as a CA cert.  Be sure to compare this with OpenSSL's documentation on
how hashed directories are intended to work, maybe you shouldn't trust
all file in that directory.

 I remember some issues getting CRLs to work with exim and gnutls, but
 that may have either been an error in the exim implementation or an
 error on my part - gnutls would not be very useful if it couldn't handle
 revocations.

Please report it to us if you can reproduce it.  I don't think many
people use CRLs.

/Simon



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Bug#446036: exim4: please compile against openssl instead of gnutls

[Stephen Gran]

This one time, at band camp, Simon Josefsson said:
 Hi!  I'm commenting one thing only in this post, prompted by
 http://lists.gnu.org/archive/html/gnutls-devel/2008-01/msg4.html.
 
  and most importantly for me, openssl actually supports full
  certificate chain lookups, so you can be guaranteed that this cert was
  signed was signed by that ca.  gnutls does not, to the best of my
  knowledge.
 
 That is not true.  GnuTLS can verify that the client certificate chains
 back to the CA, and has been doing so for a long time (before I became
 GnuTLS maintainer).  Naturally, the application needs to do the right
 thing to trigger that feature, but there are examples and documentation
 on how to do it.  I looked in the source for exim4 in src/tls-gnu.c
 which contains:

I spoke imprecisely, and for that I'm sorry.  I meant that when exim is 
compiled against openssl, it can be pointed to a directory of hashed
certs and it will perform validation against certs found there.  gnutls
does not seem to have this ability, to the best of my knowledge, and you
have to instead manually include the ca.crts you are interested in a
file.  This may be a limitation of the parts of the gnutls API that exim
exposes, but I was under the impression this is a limitation of gnutls.

I remember some issues getting CRLs to work with exim and gnutls, but
that may have either been an error in the exim implementation or an
error on my part - gnutls would not be very useful if it couldn't handle
revocations.

Cheers,
-- 
 -
|   ,''`.Stephen Gran |
|  : :' :sg...@debian.org |
|  `. `'Debian user, admin, and developer |
|`- http://www.debian.org |
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Bug#446036: exim4: please compile against openssl instead of gnutls

[Simon Josefsson]

Hi!  I'm commenting one thing only in this post, prompted by
http://lists.gnu.org/archive/html/gnutls-devel/2008-01/msg4.html.

 and most importantly for me, openssl actually supports full
 certificate chain lookups, so you can be guaranteed that this cert was
 signed was signed by that ca.  gnutls does not, to the best of my
 knowledge.

That is not true.  GnuTLS can verify that the client certificate chains
back to the CA, and has been doing so for a long time (before I became
GnuTLS maintainer).  Naturally, the application needs to do the right
thing to trigger that feature, but there are examples and documentation
on how to do it.  I looked in the source for exim4 in src/tls-gnu.c
which contains:

/* Called after a successful handshake, when certificate verification is
required or optional, for both server and client.

Arguments:
  sessionGNUTLS session
  error  where to put text giving a reason for failure

Returns: TRUE/FALSE
*/

static BOOL
verify_certificate(gnutls_session session, uschar **error)

The function calls the relevant gnutls function,
gnutls_certificate_verify_peers.  It looks reasonable correct, although
I did not audit the code.

My conclusion is that the feature is implemented by exim4, and if there
is any problem in this area, it would be a bug.  Can you provide more
information on what made you reach the conclusion above?

/Simon



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Bug#446036: exim4: please compile against openssl instead of gnutls

[Marc Haber]

On Sun, Nov 04, 2007 at 06:47:08PM +0100, Marc Haber wrote:
 I have asked for external input, see 
 http://blog.zugschlus.de/archives/585-exim4-vs.-OpenSSL-vs.-GnuTLS.html

Since we still have some time until lenny release, I have decided to
give GnuTLS two more months to clear up their issues. The most
pressing issue is the entropy issue, IMO, which has lost some of its
threat since exim does not block on entropy depletion. The
interoperability issues with mobile phones might be the fault of a
commercial library vendor.

You might want to subscribe [EMAIL PROTECTED] to join the discussion.

Greetings
Marc

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Bug#446036: exim4: please compile against openssl instead of gnutls

[Marc Haber]

On Sat, Oct 27, 2007 at 02:51:32PM +0100, Stephen Gran wrote:
 Have you had a chance to think about this, in light of the fact that
 there is no license incompatibility?  I'm not trying to rush you, I just
 didn't want this bug forgotten.


I have asked for external input, see 
http://blog.zugschlus.de/archives/585-exim4-vs.-OpenSSL-vs.-GnuTLS.html

Greetings
Marc

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Bug#446036: exim4: please compile against openssl instead of gnutls

[Stephen Gran]

Hi,

Have you had a chance to think about this, in light of the fact that
there is no license incompatibility?  I'm not trying to rush you, I just
didn't want this bug forgotten.

Thanks,
-- 
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Bug#446036: exim4: please compile against openssl instead of gnutls

[Marc Haber]

On Wed, Oct 10, 2007 at 04:58:46PM +0100, Stephen Gran wrote:
 This one time, at band camp, Marc Haber said:
  On Wed, Oct 10, 2007 at 01:12:51AM +0100, Stephen Gran wrote:
   It's not as if
   there's a licensing issue - there is an explicit excemption for openssl.
  
  So you want to have the mysql binding removed from exim4-daemon-heavy?
  Or exim4-daemon-heavy against gnutls and -light against openssl?
 
 Why would that be an issue?  mysql isn't linking to openssl, exim is.

I'd say that the links attribute is transitive, so that we'd have
linkage of openssl via exim to mysql.

   That being said, I am not interested in BTS ping pong and won't argue
   if you decide to downgrade the bug.
  
  I will probably refer this to the tech ctte.
 
 *shrug*.  Sure, whatever you like.  ftp-master is the more obvious
 people to ask, but whichever seems reasonable to you.

I think that a question to the tech ctte has more chance of receiving
an answer.

Greetings
Marc

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Bug#446036: exim4: please compile against openssl instead of gnutls

[Stephen Gran]

This one time, at band camp, Marc Haber said:
 On Wed, Oct 10, 2007 at 04:58:46PM +0100, Stephen Gran wrote:
  This one time, at band camp, Marc Haber said:
   On Wed, Oct 10, 2007 at 01:12:51AM +0100, Stephen Gran wrote:
It's not as if there's a licensing issue - there is an explicit
excemption for openssl.
   
   So you want to have the mysql binding removed from
   exim4-daemon-heavy?  Or exim4-daemon-heavy against gnutls and
   -light against openssl?
  
  Why would that be an issue?  mysql isn't linking to openssl, exim
  is.
 
 I'd say that the links attribute is transitive, so that we'd have
 linkage of openssl via exim to mysql.

Just like you do now with libpq?  I've already explained why I don't
think this is an issue in a seperate email.

That being said, I am not interested in BTS ping pong and won't
argue if you decide to downgrade the bug.
   
   I will probably refer this to the tech ctte.
  
  *shrug*.  Sure, whatever you like.  ftp-master is the more obvious
  people to ask, but whichever seems reasonable to you.
 
 I think that a question to the tech ctte has more chance of receiving
 an answer.

Since I said ftp-master was probably more helpful, I've put my money
where my mouth is.  I've already spoken with Ganneff, and he said my
proposal would be acceptable to him, in his role in NEW processing, at
least.

My main point about the tech-ctte was that it is mainly for unresolved
disputes - it's a bit early to go running to them before we've even had
a good argument :)

TTYL,
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Bug#446036: exim4: please compile against openssl instead of gnutls

[Marc Haber]

On Wed, Oct 10, 2007 at 07:31:33PM +0100, Stephen Gran wrote:
 As I read it, there would be no GPL violation in the linking I am
 proposing.  Even more to the point, the linkage you are saying is a GPL
 violation is _already_ happening.

Which is bad. I'll discuss this.

Greetings
Marc

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Bug#446036: exim4: please compile against openssl instead of gnutls

[Stephen Gran]

This one time, at band camp, Marc Haber said:
 On Wed, Oct 10, 2007 at 07:31:33PM +0100, Stephen Gran wrote:
  As I read it, there would be no GPL violation in the linking I am
  proposing.  Even more to the point, the linkage you are saying is a GPL
  violation is _already_ happening.
 
 Which is bad. I'll discuss this.

Have you seen
http://www.mysql.com/company/legal/licensing/foss-exception.html

It appears that even if we disagree about what constitutes a GPL
violation, all relevant pieces of software have an openssl exception.

Thanks,
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Bug#446036: exim4: please compile against openssl instead of gnutls

[Marc Haber]

On Wed, Oct 10, 2007 at 01:12:51AM +0100, Stephen Gran wrote:
 It's not as if
 there's a licensing issue - there is an explicit excemption for openssl.

So you want to have the mysql binding removed from exim4-daemon-heavy?
Or exim4-daemon-heavy against gnutls and -light against openssl?

 That being said, I am not interested in BTS ping pong and won't argue
 if you decide to downgrade the bug.

I will probably refer this to the tech ctte.

Greetings
Marc

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Bug#446036: exim4: please compile against openssl instead of gnutls

[Stephen Gran]

This one time, at band camp, Marc Haber said:
 On Wed, Oct 10, 2007 at 01:12:51AM +0100, Stephen Gran wrote:
  It's not as if
  there's a licensing issue - there is an explicit excemption for openssl.
 
 So you want to have the mysql binding removed from exim4-daemon-heavy?
 Or exim4-daemon-heavy against gnutls and -light against openssl?

Why would that be an issue?  mysql isn't linking to openssl, exim is.

  That being said, I am not interested in BTS ping pong and won't argue
  if you decide to downgrade the bug.
 
 I will probably refer this to the tech ctte.

*shrug*.  Sure, whatever you like.  ftp-master is the more obvious
people to ask, but whichever seems reasonable to you.

Thanks,
-- 
 -
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|  : :' :[EMAIL PROTECTED] |
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Bug#446036: exim4: please compile against openssl instead of gnutls

[Stephen Gran]

This one time, at band camp, Marc Haber said:
 On Wed, Oct 10, 2007 at 01:12:51AM +0100, Stephen Gran wrote:
  It's not as if
  there's a licensing issue - there is an explicit excemption for openssl.
 
 So you want to have the mysql binding removed from exim4-daemon-heavy?
 Or exim4-daemon-heavy against gnutls and -light against openssl?

OK, just to be clear here, what I understand you to be arguing is that
the shared library loading will create an executable space that contains
both mysql (GPL + no excemption) and openssl, and that this will create
a GPL violation.  Am I correct?

First, there is one problem with this argument - you already link to
libpq5, which depends on openssl, and so you already have the thing
you're trying to avoid.

Second, the exim code for mysql lookups does not simultaneously use
openssl functions - they are logically seperate pieces of code.  This
means that this is not an attempt to work around the GPL by making an
application whose primary purpose is to act as a shim layer between
openssl and mysql.

As I read it, there would be no GPL violation in the linking I am
proposing.  Even more to the point, the linkage you are saying is a GPL
violation is _already_ happening.
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Bug#446036: exim4: please compile against openssl instead of gnutls

[Stephen Gran]

Package: exim4
Version: 4.63-17
Severity: normal

Hello,

The subject pretty much says it all.  I see that there are a half dozen
TLS related bugs open in the BTS about odd failures that will most likely
disappear if you use the more robust implementation.  Additionally,
openssl uses less system entropy for the same cryptographic strength
(there go your bugs about the gnutls random seed) and most importantly
for me, openssl actually supports full certificate chain lookups, so
you can be guaranteed that this cert was signed was signed by that ca.
gnutls does not, to the best of my knowledge.

I fully understand the desire to assist gnutls, but until it provides a
comparable feature set at a comparable performance level, I think that
the default MTA in Debian could do slightly better.  It's not as if
there's a licensing issue - there is an explicit excemption for openssl.

Ordinarily I would make a 'please do such and such in the packaging'
bug severity: wishlist, but given how many other open bugs appear to be
directly related to this choice, and how far gnutls is from providing some
fairly crucial features, I think that wishlist is too low a priority.
That being said, I am not interested in BTS ping pong and won't argue
if you decide to downgrade the bug.

Thanks,

-- System Information:
Debian Release: 4.0
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  APT policy: (500, 'stable')
Architecture: i386 (i686)
Shell:  /bin/sh linked to /bin/bash
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Locale: LANG=en_US.utf-8, LC_CTYPE=en_US.utf-8 (charmap=UTF-8) (ignored: LC_ALL 
set to en_US.utf-8)

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