This will be useful in preference to the regular Mac trait for the
places where we need to pass a Mac key around, but we don't need to
support incremental operation.
Part of arti#993, where we want to expose a MAC object without
exposing sensitive data.
In `ArtiNativeKeyStore`, private keys are stored in OpenSSH format.
However, `ssh-key` (the crate we use for parsing OpenSSH keys) doesn't
support x25519 keys. As a workaround, this type of key will stored
as ed25519 and converted to x25519 upon retrieval.
This commit implements the `convert_ed25519_to_curve25519_private`
conversion function (needed by `ArtiNativeKeyStore` to support x25519
keys).
Part of #900
This is mostly code movement; you may want to review it with
`--color-moved`.
I'm doing this so we can also use the function in netdoc for
looking up hsdesc authentication.
There are some places in the protocol where we have an all-zero RSA
identity that does not truly represent a key, but rather represents
an absent or unknown key. For these, it's better to use
`RsaIdentity::is_zero` instead of manually checking for a set of
zero bytes: it expresses the intent better, and ensures that the
operation is constant-time.
I am deliberately not introducing a more general IsZero trait here,
or implementing is_zero for anything else: This is the only one we
seem to need right now. We can generalize it later if we have to.
Nick Mathewson
Gabriela Moldovan