Gitweb:
http://git.exim.org/exim.git/commitdiff/83f4c7515f3eb06dc070e78edd2694c1d088e5fd
Commit: 83f4c7515f3eb06dc070e78edd2694c1d088e5fd
Parent: 3ecab1575ef1f45a5e7cd3c48cd937ffa8eb0ad9
Author: Phil Pennock <pdp@???>
AuthorDate: Wed May 30 19:38:20 2012 -0400
Committer: Phil Pennock <pdp@???>
CommitDate: Wed May 30 19:38:20 2012 -0400
Lower EXIM_CLIENT_DH_MIN_BITS 1024 -> 512.
Wolfgang Breyha saw a real-world site using 768 bits.
---
doc/doc-txt/ChangeLog | 4 ++++
doc/doc-txt/GnuTLS-FAQ.txt | 8 ++++++--
src/src/tls-gnu.c | 2 +-
3 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index 6c0554b..46e2dcf 100644
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -165,6 +165,10 @@ PP/38 Overhaul DH prime handling, supply RFC-specified DH primes as built
PP/39 Disable SSLv2 by default in OpenSSL support.
+PP/40 Lower default size of EXIM_CLIENT_DH_MIN_BITS constant (used only by
+ GnuTLS at this time) from 1024 to 512. Cautious folk can override
+ in Local/Makefile.
+
Exim version 4.77
-----------------
diff --git a/doc/doc-txt/GnuTLS-FAQ.txt b/doc/doc-txt/GnuTLS-FAQ.txt
index 8d5887b..be46753 100644
--- a/doc/doc-txt/GnuTLS-FAQ.txt
+++ b/doc/doc-txt/GnuTLS-FAQ.txt
@@ -248,7 +248,7 @@ left with no way to actually know the size of the freshly generated DH prime.
Thus we check if the the value returned is at least 10 more than the minimum
we'll accept as a client (EXIM_CLIENT_DH_MIN_BITS, see below, defaults to
-1024) and if it is, we subtract 10. Then we reluctantly deploy a strategy
+512) and if it is, we subtract 10. Then we reluctantly deploy a strategy
called "hope". This is not guaranteed to be successful; in the first code
pass on this logic, we subtracted 3, asked for 2233 bits and got 2240 in the
first test.
@@ -275,7 +275,11 @@ prime from section 2.2 of RFC 5114.
A TLS client does not get to choose the DH prime used, but can choose a
minimum acceptable value. For Exim, this is a compile-time constant called
-"EXIM_CLIENT_DH_MIN_BITS" of 1024, which can be overruled in "Local/Makefile".
+"EXIM_CLIENT_DH_MIN_BITS" of 512, which can be overruled in "Local/Makefile".
+(It should be higher, but some real-world sites are using dangerously small
+values. Although some might argue that our old size of 1024 was dangerously
+low; "opinions vary". This is expected to be a configure file option for
+the Exim 4.81 release.)
diff --git a/src/src/tls-gnu.c b/src/src/tls-gnu.c
index c8bf634..db0e211 100644
--- a/src/src/tls-gnu.c
+++ b/src/src/tls-gnu.c
@@ -152,7 +152,7 @@ callbacks. */
#endif
#ifndef EXIM_CLIENT_DH_MIN_BITS
-#define EXIM_CLIENT_DH_MIN_BITS 1024
+#define EXIM_CLIENT_DH_MIN_BITS 512
#endif
/* With GnuTLS 2.12.x+ we have gnutls_sec_param_to_pk_bits() with which we
