openpgp: Improve tracking of secret keys.

  - We use marker traits to track with the type system if a Key has
    secret key material attached.  Previously, it was possible to
    subvert that by taking the secret key material using
    Key4::set_secret, creating a Key4<SecretParts, ..> without any
    secrets.

  - Related, the accessor functions returned an
    Option<SecretKeyMaterial> even for Key4<SecretParts, ..>.

  - Replace set_secret by add_secret and take_secret that also change
    the Key's type accordingly.  Make the accessors infallible if we
    know we have a secret key, rename Key4<P, R>::secret to
    Key4<P, R>::optional_secret to make the distinction clear.

  - Fixes #435.

0 files changed, 0 insertions, 0 deletions