This is an escrow meta-contract that allows multiple users to create independent escrows. Each escrow involves two users and has a unique id (for future calls to reference it).
Party A (the creator) locks some funds in an escrow, with a given recipient and
a lock. The lock is the public part of a cryptographic key-pair. Anyone with the
private key corresponding to the lock, can call the withdraw method to release
the funds to the recipient. At any time, the creator can call the cancel
method to cancel the escrow and get their deposit back.
Note that only the creator can call the cancel method, but anyone can call the
withdraw method as long as they have the secret key.