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//usr/share/doc/crda-3.13_2015.10.22/README.crda

Central Regulatory Domain Agent (CRDA)
========================================

This is the Central Regulatory Domain Agent for Linux. It serves one
purpose: tell Linux kernel what to enforce. In essence it is a udev
helper for communication between the kernel and userspace. You only
need to run this manually for debugging purposes. For manual changing
of regulatory domains use iw (iw reg set) or wpa_supplicant (feature
yet to be added).

HOST REQUIREMENTS
===================

CRDA is provided as a binary file so all the host needs is libc/uclibc.
You will also need udev and at least libnl1.

BUILD REQUIREMENTS
====================

The package build requirements currently are:

* python and the m2crypto package (python-m2crypto)
 * libgcrypt or libssl (openssl) header files
 * nl library and header files (libnl1 and libnl-dev)
   available at git://git.kernel.org/pub/scm/libs/netlink/libnl.git
 * RSA public key of John Linville, we include this as part of this package
   so you do not need to install it. This RSA public key comes
   from the wireless-regdb.git tree and we keep it up to date here.
 * regulatory database, clone this tree:

git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-regdb.git

and then stuff regulatory.bin (no need to build) provided there in
   REG_BIN location specified in this Makefile. This regulatory.bin file
   is only required to verify the CRDA built here can read its database file
   which has been signed with the RSA private key.

CALLING CRDA -- UDEV
======================

Distributions can set up a udev rule to allow the kernel's regulatory
domain change request to be reviewed by CRDA so CRDA can pass an
appropriate regulatory domain. An example regulatory rule is provided
with this package as regulatory.rules

OVERVIEW
==========

The database is maintained on the wireless-regdb.git tree. This git
tree maintains a binary regulatory database file which is produced
using its own ASCII db.txt into binary form for size efficiency. The
contents of the binary database are then signed using the private key.

CRDA will use regulatory.bin if its signature checks out with the public
key provided. This will prevent us from using corrupted data (in case
of hard drive failure) in the running kernel. This separation between
CRDA and the regulatory database also allows us to provide regulatory
updates on distributions without having to require an update on CRDA.

Note that upon updating the regulatory database it is advised the
user reboots or all the wireless modules get unloaded and reloaded.

Under certain circumstances it may be desirable to have the regulatory
agent accept multiple keys, this can be achieved by stuffing all the keys
desired into pubkeys. Right now we only use John Linville's public key.

REGDB AUTHORS
===============

Authors of regulatory.bin (John Linville) first need a private key, which can
be generated with something like this:

openssl genrsa -out your.key.priv.pem 2048

You'll then need to generate the public key and publish it. You
can generate it as follows:

openssl rsa -in your.key.priv.pem -out your.key.pub.pem -pubout -outform PEM

Then with this key you can generate regulatory.bin files like this:

./utils/db2bin.py regulatory.bin db.txt your.key.priv.pem

MAGIC PATTERN
===============

Use the following magic(5) pattern to recognise CRDA binary regulatory
database files:

---- %< ----
# CRDA Regulatory database file
# http://git.kernel.org/?p=linux/kernel/git/mcgrof/crda.git;a=summary
# (see regdb.h)
0	belong		0x52474442	CRDA regulatory database file
>4	belong		19		(Version 1)
---- >% ----