NAME
tlsproxy - 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".
SEE ALSO
postscreen(8), Postfix zombie blocker
smtpd(8), Postfix SMTP server
postconf(5), configuration parameters
syslogd(5), 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