Merge branch 'master' of ssh://git.exim.org/home/git/exim

[users/heiko/exim.git] / doc / doc-txt / experimental-spec.txt

diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt
index 333307b74e9f1a7d78c5368ef2c572b1af19d340..e7a0d06682e95e507edf0d8c376bb1b6788e9a65 100644 (file)
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -762,87 +762,94 @@ b. Configure, somewhere before the DATA ACL, the control option to
 Transport post-delivery actions
 --------------------------------------------------------------
 
 Transport post-delivery actions
 --------------------------------------------------------------
 

-An arbitrary per-transport string can be expanded on successful delivery,
+An arbitrary per-transport string can be expanded upon various transport events

 and (for SMTP transports) a second string on deferrals caused by a host error.
 and (for SMTP transports) a second string on deferrals caused by a host error.

+Additionally a main-section configuration option can be expanded on some
+per-message events.

 This feature may be used, for example, to write exim internal log information
 (not available otherwise) into a database.
 
 This feature may be used, for example, to write exim internal log information
 (not available otherwise) into a database.
 

-In order to use the feature, you must set
+In order to use the feature, you must compile with

 
 EXPERIMENTAL_TPDA=yes
 
 in your Local/Makefile
 
 
 EXPERIMENTAL_TPDA=yes
 
 in your Local/Makefile
 

-and define the expandable strings in the runtime config file, to
-be executed at end of delivery.
+and define one or both of
+- the tpda_event_action option in the transport
+- the delivery_event_action
+to be expanded when the event fires.

 
 

-Additionally, there are 6 more variables, available at end of
-delivery:
+A new variable, $tpda_event, is set to the event type when the
+expansion is done.  The current list of events is:

 
 

-tpda_delivery_ip             IP of host, which has accepted delivery
-tpda_delivery_port           Port of remote host which has accepted delivery
-tpda_delivery_fqdn           FQDN of host, which has accepted delivery
-tpda_delivery_local_part     local part of address being delivered
-tpda_delivery_domain         domain part of address being delivered
-tpda_delivery_confirmation   SMTP confirmation message
+       msg:complete            main            per message
+       msg:delivery            transport       per recipient
+       msg:host:defer          transport       per attempt
+       msg:fail:delivery       main            per recipient
+       msg:fail:internal       main            per recipient
+       tcp:connect             transport       per connection
+       tcp:close               transport       per connection
+       tls:cert                transport       per certificate in verification chain
+       smtp:connect            transport       per connection

 
 

-In case of a deferral caused by a host-error:
-tpda_defer_errno             Error number
-tpda_defer_errstr            Error string possibly containing more details
+The expansion is called for all event types, and should use the $tpda_event
+value to decide when to act.  The variable data is a colon-separated
+list, describing an event tree.

 
 

-The $router_name and $transport_name variables are also usable.
+There is an auxilary variable, $tpda_data, for which the
+content is event_dependent:

 
 

+       msg:delivery            smtp confirmation mssage
+       msg:host:defer          error string
+       tls:cert                verification chain depth
+       smtp:connect            smtp banner

 
 

-To take action after successful deliveries, set the following option
-on any transport of interest.
+The msg:host:defer event populates one extra variable, $tpda_defer_errno.
+
+The following variables are likely to be useful depending on the event type:
+
+       router_name, transport_name
+       local_part, domain
+       host, host_address, host_port
+       tls_out_peercert
+       lookup_dnssec_authenticated, tls_out_dane
+       sending_ip_address, sending_port
+       message_exim_id

 
 

-tpda_delivery_action

 
 An example might look like:
 
 
 An example might look like:
 

-tpda_delivery_action = \
-${lookup pgsql {SELECT * FROM record_Delivery( \
+tpda_event_action = ${if = {msg:delivery}{$tpda_event} \
+{${lookup pgsql {SELECT * FROM record_Delivery( \

     '${quote_pgsql:$sender_address_domain}',\
     '${quote_pgsql:${lc:$sender_address_local_part}}', \
     '${quote_pgsql:$sender_address_domain}',\
     '${quote_pgsql:${lc:$sender_address_local_part}}', \

-    '${quote_pgsql:$tpda_delivery_domain}', \
-    '${quote_pgsql:${lc:$tpda_delivery_local_part}}', \
-    '${quote_pgsql:$tpda_delivery_ip}', \
-    '${quote_pgsql:${lc:$tpda_delivery_fqdn}}', \
-    '${quote_pgsql:$message_exim_id}')}}
-
-The string is expanded after the delivery completes and any
+    '${quote_pgsql:$domain}', \
+    '${quote_pgsql:${lc:$local_part}}', \
+    '${quote_pgsql:$host_address}', \
+    '${quote_pgsql:${lc:$host}}', \
+    '${quote_pgsql:$message_exim_id}')}} \
+} {}}
+
+The string is expanded for each of the supported events and any

 side-effects will happen.  The result is then discarded.
 Note that for complex operations an ACL expansion can be used.
 
 
 side-effects will happen.  The result is then discarded.
 Note that for complex operations an ACL expansion can be used.
 
 

-In order to log host deferrals, add the following option to an SMTP
-transport:
+The expansion of the tpda_event_action option should normally
+return an empty string.  Should it return anything else the
+following will be forced:

 
 

-tpda_host_defer_action
+       msg:delivery    (ignored)
+       msg:host:defer  (ignored)
+       msg:fail:delivery (ignored)
+       tcp:connect     do not connect
+       tcp:close       (ignored)
+       tls:cert        refuse verification
+       smtp:connect    close connection

 
 

-This is a private option of the SMTP transport. It is intended to
-log failures of remote hosts. It is executed only when exim has
-attempted to deliver a message to a remote host and failed due to
-an error which doesn't seem to be related to the individual
-message, sender, or recipient address.
-See section 47.2 of the exim documentation for more details on how
-this is determined.

 
 

-Example:

 
 

-tpda_host_defer_action = \
-${lookup mysql {insert into delivlog set \
-    msgid = '${quote_mysql:$message_exim_id}', \
-    senderlp = '${quote_mysql:${lc:$sender_address_local_part}}', \
-    senderdom = '${quote_mysql:$sender_address_domain}', \
-    delivlp = '${quote_mysql:${lc:$tpda_delivery_local_part}}', \
-    delivdom = '${quote_mysql:$tpda_delivery_domain}', \
-    delivip = '${quote_mysql:$tpda_delivery_ip}', \
-    delivport = '${quote_mysql:$tpda_delivery_port}', \
-    delivfqdn = '${quote_mysql:$tpda_delivery_fqdn}', \
-    deliverrno = '${quote_mysql:$tpda_defer_errno}', \
-    deliverrstr = '${quote_mysql:$tpda_defer_errstr}' \
-    }}

 
 
 Redis Lookup
 
 
 Redis Lookup


@@ -1171,6 +1178,10 @@ admins of the target server.   The attack surface presented
 by (a) is thought to be smaller than that of the set
 of root CAs.
 
 by (a) is thought to be smaller than that of the set
 of root CAs.
 

+It also allows the server to declare (implicitly) that
+connections to it should use TLS.  An MITM could simply
+fail to pass on a server's STARTTLS.
+

 DANE scales better than having to maintain (and
 side-channel communicate) copies of server certificates
 for every possible target server.  It also scales
 DANE scales better than having to maintain (and
 side-channel communicate) copies of server certificates
 for every possible target server.  It also scales


@@ -1181,7 +1192,10 @@ means not having to pay a CA for certificates.
 DANE requires a server operator to do three things:
 1) run DNSSEC.  This provides assurance to clients
 that DNS lookups they do for the server have not
 DANE requires a server operator to do three things:
 1) run DNSSEC.  This provides assurance to clients
 that DNS lookups they do for the server have not

-been tampered with.
+been tampered with.  The domain MX record applying
+to this server, its A record, its TLSA record and
+any associated CNAME records must all be covered by
+DNSSEC.

 2) add TLSA DNS records.  These say what the server
 certificate for a TLS connection should be.
 3) offer a server certificate, or certificate chain,
 2) add TLSA DNS records.  These say what the server
 certificate for a TLS connection should be.
 3) offer a server certificate, or certificate chain,


@@ -1192,12 +1206,12 @@ There are no changes to Exim specific to server-side
 operation of DANE.
 
 The TLSA record for the server may have "certificate
 operation of DANE.
 
 The TLSA record for the server may have "certificate

-usage" of DANE_TA(2) or DANE_EE(3).  The latter specifies
+usage" of DANE-TA(2) or DANE-EE(3).  The latter specifies

 the End Entity directly, i.e. the certificate involved
 is that of the server (and should be the sole one transmitted
 during the TLS handshake); this is appropriate for a
 single system, using a self-signed certificate.
 the End Entity directly, i.e. the certificate involved
 is that of the server (and should be the sole one transmitted
 during the TLS handshake); this is appropriate for a
 single system, using a self-signed certificate.

-  DANE_TA usage is effectively declaring a specific CA
+  DANE-TA usage is effectively declaring a specific CA

 to be used; this might be a private CA or a public,
 well-known one.  A private CA at simplest is just
 a self-signed certificate which is used to sign
 to be used; this might be a private CA or a public,
 well-known one.  A private CA at simplest is just
 a self-signed certificate which is used to sign


@@ -1209,43 +1223,84 @@ the entire certificate chain from CA to server-certificate.
 If a public CA is used then all clients must be primed with it
 (losing one advantage of DANE) - but the attack surface is
 reduced from all public CAs to that single CA.
 If a public CA is used then all clients must be primed with it
 (losing one advantage of DANE) - but the attack surface is
 reduced from all public CAs to that single CA.

-DANE_TA is commonly used for several services and/or
+DANE-TA is commonly used for several services and/or

 servers, each having a TLSA query-domain CNAME record,
 all of which point to a single TLSA record.
 
 The TLSA record should have a Selector field of SPKI(1)
 servers, each having a TLSA query-domain CNAME record,
 all of which point to a single TLSA record.
 
 The TLSA record should have a Selector field of SPKI(1)

-and a Matching Type fiels of SHA2-512(2).
+and a Matching Type field of SHA2-512(2).
+
+At the time of writing, https://www.huque.com/bin/gen_tlsa
+is useful for quickly generating TLSA records; and commands like
+
+  openssl x509 -in -pubkey -noout <certificate.pem \
+  | openssl rsa -outform der -pubin 2>/dev/null \
+  | openssl sha512 \
+  | awk '{print $2}'
+
+are workable for 4th-field hashes.

 
 

-For use with the DANE_TA model, server certificates
+For use with the DANE-TA model, server certificates

 must have a correct name (SubjectName or SubjectAltName).
 
 The use of OCSP-stapling should be considered, allowing
 for fast revocation of certificates (which would otherwise
 must have a correct name (SubjectName or SubjectAltName).
 
 The use of OCSP-stapling should be considered, allowing
 for fast revocation of certificates (which would otherwise

-be limited by the DNS TTL on the TLSA records).
+be limited by the DNS TTL on the TLSA records).  However,
+this is likely to only be usable with DANE-TA.  NOTE: the
+default of requesting OCSP for all hosts is modified iff
+DANE is in use, to:

 
 

+  hosts_request_ocsp = ${if or { {= {0}{$tls_out_tlsa_usage}} \
+                                {= {4}{$tls_out_tlsa_usage}} } \
+                         {*}{}}

 
 

-For client-side DANE there is a new smtp transport option,
-hosts_try_dane.  It does the obvious thing.
-[ may add a hosts_require_dane, too? ]
-[ should it be domain-based rather than host-based? ]
+The (new) variable $tls_out_tlsa_usage is a bitfield with
+numbered bits set for TLSA record usage codes.
+The zero above means DANE was not in use,
+the four means that only DANE-TA usage TLSA records were
+found. If the definition of hosts_request_ocsp includes the
+string "tls_out_tlsa_usage", they are re-expanded in time to
+control the OCSP request.
+
+This modification of hosts_request_ocsp is only done if
+it has the default value of "*".  Admins who change it, and
+those who use hosts_require_ocsp, should consider the interaction
+with DANE in their OCSP settings.
+
+
+For client-side DANE there are two new smtp transport options,
+hosts_try_dane and hosts_require_dane.  They do the obvious thing.
+[ should they be domain-based rather than host-based? ]

 
 DANE will only be usable if the target host has DNSSEC-secured
 MX, A and TLSA records.
 
 
 DANE will only be usable if the target host has DNSSEC-secured
 MX, A and TLSA records.
 

+A TLSA lookup will be done if either of the above options match
+and the host-lookup succeded using dnssec.
+If the TLSA lookup succeeds, a TLS connection will be required
+for the host.
+

 (TODO: specify when fallback happens vs. when the host is not used)
 
 If dane is in use the following transport options are ignored:
 (TODO: specify when fallback happens vs. when the host is not used)
 
 If dane is in use the following transport options are ignored:

+  hosts_require_tls

   tls_verify_hosts
   tls_try_verify_hosts
   tls_verify_certificates
   tls_crl
   tls_verify_cert_hostnames
   tls_verify_hosts
   tls_try_verify_hosts
   tls_verify_certificates
   tls_crl
   tls_verify_cert_hostnames

-  hosts_require_ocsp           (might rethink those two)
-  hosts_request_ocsp

 
 Currently dnssec_request_domains must be active (need to think about that)
 and dnssec_require_domains is ignored.
 
 
 Currently dnssec_request_domains must be active (need to think about that)
 and dnssec_require_domains is ignored.
 

+If verification was successful using DANE then the "CV" item
+in the delivery log line will show as "CV=dane".
+
+There is a new variable $tls_out_dane which will have "yes" if
+verification succeeded using DANE and "no" otherwise (only useful
+in combination with EXPERIMENTAL_TPDA), and a new variable
+$tls_out_tlsa_usage (detailed above).
+

 
 --------------------------------------------------------------
 End of file
 
 --------------------------------------------------------------
 End of file