The local hash[] buffer may contain parts of the derived key, so clear
it explicitly to minimize number of unnecessary copies of key material
in memory.
Signed-off-by: Jouni Malinen <j@w1.fi>
Some crypto libraries can return in these functions (e.g., if a specific
hash function is disabled), so we better provide the caller a chance to
check whether the call failed. The return values are not yet used
anywhere, but they will be needed for future changes.
