.end -> .wen

[exim.git] / doc / doc-docbook / spec.xfpt

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index da97d40823c5b51b91de3c95e87091713da8c921..1c2fa8401460f4833d3580ef1a9c75b3c7fc32fe 100644 (file)
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -15710,7 +15710,7 @@ ignored. See section &<<SECTopenvsgnu>>& for further details.
 .new
 If the DH bit-count from loading the file is greater than tls_dh_max_bits then
 it will be ignored.
 .new
 If the DH bit-count from loading the file is greater than tls_dh_max_bits then
 it will be ignored.

-.end
+.wen

 
 
 .option tls_on_connect_ports main "string list" unset
 
 
 .option tls_on_connect_ports main "string list" unset


@@ -24963,10 +24963,11 @@ The &%tls_verify_certificates%& option must contain the name of a file, not the
 name of a directory (for OpenSSL it can be either).
 .next
 The &%tls_dhparam%& option is ignored, because early versions of GnuTLS had no
 name of a directory (for OpenSSL it can be either).
 .next
 The &%tls_dhparam%& option is ignored, because early versions of GnuTLS had no

-facility for varying its Diffie-Hellman parameters. I understand that this has
-changed, but Exim has not been updated to provide this facility.
+facility for varying its Diffie-Hellman parameters.

 .new
 .new

-Instead, the GnuTLS support will use a file from the spool directory.
+Since then, the GnuTLS support has been updated to generate parameters upon
+demand, keeping them in the spool directory.  See &<<SECTgnutlsparam>>& for
+details.

 .wen
 .next
 .vindex "&$tls_peerdn$&"
 .wen
 .next
 .vindex "&$tls_peerdn$&"


@@ -24975,10 +24976,11 @@ separating fields; GnuTLS uses commas, in accordance with RFC 2253. This
 affects the value of the &$tls_peerdn$& variable.
 .next
 OpenSSL identifies cipher suites using hyphens as separators, for example:
 affects the value of the &$tls_peerdn$& variable.
 .next
 OpenSSL identifies cipher suites using hyphens as separators, for example:

-DES-CBC3-SHA. GnuTLS uses underscores, for example: RSA_ARCFOUR_SHA. What is
-more, OpenSSL complains if underscores are present in a cipher list. To make
-life simpler, Exim changes underscores to hyphens for OpenSSL and hyphens to
-underscores for GnuTLS when processing lists of cipher suites in the
+DES-CBC3-SHA. GnuTLS historically used underscores, for example:
+RSA_ARCFOUR_SHA. What is more, OpenSSL complains if underscores are present
+in a cipher list. To make life simpler, Exim changes underscores to hyphens
+for OpenSSL and passes the string unchanged to GnuTLS (expecting the library
+to handle its own older variants) when processing lists of cipher suites in the

 &%tls_require_ciphers%& options (the global option and the &(smtp)& transport
 option).
 .next
 &%tls_require_ciphers%& options (the global option and the &(smtp)& transport
 option).
 .next


@@ -24994,7 +24996,7 @@ implementation, then patches are welcome.
 .endlist
 
 
 .endlist
 
 

-.section "GnuTLS parameter computation" "SECID181"
+.section "GnuTLS parameter computation" "SECTgnutlsparam"

 .new
 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.
 .new
 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.


@@ -25028,14 +25030,14 @@ and letting Exim re-create it, you can generate new parameters using
 renaming. The relevant commands are something like this:
 .code
 # ls
 renaming. The relevant commands are something like this:
 .code
 # ls

-[ look for file; assume gnutls-params-1024 is the most recent ]
+[ look for file; assume gnutls-params-2236 is the most recent ]

 # rm -f new-params
 # touch new-params
 # chown exim:exim new-params
 # chmod 0600 new-params
 # rm -f new-params
 # touch new-params
 # chown exim:exim new-params
 # chmod 0600 new-params

-# certtool --generate-dh-params --bits 1024 >>new-params
+# certtool --generate-dh-params --bits 2236 >>new-params

 # chmod 0400 new-params
 # chmod 0400 new-params

-# mv new-params gnutls-params-1024
+# mv new-params gnutls-params-2236

 .endd
 If Exim never has to generate the parameters itself, the possibility of
 stalling is removed.
 .endd
 If Exim never has to generate the parameters itself, the possibility of
 stalling is removed.


@@ -25044,10 +25046,18 @@ The filename changed in Exim 4.80, to gain the -bits suffix.  The value which
 Exim will choose depends upon the version of GnuTLS in use.  For older GnuTLS,
 the value remains hard-coded in Exim as 1024.  As of GnuTLS 2.12.x, there is
 a way for Exim to ask for the "normal" number of bits for D-H public-key usage,
 Exim will choose depends upon the version of GnuTLS in use.  For older GnuTLS,
 the value remains hard-coded in Exim as 1024.  As of GnuTLS 2.12.x, there is
 a way for Exim to ask for the "normal" number of bits for D-H public-key usage,

-and Exim does so.  Exim thus removes itself from the policy decision, and the
-filename and bits used change as the GnuTLS maintainers change the value for
-their parameter &`GNUTLS_SEC_PARAM_NORMAL`&.  At the time of writing, this
-gives 2432 bits.
+and Exim does so.  This attempt to remove Exim from TLS policy decisions
+failed, as GnuTLS 2.12 returns a value higher than the current hard-coded limit
+of the NSS library.  Thus Exim gains the &%tls_dh_max_bits%& global option,
+which applies to all D-H usage, client or server.  If the value returned by
+GnuTLS is greater than &%tls_dh_max_bits%& then the value will be clamped down
+to &%tls_dh_max_bits%&.  The default value has been set at the current NSS
+limit, which is still much higher than Exim historically used.
+
+The filename and bits used will change as the GnuTLS maintainers change the
+value for their parameter &`GNUTLS_SEC_PARAM_NORMAL`&, as clamped by
+&%tls_dh_max_bits%&.  At the time of writing (mid 2012), GnuTLS 2.12 recommends
+2432 bits, while NSS is limited to 2236 bits.

 .wen
 
 
 .wen