Doc: SECTgnutlsparam referencing tls_dhparam

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index beb0522be5542f2490d063c7f32101f87f3c8cce..c71dfb1820e1a385ea502554ab9124c72632758f 100644 (file)
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -25061,6 +25061,12 @@ implementation, then patches are welcome.
 
 .section "GnuTLS parameter computation" "SECTgnutlsparam"
 .new
 
 .section "GnuTLS parameter computation" "SECTgnutlsparam"
 .new

+This section only applies if &%tls_dhparam%& is set to &`historic`& or to
+an explicit path; if the latter, then the text about generation still applies,
+but not the chosen filename.
+By default, as of Exim 4.80 a hard-coded D-H prime is used.
+See the documentation of &%tls_dhparam%& for more information.
+

 GnuTLS uses D-H parameters that may take a substantial amount of time
 to compute. It is unreasonable to re-compute them for every TLS session.
 Therefore, Exim keeps this data in a file in its spool directory, called
 GnuTLS uses D-H parameters that may take a substantial amount of time
 to compute. It is unreasonable to re-compute them for every TLS session.
 Therefore, Exim keeps this data in a file in its spool directory, called


@@ -25076,6 +25082,10 @@ place, new Exim processes immediately start using it.
 
 For maximum security, the parameters that are stored in this file should be
 recalculated periodically, the frequency depending on your paranoia level.
 
 For maximum security, the parameters that are stored in this file should be
 recalculated periodically, the frequency depending on your paranoia level.

+If you are avoiding using the fixed D-H primes published in RFCs, then you
+are concerned about some advanced attacks and will wish to do this; if you do
+not regenerate then you might as well stick to the standard primes.
+

 Arranging this is easy in principle; just delete the file when you want new
 values to be computed. However, there may be a problem. The calculation of new
 parameters needs random numbers, and these are obtained from &_/dev/random_&.
 Arranging this is easy in principle; just delete the file when you want new
 values to be computed. However, there may be a problem. The calculation of new
 parameters needs random numbers, and these are obtained from &_/dev/random_&.