bittorrent-nodeID
===

Javascript implementation of [BEP42 - DHT Security extension](http://www.bittorrent.org/beps/bep_0042.html) to calculate or check the nodeID of a peer.

BEP42 is implemented in projects uTorrent, libtorrent and bootstrap-dht.

## Installation and use

This is using [node-fast-crc32c](https://github.com/ashi009/node-fast-crc32c) from Xiaoyi and/or [sse4_crc32](https://github.com/Voxer/sse4_crc32) from Anand Suresh.

	npm install bittorrent-nodeid
	
Then:

	var generate_id=require('bittorent-nodeid');

	generate_id('W.X.Y.Z',Random_byte) --> prefix abcdefgh --> nodeID: (first 20 bits of prefix) (random number) Random_byte
	generate_id('124.31.75.21',1) --> prefix 5fbfbdb2 --> nodeID: 5fbfb e7519910c34ae7026c3e64eacc13c5159 01
	generate_id('21.75.31.124',86) --> prefix 5a3ce9b0 --> nodeID: 5a3ce 91f3dc70a057e9a9fe0cc900d52b4e61e 56
	generate_id('65.23.51.170',22) --> prefix a5d4344a --> a5d43 396da271c1a4d1dc7149247f021eabc34 16
	
## Note about the binary format

BEP42 does define the following calculation to compute the nodeID:

	crc32c((ip & 0x030f3fff) | (r << 29))

Where ip is the ip address representation in network bytes order.

For ip 124.31.75.21, the calculation with a random number set to 1 will be ``crc32c((0x7c1f4b15 & 0x030f3fff) | (1 << 29))``, so ``crc32c(0x200f0b15)`` which is computed as ``crc32c(new Buffer('200f0b15','hex'))`` or ``crc32c(new Buffer([0x20,0xf,0xb,0x15]))`` or ``crc32c('ABCD')`` where ABCD are the characters corresponding to the ascii code of each byte.

In javascript a character outside of the normal ascii range like 'Á' will be interpreted as utf8 ``0xc381`` and ``crc32c.calculate('Á')`` will give ``b1cf5bcd``

But most of the c++ libraries does handle this byte by byte, so 'Á' will be interpreted as ``0xc1`` and ``crc32c.calculate('Á')`` will give ``639bf696``

## Related projects :

* [Ayms/torrent-live](https://github.com/Ayms/torrent-live)
* [Ayms/node-Tor](https://github.com/Ayms/node-Tor)
* [Ayms/iAnonym](https://github.com/Ayms/iAnonym)
* [Interception Detector](http://www.ianonym.com/intercept.html)
* [Ayms/abstract-tls](https://github.com/Ayms/abstract-tls)
* [Ayms/websocket](https://github.com/Ayms/websocket)
* [Ayms/node-typedarray](https://github.com/Ayms/node-typedarray)
* [Ayms/node-dom](https://github.com/Ayms/node-dom)
* [Ayms/node-bot](https://github.com/Ayms/node-bot)
* [Ayms/node-gadgets](https://github.com/Ayms/node-gadgets)