[bitcoin-dev] BIP: Bitcoin Integrated Address Feature?

[<nathanw@tutanota.com>]

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To whom it may concern,

I believe a missing feature in Bitcoin is the ability to have an "integrated address", where the address resolves into a Bitcoin address, and also a transaction message or some other kind of identifier.

By having this feature we could enhance the security of exchange cold-wallet systems, by allowing them to easily receive all payments to a single address from an infinite number of customers. We would also greatly simplify the process of setting up and managing exchange cold-wallet systems, because we would eliminate the "sweeping" step required to move multiple customer deposits from a hot address into a single cold address.

Although it would be nice to have all customers deposit directly into cold addresses, this quickly becomes impractical when large amounts of customers begin to use exchange wallets as their personal web-wallet, frequently depositing and withdrawing without trading action. You end up needing to have a staff member moving funds away from cold deposit addresses as a full time job - if you wish to handle customer funds in a completely secure manner.

Thus we see that most exchanges now use the hot-deposit system, where customers deposit into a hot address that is then automatically swept into a singular cold address, by a service which holds customers private keys online. You can observe this service at work simply by making a deposit to most major exchanges (including the largest exchange Binance), as you will see the funds quickly being "swept" to their cold wallet address in a manner which heavily suggests automation by a program which possesses private keys to the address you are sending funds to. This means there is always the danger of a sophisticated hacker being able to capture private keys to customer deposit addresses (as they are clearly being held online). An integrated address would allow all exchanges using this automated hot-deposit service to easily switch to a far more secure alternative of having all customers depositing directly into their singular cold wallet address.

There are several other more minor advantages such a feature would have, including:
- Lower fees for exchanges (which could be passed onto customers), by reducing a transaction step out of the deposit-to-withdrawal flow.
- Less need for large rescans after loading huge amounts of customer addresses into client software.
- Exchanges can more easily provision deposit addresses to new customers in a secure manner, by simply generating a hex or other value, creating an integrated address from the cold wallet address, and then providing this to the customer.
- By providing a singular cold address for exchanges publicly, customers can more easily verify that no man-in-the-middle has given them an incorrect address to deposit to.
The integrated address could work by combining the Bitcoin address together with some kind of hex or other value, allowing users to choose the amount they wish to deposit themselves, but ensuring their deposits are uniquely trackable.

I'm not sure if some kind of functionality already exists in BTC, as I haven't been able to find it. If not, can I submit a proposal to implement this? This feature would be a godsend to all exchange developers if it was widely accepted.

Thanks for your time.
Regards,

Nathan Worsley
CTO - LocalCoinSwap.Com

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