Shadow BTC coins

[Kouye]

Since I like to keep my BTC in my offline wallet, I was wondering...

Would it be hard to implement a new protocol layer to 'shadow' coins ?
If I have 50BTC, and I want to potentially trade 10 of them on any exchange, I would love to be able to:

- Prove the exchange I have them by letting then mark 10 of my BTC with their signature for a given period - 1 year minimum (or any period agreed upon).
- Exchange would allow me to sell those, as if they owned it, while they are still in my cold storage.
- The network would refuse any of those coin if I was to send them elsewhere, since they are "marked" with someone else signature.
- If the exchange actually sells some of my BTC, it requires a confirmation from me to allow it (I still have to send them, as current protocol)
- If I don't give the confirmation, then they can rollback the transaction, but the coins are still marked and unusable until period expires.

Exchanges would just then become escrow, and they would not hold any BTC.

Would it be exploitable ?

[CasinoBit]

Since I like to keep my BTC in my offline wallet, I was wondering...

Would it be hard to implement a new protocol layer to 'shadow' coins ?
If I have 50BTC, and I want to potentially trade 10 of them on any exchange, I would love to be able to:

- Prove the exchange I have them by letting then mark 10 of my BTC with their signature for a given period - 1 year minimum (or any period agreed upon).
- Exchange would allow me to sell those, as if they owned it, while they are still in my cold storage.
- The network would refuse any of those coin if I was to send them elsewhere, since they are "marked" with someone else signature.
- If the exchange actually sells some of my BTC, it requires a confirmation from me to allow it (I still have to send them, as current protocol)
- If I don't give the confirmation, then they can rollback the transaction, but the coins are still marked and unusable until period expires.

Exchanges would just then become escrow, and they would not hold any BTC.

Would it be exploitable ?

Couldn't you just use a seed of (your secret) + (exchange secret) as the hash for the private key?

[Abdussamad]

If you make something like what's there to prevent someone from marking all the coins in the entire blockchain? Then no one will be able to spend any of those coins.

[Kouye]

You'd have full control over who you choose to send your shadow coins, exactly as when you send real coins today.
But instead, they stay in your wallet, they're just tempered with the recipient's key/address for a certain time - agreed upon.

It's not the other way around where people can just walk in and mark your coins. So no fear about having any sort of 51% or anything.

This way the recipient makes sure you don't send the coin to anyone else during that period.
And you make sure a hacker cannot just take control of the web server and steal your coins.

I really don't see any major drawback, but I'm fairly new to crypto currencies, so...

[jackjack]

https://en.bitcoin.it/wiki/Contracts

[ixne]

Your scheme seems needlessly complicated. What is the practical difference between what you propose and just sending your coins to an exchange that supports some sort of escrow protocol?

[Kouye]

https://en.bitcoin.it/wiki/Contracts

Thank you, jackjack, this is very interesting.
This BTC protocol is really awesome. But what I'm talking about is a bit more simple. Issue Shadow coins. That would be a simplified form of contract, which, as powerful as it seems, looks too complicated for casual users.
And we do want casual users to adopt BTC, don't we ?

Your scheme seems needlessly complicated. What is the practical difference between what you propose and just sending your coins to an exchange that supports some sort of escrow protocol?

Difference is that coins would still be safe in your wallet. And which exchange are you using, that are accepting escrow, just out of curiosity ?

[ixne]

Difference is that coins would still be safe in your wallet. And which exchange are you using, that are accepting escrow, just out of curiosity ?

"Safe" is subjective here.  When an exchange has the ability to keep you from spending the money in your wallet "as if they owned it," then you trust that exchange just as much as if you sent those coins to them - at least for the time period specified.

Also, I don't see how the exchanges benefit from this system.  Why would they spend the effort marking and keeping track of your coins only so that you could roll back a transaction whenever you felt like it? How mad would you be if you made a transaction on an exchange for bitcoins, the price went through the roof, and the next day the exchange told you that the deal was cancelled by the original owner?

The escrow scheme I mentioned is just hypothetical.