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.

       -user=username
           Used when couriertls needs to get started as root and fork off a root child process (see below),
           before dropping root and running as the specified user.

       -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. This is done before the -user option drops root and couriertls continues to run as the
       indicated user. 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_PRIVATE_KEYFILE=filename
           SSL/TLS private key for decrypting client data.  TLS_PRIVATE_KEY is optional because
           <term>TLS_CERTFILE</term> is generated including cert and private key both.  filename must not be
           world-readable, and must be accessible without a pass-phrase, i.e. it must not be encrypted.

       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].

AUTHOR

       Sam Varshavchik
           Author

NOTES

        1. couriertcpd(1)
           http://www.courier-mta.org/couriertcpd.html

        2. courier(8)
           http://www.courier-mta.org/courier.html