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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 allowlisted (including clients whose allowlist 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.



  

  
Append the system-supplied default Certification Authority certificates to
      the ones specified with *_tls_CApath or *_tls_CAfile.

  

  
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).

  

  
The OpenSSL cipherlist for "high" grade ciphers.

  

  
The OpenSSL cipherlist for "medium" or higher grade
    ciphers.

  

  
The OpenSSL cipherlist for "NULL" grade ciphers that provide
      authentication without encryption.

  

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

  

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

  

  
List or bit-mask of OpenSSL bug work-arounds to disable.

  

  
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 2.8..3.7:



  

  
The OpenSSL cipherlist for "low" or higher grade ciphers.

  

  
The OpenSSL cipherlist for "export" or higher grade
    ciphers.




Available in Postfix version 2.9 and later:



  

  
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:



  

  
Configure RFC7671 DANE TLSA digest algorithm agility.

  

  
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:



  

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




Available in Postfix version 3.0 and later:



  

  
Algorithm used to encrypt RFC5077 TLS session tickets.

  

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




Available in Postfix version 3.2 and later:



  

  
The prioritized list of elliptic curves supported by the Postfix SMTP
      client and server.




Available in Postfix version 3.4 and later:



  

  
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:



  

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




Available in Postfix version 3.8 and later:



  

  
The prioritized list of finite-field Diffie-Hellman ephemeral (FFDHE) key
      exchange groups supported by the Postfix SMTP client and server.




Available in Postfix 3.9, 3.8.1, 3.7.6, 3.6.10, 3.5.20 and
  later:



  

  
Optional configuration file with baseline OpenSSL settings.

  

  
The application name passed by Postfix to OpenSSL library initialization
      functions.








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.



  

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

  

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

  

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

  

  
Ask a remote SMTP client for a client certificate.

  

  
The verification depth for remote SMTP client certificates.

  

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

  

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

  

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

  

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

  

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

  

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

  

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

  

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

  

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

  

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

  

  
The message digest algorithm to construct remote SMTP client-certificate
      fingerprints.

  

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

  

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

  

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

  

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

  

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

  

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

  

  
With mandatory TLS encryption, require a trusted remote SMTP client
      certificate in order to allow TLS connections to proceed.

  

  
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.

  

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




Available in Postfix version 3.9 and later:



  

  
Request that remote SMTP clients send an RFC7250 raw public key instead of
      an X.509 certificate, when asking or requiring client authentication.








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:



  

  
A file containing CA certificates of root CAs trusted to sign either
      remote TLS server certificates or intermediate CA certificates.

  

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

  

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

  

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

  

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

  

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

  

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

  

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

  

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

  

  
The message digest algorithm used to construct remote TLS server
      certificate fingerprints.

  

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

  

  
The name of the parameter that provides the tlsproxy_client_loglevel
      value.

  

  
The verification depth for remote TLS server certificates.

  

  
Opportunistic mode: use TLS when a remote server announces TLS
    support.

  

  
Enforcement mode: require that SMTP servers use TLS encryption.

  

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




Available in Postfix version 3.4-3.6:



  

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

  

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




Available in Postfix version 3.7 and later:



  

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

  

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








OBSOLETE STARTTLS SUPPORT CONTROLS




These parameters are supported for compatibility with
    smtpd(8) legacy parameters.



  

  
Opportunistic TLS: announce STARTTLS support to remote SMTP clients, but
      do not require that clients use TLS encryption.

  

  
Mandatory TLS: announce STARTTLS support to remote SMTP clients, and
      require that clients use TLS encryption.

  

  
Opportunistic mode: use TLS when a remote server announces TLS
    support.

  

  
Enforcement mode: require that SMTP servers use TLS encryption.








RESOURCE CONTROLS





  

  
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





  

  
The default location of the Postfix main.cf and master.cf configuration
      files.

  

  
The process ID of a Postfix command or daemon process.

  

  
The process name of a Postfix command or daemon process.

  

  
The syslog facility of Postfix logging.

  

  
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:



  

  
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