NaCl(1)                     General Commands Manual                    NaCl(1)

       CurveCP — Message-handling programs

       curvecpclient [-q (optional)]  [-Q (optional)]  [-v (optional)]  [-c
       keydir(optional)]  [sname]  [pk]  [ip]  [port]  [ext]  [prog]

       This manual page documents briefly the CurveCP commands.

       A traditional UNIX-style server such as ftpd handles just one network
       connection, reading input from stdin and writing output to stdout. A
       "superserver" such as inetd or tcpserver listens for network
       connections and starts a separate server process for each connection.

       The CurveCP command-line tools have an extra level of modularity. The
       curvecpserver  superserver listens for network connections. For each
       connection, curvecpserver starts the curvecpmessage message handler;
       curvecpmessage then starts a server such as ftpd.  Then ftpd sends a
       stream of data to curvecpmessage, which in turn sends messages to
       curvecpserver, which encrypts and authenticates the messages and sends
       them inside network packets. At the same time curvecpclient receives
       network packets, verifies and decrypts messages inside the packets, and
       passes the messages to curvecpmessage; curvecpmessage sends a stream of
       data to ftpd.  The same curvecpmessage tool is also used by

       curvecpserver and curvecpclient can use programs other than
       curvecpmessage. Those programs can directly generate messages in the
       CurveCP message format without talking to separate tools such as ftpd;
       or they can support a completely different protocol that reuses
       CurveCP's cryptographic layer but transmits different kinds of

       This page explains what programmers have to do to write curvecpmessage
       replacements that talk to curvecpserver and curvecpclient.

Incoming messagess
       File descriptor 8 is a pipe. Read from this pipe a length byte n,
       between 1 and 68, and a 16*n-byte message. Repeat.  The pipe is set to
       non-blocking mode; be prepared for EAGAIN and EWOULDBLOCK, even in the
       middle of a message.

       This pipe reading must always be active. The curvecpclient and
       curvecpserver programs assume that every message is read immediately.
       If you can't handle a message immediately, read it and put it onto a
       queue. If you don't have queue space, throw the message away; this
       shouldn't cause trouble, since you have to be able to handle missing
       messages in any case.

Outgoing messagess
       File descriptor 9 is a pipe. Write to this pipe a length byte n,
       between 1 and 68, and a 16*n-byte message. Repeat.  The pipe is set to
       non-blocking mode; be prepared for EAGAIN and EWOULDBLOCK, even in the
       middle of a message.

       As a client, do not use length bytes above 40 until a message has
       arrived from the server. (The messages inside CurveCP Initiate packets
       are limited to 640 bytes.)

       The CurveCP server does not start until it has received a message from
       the client. Furthermore, the CurveCP server must receive this message
       within 60 seconds of the client starting up. (The CurveCP Initiate
       packet is valid for only 60 seconds after the corresponding CurveCP
       Cookie packet.)  This does not mean that the client must start sending
       messages immediately, but it does mean that waiting for more than a
       second to send a message is a bad idea.

       How to use curvecpclient:

       -q           optional
                 no error messages

       -Q           optional
                 print error messages (default)

       -v           optional
                 print extra information

       -c keydir           optional
                 use this public-key directory

       sname     server's name

       pk        server's public key

       ip        server's IP address

       port      server's UDP port

       ext       server's extension

       prog      run this client

       curvecpserver (1), curvecpmessage (1), inetd (8), tcpserver (1).

       This manual page was written by Sergiusz Pawlowicz for the Debian system (and may be used by
       others). The source of this page is a webpage .  Permission is granted to copy,
       distribute and/or modify this document under public domain.

       This manual page was rewritten for the Debian distribution because the
       original program does not have a manual page.