$Id: architecture.txt,v 1.11 2005/12/09 22:41:24 droggo Exp $

Architecture document - BSD Privacy Guard
=========================================

This document contains information about BPG internal
architecture. Section 1 covers the system general design, which
modules conform BPG and how they interact. Section 2 explains the
internals of each module.

1. System design
----------------

The main goal of BPG is to provide applications with a toolkit for
using OpenPGP facilities. For that, we packed that functionality in
libraries.

The BPG project includes three libraries: an OpenPGP implementation (bpg),
a key manager (bpgkey) and a trust manager (bpgtrust). Also, BPG relies on
the OpenSSL Cryptographic Library for ciphers and hashing algorithms.

The project also includes programs and scripting wrappers for this libraries.

2. Modules internals
--------------------

2.1. bpg
--------

This library manages the processing of OpenPGP data, including OpenPGP
general functions (section 2, RFC 2440), which are signing, encryption,
compression and radix-64 conversion. It also defines all the other data types
and formats in OpenPGP.

DEPENDECIES

* bpgkey: PKI keys are especified in the API with user-IDs and obtained
  from the BPG key management library.

* OpenSSL Cryptographic Library (libcrypto): for performing low-level
  encryption, hashing and compression, it uses the BPG algorithms library.

* libzip: BPG uses libzip for compression (http://www.nih.at/libzip/).

API

Read bpg(3) for a detailed explanation of the API.

2.2. bpgkey
-----------

This library manages the creation, storage and use of asymmetric keys like
those used in OpenPGP.

The "BPG Key Management" document defines all key-related operations
in BPG in detail.

API

Read bpgkey(3) for a detailed explanation of the API.

2.3. bpgtrust
-------------

This library handles the trust level of asymmetric keys like those involved
in OpenPGP.

In BPG, the trust level of a key depends on how much we trust the
signer of that key.

The trust library handles the trust database and the trust policy. The
trust database contains a list of [UserID, trust level] pairs. The
policy defines the rules for deriving trust level of a given key from
the trust database (i.e. OpenPGP web of trust, X.509 hierarchical
trust model, ...).

Read more on this in the "BPG Key Management" document.

API

Read bpgtrust(3) for a detailed explantation of the API.