Revokes the specified key.
This method revokes the key specified by KeyId and returns the revocation certificate.
When creating a revocation certificate there are two supported formats. The first format includes only the revocation signature. This format is returned by this method. The second format includes both the public key and the revocation signature. This format can be obtained by calling ExportPublicKey after calling this method. Both formats are common, and both formats are acceptable when calling ImportKey.
Before calling this method a key must be selected and available in the Key property.
The KeyId may be the Id of the main key or a subkey.