Crypto-currencies or cryptographic currencies emerged in 2009 with the Bitcoin, its vedette, as an alternative to generate value transactions without intermediaries. With a punk rebelliousness mark, they are proposed as a digital currency, independent from any state and financial institution, to generate commercial exchanges person to person, anonymously and eliminating the intervention of third parties. The Bitcoin protocol and its software are public and any programmer in the world can access or create its own software modified version.