Use SSL with PennMUSH
                           Revised: 11 August 2003


As of version 1.7.7p17, PennMUSH supports SSL connections when linked
with the OpenSSL library (http://www.openssl.org). The following
features are supported:

  * Encrypted sessions using SSLv2, SSLv3, and TLSv1 protocols
    with ephemeral Diffie-Hellman keying.
  * Authentication of the server via certificates
  * Authentication of the clients via certificates

This document explains how to use SSL with PennMUSH, and covers
the following issues:

   I. An SSL overview
   II. Compiling with OpenSSL
   III. Mush configuration overview
   IV. Installing a server certificate (required)
   V. Using client certificates for authentication (optional)
   VI. Legal issues


I. An SSL overview

  When an SSL client connects to an SSL server, it performs a 
  "handshake" that looks something like this:

  Client says hello, offers a menu of cipher options
  Server says hello, selects a cipher.
  Server presents its certificate, requests a client certificate
  Client presents a certificate (or not)
  Client and server exchange cryptographic session keys

  The server is identified to the client by a certificate, an encoded
  text that gives the server's name and other attributes and is
  signed by a certifying authority (CA), like Verisign. The client
  checks that the signature is by a CA that it trusts, and may perform
  other validation on the certificate (e.g., checking that the hostname
  in the certificate matches the hostname it's trying to connect to).

  If the client chooses to present a certificate (or is required to
  by the server), the server will likewise attempt to validate it
  against its list of trusted CAs, and may perform other verification.

  Once session keys have been exchanged, the client and server can
  communicate secure from eavesdropping.

II. Compiling with OpenSSL

  The Configure script distributed with PennMUSH automatically detects
  the OpenSSL libraries (libssl and libcrypto) and attempts to link
  them into the executable, defining HAS_OPENSSL in config.h.
  If you have SSL libraries but wish to avoid linking with them,
  give the -D no_openssl argument to Configure when you run it.

  You can compile the OpenSSL libraries yourself from source code
  at http://www.openssl.org.

  OpenSSL can also be compiled on Windows, and you could add its
  libraries to the PennMUSH project file and link it in that way.
  Noltar has done this succesfully; it requires compiling both
  OpenSSL and PennMUSH in /MD (multithread dll) mode.

III. Mush configuration overview

  mush.cnf includes three directives that configure the SSL support:

  ssl_port selects the port number for the MUSH to listen for SSL 
  connections. Any port number other than the MUSH's ordinary listening
  port can be chosen (subject, of course, to other system restrictions
  on choosing port numbers).

  ssl_private_key_file specifies the name of the file (relative to the
  game/ directory if it's not an absolute path) that contains the
  MUSH server's certificate and private key. See section IV below.

  ssl_ca_file specifies the name of the file that contains certificates
  of trusted certificate authorities. OpenSSL distributes a file containing
  the best known CAs that is suitable for use here.  If you comment this
  out, client certificate checking will not be performed.

  ssl_require_client_cert is a boolean option that controls whether the
  MUSH server will require clients to present valid (that is, signed by
  a CA for which ssl_ca_file holds a certificate) certificates in order
  to connect. As no mud clients currently do this, you probably want it 
  off. See section V below.

IV. Installing a server certificate

  SSL support requires that the MUSH present a server certificate (except
  as discussed below).  You must create a file containing the certificate
  and the associated private key (stripped of any passphrase protection)
  and point the ssl_private_key_file directive at this file. This file
  should only be readable by the MUSH account!

  How do you get such a certificate and private key? Here are the
  steps you can use with openssl's command-line tool:

  1. Generate a certificate signing request (mymush.csr) and a private key
     (temp.key). You will be asked to answer several questions. 
     Be sure the Common Name you request is your MUSH's hostname:

     $ openssl req -new -out mymush.csr -keyout temp.key -passin pass:foobar

  2. Strip the passphrase off of your private key, leaving you 
     with an unpassworded mymush.key file:
 
     $ openssl rsa -in temp.key -out mymush.key -passin pass:foobar
     $ rm temp.key

  3. Send the certificate signing request to a certifying authority
     to have it signed. If the CA needs the private key, send the
     passphrased one. The CA will send you back a certificate
     which you save to a file (mymush.crt)

  4. Concatenate the certificate with the unpassworded private key and 
     use this as the ssl_private_key_file:

     $ cat mymush.key >> mymush.crt

  Commercial CAs like Verisign sign certificates for a yearly or two-yearly
  fee that is probably too steep for most MUSH Gods. Instead of using
  a commercial CA, you can generate a self-signed certificate by 
  changing step 1 above to:

  $ openssl req -new -x509 -days 3650 -out mymush.crt -keyout temp.key -passin pass:foobar

  A self-signed certificate is free, but clients that attempt to validate
  certificates will fail to validate a self-signed certificate unless
  the user manually installs the certificate in their client and configures
  it to be trusted. How to do that is beyond the scope of this document,
  and highly client-dependent.

  Another option is to skip the use of a certificate altogether.
  If you don't provide an ssl_private_key_file, the server will only
  accept connections from clients that are willing to use the
  anonymous Diffie-Hellman cipher; it is unknown which clients
  are configured to offer this. This provides clients with no 
  security that they are actually connecting to your server, and
  exposes them to a man-in-the-middle attack, but requires no
  work on your part at all.

  Hosting providers or other parties may one day provide CA service
  to PennMUSHes for free. When they do, you'll have to install those
  CAs' certificates in your client as trusted in order to have the
  server's certificate validate, but if a few CAs certify many MUSHes,
  this is efficient.


V. Using client certificates for authentication

  If you provide PennMUSH with a file containing the certificates of
  trusted CAs (using the ssl_ca_file directive in mush.cnf), it will,
  by default, request that clients present certificates when they connect.
  Clients that do not present certificates will still be allowed to 
  connect (unless ssl_require_client_cert is enabled).
 
  Clients that do present certificates must present certificates signed
  by a trusted CA, or they will be disconnected. Both valid and invalid
  certificates are logged (to connect.log and netmush.log, respectively).

  If you were really serious about this, you probably would issue your
  own certs and not allow Verisign, etc. certs. You'd probably want to
  have the server validate extra attributes on each client cert, which
  should probably include the player's dbref and creation time. This is
  left as an exercise for the reader for now.


VI. Legal issues

  OpenSSL is used in PennMUSH and may be redistributed with PennMUSH
  under the following license(s):

  OpenSSL License
  ---------------

/* ====================================================================
 * Copyright (c) 1998-2001 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *    the documentation and/or other materials provided with the
 *    distribution.
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 *    software must display the following acknowledgment:
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 * ====================================================================
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 * This product includes cryptographic software written by Eric Young
 * (eay@cryptsoft.com).  This product includes software written by Tim
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 */

 Original SSLeay License
 -----------------------

/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 * 
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 * 
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
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 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from 
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
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