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couriertls - the Courier mail server TLS/SSL protocol wrapper


couriertls [option...] {program} {arg...}


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.


-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.

Read and write data to encrypt via SSL/TLS from file descriptor 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

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.

File descriptor n is the network connection where SSL/TLS encryption is to be used.

Negotiate server side of the SSL/TLS connection. If this option is not used the client
side of the SSL/TLS connection is negotiated.


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 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).

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.


couriertls reads the following environment variables in order to configure the SSL/TLS

Set the protocol version. The possible versions are: SSL2, SSL3, TLS1.

Optionally set the list of protocol ciphers to be used. See OpenSSL´s documentation
for more information.

Currently not implemented, and reserved for future use. This is supposed to be an
inactivity timeout, but it´s not yet implemented.

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.

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.

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

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).

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