                      _             _ 
  _ __ ___   ___   __| |    ___ ___| |
 | '_ ` _ \ / _ \ / _` |   / __/ __| | 
 | | | | | | (_) | (_| |   \__ \__ \ | ``mod_ssl combines the flexibility of
 |_| |_| |_|\___/ \__,_|___|___/___/_|   Apache with the security of OpenSSL.''
                      |_____|                                           
 mod_ssl                               ``Ralf Engelschall has released an
 Apache Interface to OpenSSL             excellent module that integrates
 http://www.modssl.org/                  Apache and SSLeay.''                 
 Version 2.8                                               -- Tim J. Hudson

 SYNOPSIS

 This Apache module provides strong cryptography for the Apache 1.3 webserver
 via the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS
 v1) protocols by the help of the SSL/TLS implementation library OpenSSL which
 is based on SSLeay from Eric A. Young and Tim J. Hudson. The mod_ssl package
 was created in April 1998 by Ralf S. Engelschall and was originally derived
 from software developed by Ben Laurie for use in the Apache-SSL HTTP server
 project. 

 SOURCES

 Here is a short overview of the source files:

 # Makefile.in ............. Makefile template for Unix platform
 # config.m4 ............... Autoconf stub for the Apache config mechanism
 # mod_ssl.c ............... main source file containing API structures
 - mod_ssl.h ............... common header file of mod_ssl
 - ssl_engine_config.c ..... module configuration handling
 # ssl_engine_dh.c ......... DSA/DH support
 # ssl_engine_ds.c ......... data structures
 - ssl_engine_ext.c ........ Extensions to other Apache parts
 - ssl_engine_init.c ....... module initialization
 - ssl_engine_io.c ......... I/O support
 - ssl_engine_kernel.c ..... SSL engine kernel
 - ssl_engine_log.c ........ logfile support
 # ssl_engine_mutex.c ...... mutual exclusion support
 - ssl_engine_pphrase.c .... pass-phrase handling
 - ssl_engine_rand.c ....... PRNG support
 - ssl_engine_vars.c ....... Variable Expansion support
 - ssl_expr.c .............. expression handling main source
 - ssl_expr.h .............. expression handling common header
 - ssl_expr_scan.c ......... expression scanner automaton (pre-generated)
 - ssl_expr_scan.l ......... expression scanner source
 - ssl_expr_parse.c ........ expression parser automaton  (pre-generated)
 - ssl_expr_parse.h ........ expression parser header     (pre-generated)
 - ssl_expr_parse.y ........ expression parser source
 - ssl_expr_eval.c ......... expression machine evaluation
 - ssl_scache.c ............ session cache abstraction layer
 - ssl_scache_dbm.c ........ session cache via DBM file
 - ssl_scache_shmcb.c ...... session cache via shared memory cyclic buffer
 - ssl_scache_shmht.c ...... session cache via shared memory hash table
 # ssl_util.c .............. utility functions
 # ssl_util_ssl.c .......... the OpenSSL companion source
 # ssl_util_ssl.h .......... the OpenSSL companion header
 # ssl_util_table.c ........ the hash table library source
 # ssl_util_table.h ........ the hash table library header

 Legend: # = already ported to Apache 2.0
         - = port still not finished

 The source files are written in clean ANSI C and pass the ``gcc -O -g
 -ggdb3 -Wall -Wshadow -Wpointer-arith -Wcast-align -Wmissing-prototypes
 -Wmissing-declarations -Wnested-externs -Winline'' compiler test
 (assuming `gcc' is GCC 2.95.2 or newer) without any complains. When
 you make changes or additions make sure the source still passes this
 compiler test.

 FUNCTIONS
  
 Inside the source code you will be confronted with the following types of
 functions which can be identified by their prefixes:

   ap_xxxx() ............... Apache API function
   ssl_xxxx() .............. mod_ssl function
   SSL_xxxx() .............. OpenSSL function (SSL library)
   OpenSSL_xxxx() .......... OpenSSL function (SSL library)
   X509_xxxx() ............. OpenSSL function (Crypto library)
   PEM_xxxx() .............. OpenSSL function (Crypto library)
   EVP_xxxx() .............. OpenSSL function (Crypto library)
   RSA_xxxx() .............. OpenSSL function (Crypto library)

 DATA STRUCTURES

 Inside the source code you will be confronted with the following
 data structures:

   ap_ctx .................. Apache EAPI Context
   server_rec .............. Apache (Virtual) Server
   conn_rec ................ Apache Connection
   BUFF .................... Apache Connection Buffer
   request_rec ............. Apache Request
   SSLModConfig ............ mod_ssl (Global)  Module Configuration
   SSLSrvConfig ............ mod_ssl (Virtual) Server Configuration
   SSLDirConfig ............ mod_ssl Directory Configuration
   SSL_CTX ................. OpenSSL Context
   SSL_METHOD .............. OpenSSL Protocol Method
   SSL_CIPHER .............. OpenSSL Cipher
   SSL_SESSION ............. OpenSSL Session
   SSL ..................... OpenSSL Connection
   BIO ..................... OpenSSL Connection Buffer

 For an overview how these are related and chained together have a look at the
 page in README.dsov.{fig,ps}. It contains overview diagrams for those data
 structures. It's designed for DIN A4 paper size, but you can easily generate
 a smaller version inside XFig by specifing a magnification on the Export
 panel.

 EXPERIMENTAL CODE

 Experimental code is always encapsulated as following:

   | #ifdef SSL_EXPERIMENTAL_xxxx
   | ...
   | #endif

 This way it is only compiled in when this define is enabled with
 the APACI --enable-rule=SSL_EXPERIMENTAL option and as long as the
 C pre-processor variable SSL_EXPERIMENTAL_xxxx_IGNORE is _NOT_
 defined (via CFLAGS). Or in other words: SSL_EXPERIMENTAL enables all
 SSL_EXPERIMENTAL_xxxx variables, except if SSL_EXPERIMENTAL_xxxx_IGNORE
 is already defined. Currently the following features are experimental:

   o SSL_EXPERIMENTAL_PERDIRCA
     The ability to use SSLCACertificateFile and SSLCACertificatePath
     in a per-directory context (.htaccess). This is provided by some nasty
     reconfiguration hacks until OpenSSL has better support for this. It
     should work on non-multithreaded platforms (all but Win32).

   o SSL_EXPERIMENTAL_PROXY
     The ability to use various additional SSLProxyXXX directives in
     oder to control extended client functionality in the HTTPS proxy
     code.

   o SSL_EXPERIMENTAL_ENGINE
     The ability to support the new forthcoming OpenSSL ENGINE stuff.
     Until this development branch of OpenSSL is merged into the main
     stream, you have to use openssl-engine-0.9.x.tar.gz for this.
     mod_ssl automatically recognizes this OpenSSL variant and then can
     activate external crypto devices through SSLCryptoDevice directive.

 INCOMPATIBILITIES

 The following intentional incompatibilities exist between mod_ssl 2.x
 from Apache 1.3 and this mod_ssl version for Apache 2.0:

 o The complete EAPI-based SSL_VENDOR stuff was removed.
 o The complete EAPI-based SSL_COMPAT stuff was removed.
 o The <IfDefine> variable MOD_SSL is no longer provided automatically 
 o The complete SSL_CONSERVATIVE stuff was removed, i.e.,
   SSL renegotiations in combination with POST request are not supported
   unless the problem is solved again, but this time through layered I/O.

 MAJOR CHANGES 

 The following major changes were made between mod_ssl 2.x
 from Apache 1.3 and this mod_ssl version for Apache 2.0:

 o The DBM based session cache is now based on APR's DBM API only.
 
 TODO

 o Whether to unregister and how to unregister?
   ssl_var_unregister();
   ssl_ext_unregister();
   ssl_io_unregister();
 o We certainly need CRYPTO_set_locking_callback() now also under Unix!

