Bitmessage

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From the Bitmessage wiki:

"Bitmessage is a P2P communications protocol used to send encrypted messages to another person or to many subscribers. It is decentralized and trustless, meaning that you need-not inherently trust any entities like root certificate authorities. It uses strong authentication which means that the sender of a message cannot be spoofed, and it aims to hide "non-content" data, like the sender and receiver of messages, from passive eavesdroppers like those running warrantless wiretapping programs."

Bitmessage may be used independently or with Tor. Using it with Tor has additional security benefits.

Installation

Install pybitmessage^AUR or pybitmessage-git^AURfrom the AUR. In order to use it with Tor, install tor from the official repositories. For using the given python script to create magnet links, install the package python2-bencode^AUR.

Set up

Without Tor

After launching bitmessage (the name of the bitmessage main python2 script is pybitmessage) for the first time, disregard any popups and:

Navigate to the Your Identities tab
Hit the New button and create a few new addresses. Since bitmessage is built to be used with different (ideally disposable) addresses, feel free to create more than one address (for instance this user created four addresses)
You can use either a passphrase or a random number as the basis for the generation of your address. A random number is better for security and a passphrase is better for convenience (you can recreate your identity more easily with a passphrase than with a random number)
Remember the address version number and the stream number. These will be useful if you need to re-make your address for any reason (Currently the default address version is 4 and stream number 1 will be fine)

With Tor

The same steps apply as above, except that you would need to do the following (ideally before you set up your first identity):

Navigate to Settings > Network Settings and select SOCKS5 from the Type drop down under the Proxy server / Tor section
Next to Server hostname enter "localhost" and next to Port enter "9050" (If using the Tor browser bundle enter "9150")
Restart bitmessage

Usage

Testing

Using bitmessage is the same as using an email client. The addresses you have are, however, in Bitmessage format. To test if bitmessage is working properly for you or not, you can send a test message to BM-orkCbppXWSqPpAxnz6jnfTZ2djb5pJKDb. This is an echo server and will send your message back to you if you have configured everything correctly.

Attachments

Attachments are not possible for the moment in mainline bitmessage, but the wiki offers links to API tools which allow to send binaries (.zip , .jar (texts readable in GUI in lowest jar-compression setting)) and pictures (from local files or weblinks via clipboard). Alternatively, 3 more options are available: One is to convert your files using base64 and concatenating them to the end of your bitmessage itself.

base64 < binary.file > text.file

The concatenated text can be copied to a text file by the recipient and the following command can be used to reconvert the file back to its original state:

base64 -d < text.file > binary.file

This method, however, is neither in the interests of bitmessage (as it increases the length of the message unnaturally) nor is it very elegant. Hence it is advised to upload your file to a cloud-based storage provider (ala dropbox or box) and send the link over using bitmessage. Of course, if the file contains anything sensitive, it may be a good idea to use PGP or some other program to encrypt your file. You can send the passphrase used to encrypt the file over bitmessage.

An extreme method, especially if you wish to wish larger files, is to create a magnet link or a torrent file and use that to share your data. You need not list the torrent on a public torrent site for this to work. To use this method, first create the torrent with all the files you wish to share using your favorite torrent application. You can now share this torrent file using the base64 method described above, or you can use the following script to convert it into a magnet (source blogpost):

~/.scripts/createMagnetLink.py

!/usr/bin/python2

import sys
import urllib
import bencode
import hashlib
import base64

if len(sys.argv) == 0:
print("Usage: file")
exit()

torrent = open(sys.argv[1], 'r').read()
metadata = bencode.bdecode(torrent)

hashcontents = bencode.bencode(metadata['info'])
digest = hashlib.sha1(hashcontents).digest()
b32hash = base64.b32encode(digest)

params = {'xt': 'urn:btih:%s' % b32hash,
'dn': metadata['info']['name']}

announcestr = ''
for announce in metadata['announce-list']:
announcestr += '&' + urllib.urlencode({'tr':announce[0]})

paramstr = urllib.urlencode(params) + announcestr
magneturi = 'magnet:?%s' % paramstr

print(magneturi)

You need to have python2-bencode^AUR installed in order to make this script work. The magnet link can be shared with the intended recipient without using base64.

Torrents might raise privacy issues, so the third way is to embed binaries or pictures employing BM API client, currently of version 1.2.8. A python script (published on UBF) will post binaries as encoded bitmessages much like method 1 but offers additional features.

Chans

According to the bitmessage wiki:

A Mailing List without the requirement of a central "authority". Sometimes called Chan (short for channel) because they usually focus on a subject which also is the password for the deterministic address.

A Chan (or a Distributed Mailing List) can be joined or created by hitting "Join/Create Chan" in the file menu. A Passphrase must be entered and the address is being generated for a (new or old) chan. To join an existing Chan, you must enter a passphrase (the chan name, essentially) and optionally the chan's BM-2... address (for verification against typos in the chan name). The simpler method for joining in omits the hard to memorize BM-2... address (key) and requires entering the passphrase ("chan name") only: Add Chan / Create New Chan. By far for the most popular chan is general, to join it, Create New Chan and enter: general as the passphrase.

Additional resources