#!/bin/sh

# Must edit
###########
# Wireless interface
IFACE="wlan0"
# Base key used to compute the actual key
KEY_BASE="My WEP is better than yours"
# Security mode (open/restricted)
SECURITY_MODE="open"
# Comment this if you don't want to rotate the channel
ROTATE_CHANNEL="on"
# Channels supported by the wireless interface
MAX_CHANNEL=11
# Uncomment if you want the script to work only if you're on a specific essid
#ESSID="myessid"
# Uncomment if your wireless interface need the commit command
#COMMIT="commit"

# May edit
##########
# The format has to be in date(1) format, and probably has to have a relation
# with the frequency the script is executed. The default value is useful for a
# 1/2 day frequency (rotation every 12 hs). date(1) is executed with C locale so
# %p can be used.
# A good crontab line for this is:
# 0 0,12 * * * /path/to/script
KEY_FORMAT="$KEY_BASE%D%p"
# Key size, 1-5 for 64bit encryption, 6-13 for 128bit encryption
KEY_SIZE=13
# Hash command/algorithm used to compute the actual key
HASH_PROG="sha1sum"

# Do not touch
##############
# Unless you know what you're doing, and in that case, send me the patch ;)

export LANG=C

# Check if they are using our essid
if [ -n "$ESSID" ]
then
  curr_essid=`iwconfig $IFACE | grep ESSID | sed 's/.*ESSID:"\([^"]\+\)".*/\1/'`
  if [ "$curr_essid" != "$ESSID" ]
  then
    exit 0
  fi
fi

# Compute the new key
str=`date +"$KEY_FORMAT"`
size=$(($KEY_SIZE * 2))
key=`echo "$str" | $HASH_PROG | cut -c-$size`

# Compute the new channel
if [ -n "$ROTATE_CHANNEL" ]
then
  chan=`echo $key | tr abcdef 847502 | cut -c-6`
  chan=$(($chan % $MAX_CHANNEL + 1))
  channel="channel $chan"
fi

# Commit changes
/sbin/iwconfig $IFACE key $SECURITY_MODE $key $channel $COMMIT

# vim: set et sw=2 sts=2 :