The null crypto algorithms are intended to do nothing: the null digest
algorithm accepts all input and generates a zero-length digest, and
the null cipher algorithm simply copies the input unmodifed to the
output.
The null public-key algorithm currently does nothing successfully.
Unlike the null digest and cipher algorithms, the null public-key
algorithm's methods are never called.
Change the null public-key algorithm to fail all operations, thereby
allowing its methods to be used as stubs by algorithms such as ECDSA
that do not implement all of the possible public-key operations.
Signed-off-by: Michael Brown <mcb30@ipxe.org>