* bug#9036: [PATCH] gnutls: Add option to set minimum acceptable Diffie-Hellman key size
@ 2011-07-09 14:44 Lawrence Mitchell
2011-07-15 16:47 ` Ted Zlatanov
2011-07-15 17:34 ` Lars Magne Ingebrigtsen
0 siblings, 2 replies; 6+ messages in thread
From: Lawrence Mitchell @ 2011-07-09 14:44 UTC (permalink / raw)
To: 9036
* gnutls.c (Qgnutls_bootprop_min_prime_bits): New variable.
(Fgnutls_boot): Use it
* net/gnutls.el (gnutls-min-prime-bits): New variable.
(gnutls-negotiate): Use it.
The default acceptable key size used by gnutls in Diffie-Hellman key
exchange is larger than that advertised by many servers. Introduce a
customization option to set the minimum acceptable value so that we
can still connect to such servers using TLS.
---
With the recent gnutls changes I could no longer send mail with
STARTTLS since the smtp server I connect to only advertises a D-H
key with 512bits. This is smaller than the default value gnutls
allows and so the connection would be aborted. This patch adds
the ability to set the minimum acceptable size of key, so that I
can send email again!
lisp/ChangeLog | 5 +++++
lisp/net/gnutls.el | 22 ++++++++++++++++++++--
src/ChangeLog | 5 +++++
src/gnutls.c | 16 ++++++++++++++++
4 files changed, 46 insertions(+), 2 deletions(-)
diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index c3162c3..ca20415 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2011-07-09 Lawrence Mitchell <wence@gmx.li>
+
+ * net/gnutls.el (gnutls-min-prime-bits): New variable.
+ (gnutls-negotiate): Use it.
+
2011-07-07 Lars Magne Ingebrigtsen <larsi@gnus.org>
* mail/smtpmail.el (smtpmail-stream-type): Note that `plain' can
diff --git a/lisp/net/gnutls.el b/lisp/net/gnutls.el
index 67d7b2d..83726d0 100644
--- a/lisp/net/gnutls.el
+++ b/lisp/net/gnutls.el
@@ -47,6 +47,19 @@
:type 'integer
:group 'gnutls)
+;;;###autoload
+(defcustom gnutls-min-prime-bits nil
+ "The minimum number of bits to be used in Diffie-Hellman key exchange.
+
+This sets the minimum accepted size of the key to be used in a
+client-server handshake. If the server sends a prime with fewer than
+the specified number of bits the handshake will fail.
+
+A value of nil says to use the default gnutls value."
+ :type '(choice (const :tag "Use default value" nil)
+ (integer :tag "Number of bits" 512))
+ :group 'gnutls)
+
(defun open-gnutls-stream (name buffer host service)
"Open a SSL/TLS connection for a service to a host.
Returns a subprocess-object to represent the connection.
@@ -90,8 +103,8 @@ trust and key files, and priority string."
(defun* gnutls-negotiate
(&rest spec
&key process type hostname priority-string
- trustfiles crlfiles keylist verify-flags
- verify-error verify-hostname-error
+ trustfiles crlfiles keylist min-prime-bits
+ verify-flags verify-error verify-hostname-error
&allow-other-keys)
"Negotiate a SSL/TLS connection. Returns proc. Signals gnutls-error.
@@ -104,6 +117,9 @@ PRIORITY-STRING is as per the GnuTLS docs, default is \"NORMAL\".
TRUSTFILES is a list of CA bundles.
CRLFILES is a list of CRL files.
KEYLIST is an alist of (client key file, client cert file) pairs.
+MIN-PRIME-BITS is the minimum acceptable size of Diffie-Hellman keys
+\(see `gnutls-min-prime-bits' for more information). Use nil for the
+default.
When VERIFY-HOSTNAME-ERROR is not nil, an error will be raised
when the hostname does not match the presented certificate's host
@@ -146,9 +162,11 @@ defaults to GNUTLS_VERIFY_ALLOW_X509_V1_CA_CRT."
"NORMAL:+ANON-DH:!ARCFOUR-128")
((eq type 'gnutls-x509pki)
"NORMAL"))))
+ (min-prime-bits (or min-prime-bits gnutls-min-prime-bits))
(params `(:priority ,priority-string
:hostname ,hostname
:loglevel ,gnutls-log-level
+ :min-prime-bits ,min-prime-bits
:trustfiles ,trustfiles
:crlfiles ,crlfiles
:keylist ,keylist
diff --git a/src/ChangeLog b/src/ChangeLog
index ac20a60..7ea45e7 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2011-07-09 Lawrence Mitchell <wence@gmx.li>
+
+ * gnutls.c (Qgnutls_bootprop_min_prime_bits): New variable.
+ (Fgnutls_boot): Use it.
+
2011-07-07 Kenichi Handa <handa@m17n.org>
* character.h (unicode_category_t): New enum type.
diff --git a/src/gnutls.c b/src/gnutls.c
index 76cfa5d..26a88a7 100644
--- a/src/gnutls.c
+++ b/src/gnutls.c
@@ -50,6 +50,7 @@ static Lisp_Object Qgnutls_bootprop_crlfiles;
static Lisp_Object Qgnutls_bootprop_callbacks;
static Lisp_Object Qgnutls_bootprop_loglevel;
static Lisp_Object Qgnutls_bootprop_hostname;
+static Lisp_Object Qgnutls_bootprop_min_prime_bits;
static Lisp_Object Qgnutls_bootprop_verify_flags;
static Lisp_Object Qgnutls_bootprop_verify_hostname_error;
@@ -105,6 +106,8 @@ DEF_GNUTLS_FN (int, gnutls_certificate_verify_peers2,
DEF_GNUTLS_FN (int, gnutls_credentials_set,
(gnutls_session_t, gnutls_credentials_type_t, void *));
DEF_GNUTLS_FN (void, gnutls_deinit, (gnutls_session_t));
+DEF_GNUTLS_FN (void, gnutls_dh_set_prime_bits,
+ (gnutls_session_t, unsigned int));
DEF_GNUTLS_FN (int, gnutls_error_is_fatal, (int));
DEF_GNUTLS_FN (int, gnutls_global_init, (void));
DEF_GNUTLS_FN (void, gnutls_global_set_log_function, (gnutls_log_func));
@@ -167,6 +170,7 @@ init_gnutls_functions (Lisp_Object libraries)
LOAD_GNUTLS_FN (library, gnutls_certificate_verify_peers2);
LOAD_GNUTLS_FN (library, gnutls_credentials_set);
LOAD_GNUTLS_FN (library, gnutls_deinit);
+ LOAD_GNUTLS_FN (library, gnutls_dh_set_prime_bits);
LOAD_GNUTLS_FN (library, gnutls_error_is_fatal);
LOAD_GNUTLS_FN (library, gnutls_global_init);
LOAD_GNUTLS_FN (library, gnutls_global_set_log_function);
@@ -213,6 +217,7 @@ init_gnutls_functions (Lisp_Object libraries)
#define fn_gnutls_certificate_verify_peers2 gnutls_certificate_verify_peers2
#define fn_gnutls_credentials_set gnutls_credentials_set
#define fn_gnutls_deinit gnutls_deinit
+#define fn_gnutls_dh_set_prime_bits gnutls_dh_set_prime_bits
#define fn_gnutls_error_is_fatal gnutls_error_is_fatal
#define fn_gnutls_global_init gnutls_global_init
#define fn_gnutls_global_set_log_function gnutls_global_set_log_function
@@ -641,6 +646,9 @@ gnutls_certificate_set_verify_flags.
:verify-hostname-error, if non-nil, makes a hostname mismatch an
error. Otherwise it will be just a warning.
+:min-prime-bits is the minimum accepted number of bits the client will
+accept in Diffie-Hellman key exchange.
+
The debug level will be set for this process AND globally for GnuTLS.
So if you set it higher or lower at any point, it affects global
debugging.
@@ -693,6 +701,7 @@ one trustfile (usually a CA bundle). */)
Lisp_Object verify_flags;
/* Lisp_Object verify_error; */
Lisp_Object verify_hostname_error;
+ Lisp_Object prime_bits;
CHECK_PROCESS (proc);
CHECK_SYMBOL (type);
@@ -714,6 +723,7 @@ one trustfile (usually a CA bundle). */)
verify_flags = Fplist_get (proplist, Qgnutls_bootprop_verify_flags);
/* verify_error = Fplist_get (proplist, Qgnutls_bootprop_verify_error); */
verify_hostname_error = Fplist_get (proplist, Qgnutls_bootprop_verify_hostname_error);
+ prime_bits = Fplist_get (proplist, Qgnutls_bootprop_min_prime_bits);
if (!STRINGP (hostname))
error ("gnutls-boot: invalid :hostname parameter");
@@ -931,6 +941,11 @@ one trustfile (usually a CA bundle). */)
GNUTLS_INITSTAGE (proc) = GNUTLS_STAGE_PRIORITY;
+ if (!EQ (prime_bits, Qnil))
+ {
+ fn_gnutls_dh_set_prime_bits (state, XUINT (prime_bits));
+ }
+
if (EQ (type, Qgnutls_x509pki))
{
ret = fn_gnutls_credentials_set (state, GNUTLS_CRD_CERTIFICATE, x509_cred);
@@ -1109,6 +1124,7 @@ syms_of_gnutls (void)
DEFSYM (Qgnutls_bootprop_crlfiles, ":crlfiles");
DEFSYM (Qgnutls_bootprop_callbacks, ":callbacks");
DEFSYM (Qgnutls_bootprop_callbacks_verify, "verify");
+ DEFSYM (Qgnutls_bootprop_min_prime_bits, ":min-prime-bits");
DEFSYM (Qgnutls_bootprop_loglevel, ":loglevel");
DEFSYM (Qgnutls_bootprop_verify_flags, ":verify-flags");
DEFSYM (Qgnutls_bootprop_verify_hostname_error, ":verify-hostname-error");
--
1.7.6.131.g99019
^ permalink raw reply related [flat|nested] 6+ messages in thread
* bug#9036: [PATCH] gnutls: Add option to set minimum acceptable Diffie-Hellman key size
2011-07-09 14:44 bug#9036: [PATCH] gnutls: Add option to set minimum acceptable Diffie-Hellman key size Lawrence Mitchell
@ 2011-07-15 16:47 ` Ted Zlatanov
2011-07-15 17:34 ` Lars Magne Ingebrigtsen
1 sibling, 0 replies; 6+ messages in thread
From: Ted Zlatanov @ 2011-07-15 16:47 UTC (permalink / raw)
To: Lawrence Mitchell; +Cc: 9036
On Sat, 9 Jul 2011 15:44:28 +0100 Lawrence Mitchell <wence@gmx.li> wrote:
LM> * gnutls.c (Qgnutls_bootprop_min_prime_bits): New variable.
LM> (Fgnutls_boot): Use it
LM> * net/gnutls.el (gnutls-min-prime-bits): New variable.
LM> (gnutls-negotiate): Use it.
I'm unable to get online for at least another week so please don't wait
for me on any GnuTLS-related issues.
If you can wait for me, I'll apply this; otherwise Lars or someone else
can make the change. It looks fine FWIW but I haven't tested it.
Thanks
Ted
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#9036: [PATCH] gnutls: Add option to set minimum acceptable Diffie-Hellman key size
2011-07-09 14:44 bug#9036: [PATCH] gnutls: Add option to set minimum acceptable Diffie-Hellman key size Lawrence Mitchell
2011-07-15 16:47 ` Ted Zlatanov
@ 2011-07-15 17:34 ` Lars Magne Ingebrigtsen
2011-07-16 10:27 ` Lawrence Mitchell
1 sibling, 1 reply; 6+ messages in thread
From: Lars Magne Ingebrigtsen @ 2011-07-15 17:34 UTC (permalink / raw)
To: Lawrence Mitchell; +Cc: 9036
Lawrence Mitchell <wence@gmx.li> writes:
> With the recent gnutls changes I could no longer send mail with
> STARTTLS since the smtp server I connect to only advertises a D-H
> key with 512bits. This is smaller than the default value gnutls
> allows and so the connection would be aborted. This patch adds
> the ability to set the minimum acceptable size of key, so that I
> can send email again!
Thanks; I'll apply your patch.
However, is there any way to make the gnutls library adjust the size
downwards automatically if it's too big?
--
(domestic pets only, the antidote for overdose, milk.)
bloggy blog http://lars.ingebrigtsen.no/
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#9036: [PATCH] gnutls: Add option to set minimum acceptable Diffie-Hellman key size
2011-07-15 17:34 ` Lars Magne Ingebrigtsen
@ 2011-07-16 10:27 ` Lawrence Mitchell
2011-07-16 16:08 ` Lars Magne Ingebrigtsen
0 siblings, 1 reply; 6+ messages in thread
From: Lawrence Mitchell @ 2011-07-16 10:27 UTC (permalink / raw)
To: 9036
Lars Magne Ingebrigtsen wrote:
> Lawrence Mitchell <wence@gmx.li> writes:
>> With the recent gnutls changes I could no longer send mail with
>> STARTTLS since the smtp server I connect to only advertises a D-H
>> key with 512bits. This is smaller than the default value gnutls
>> allows and so the connection would be aborted. This patch adds
>> the ability to set the minimum acceptable size of key, so that I
>> can send email again!
> Thanks; I'll apply your patch.
> However, is there any way to make the gnutls library adjust the size
> downwards automatically if it's too big?
The handshake returns GNUTLS_E_DH_PRIME_UNACCEPTABLE if the
number of server prime bits is too low. I don't know how to
query the size of the server prime. Maybe
gnutls_dh_get_prime_bits? I'm wary to automatically adjust
downwards.
A better error message (pointing at the existance of
gnutls-min-prime-bits) in the case of this failure mode would
probably be good though. I'll try and cook up a patch in the
next few days.
Lawrence
--
Lawrence Mitchell <wence@gmx.li>
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#9036: [PATCH] gnutls: Add option to set minimum acceptable Diffie-Hellman key size
2011-07-16 10:27 ` Lawrence Mitchell
@ 2011-07-16 16:08 ` Lars Magne Ingebrigtsen
2011-11-10 15:21 ` Lawrence Mitchell
0 siblings, 1 reply; 6+ messages in thread
From: Lars Magne Ingebrigtsen @ 2011-07-16 16:08 UTC (permalink / raw)
To: Lawrence Mitchell; +Cc: 9036
Lawrence Mitchell <wence@gmx.li> writes:
> The handshake returns GNUTLS_E_DH_PRIME_UNACCEPTABLE if the
> number of server prime bits is too low. I don't know how to
> query the size of the server prime. Maybe
> gnutls_dh_get_prime_bits? I'm wary to automatically adjust
> downwards.
I think adjusting it downwards automatically until you reach a
(user-definable) absolute lower limit would be fine. But I have no idea
what an acceptable default lower limit would be, or what the impact on
security this would have.
> A better error message (pointing at the existance of
> gnutls-min-prime-bits) in the case of this failure mode would
> probably be good though. I'll try and cook up a patch in the
> next few days.
Great!
--
(domestic pets only, the antidote for overdose, milk.)
bloggy blog http://lars.ingebrigtsen.no/
^ permalink raw reply [flat|nested] 6+ messages in thread
* bug#9036: [PATCH] gnutls: Add option to set minimum acceptable Diffie-Hellman key size
2011-07-16 16:08 ` Lars Magne Ingebrigtsen
@ 2011-11-10 15:21 ` Lawrence Mitchell
0 siblings, 0 replies; 6+ messages in thread
From: Lawrence Mitchell @ 2011-11-10 15:21 UTC (permalink / raw)
To: 9036
Lars Magne Ingebrigtsen wrote:
> Lawrence Mitchell <wence@gmx.li> writes:
>> The handshake returns GNUTLS_E_DH_PRIME_UNACCEPTABLE if the
>> number of server prime bits is too low. I don't know how to
>> query the size of the server prime. Maybe
>> gnutls_dh_get_prime_bits? I'm wary to automatically adjust
>> downwards.
> I think adjusting it downwards automatically until you reach a
> (user-definable) absolute lower limit would be fine. But I have no idea
> what an acceptable default lower limit would be, or what the impact on
> security this would have.
>> A better error message (pointing at the existance of
>> gnutls-min-prime-bits) in the case of this failure mode would
>> probably be good though. I'll try and cook up a patch in the
>> next few days.
> Great!
So it turns out this wasn't a few days.
And I couldn't figure out a nice way to fix things up properly.
So no patch sorry :(. However, I think the original bug can be
closed, because there is now an option to set the DH key size.
Lawrence
--
Lawrence Mitchell <wence@gmx.li>
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2011-11-10 15:21 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2011-07-09 14:44 bug#9036: [PATCH] gnutls: Add option to set minimum acceptable Diffie-Hellman key size Lawrence Mitchell
2011-07-15 16:47 ` Ted Zlatanov
2011-07-15 17:34 ` Lars Magne Ingebrigtsen
2011-07-16 10:27 ` Lawrence Mitchell
2011-07-16 16:08 ` Lars Magne Ingebrigtsen
2011-11-10 15:21 ` Lawrence Mitchell
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