Casper CBC: Detect equivocating message

Description

equivocating

e.g. a validator simultaneously makes two messages, one with an estimate of 0 and another the estimate 1.

Definitions

$ Sender(m_1) = Sender(m_2) ~ \land ~ m_1 \neq m_2 ~ \land ~ m_1 \not\in Justification(m_2) ~ \land ~ m_2 \not\in Justification(m_1)

Note

Not only message itself but also messages in justification can be equivocating. (see: Casper CBC: Detect invalid message)

e.g. Message acknowledges (i.e. includes in its justification) one message from the malicious validator.

Requirement

Each Message from one validator has different sequence number.

There doesn't exist two blocks from the same sender where there is not a clear order between the two protocol states attested to by the justifications ( see: https://github.com/ethereum/cbc-casper/issues/130#issuecomment-349122525 )

e.g. A validator AA sends two messages estimating two different values 0 and 1, and neither references the other in its justification. ( see: http://hackingresear.ch/cbc-finality/index.html )

References

Casper CBC: Detect invalid message

https://github.com/ethereum/cbc-casper/issues/130#issuecomment-349122525

http://hackingresear.ch/cbc-finality/index.html

#Casper