  The Bitcoin system only provides eventual consistency. For everyday life, the
time to confirm a Bitcoin transaction is prohibitively slow. In this paper we
propose a new system, built on the Bitcoin blockchain, which enables strong
consistency. Our system, PeerCensus, acts as a certification authority, manages
peer identities in a peer-to-peer network, and ultimately enhances Bitcoin and
similar systems with strong consistency. Our extensive analysis shows that
PeerCensus is in a secure state with high probability. We also show how
Discoin, a Bitcoin variant that decouples block creation and transaction
confirmation, can be built on top of PeerCensus, enabling real-time payments.
Unlike Bitcoin, once transactions in Discoin are committed, they stay
committed.
