SIGHASH_ANYPREVOUT

SIGHASH_ANYPREVOUT, or BIP-118 (previously named SIGHASH_NOINPUT), is a soft-fork that allows a transaction to be signed without reference to any specific previous output, such that later any output with a matching signature can be dynamically added later.

Use Cases

There are two main super-powerful things you can do with BIP-118 that you cannot do otherwise:

Steps to Activation

  1. Get the updated BIP merged.
  2. Have the benefits and tradeoffs of the change explained in clear form and acknowledged by anyone who may be interested (this website is an attempt at this).
  3. Get working (?) code for it.
  4. Make a testnet for it.
  5. (Who knows what has to happen for something to be soft-forked in, but let's hope at this point miners will push for it themselves so it won't take 2 years.)