Bitcoin and Cryptocurrency Technologies

you. In particular, you can’t use a thin SPV client like you can for regular Bitcoin. That makes it harder
to use colored coins on computationally limited devices like mobile phones.
Uses of colored coins and smart property​. ​Stock in a Company.​A frequently cited motivation for
smart property is stock in a company. A company wishing to issue colored coins as stock would
publicize its issuing address, and bitcoins that are colored with this address function as shares. One
satoshi might represent one share in the company. Shareholders can then trade the stock on the
block chain without needing a centralized intermediary like a stock exchange. Of course, shareholders
will have to trust that the company will honor the shares. For example, the company may promise to
disburse dividends proportionally to each stock or to give shareholders voting power in the company’s
decisions. With traditional shares these promises are enforced legally. As of 2015, colored coins or
other block chain‐based assets don’t have legal recognition in any jurisdiction.
Physical property. ​Another potential use is that colored coins might represent a claim to some
real‐world property. For example, a colored coin could be associated with a house or a car. Maybe
you have a sophisticated car that actually tracks a specific colored coin on the block chain, and
automatically starts and drives for anybody who owns that colored coin. Then you could sell your car,
or at least transfer control of it, simply by making a single transaction in the block chain. We’ll see in
Chapter 11 how this can potentially be implemented technologically as well as the social and legal
obstacles to making it happen. But the dream of colored coins and smart property is that any
real‐world property could be represented in the world of Bitcoin and transferred or traded as easily as
bitcoins themselves.
Domain Names​. As a final example, consider using colored coins to perform some of the functions of
the existing Domain Name System: tracking the ownership and transfer of internet domain names as
well as the mapping of domain names to IP addresses. The domain name market has a variety of
interesting properties: there are a potentially infinite number of names, these names have widely
different values based on their memorability and other factors, and the same name might have very
different utility to different people. It is possible to use colored coins to handle domain name
registration and the functions we listed. However, supporting this application has also been the focus
of a prominent altcoin called Namecoin, which we’ll look at in detail in the next chapter. Each
approach has benefits: with colored coins you get the security of Bitcoin’s block chain whereas with
an altcoin it’s easier to implement the complex logic needed for domain name ownership, transfer,
and IP address mapping.
9.3: Secure Multi‐Party Lotteries in Bitcoin
Now we're going to talk about hosting a “coin flip” game in Bitcoin. Again, we'll start off by describing
the offline version of what we're trying to build.
Alice and Bob want to bet five dollars. They both agree to the bet ahead of time and the method for
determining the winner. Bob will flip a coin in the air, and while it’s rotating Alice calls out “Heads” or
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