_ _

_ __ ___ ___ __| | ___ ___| |

| '_ ` _ \ / _ \ / _` | / __/ __| |

| | | | | | (_) | (_| | \__ \__ \ | ``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:

* README .................. This file ;)

# 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_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 and is cleaned up

* = ported to Apache 2.0 but still needs cleaning up

~ = ported to Apache 2.0 but still needs work

- = 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:

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_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.

o Introduced Filter logic (similar to mod_tls)

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

TODO

o Port all remaining code (code inside #if 0...#endif blocks)

o Do we need SSL_set_read_ahead()?

o Enable SSL extensions (ssl_engine_ext.c)

o add configure check for SSL_set_cert_store to support per-dir

SSLCACertificate{File,Path}

o the ssl_expr api is NOT THREAD SAFE. race conditions exist:

-in ssl_expr_comp() if SSLRequire is used in .htaccess

(ssl_expr_info is global)

-is ssl_expr_eval() if there is an error

(ssl_expr_error is global)

o SSLRequire directive (parsing of) leaks memory

o Diffie-Hellman-Parameters for temporary keys are hardcoded in

ssl_engine_dh.c, while the comment in ssl_engine_kernel.c says:

"it is suggested that keys be changed daily or every 500

transactions, and more often if possible."