SYNOPSIS

This Apache module provides strong cryptography for the Apache 2 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-2.1 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:

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 mod_ssl, see the

CHANGES file in the top-level httpd-2.1 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:

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-2.1 for current efforts and goals.