- Does Kraken use cold storage (an offline wallet that cannot be accessed should the exchange's service become compromised)
Most definitely. A small percentage of the funds are kept in a hot wallet for withdrawals but the vast majority are kept in cold storage, offline.
If so, then there are other questions:
- Is there a target as to how much of customer's funds are kept in cold storage? (e.g., percent of total, or perhaps relative to recent withdrawal requirements)?
- Do new deposits go to cold storage? (if the hot wallet is compromised, new deposits made (e.g., automated payouts by mining pools) would still be secure)
- Does the offline wallet where the cold storage resides remain protected due to an "air gap" (no access to it electronically, not connected to the network)?
1. We don't have enough (any) experience here to give solid numbers. It's going to depend on our daily withdrawal requirements. My feeling is that if you need to withdraw a lot of BTC at once, you can probably wait a bit so it's better to sacrifice a little convenience for better security and only keep what is likely to be necessary in the hot wallet.
2. Yes, all new deposits go directly to cold storage, for exactly that reason.
3. Yes, cold storage is completely offline.
Hum, that seems too perfect to be true. You are stating cold storage is completely offline. When refilling the hotwallet, at some point you have to broadcast the transaction to the network (be online). I guess you are signing the transaction offline then and broadcasting it from a connected node. What software do you use to perform such a task ? (the only one I know of is Armory available at
https://bitcoinarmory.com/get-armory/ which is no longer usable for most of computers) Is it a self-made solution ? Are you using the native API calls createrawtransaction and signrawtransaction ? (which are tricky to manipulate because of local change addresses and require an in-depth understanding of the bitcoin protocol). I would love to see such an implementation if that's the case.
Otherwise, no chance your cold storage is completely offline.
For the new deposits security issues, one can argue it's not completely true. Since compromising the hotwallet generally means compromising the webserver, an attacker can then just modify the deposit addresses shown and new deposits will go right into his pocket. (Of course deposits to old addresses will still be secure)
Good luck guys, your project seems solid and looks like it may be the one serious professional-grade exchange the community is desperatly looking for.