garage door opener

experiments in building a rolling code in javascript

rolling code schemes allows a sender to authenticate herself to a receiver without trading keys often. by transmitting a single, shared key one time, a sender can identify herself to a receiver a number of times (in this case, 1024 times) over a potentially public channel.

rolling codes are amazingly simple. by relying on the fact that two, identical pseudorandom number generators will spit out the same numbers given the same seed, you and i can use a seed as our shared secret, then build a list of identical numbers independently. we can use these numbers to authenticate ourselves to one another. to an eavesdropper (someone who doesn't know our seed), the numbers we use will look perfectly random.*

*assuming a cryptographically secure PRNG. we use the Mersenne Twister implemented in random-js.

usage

use garage-door-opener to create a sender or a receiver:

var garagedoor = require('garage-door-opener')
var my_seed    = 59823

s = garagedoor.sender(my_seed, 43)
r = garagedoor.receiver(my_seed, 43)

// sender generates the next random key
code_to_send = s.next()
// receiver makes sure this key looks good
r.check(code_to_send)
// > True

// works even if receiver misses a few messages from sender (up to 255)
s.next()
s.next()
r.check(s.next())
// > True

// good luck guessing codes if you don't know the seed!
r.check(5326294)
// > False

See examples/dnode_example.js for a more complete simulation.

API

sender

sender(seed, start_i)

Takes a seed (a 32-bit integer) and a code index to start at (0 by default).

Returns an object with the method next(), which returns the next key in its buffer.

receiver

receiver(seed, start_i)

Takes a seed (a 32-bit integer) and a code index to start at (0 by default).

Returns an object with the method check(code), which returns True or False depending on whether the code matches authentication criteria.

installation

with npm do:

npm install garage-door-opener

developing

first, npm install

then, npm test

license

MIT