One of the features of many storage systems and even disk drives is the ability to encrypt the data at rest. This protects against a specific threat – the disk drive going out the back door for replacement or repair. So it was only a matter of time before we would see this important feature start to be offered for Cloud Storage as well. Well, today Amazon announced their Server Side Encryption capability for their S3 cloud offering. This feature was anticipated by the CDMI standard interface when it was finalized as a standard back in April 2010.
Standard Server Side Encryption
So, how does CDMI standardize this feature? Well, as usual, it starts with finding out if the cloud actually supports the feature and what choices are available. In CDMI, this is done through the capabilities resource – a kind of catalog or discovery mechanism. By fetching the capabilities resource for objects, containers, domain or queues, you can tell whether server side encryption of data at rest if available from the cloud offering (yes this is granular for a reason). The actual capability name is: cdmi_encryption (see section 12.1.3). This indicates that the cloud can do encryption for the data at rest, but also indicates whatÂ algorithms are available to do this encryption. The algorithms are expressedÂ in the form of: ALGORITHM_MODE_KEYLENGTH, where:
â€¢ “ALGORITHM” is the encryption algorithm (e.g., “AES” or “3DES”).
â€¢ “MODE” is the mode of operation (e.g.,”XTS”, “CBC”, or “CTR”).
â€¢ “KEYLENGTH” is the key size (e.g.,”128″,”192″, “256”).
So the cloud can offer the user several different algorithms of different strengths and types, or if it only offers a single algorithm (such as the Amazon offering), the cloud storage client can at least understand what that algorithm is.
So how does the user tell the cloud that she wants her data encrypted? Amazon does this with a proprietary header of course, but CDMI does it with standard Data System Metadata that can be placed on any object, container of objects, queue or domain. This metadata is calledÂ cdmi_encryption (seeÂ section 16.4), and contains merely a string with a value chosen from the list of available algorithms in the corresponding capability. There is also a cdmi_encryption_provided metadata value to tell the client whether their data is being encrypted or not by the cloud.
Lastly, there is a system-wide capability calledÂ cdmi_security_encryption (section 12.1.1) that tells the user whether the cloud does server side encryption at all.
Server side encryption is an important capability for cloud storage offerings to provide, which is why CDMI standardized this in advance of having cloud offerings available. We expect more clouds to offer this in the future, and customers to soon realize that – without CDMI implementations, these offerings are locking them in and causing a high cost of exiting that vendor.