Bitcoin Covenants Wiki

Introduction

This collaborative web page attempts to be a comprehensive overview of different Bitcoin covenant use cases and consensus change proposals.

Use the side-bar to explore the different use cases and proposals or check out the summary table.

What are "covenants"

The term covenant is borrowed from legal speak and is not very well known in common language. When we talk about "covenants" in bitcoin terms, what we actually mean is the ability for bitcoin Script to introspect the transaction it is executed in. So another, more descriptive, term to use instead of covenants would be "transaction introspection" or "introspection opcodes" specifically when we're talking about Script opcodes.

Bitcoin Script, the scripting language that we use to express conditions for spending unspent transaction outputs (UTXOs), has a set of opcodes that enables users to restrict spending of outputs based mostly on signatures and timing constraints (so-called time-locks).

In principle, Script already has certain introspective capabilities:

  • OP_CHECKSIG, which checks a signature over the "sighash" of a transaction, which hashes together a bunch of properties of the transaction. It only checks the signature though, and doesn't allow for actually looking into the fields that make up the sighash.
  • OP_CHECKLOCKTIMEVERIFY, which checks that the nLockTime field of the transaction is higher than a certain value
  • OP_CHECKSEQUENCEVERIFY, which equivalently checks that the nSequence field of an input is higher than a certain value.

However, even though the above three opcodes exist today and in principle provide some very rudimentary introspection in the spending transaction, their capabilities is extremely restricted and intended for some very specific usage.

So, when we speak about "covenants" or "transaction introspection", what we mean is the generalized capability of Script to look into or assert various properties of the spending transaction.

Contributing

This web page is definitely not a finished work. Since it is collaborative, everyone is very much invited to contribute to it on GitHub!

Apart from content contributors, some help would also be appreciated on the website; we use the static site generator Zola and the AdiDoks theme.

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