A small amount of information can be stored in the block chain using an OP_RETURN transaction.

And encrypting said message

One can use services like CryptoGraffiti to easily embed messages on the blockchain.

this isnt the best method (mem limits), but yes, there are services like the aforementioned that can embed messages in the blockchain.

with that being said, much easier to publically blast a coded message (https://en.wikipedia.org/wiki/Numbers_station) or send an encrypted message. Hiding in plain site isn't the best choice for information that is highly sensitive.

It can be done....and much more.  But, my question would be: is there a more efficient way to send and preserve communications that wouldn't bloat the block chain ledger?  There are several unnecessary messages already bloating the ledger (photos and quotes of Nelson Mandella, frivolous code...etc)¹; however, there is some amount of utility to the practice such as; copyright posterity, identification verification, and such....


1. Citation here

@cjmoles - Excellent link, appreciate reading all the wacky things people have done.
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So does adding stuff slow down the transaction as well? I see it takes up more room but does it confirm slower!

Some people argue that services like CryptoGraffiti are bad for Bitcoin in general, the Blockchain size is growing, and embedding messages on it is not helping, every node in the world will have to carry your message to support the blockchain.
This is a waste of space, nodes don't get paid, and yet, they have to store your transactions in their hard drives.

Alice and Bob want to tranfer a secret letter. How can they transfer the information with the use of the chess game?

I would just use Steganography & Digital Watermarking on a image and post it on one of the popular image hosting sites and then send the url to that image as a message via a transaction to someone else. You could do the same with a link to a youtube video.

You do not need to make it too complex, but if you want it to last, I would insert it into the OP_Return as previously suggested.  

Secret information should be sent via an anonymous and encrypted way, although there have been a lot of hype over TOR that it can be denonymized but the FBI haven't tell us yet how they have done so and in their largest operation by taking down a child-pornography website in deepweb they only managed to get 1300 IP from 22.000 users that means TOR is still the best tool to use together with sigaint email there.
Its not fault of TOR but the users of it not taking precaution if they get their email intercepted. I think TOR is the best option we have yet and TOR developers now have responded they will not let any other attack like this of the FBI happen, they admitted that they saw the attack but let it run as they thought nothing is wrong, now they claim to not let anyone servers when they see alot of activity and they remove it from the network.

As a security paranoia which I am this is the best way to send secret information via TOR and SIGAINT email service. Sorry for explaining long and with a not so good example but I want to warn users concerned with security its based on them, no browser or software can protect you 100% it depends on your measures. Use even TAILS or WHONIX to be even more safe. That should be enough.

I personally think this is the best answer... combine this approach with a service like https://privnote.com/ and you have a pretty secure method of sending messages to eachother...