Re: libnettle/libhogweed WIP

[Paul Eggert <eggert@cs.ucla.edu>]

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Paul Eggert wrote:
> it would take some time for me to come up to speed on GnuTLS.

Although I'm still not up to speed at all, I think I tracked the problem down. I 
installed the attached patch which fixes things for me on Ubuntu 16.04.2 LTS, by 
having Emacs use AEAD only on GnuTLS 3.5.1 and later.

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From fcd7c6b8605dbfb0c38da39a50d5ac882c2c0ba3 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 3 Aug 2017 01:00:10 -0700
Subject: [PATCH] Port GnuTLS usage to Ubuntu 16.04.2 LTS

* src/gnutls.h (HAVE_GNUTLS3_AEAD): Define only if GnuTLS 3.5.1 or
later, as opposed to the old 3.4.0 or later.
---
 src/gnutls.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/gnutls.h b/src/gnutls.h
index 19c1686..8fe4ac3 100644
--- a/src/gnutls.h
+++ b/src/gnutls.h
@@ -29,12 +29,21 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #endif
 
 #if 0x030400 <= GNUTLS_VERSION_NUMBER
-# define HAVE_GNUTLS3_AEAD
 # define HAVE_GNUTLS3_CIPHER
 # define HAVE_GNUTLS3_DIGEST
 # define HAVE_GNUTLS3_HMAC
 #endif
 
+/* Although AEAD support started in GnuTLS 3.4.0 and works in 3.5.14,
+   it was broken through at least GnuTLS 3.4.10; see:
+   https://lists.gnu.org/archive/html/emacs-devel/2017-07/msg00992.html
+   The relevant fix seems to have been made in GnuTLS 3.5.1; see:
+   https://gitlab.com/gnutls/gnutls/commit/568935848dd6b82b9315d8b6c529d00e2605e03d
+   So use 3.5.1 for now.  */
+#if 0x030501 <= GNUTLS_VERSION_NUMBER
+# define HAVE_GNUTLS3_AEAD
+#endif
+
 #include "lisp.h"
 
 /* This limits the attempts to handshake per process (connection).  It
-- 
2.7.4