2

Coinkite Opendime

REVIEW

FIELD TEST

017 was the year cryptocurrencies

truly went mainstream. Previously

the reserve of computer scientists and

crypto-anarchists, cryptocurrencies like

Bitcoin and Litecoin dominated headlines

• thanks in no small part to an explosion
  in value that saw the value of Bitcoin increase tenfold
  over the year.
  Bitcoin, though, has a problem: scaling. Its peer-to-
  peer trustless ‘blockchain’ technology only supports
  between four and eight transactions per second,
  gathered and processed in 1MB blocks every ten
  minutes. What was plenty in 2010, when a handful of
  early adopters were buying pizzas for 10 000 Bitcoin,
  is woefully inadequate now millions of users around
  the globe are looking to play.
  Coinkite’s solution to the problem is unique: the
  Opendime, a hardware wallet which turns Bitcoin into
  a highly secure and tamperproof digital bearer bond.
  Measuring 47 mm long, the Opendime looks like
  a USB flash drive stripped of its casing. When first
  connected to a PC it shows up as a flash drive with a
  set of instructions telling you to drag-and-drop a file
  of at least 256kB in size. This file provides entropy,
  or randomness, which is combined with data from a
  hardware true random number generator (TRNG) to
  generate a Bitcoin private key – the part of a Bitcoin
  wallet you need in order to actually spend your hard-
  earned cryptocurrency.
  So far, so standard-hardware-wallet. Where the
  Opendime differs is in how it uses the private key
  post-generation: the key is stored in a secure enclave
  on the device’s processor, wholly inaccessible to
  the user. In this state you can load Bitcoin onto the
  Opendime – the public key being accessible on any
  PC, smartphone, or tablet with USB mass storage
  support – but have no way to retrieve it again.
  To spend any stored Bitcoin, you need to physically
  cut off the transparent protective heat-shrink
  wrapping surrounding the device and push a pin
  through a hole on the underside of the Opendime.
  Doing so pops a small resistor off the board, and the

2

Coinkite Opendime

A smart, secure,

attractive, but

ultimately

expensive way to

transact Bitcoin

in person.

7 / 10

VERDICT

Below

An Opendime’s

public key is always

accessible, but its

private key stays

locked away

Above

The Coinkite

Opendime offers

a secure way to

transact the Bitcoin

cryptocurrency

in person

$37.50 for three opendime.com

next time the Opendime is connected it permanently

and irrevocably unlocks itself – providing a copy of the

previously hidden private key which can then be used

to ‘sweep’ the coins away from the Opendime and

into a more traditional ‘hot’ Bitcoin wallet for spending

on whatever you fancy.

It’s a trick that makes the Opendime an expensive

way to spend Bitcoin: while you can technically reuse

an Opendime once unlocked, doing so loses its

security. Coinkite’s vision is that Opendimes can be

used for in-person transactions – buying a car, say, or

giving someone Bitcoin as a birthday present – with

the cast-iron guarantee, not available from traditional

wallets, that nobody has sneakily kept a copy of the

private key in order to steal the coins away again.

It’s a fantastic idea with only one issue: price. At

$37.50 plus shipping and VAT for a three-pack, a

single Opendime will set you back around £15 – an

expensive ‘gift card’ to be handing someone, but one

they are sure to find interesting.

By Gareth Halfacree @ghalfacree