[Bitcoin-development] To prevent arbitrary data storage in txouts — The Ultimate Solution

[Gregory Maxwell <gmaxwell@gmail.com>]

(1) Define a new address type, P2SH^2 like P2SH but is instead
H(H(ScriptPubKey)) instead of H(ScriptPubKey). A P2SH^2 address it is
a hash of a P2SH address.

(2) Make a relay rule so that to relay a P2SH^2  you must include
along the inner P2SH address.  All nodes can trivially verify it by
hashing it.

(2a) If we find that miners mine P2SH^2 addresses where the P2SH
wasn't relayed (e.g. they want the fees) we introduce a block
discouragement rule where a block is discouraged if you receive it
without receiving the P2SH^2 pre-images for it.

With this minor change there is _no_ non-prunable location for users
to cram data into except values.  (and the inefficiency of cramming
data into values is a strong deterrent in any case)

The same thing could also be done for OP_RETURN PUSH value outputs
used to link transactions to data. Make the data be a hash, outside of
the txn include the preimage of the hash.