NAME
couriertls - the Courier mail server TLS/SSL protocol wrapper
SYNOPSIS
couriertls [option...] {program} {arg...}
DESCRIPTION
The couriertls program is used by applications to encrypt a network
connection using SSL/TLS, without having the application deal with the
gory details of SSL/TLS. couriertls is used by the Courier mail server
IMAP and ESMTP servers.
couriertls is not usually run directly from the commandline. An
application typically creates a network connection, then runs
couriertls with appropriate options to encrypt the network connection
with SSL/TLS.
OPTIONS
-host=host, -port=port
These options are used instead of -remotefd, mostly for debugging
purposes. couriertls connects to the specified server and
immediately starts SSL/TLS negotation when the connection is
established.
-localfd=n
Read and write data to encrypt via SSL/TLS from file descriptor n.
-statusfd=n
Write SSL negotiation status to file descriptor n, then close this
file descriptor. If SSL starts succesfully, reading on n gets an
immediate EOF. Otherwise, a single line of text - the error message
- is read; the file descriptor is closed; and couriertls
terminates.
-printx509=n
Print the x509 certificate on file descriptor n then close it. The
x509 certificate is printed before SSL/TLS encryption starts. The
application may immediately read the certificate after running
couriertls, until the file descriptor is closed.
-remotefd=n
File descriptor n is the network connection where SSL/TLS
encryption is to be used.
-server
Negotiate server side of the SSL/TLS connection. If this option is
not used the client side of the SSL/TLS connection is negotiated.
-tcpd
couriertls is being called from couriertcpd, and the remote socket
is present on descriptors 0 and 1. -tcpd means, basically, the
same as -remotefd=0, but couriertls closes file descriptor 1, and
redirects file descriptor 1 to file descriptor 2.
-verify=domain
Verify that domain is set in the CN field of the trusted X.509
certificate presented by the SSL/TLS peer. TLS_TRUSTCERTS must be
initialized (see below), and the certificate must be signed by one
of the trusted certificates. The CN field can contain a wildcard:
CN=*.example will match -verify=foo.example.com. For SSL/TLS
clients, TLS_VERIFYPEER must be set to PEER (see below).
-protocol=proto
Send proto protocol commands before enabling SSL/TLS on the remote
connection. proto is either "smtp" or "imap". This is a debugging
option that can be used to troubleshoot SSL/TLS with a remote IMAP
or SMTP server.
If the -remotefd=n option is not specified, the rest of the command
line specifies the program to run -- and its arguments -- whose
standard input and output is encrypted via SSL/TLS over the network
connection. If the program is not specified, the standard input and
output of couriertls itself is encrypted.
ENVIRONMENT VARIABLES
couriertls reads the following environment variables in order to
configure the SSL/TLS protocol:
TLS_PROTOCOL=proto
Set the protocol version. The possible versions are: SSL2, SSL3,
TLS1.
TLS_CIPHER_LIST=cipherlist
Optionally set the list of protocol ciphers to be used. See
OpenSSL´s documentation for more information.
TLS_TIMEOUT=seconds
Currently not implemented, and reserved for future use. This is
supposed to be an inactivity timeout, but it´s not yet implemented.
TLS_DHCERTFILE=filename
PEM file that stores our Diffie-Hellman cipher pair. When OpenSSL
is compiled to use Diffie-Hellman ciphers instead of RSA you must
generate a DH pair that will be used. In most situations the DH
pair is to be treated as confidential, and filename must not be
world-readable.
TLS_CERTFILE=filename
The certificate to use. TLS_CERTFILE is required for SSL/TLS
servers, and is optional for SSL/TLS clients. filename must not be
world-readable.
TLS_TRUSTCERTS=pathname
Load trusted root certificates from pathname. pathname can be a
file or a directory. If a file, the file should contain a list of
trusted certificates, in PEM format. If a directory, the directory
should contain the trusted certificates, in PEM format, one per
file and hashed using OpenSSL´s c_rehash script. TLS_TRUSTCERTS is
used by SSL/TLS clients (by specifying the -domain option) and by
SSL/TLS servers (TLS_VERIFYPEER is set to PEER or REQUIREPEER).
TLS_VERIFYPEER=level
Whether to verify peer´s X.509 certificate. The exact meaning of
this option depends upon whether couriertls is used in the client
or server mode. In server mode: NONE - do not request an X.509
certificate from the client; PEER - request an optional X.509
certificate from the client, if the client returns one, the SSL/TLS
connection is shut down unless the certificate is signed by a
trusted certificate authority (see TLS_TRUSTCERTS); REQUIREPEER -
same as PEER, except that the SSL/TLS connects is also shut down if
the client does not return the optional X.509 certificate. In
client mode: NONE - ignore the server´s X.509 certificate; PEER -
verify the server´s X.509 certificate according to the -domain
option, (see above).
SEE ALSO
couriertcpd(1)[1], courier(8)[2].
NOTES
1. couriertcpd(1)
[set $man.base.url.for.relative.links]/couriertcpd.html
2. courier(8)
[set $man.base.url.for.relative.links]/courier.html