interesting books

i ran across a couple of books that look interesting. the first is 'Impossible?: Surprising Solutions to Counterintuitive Conundrums' by julian havil. a great way to challenge students and keep the puzzler sharp. the second book is 'How Round Is Your Circle?: Where Engineering and Mathematics Meet'. i was thinking this might help people who struggle with the traditional approach to mathematics instruction to develop a more physical intuition.

kindle

amazon is selling a device called the kindle. it's an ebook reader that looks like it uses electronic ink. looks like a very high-quality display and has a long battery life. built-in qwerty, too. i wonder how hackable? if there's a way for me to break off amazon's manacles, this might be my zaurus replacement.... UPDATE: apparently the kindle runs linux and a number of other os packages. amazon has released source of their changes, as they are obligated to do. maybe this thing is hackable, after all. i'm guessing amazon will not be forthcoming with hardware specs, though.

latex images

found a neat little tool for producing pngs from latex: pytexipng. fast, simple, and python. can't beat that. great for making equations for presentations. try to mangle that, powerpoint!

pycrypto

i found a recipe that gives a simple example of how to use pycrypto. Here's the important part:

import os, sys
from random import randrange
from Crypto.Cipher import Blowfish
from getpass import getpass
import getopt

class BFCipher:
    def __init__(self, pword):
        self.__cipher = Blowfish.new(pword)
    def encrypt(self, file_buffer):
        ciphertext = self.__cipher.encrypt(self.__pad_file(file_buffer))
        return ciphertext
    def decrypt(self, file_buffer):
        cleartext = self.__depad_file(self.__cipher.decrypt(file_buffer))
        return cleartext
    # Blowfish cipher needs 8 byte blocks to work with
    def __pad_file(self, file_buffer):
        pad_bytes = 8 - (len(file_buffer) % 8)                                
        for i in range(pad_bytes - 1): file_buffer += chr(randrange(0, 256))
        # final padding byte; % by 8 to get the number of padding bytes
        bflag = randrange(6, 248); bflag -= bflag % 8 - pad_bytes
        file_buffer += chr(bflag)
        return file_buffer
    def __depad_file(self, file_buffer):
        pad_bytes = ord(file_buffer[-1]) % 8
        if not pad_bytes: pad_bytes = 8
        return file_buffer[:-pad_bytes]

wireless measurements

right now, with one of the default whip monopoles, i get about 30 yards range outside my house for my wap. i'd like to go about 10 times that in one direction. so that would be 10 dbi gain needed for an antenna. that should be doable with a homebrew.

grandcentral

so, google bought grandcentral.com and is now letting people into a free beta. but they don't have any numbers available in my area. i wonder if that's because other people here already took them or if they haven't put any in yet. i guess i'll check it later, just in case.

homebrew wifi antennae, aircrack

i found a few good links on homebrew directional wifi antennae. this one gives a comparison between different designs and shows that soup can wave guides beat pringles cans. bottom line: nalley 40oz 'big chunk' beef stew wins, with a 16 dbi gain. here's a design for a helical, also advertised at 16 dbi. maybe i could make it better by increasing the length, but if it's the same gain as the soup can, i might as well make the easier one (which costs practically nothing considering i can eat the soup). some dish designs might do even better, but that means i have to buy a usb wifi and set up network bridging with the server. either of the other two can connect directly to the wap, after i remove one of the built-ins. speaking of which, that means i'll need to pick up a RP-TNC connect at radio smack. on a related subject, here's a tutorial on using aircrack. no, i don't plan to use these together, and neither should you.