Bitcoins get real as physical currency launches

It's the perfect gift for the geek who has everything: 'real' Bitcoins you can hold in your hand, but which still function as legal tender for the online, open-source currency.

Bitcoins are familiar to many as the peer-to-peer 'cryptocurrency' that can be sent over the internet without the need for a bank or payment service - but until now, they didn't exist. At least, not physically. But thanks all changed thanks to an enterprising man from Utah.

Mike Caldwell has created Casascius Bitcoins - physical coins, available in denominations of one and 25 Bitcoins. According to Caldwell's website, each coin has its own Bitcoin address and a redeemable 'private key' hidden inside.

The 25 Bitcoin piece is electroplated with real gold, measures 44.5mm in diameter by 2.9mm thick, and weighs about 35 grams. The 28.6mm one-Bitcoin piece is made from solid brass, and weighs around seven grams.

Each coin contains its own private key, which owners can use to redeem the Bitcoin's value online. It's printed on a card embedded inside the coin, protected by a tamper-proof hologram sticker. If the hologram is peeled back, it leaves behind a honeycomb pattern.

An eight-character code appears around the outside of each coin, matching the first eight characters of the coin's Bitcoin address. As Caldwell's site describes: "There is a mathematical relationship between the Bitcoin address and the private key inside the coin. The digital bitcoin is actually located on the public 'block chain' stored on the internet, but it is completely inaccessible to anyone unless the private key from the coin is loaded into a Bitcoin wallet."

To find out more and to buy your own Bitcoins, visit Mike Caldwell's site here.