Fidelity bond wallets are intended to be used when at a later date
using fidelity bonds to greatly increase joinmarket's resistance to
sybil attacks. This commit adds support for timelocked addresses.
It allows users to optionally create wallet which support such
addresses. The synchronization code is modified to also scan for
timelocked addresses. The keypairs of the timelocked addresses go in
the newly created 2nd address type, where before the zeroth index were
receive addresses and first index was change.
The locktime dates are fixed at the first of each month for the next 30
years. This means users dont need to remember any dates, and so just
their seed phrase and wallet type will still be enough to recover all
funds. Each keypair used for timelocking requires an additional 360
addresses to be scanned for, which isn't a problem for Bitcoin Core.
Fidelity bonds are only stored in the zeroth mixdepth, as they are not
used in repeated coinjoins so theres no point having them in multiple
mixdepths.
Timelocked addresses don't use the get_new_script() family of functions
because they all assume that one index equals one address, and that
therefore it's possible to ask for a "next" address. For timelocked
addresses knowing the index is not enough to know the address, the
timestamp must be known too. Also once one address made of
(index, timestamp) is used you mustn't use that index and pubkey again,
even though all the other timelocks for that index/pubkey are unused.
This is for privacy reasons, as its equivalent to address reuse.
chris-belcher
dc715c9481