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SYNOPSIS
This Apache module provides strong cryptography for the Apache 2.0 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. The mod_ssl implementation
for Apache 1.3 continues to be supported by the modssl project
<http://www.modssl.org/>.
SOURCES
See the top-level LAYOUT file in httpd-2.0 for file descriptions.
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:
server_rec .............. Apache (Virtual) Server
conn_rec ................ Apache Connection
request_rec ............. Apache Request
SSLModConfig ............ mod_ssl (Global) Module Configuration
SSLSrvConfig ............ mod_ssl (Virtual) Server Configuration
SSLDirConfig ............ mod_ssl Directory Configuration
SSLConnConfig ........... mod_ssl Connection Configuration
SSLFilterRec ............ mod_ssl Filter Context
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_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
MAJOR CHANGES
For a complete history of changes for Apache 2.0 mod_ssl, see the
CHANGES file in the top-level httpd-2.0 directory. The following
is a condensed summary of the 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.
o The shared memory based session cache is now based on APR's APIs.
o SSL I/O is now implemented in terms of filters rather than BUFF
o Eliminated ap_global_ctx. Storing Persistant information in
process_rec->pool->user_data. The ssl_pphrase_Handle_CB() and
ssl_config_global_* () functions have an extra parameter now -
"server_rec *" - which is used to retrieve the SSLModConfigRec.
o Properly support restarts, allowing mod_ssl to be added to a server
that is already running and to change server certs/keys on restart
o Various performance enhancements
o proxy support is no longer an "extension", much of the mod_ssl core
was re-written (ssl_engine_{init,kernel,config}.c) to be generic so
it could be re-used in proxy mode.
- the optional function ssl_proxy_enable is provide for mod_proxy
to enable proxy support
- proxy support now requires 'SSLProxyEngine on' to be configured
- proxy now supports SSLProxyCARevocation{Path,File} in addition to
the original SSLProxy* directives
o per-directory SSLCACertificate{File,Path} is now thread-safe but
requires SSL_set_cert_store patch to OpenSSL
o RSA sslc is supported via ssl_toolkit_compat.h
o the ssl_engine_{ds,ext}.c source files are obsolete and no longer
exist
TODO
See the top-level STATUS file in httpd-2.0 for current efforts and goals.
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