[T]

I have a proposal that might or might not be feasible in Bitcoin. I do not fully understand the capabilities of the Bitcoin script and would like to know if it supports such a functionality.

Say Alice wants to mix her coins with a mixing service but she does not trust that the mixer will not run off with her coins.

Alice produces an order that says the following:
    I will give you 10 btc from address A and you must send that amount minus the fees to addresses B and C in a specified time frame.
Alice signs this order and privately sends both the order and its signature to the mixer.
Alice sends 10 btc to the mixer in a special transaction T that locks her coins and is not accepted by the network until it fulfills one of these three properties
-Alice signs T, then the coins go to the mixer
-The mixer provides a proof that B and C have received the expected btc in the expected time frame and produces the signed order, then the coins go to the mixer
-A timeout (say 2 weeks) makes the coins go back to Alice

The result is the following
-If everything goes as planned, Alice signs T, T goes to the mixer, the mixer never publicizes the order and Alice has gained her anonymity
-If the mixer never pays B and C, Alice doesn't have to do anything and her coins are refunded as T refunds the coins to Alice after the expiration period.
-If the mixer pays as expected but Alice does not sign in a timely manner, the mixer can produce the signed order as well as the txs used to pay B and C and T pays the mixer. In this case, Alice loses her anonymity.

It seems to me that neither party can cheat the other out of its money, and both parties will want the transaction to go through. Does that seem right?


There are a few technical things that I am uncertain about
1. Can Alice lock the coins from A in such a manner?
2. Can a transaction be such that depending on how the are conditions met, the coins are output to different addresses?
3. Is is possible to make the script understand the contract and to "prove" that B and C were paid?

I know that many exchanges/services have ran/gone out of business, taking the user's coins with them, but has this already happened with mixing/laundry services? I'd expect that to be the case, but I have found no reports of such events happening.

I couldn't find a similar thread, but if I missed it, please refer me and close this one.

I found this list of the things that can theoretically be bought with Bitcoin but I was wondering what typical users actually buy.
https://en.bitcoin.it/wiki/Trade

Do you buy actual stuff (or services) with Bitcoin? Do you keep your Bitcoins in a wallet and hope the value goes up to sell them? Do you pay debts to people you know? What is the size of your typical transaction of this type?

Ofc, if you buy drugs or other illegal items, you probably won't want to just say it here, but you are welcome to post what is the amount of btc in your typical transaction anyways.

I know I could just look at the blockchain to see the size of the average transaction but I can't think of an easy way to differentiate the sale of a product/services from an attempt to anonymize oneself.

I know multi-sender transactions with sending addresses that belong to different people are possible in theory in bitcoin, but does anyone actually use them? Many analyses of the bitcoin network assume that they are seldom used, I'm just trying to get an idea of how much that is true in practice.

Is there a section to discuss scholarly articles somewhere on the forum? I'm trying to understand the Reid and Harrigan analysis of anonymity in bitcoin but I can't find a forum thread on it. http://anonymity-in-bitcoin.blogspot.ca/2011/07/bitcoin-is-not-anonymous.html

I saw that Shamir's paper was discussed in general discussion, is there a better place?

Edit: found out how to get out of the newbie forum

Hello everyone

I have been browsing the forum for a few weeks and I decided to jump in and create an account.

While I do have Bitcoin addresses, I do not currently actively trade BTC so their balance is very low. I have more of a theoretical interest in Bitcoin especially in its cryptography. I am also interested in other crypto-currencies as well as e-cash in general.

I have already read quite a bit about Bitcoin, and produced an introduction to Bitcoin's cryptography talk that I will link to once it's edited.

I am currently interested in finding out just how anonymous Bitcoin is or can be against someone with a large amount of ressources (i.e. government, etc.), as well as the implications of such anonymity.

You can sometimes find me on irc in #bitcoin.