[openpgp] cv25519 scalar byte order

[Daniel Kahn Gillmor]

Over in
https://lists.gnupg.org/pipermail/gnupg-devel/2018-February/033437.html,
a discussion was started about scalar byte order for OpenPGP curve 25519

[ gniibe wrote: ]

That would be incorrect. The prefix (e.g. 0x40) indicates a _point_
format and not the format of a scalar. Thus skey[3] MAY not have this
prefix.

what does this "MAY NOT" mean? if this is an attempt at RFC 2119
language, i don't understand it. Do you mean "MUST NOT" ?

I was thinking SHOULD NOT but indeed it MUST be MUST NOT.

What steps are needed to clarify the documentation here so that we can
have interoperable implementations?

I can't remember an open issue regaring this in the WG. Should be
handled there anyway,

I'm moving this discussion to the WG :)

--dkg