Bitcoin Forum

Short Question:

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

Thanks!

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

Is there any other token?
Other than Bitcoin, that's leveraging blockchain to transfer information?

And encrypting said message :)

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

as said above by odolvlobo and unamis76. but I think that's kind of impractical because Bob would have to know the transaction hash or having the transaction sent to his address. might as well go without the blockchain.

oh. and the "secret" letter can be seen by anyone that have the transaction hash. forever.

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.

Why the need for the blockchain?

1) just a secret message transfer:
bob publishes his public key, alice encrypts the message to that key and sends to bob.

2) a secret message transfer with some deniability for both:
as in (1) except alice transfers encrypted message to a dropbox like mailinator

Use of a blockchain would be indicated if you wanted the message to remain around forever, immutable. 
Do you really need this? Possibly you only need the hash of the message to be kept immutable forever?

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 (http://www.righto.com/2014/02/ascii-bernanke-wikileaks-photographs.html)

Not possible. Anything can be cracked with enough motivation and know how.
There is evidence all over the internet you just have to know where to find it.

@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!

Depends what fee you attached to the transaction? A higher fee would give a miner more incentive to include the larger TX.

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.

Also easy to intercept, without proper encryption. In the case of sending it via blockchain, everyone who knows the tx hash would also know what message was embedded within that tx, so no, that's not so secret at all.

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

I think that is impossible to tranfer your message in blockchain. But if you want to transfer a secret message try to use email or facebook. You can create a message there that secretly by downloading the apps that can convert your mesage into other form of message and teach your chatmate that convert it using the app that you use.

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.  

Well maybe they will use a system of letters and numbers that are engraved on the chess board already like from 1 to 8 and from a to h and every other move will have a secret meaning for both parties. Encoding and decoding a letter during a chess game would be fabulous though and for spectators of the game it would be very hard to have a sniff of what has been going on. It's always the best to hide secret information in plain sight right?  ;)

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.

You can always send a message with a note attached. With that you can write messages.

You can also encrypt that message with some sort of security to make it private, because as people before me said, anyone with the txid would be able to read the message.

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...

Correct,i think OP just want to know about this,and not try to send any letter to his friend. and yes i agree with you,email is better than any secret letter services,but the only one to make sure the security of email is signature and private connection,mportant and secret letter should have better security.

Isn't it a little bit unsafe to send secret messages via the Blockchain as these will stay forever online and everyone will be able to see them? Wouldn't it be better to use an app that deletes every message after been delivered and read like Telegram? Surely we could encrypt and decrypt messages on the Blockchain but I think there are better methods out there for that.

I would have to disagree that email is 'better' than any secret letter services. I mean, it's really easy to get an access and intercept that email using the right tools and commands. Besides, the OP is asking how he could send private information using blockchain, which is apparently I have nearly no idea how.

I am doing PGP encryption service provided by https://www.igolder.com/pgp/encryption/
this is great way to send encrypted message. Keybase.io also seems to provide similar service but they have limited invitation to new registration.

The blockchain is public for everyone to see, so it is a dumb idea to send a secret message. This is possible though, by creating an irregular output axript that has the secret message. They could also encrypt it before making it public on the blockchain. Eternitywall is a service you can use to forever store a message on the blockchain and basically does what I mentioned. Check it out.

It depends on what email service you are using, because anything done via Gmail/Yahoo or one of these email providers are compromised from day 1. You could try ProtonMail, but they are under funded and there are rumors that they are working with the US government, to prevent global terrorism.

The Blockchain is too public, and accessible to everyone. ^hmmmmm^

Wow.
I can't see any way to read what you wrote without concluding that you don't know what 'encryption' actually means.
A properly encrypted message can't be 'accessed' no matter what tools are used., assuming you mean access to the plain text.
'Interception' gets you the unreadable encrypted text only, plus maybe the destination (which can be worked around via a drop box, for example).

Hi. What's the max message length that can be stored in OP_RETURN field?

Enigma already solved this problem, back in the 1930s. No need to reinvent the wheel.

Split the message into two. One to set the keys for the decryption; one to send the random message.

I guess if someone is listening for the first message, it'll be public anyway  :P

This... if it's so secretive, then you want the person to read the information as quickly as possible for them to retain the information and then be deleted from existence forever.

There are tons of software/apps out there that allow this type of communication.