Which of the following are true about trusted or untrusted clouds? (Select all that apply.)

	a.	Challenge-response is used to ensure data is stored in the cloud.
	b.	Open Authentication is a protocol used to grant temporary access to cloud resources.
	c.	BBS Proxy Re-encryption is used to enable access control to cloud resources without divulging credentials to the cloud.
	d.	There is no mechanism to prevent other cloud clients from intercepting data during computation.