tlsproxy(8) Postfix TLS proxy

SYNOPSIS

tlsproxy [generic Postfix daemon options]

DESCRIPTION

The tlsproxy(8) server implements a server-side TLS proxy. It is used by postscreen(8) to talk SMTP-over-TLS with remote SMTP clients that are not whitelisted (including clients whose whitelist status has expired), 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).





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 SUPPORT CONTROLS









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.




Available in Postfix version 2.11 and later:



tlsmgr_service_name (tlsmgr)

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








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)

The mail system name that is prepended to the process name in syslog
records, so that "smtpd" becomes, for example, "postfix/smtpd".








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





      

    



  









  

  


    

      
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