Bitmessage Broadcasts

By now you will be familiar with some of the concepts underlying Bitmessage, and your first message will be encrypted and working its way through the P2P network to be decoded by your recipient.

This is fantastic for one-to-one communication, but in some situations you might want to message a number of people at once, such as when sending a newsletter. Broadcasts serve as a form of universal inbox – anyone who knows the correct name and Bitmessage address can receive messages.

Click on the Subscriptions tab to get started. One of the more useful subs is Timeservice, which posts regular updates about the Bitmessage network. WikiLeaks also broadcasts over Bitmessage.

Give Chans a Chance

As useful as subscriptions are, they are only useful for one-way communication. They also rely on a single central client, such as the WikiLeaks server, to be constantly online and broadcast messages.

Chans (short for Channels) are one solution to this dilemma. They are a form of DML (decentralized mailing list) – this involves sharing the private key for an address between multiple clients and means that anyone can send and receive from this address (Figure 3). By comparison, it's similar to an email address to which everyone has the password.

Figure 3: The general chan contains useful links and information for new subscribers. A full list of all registered chans is available online [6].

Click on the Chans tab to join or create a chan. PyBitmessage will explain that the decryption keys for the chan and the Bitmessage address are derived from a human-friendly word or phrase, such as the word hello.

A list of the more popular chans, such as hello and general, which are for new Bitmessage users and general chat respectively, is available from the Bitmessage forums [7].

One of the chans' abiding strengths is that, because anyone is in possession of the decryption keys, they can send a message from the chan address to itself without revealing their identity. To this end, chan users will sometimes post private encoded messages, knowing the recipient will see it.

Nevertheless, you can choose to message the chan from your personal Bitmessage address if you like. For this reason, messages will sometimes appear to be From the chan itself or from a individual address. Righ-click Bitmessage addresses to reply directly to a sender if you like.

In light of the above, chans have built-in protection against spam and illegal content besides the work involved to send larger messages.

Bitmessage Blacklists

Although chans may be prone to spam, you can keep your Inbox clutter free by following a few best practices. Use the New Identity feature in the Messages tab as often as possible to provide each new party with your Bitmessage address. If the address then ends up in the hands of a scammer, simply right-click to disable.

In extreme situations where you are inundated with spam, or if you only want to use Bitmessage to communicate with a select few, then head over to the Blacklist tab. The interface here could not be simpler. First, decide whether you want to Use a Blacklist, which will allow all incoming messages except those from addresses you specify, or Use a Whitelist, which will block all incoming messages except those from people you have pre-approved. Click Add new entry when you have decided to enter the label and address of the relevant users (Figure 4).

Figure 4: Click Add new entry to Blacklist/Whitelist specific addresses.

Sending messages requires computing power. The more messages and the larger their size, the greater amount of work must be done. To make the task even more difficult for those not already in your address book, head over to Settings and choose the Demanded difficulty tab. Alter the values here for larger and smaller messages to make it much harder for people who don't know you to send messages. Note that this doesn't apply to people already in your address book.

By default, the Bitmessage client will do as much work as is necessary to send a message. You and your contacts can change this from the Max acceptable difficulty tab under Settings if you want to save precious resources.