Only store your bitcoins with someone who lets you audit them from the blockchain.

Last week, Facebook bought WhatsApp for $19 billion. Right now, the total value of all mined bitcoins at the Bitstamp exchange rate is less than $6 billion. In raw monetary terms, it’s hardly a blip on the radar.

Yet, every day, Bitcoin seems to be grabbing headlines, in both mainstream and technical media, apparently punching well above its dollar weight. Why is everyone so interested?

Bitcoin attracts all of this attention because, fundamentally, it is a groundbreaking new technology. Like so many great inventions before it, this leads to a wealth of new applications, both good and bad, legal and illegal, and the world has taken notice.

One exciting application of the Bitcoin protocol, and the one most talked about to date, is its use as a decentralised form of currency. In the wake of the recent financial crisis, people want more control of their own money, and want to be less reliant on opaque layers of costly transactional services.

In this context, one of the huge benefits of Bitcoin is that all transactions are recorded in a public ledger, the “blockchain”. This empowers users to track their own funds, and to verify their balances without being reliant on an account balance reported by a third party. In short, wherever you store your money, you can check independently that it’s still there.

So what happened at Mt.Gox? While the details are still unclear, it now looks like most customer funds stored at Mt.Gox have been lost. But if it’s all visible in the blockchain, why did nobody notice their account balance dropping?

While I won’t go into the technical details of how Mt.Gox was hacked (see here for more on that), a key part of the problem was their lack of transparency. What the blockchain giveth, Mt.Gox taketh away.

When you make a Bitcoin deposit at Mt.Gox (and at several other wallet/exchange services), your funds are pooled with every other customer’s. If Alice, Bob, and Carol all deposit 5 BTC (bitcoins) each, the exchange puts them all in a pot together, and keeps a record of each customer’s balance in its own database. If Alice sends 2 BTC to Bob, the pool remains unchanged but the exchange updates its database.

This is much like how a traditional bank operates, and works fine when everything is going well. The problem arises when somebody starts stealing from the pooled funds. Because there is no intrinsic link between the funds in the pool and a user’s balance, Carol might log into her account at the exchange and see a balance of 5 BTC, despite the fact that all funds in the pool have been stolen.

So what’s the alternative? Shouldn’t Carol be able to check her balance using the blockchain? At Elliptic, we don’t pool client funds for exactly this reason. When Alice, Bob, and Carol deposit in our Vault, their funds remain segregated. We don’t maintain a separate database to record account balances, because everything is auditable in the blockchain. If Alice wants to transfer 2 BTC to Bob, we make a standard Bitcoin transaction from her wallet to his, and it is recorded publicly in the blockchain.

The grand result of this fund segregation is that all of the bitcoins stored with Elliptic can be verified independently. If you want to know if your funds are still in the Vault, you don’t have to take our word for it – you can audit us using the blockchain. There are several information services out there (e.g. blockchain.info) that allow you to view the balance of a Bitcoin address externally, so you have peace of mind that the bitcoins stored with Elliptic are really there.

In short, if you decide to store your bitcoins with anybody, ensure that you can independently verify your balance. If you have to take their word for it, then you’ve lost the transparency that you first came to Bitcoin looking for.