When looking for a secure way to store your bitcoin wallet details, paper wallets are one way to go. Software engineer Chris Cassano has a solution in the form of Piper wallet. It's a self-contained device that generates strong keys and prints them on a till-roll for safe keeping.

The Piper wallet is a Raspberry Pi powered device that can either be used as a standalone machine, or can be connected to a display (via HDMI), keyboard (and mouse), and even a USB printer.

As we recently saw with the flaw in the Android operating system, the randomness of numbers used to generate a private encryption key is crucial to protecting your wallet. Because bitcoin uses elliptic curve key cryptography, it's possible to reverse engineer a wallet's private key if the random numbers used in their generation and subsequent transactions are at all predictable.

Cassano claims that the hardware random number generator used in his Raspberry Pi based device satisfies all 26 of the "diehard" random number statistical analysis tests. In addition to being printed, private keys can be backed up on to a USB key in JSON format (as used by blockchain.info and others).

In addition to bitcoin wallets, the Piper Wallet also supports Litecoin and works with the Electrum desktop bitcoin client.

Piper Wallet uses a thermal printer rather than laying down ink. Thermal printing uses a special paper that is coated with a chemical that changes colour when exposed to heat. This means you won't have to spend money on ink to keep the device running. Cassano claims that the prints produced by the Piper will last for 10 years if kept in a cool, dark and dry environment.

There are two versions of the Piper Wallet, respectively based on the Model A and Model B Raspberry Pi designs. The Piper Wallet models cost 1.95 BTC ($199) and 2.14 BTC ($219) respectively.