Hi,

A few weeks ago, I stumbled on
https://hdevalence.ca/blog/2020-10-04-its-25519am. Summary: The
specification for Ed25519 signatures, RFC 8032, doesn't specify
unambiguously which bit strings are valid signatures, and which aren't.
And implementations differ on the details.

This could matter in particular if you have a system that depends on
consensus, one could then feed the system a signed data item, where
different components of the system disagree on whether or not the
signature is valid.

It's not clear to me what's the desired behavior for Nettle's
ed25519_sha512_verify function, advice appreciated. A first step would
be to add tests with the different kinds of corner-case inputs that may
or may not be recognized as valid signatures, and at least document how
they are handled.

Regards,
/Niels

-- 
Niels Möller. PGP key CB4962D070D77D7FCB8BA36271D8F1FF368C6677.
Internet email is subject to wholesale government surveillance.

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