The keyUsage object describes the key usage settings that
are required for the signing certificate. It is constructed with
a character that is used to represent each key usage type. The first
through ninth characters, from left to right, represent the required
value for these properties: digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment, keyAgreement, keyCertSign, crlSign, encipherOnly, decipherOnly.
Any additional characters are ignored.