Updated: 2021/Apr/14


TLSPROXY(8)                 System Manager's Manual                TLSPROXY(8)




NAME
       tlsproxy - Postfix TLS proxy

SYNOPSIS
       tlsproxy [generic Postfix daemon options]

DESCRIPTION
       The tlsproxy(8) server implements a two-way TLS proxy. It is used by
       the postscreen(8) server to talk SMTP-over-TLS with remote SMTP clients
       that are not whitelisted (including clients whose whitelist status has
       expired), and by the smtp(8) client to support TLS connection reuse,
       but it should also work for non-SMTP protocols.

       Although one tlsproxy(8) process can serve multiple sessions at the
       same time, it is a good idea to allow the number of processes to
       increase with load, so that the service remains responsive.

PROTOCOL EXAMPLE
       The example below concerns postscreen(8). However, the tlsproxy(8)
       server is agnostic of the application protocol, and the example is
       easily adapted to other applications.

       After receiving a valid remote SMTP client STARTTLS command, the
       postscreen(8) server sends the remote SMTP client endpoint string, the
       requested role (server), and the requested timeout to tlsproxy(8).
       postscreen(8) then receives a "TLS available" indication from
       tlsproxy(8).  If the TLS service is available, postscreen(8) sends the
       remote SMTP client file descriptor to tlsproxy(8), and sends the
       plaintext 220 greeting to the remote SMTP client.  This triggers TLS
       negotiations between the remote SMTP client and tlsproxy(8).  Upon
       completion of the TLS-level handshake, tlsproxy(8) translates between
       plaintext from/to postscreen(8) and ciphertext to/from the remote SMTP
       client.

SECURITY
       The tlsproxy(8) server is moderately security-sensitive.  It talks to
       untrusted clients on the network. The process can be run chrooted at
       fixed low privilege.

DIAGNOSTICS
       Problems and transactions are logged to syslogd(8) or postlogd(8).

CONFIGURATION PARAMETERS
       Changes to main.cf are not picked up automatically, as tlsproxy(8)
       processes may run for a long time depending on mail server load.  Use
       the command "postfix reload" to speed up a change.

       The text below provides only a parameter summary. See postconf(5) for
       more details including examples.

STARTTLS GLOBAL CONTROLS
       The following settings are global and therefore cannot be overruled by
       information specified in a tlsproxy(8) client request.

       tls_append_default_CA (no)
              Append the system-supplied default Certification Authority
              certificates to the ones specified with *_tls_CApath or
              *_tls_CAfile.

       tls_daemon_random_bytes (32)
              The number of pseudo-random bytes that an smtp(8) or smtpd(8)
              process requests from the tlsmgr(8) server in order to seed its
              internal pseudo random number generator (PRNG).

       tls_high_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "high" grade ciphers.

       tls_medium_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "medium" or higher grade ciphers.

       tls_low_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "low" or higher grade ciphers.

       tls_export_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "export" or higher grade ciphers.

       tls_null_cipherlist (eNULL:!aNULL)
              The OpenSSL cipherlist for "NULL" grade ciphers that provide
              authentication without encryption.

       tls_eecdh_strong_curve (prime256v1)
              The elliptic curve used by the Postfix SMTP server for sensibly
              strong ephemeral ECDH key exchange.

       tls_eecdh_ultra_curve (secp384r1)
              The elliptic curve used by the Postfix SMTP server for maximally
              strong ephemeral ECDH key exchange.

       tls_disable_workarounds (see 'postconf -d' output)
              List or bit-mask of OpenSSL bug work-arounds to disable.

       tls_preempt_cipherlist (no)
              With SSLv3 and later, use the Postfix SMTP server's cipher
              preference order instead of the remote client's cipher
              preference order.

       Available in Postfix version 2.9 and later:

       tls_legacy_public_key_fingerprints (no)
              A temporary migration aid for sites that use certificate
              public-key fingerprints with Postfix 2.9.0..2.9.5, which use an
              incorrect algorithm.

       Available in Postfix version 2.11-3.1:

       tls_dane_digest_agility (on)
              Configure RFC7671 DANE TLSA digest algorithm agility.

       tls_dane_trust_anchor_digest_enable (yes)
              Enable support for RFC 6698 (DANE TLSA) DNS records that contain
              digests of trust-anchors with certificate usage "2".

       Available in Postfix version 2.11 and later:

       tlsmgr_service_name (tlsmgr)
              The name of the tlsmgr(8) service entry in master.cf.

       Available in Postfix version 3.0 and later:

       tls_session_ticket_cipher (Postfix >= 3.0: aes-256-cbc, Postfix < 3.0:
       aes-128-cbc)
              Algorithm used to encrypt RFC5077 TLS session tickets.

       openssl_path (openssl)
              The location of the OpenSSL command line program openssl(1).

       Available in Postfix version 3.2 and later:

       tls_eecdh_auto_curves (see 'postconf -d' output)
              The prioritized list of elliptic curves supported by the Postfix
              SMTP client and server.

       Available in Postfix version 3.4 and later:

       tls_server_sni_maps (empty)
              Optional lookup tables that map names received from remote SMTP
              clients via the TLS Server Name Indication (SNI) extension to
              the appropriate keys and certificate chains.

       Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and later:

       tls_fast_shutdown_enable (yes)
              A workaround for implementations that hang Postfix while
              shutting down a TLS session, until Postfix times out.

STARTTLS SERVER CONTROLS
       These settings are clones of Postfix SMTP server settings.  They allow
       tlsproxy(8) to load the same certificate and private key information as
       the Postfix SMTP server, before dropping privileges, so that the key
       files can be kept read-only for root. These settings can currently not
       be overruled by information in a tlsproxy(8) client request, but that
       limitation may be removed in a future version.

       tlsproxy_tls_CAfile ($smtpd_tls_CAfile)
              A file containing (PEM format) CA certificates of root CAs
              trusted to sign either remote SMTP client certificates or
              intermediate CA certificates.

       tlsproxy_tls_CApath ($smtpd_tls_CApath)
              A directory containing (PEM format) CA certificates of root CAs
              trusted to sign either remote SMTP client certificates or
              intermediate CA certificates.

       tlsproxy_tls_always_issue_session_ids
       ($smtpd_tls_always_issue_session_ids)
              Force the Postfix tlsproxy(8) server to issue a TLS session id,
              even when TLS session caching is turned off.

       tlsproxy_tls_ask_ccert ($smtpd_tls_ask_ccert)
              Ask a remote SMTP client for a client certificate.

       tlsproxy_tls_ccert_verifydepth ($smtpd_tls_ccert_verifydepth)
              The verification depth for remote SMTP client certificates.

       tlsproxy_tls_cert_file ($smtpd_tls_cert_file)
              File with the Postfix tlsproxy(8) server RSA certificate in PEM
              format.

       tlsproxy_tls_ciphers ($smtpd_tls_ciphers)
              The minimum TLS cipher grade that the Postfix tlsproxy(8) server
              will use with opportunistic TLS encryption.

       tlsproxy_tls_dcert_file ($smtpd_tls_dcert_file)
              File with the Postfix tlsproxy(8) server DSA certificate in PEM
              format.

       tlsproxy_tls_dh1024_param_file ($smtpd_tls_dh1024_param_file)
              File with DH parameters that the Postfix tlsproxy(8) server
              should use with non-export EDH ciphers.

       tlsproxy_tls_dh512_param_file ($smtpd_tls_dh512_param_file)
              File with DH parameters that the Postfix tlsproxy(8) server
              should use with export-grade EDH ciphers.

       tlsproxy_tls_dkey_file ($smtpd_tls_dkey_file)
              File with the Postfix tlsproxy(8) server DSA private key in PEM
              format.

       tlsproxy_tls_eccert_file ($smtpd_tls_eccert_file)
              File with the Postfix tlsproxy(8) server ECDSA certificate in
              PEM format.

       tlsproxy_tls_eckey_file ($smtpd_tls_eckey_file)
              File with the Postfix tlsproxy(8) server ECDSA private key in
              PEM format.

       tlsproxy_tls_eecdh_grade ($smtpd_tls_eecdh_grade)
              The Postfix tlsproxy(8) server security grade for ephemeral
              elliptic-curve Diffie-Hellman (EECDH) key exchange.

       tlsproxy_tls_exclude_ciphers ($smtpd_tls_exclude_ciphers)
              List of ciphers or cipher types to exclude from the tlsproxy(8)
              server cipher list at all TLS security levels.

       tlsproxy_tls_fingerprint_digest ($smtpd_tls_fingerprint_digest)
              The message digest algorithm to construct remote SMTP
              client-certificate fingerprints.

       tlsproxy_tls_key_file ($smtpd_tls_key_file)
              File with the Postfix tlsproxy(8) server RSA private key in PEM
              format.

       tlsproxy_tls_loglevel ($smtpd_tls_loglevel)
              Enable additional Postfix tlsproxy(8) server logging of TLS
              activity.

       tlsproxy_tls_mandatory_ciphers ($smtpd_tls_mandatory_ciphers)
              The minimum TLS cipher grade that the Postfix tlsproxy(8) server
              will use with mandatory TLS encryption.

       tlsproxy_tls_mandatory_exclude_ciphers
       ($smtpd_tls_mandatory_exclude_ciphers)
              Additional list of ciphers or cipher types to exclude from the
              tlsproxy(8) server cipher list at mandatory TLS security levels.

       tlsproxy_tls_mandatory_protocols ($smtpd_tls_mandatory_protocols)
              The SSL/TLS protocols accepted by the Postfix tlsproxy(8) server
              with mandatory TLS encryption.

       tlsproxy_tls_protocols ($smtpd_tls_protocols)
              List of TLS protocols that the Postfix tlsproxy(8) server will
              exclude or include with opportunistic TLS encryption.

       tlsproxy_tls_req_ccert ($smtpd_tls_req_ccert)
              With mandatory TLS encryption, require a trusted remote SMTP
              client certificate in order to allow TLS connections to proceed.

       tlsproxy_tls_security_level ($smtpd_tls_security_level)
              The SMTP TLS security level for the Postfix tlsproxy(8) server;
              when a non-empty value is specified, this overrides the obsolete
              parameters smtpd_use_tls and smtpd_enforce_tls.

       tlsproxy_tls_chain_files ($smtpd_tls_chain_files)
              Files with the Postfix tlsproxy(8) server keys and certificate
              chains in PEM format.

STARTTLS CLIENT CONTROLS
       These settings are clones of Postfix SMTP client settings.  They allow
       tlsproxy(8) to load the same certificate and private key information as
       the Postfix SMTP client, before dropping privileges, so that the key
       files can be kept read-only for root. Some settings may be overruled by
       information in a tlsproxy(8) client request.

       Available in Postfix version 3.4 and later:

       tlsproxy_client_CAfile ($smtp_tls_CAfile)
              A file containing CA certificates of root CAs trusted to sign
              either remote TLS server certificates or intermediate CA
              certificates.

       tlsproxy_client_CApath ($smtp_tls_CApath)
              Directory with PEM format Certification Authority certificates
              that the Postfix tlsproxy(8) client uses to verify a remote TLS
              server certificate.

       tlsproxy_client_chain_files ($smtp_tls_chain_files)
              Files with the Postfix tlsproxy(8) client keys and certificate
              chains in PEM format.

       tlsproxy_client_cert_file ($smtp_tls_cert_file)
              File with the Postfix tlsproxy(8) client RSA certificate in PEM
              format.

       tlsproxy_client_key_file ($smtp_tls_key_file)
              File with the Postfix tlsproxy(8) client RSA private key in PEM
              format.

       tlsproxy_client_dcert_file ($smtp_tls_dcert_file)
              File with the Postfix tlsproxy(8) client DSA certificate in PEM
              format.

       tlsproxy_client_dkey_file ($smtp_tls_dkey_file)
              File with the Postfix tlsproxy(8) client DSA private key in PEM
              format.

       tlsproxy_client_eccert_file ($smtp_tls_eccert_file)
              File with the Postfix tlsproxy(8) client ECDSA certificate in
              PEM format.

       tlsproxy_client_eckey_file ($smtp_tls_eckey_file)
              File with the Postfix tlsproxy(8) client ECDSA private key in
              PEM format.

       tlsproxy_client_fingerprint_digest ($smtp_tls_fingerprint_digest)
              The message digest algorithm used to construct remote TLS server
              certificate fingerprints.

       tlsproxy_client_loglevel ($smtp_tls_loglevel)
              Enable additional Postfix tlsproxy(8) client logging of TLS
              activity.

       tlsproxy_client_loglevel_parameter (smtp_tls_loglevel)
              The name of the parameter that provides the
              tlsproxy_client_loglevel value.

       tlsproxy_client_scert_verifydepth ($smtp_tls_scert_verifydepth)
              The verification depth for remote TLS server certificates.

       tlsproxy_client_security_level ($smtp_tls_security_level)
              The default TLS security level for the Postfix tlsproxy(8)
              client.

       tlsproxy_client_policy_maps ($smtp_tls_policy_maps)
              Optional lookup tables with the Postfix tlsproxy(8) client TLS
              security policy by next-hop destination.

       tlsproxy_client_use_tls ($smtp_use_tls)
              Opportunistic mode: use TLS when a remote server announces TLS
              support.

       tlsproxy_client_enforce_tls ($smtp_enforce_tls)
              Enforcement mode: require that SMTP servers use TLS encryption.

       tlsproxy_client_per_site ($smtp_tls_per_site)
              Optional lookup tables with the Postfix tlsproxy(8) client TLS
              usage policy by next-hop destination and by remote TLS server
              hostname.

OBSOLETE STARTTLS SUPPORT CONTROLS
       These parameters are supported for compatibility with smtpd(8) legacy
       parameters.

       tlsproxy_use_tls ($smtpd_use_tls)
              Opportunistic TLS: announce STARTTLS support to remote SMTP
              clients, but do not require that clients use TLS encryption.

       tlsproxy_enforce_tls ($smtpd_enforce_tls)
              Mandatory TLS: announce STARTTLS support to remote SMTP clients,
              and require that clients use TLS encryption.

RESOURCE CONTROLS

       tlsproxy_watchdog_timeout (10s)
              How much time a tlsproxy(8) process may take to process local or
              remote I/O before it is terminated by a built-in watchdog timer.

MISCELLANEOUS CONTROLS

       config_directory (see 'postconf -d' output)
              The default location of the Postfix main.cf and master.cf
              configuration files.

       process_id (read-only)
              The process ID of a Postfix command or daemon process.

       process_name (read-only)
              The process name of a Postfix command or daemon process.

       syslog_facility (mail)
              The syslog facility of Postfix logging.

       syslog_name (see 'postconf -d' output)
              A prefix that is prepended to the process name in syslog
              records, so that, for example, "smtpd" becomes "prefix/smtpd".

       Available in Postfix 3.3 and later:

       service_name (read-only)
              The master.cf service name of a Postfix daemon process.

SEE ALSO
       postscreen(8), Postfix zombie blocker
       smtpd(8), Postfix SMTP server
       postconf(5), configuration parameters
       postlogd(8), Postfix logging
       syslogd(8), system logging

LICENSE
       The Secure Mailer license must be distributed with this software.

HISTORY
       This service was introduced with Postfix version 2.8.

AUTHOR(S)
       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA



                                                                   TLSPROXY(8)