X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/dc2d885ade485ba0d631bb7dea251e8558922648..4a7dca52352d0976f200b89a50825433b7551554:/doc/doc-txt/experimental-spec.txt diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt index 5193f1729..68366a4a9 100644 --- a/doc/doc-txt/experimental-spec.txt +++ b/doc/doc-txt/experimental-spec.txt @@ -292,10 +292,11 @@ These four steps are explained in more details below. -SRS (Sender Rewriting Scheme) Support +SRS (Sender Rewriting Scheme) Support (using libsrs_alt) -------------------------------------------------------------- +See also the main docs, for an alternative native support implementation. -Exiscan currently includes SRS support via Miles Wilton's +Exim can be built with SRS support using Miles Wilton's libsrs_alt library. The current version of the supported library is 0.5, there are reports of 1.0 working. @@ -308,10 +309,14 @@ https://opsec.eu/src/srs/ Unpack the tarball, then refer to MTAs/README.EXIM to proceed. You need to set -EXPERIMENTAL_SRS=yes +EXPERIMENTAL_SRS_ALT=yes in your Local/Makefile. +The built-in support, included by SUPPORT_SRS, +shuold *not* be enabled if you wish to use the libsrs_alt +version. + The following main-section options become available: srs_config string srs_hashlength int @@ -461,52 +466,6 @@ Rationale: Note that non-RFC-documented field names and data types are used. -LMDB Lookup support -------------------- -LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store. -It is modeled loosely on the BerkeleyDB API. You should read about the feature -set as well as operation modes at https://symas.com/products/lightning-memory-mapped-database/ - -LMDB single key lookup support is provided by linking to the LMDB C library. -The current implementation does not support writing to the LMDB database. - -Visit https://github.com/LMDB/lmdb to download the library or find it in your -operating systems package repository. - -If building from source, this description assumes that headers will be in -/usr/local/include, and that the libraries are in /usr/local/lib. - -1. In order to build exim with LMDB lookup support add or uncomment - -EXPERIMENTAL_LMDB=yes - -to your Local/Makefile. (Re-)build/install exim. exim -d should show -Experimental_LMDB in the line "Support for:". - -EXPERIMENTAL_LMDB=yes -LDFLAGS += -llmdb -# CFLAGS += -I/usr/local/include -# LDFLAGS += -L/usr/local/lib - -The first line sets the feature to include the correct code, and -the second line says to link the LMDB libraries into the -exim binary. The commented out lines should be uncommented if you -built LMDB from source and installed in the default location. -Adjust the paths if you installed them elsewhere, but you do not -need to uncomment them if an rpm (or you) installed them in the -package controlled locations (/usr/include and /usr/lib). - -2. Create your LMDB files, you can use the mdb_load utility which is -part of the LMDB distribution our your favourite language bindings. - -3. Add the single key lookups to your exim.conf file, example lookups -are below. - -${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}} -${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}fail} -${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}} - - Queuefile transport ------------------- Queuefile is a pseudo transport which does not perform final delivery. @@ -679,62 +638,32 @@ used via the transport in question. +Dovecot authenticator via inet socket +-------------------------------------------------------------- +If Dovecot is configured similar to :- + +service auth { +... +#SASL + inet_listener { + name = exim + port = 12345 + } +... +} + +then an Exim authenticator can be configured :- + + dovecot-plain: + driver = dovecot + public_name = PLAIN + server_socket = dovecot_server_name 12345 + server_tls = true + server_set_id = $auth1 + +If the server_socket does not start with a / it is taken as a hostname (or IP); +and a whitespace-separated port number must be given. -TLS Session Resumption ----------------------- -TLS Session Resumption for TLS 1.2 and TLS 1.3 connections can be used (defined -in RFC 5077 for 1.2). The support for this can be included by building with -EXPERIMENTAL_TLS_RESUME defined. This requires GnuTLS 3.6.3 or OpenSSL 1.1.1 -(or later). - -Session resumption (this is the "stateless" variant) involves the server sending -a "session ticket" to the client on one connection, which can be stored by the -client and used for a later session. The ticket contains sufficient state for -the server to reconstruct the TLS session, avoiding some expensive crypto -calculation and one full packet roundtrip time. - -Operational cost/benefit: - The extra data being transmitted costs a minor amount, and the client has - extra costs in storing and retrieving the data. - - In the Exim/Gnutls implementation the extra cost on an initial connection - which is TLS1.2 over a loopback path is about 6ms on 2017-laptop class hardware. - The saved cost on a subsequent connection is about 4ms; three or more - connections become a net win. On longer network paths, two or more - connections will have an average lower startup time thanks to the one - saved packet roundtrip. TLS1.3 will save the crypto cpu costs but not any - packet roundtrips. - - Since a new hints DB is used, the hints DB maintenance should be updated - to additionally handle "tls". - -Security aspects: - The session ticket is encrypted, but is obviously an additional security - vulnarability surface. An attacker able to decrypt it would have access - all connections using the resumed session. - The session ticket encryption key is not committed to storage by the server - and is rotated regularly (OpenSSL: 1hr, and one previous key is used for - overlap; GnuTLS 6hr but does not specify any overlap). - Tickets have limited lifetime (2hr, and new ones issued after 1hr under - OpenSSL. GnuTLS 2hr, appears to not do overlap). - - There is a question-mark over the security of the Diffie-Helman parameters - used for session negotiation. TBD. q-value; cf bug 1895 - -Observability: - New log_selector "tls_resumption", appends an asterisk to the tls_cipher "X=" - element. - - Variables $tls_{in,out}_resumption have bits 0-4 indicating respectively - support built, client requested ticket, client offered session, - server issued ticket, resume used. A suitable decode list is provided - in the builtin macro _RESUME_DECODE for ${listextract {}{}}. - -Issues: - In a resumed session: - $tls_{in,out}_cipher will have values different to the original (under GnuTLS) - $tls_{in,out}_ocsp will be "not requested" or "no response", and - hosts_require_ocsp will fail --------------------------------------------------------------