Byzantine Fault Tolerance Consensus Protocol (BFT) 解决的分布式问题是服务器里存在不诚实节点，这些不诚实节点会为了自己的利益去撒谎、向其他节点发送不同的消息、离线．而对于诚实节点，我们规定三种性质：
- Agreement All honest nodes decide on same value.
- Validity If all honest nodes decide on , then the decision is .
- Termination Eventually, all honest nodes must decide.