Jeremy jlrubin at mit.edu
Tue Nov 26 01:50:40 UTC 2019

Bitcoin Developers,

Pleased to announce refinements to the BIP draft for OP_CHECKTEMPLATEVERIFY
(replaces previous OP_SECURETHEBAG BIP). Primarily:

1) Changed the name to something more fitting and acceptable to the
2) Changed the opcode specification to use the argument off of the stack
with a primitive constexpr/literal tracker rather than script lookahead
3) Permits future soft-fork updates to loosen or remove "constexpr"
4) More detailed comparison to alternatives in the BIP, and why
OP_CHECKTEMPLATEVERIFY should be favored even if a future technique may
make it semi-redundant.

Please see:
BIP: https://github.com/JeremyRubin/bips/blob/ctv/bip-ctv.mediawiki
Reference Implementation:

I believe this addresses all outstanding feedback on the design of this
opcode, unless there are any new concerns with these changes.

I'm also planning to host a review workshop in Q1 2020, most likely in San
Francisco. Please fill out the form here https://forms.gle/pkevHNj2pXH9MGee9
if you're interested in participating (even if you can't physically attend).

And as a "but wait, there's more":

1) RPC functions are under preliminary development, to aid in testing and
evaluation of OP_CHECKTEMPLATEVERIFY. The new command `sendmanycompacted`
shows one way to use OP_CHECKTEMPLATEVERIFY. See:
`sendmanycompacted` is still under early design. Standard practices for
using OP_CHECKTEMPLATEVERIFY & wallet behaviors may be codified into a
separate BIP. This work generalizes even if an alternative strategy is used
to achieve the scalability techniques of OP_CHECKTEMPLATEVERIFY.
2) Also under development are improvements to the mempool which will, in
conjunction with improvements like package relay, help make it safe to lift
some of the mempool's restrictions on longchains specifically for
This work offers an improvement irrespective of OP_CHECKTEMPLATEVERIFY's

Neither of these are blockers for proceeding with the BIP, as they are
ergonomics and usability improvements needed once/if the BIP is activated.

See prior mailing list discussions here:


Thanks to the many developers who have provided feedback on iterations of
this design.



@JeremyRubin <https://twitter.com/JeremyRubin>
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