Multi-signature wallet

4.1. BitCorp has just noticed that Mallory has compromised one of their servers holding

their Bitcoin private keys. Luckily, they are using a 2-of-3 multi-signature wallet, so

Mallory has learnt only one of the three sets of keys. The other two sets of keys are on

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different servers that Mallory cannot access. How do they re-secure their wallet and

effectively revoke the information that Mallory has learned?

4.2. If BitCorp uses a 2-out-of-2 instead of a 2-out-3 wallet, what steps can they take in

advance so that they can recover even in the event of one of their servers getting

broken into (and Mallory not just learning but also potentially deleting the key

material on that server)?

Mallory is just a person's name