Our test framework's EC key wrapper (qa/rpc-tests/test_framwork/key.py) doesn't support a way to enforce low-S use in signatures. This is an annoyance when writing tests for mempool acceptance, as our standardness rules now enforce low-S.
If someone wants to improve this, it would be nice to add an interface that would allow us to explicitly choose a low-S or high-S signature (either when signing, or as a separate function that would do the conversion).
It's implemented upstream: https://github.com/petertodd/python-bitcoinlib/blob/master/bitcoin/core/key.py#L272
Somebody needs to update the test framework.
@jonasschnelli: I believe that if we want to use that code, we'd need the author to submit it here, as python-bitcoinlib is now LGPL, which isn't compatible with this project (sigh).
Yes, we can't do that unless we want to depend on an external library for the test framework. (it's only not compatible if we want to include it into the repository)
@sdaftuar @wumpus GPL is incompatible with MIT because GPL infects whatever uses it. So if your code uses an API of a GPL library, your code must be licensed GPL.
However, The Lesser-GPL was designed for libraries and does not infect it's consumers allowing you to license your own code as you please, while requiring the LGPL library to be distributed on the LGPL terms.
@btcdrak That's not true. Your code can remain MIT-licensed and use GPL code, so long as it's distributed under the terms of the GPL. This still allows others to rip out the GPL dependency and use your code without following the GPL terms. We don't want to have this kind of thing in the repository, but it's not a legal problem.
Ok, closing for now, as this is part of #8499.