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IaaS Encryption: Object Storage

By Rich

Sorry, but the title is a bit of a bait and switch. Before we get into object storage encryption we need to cover using proxies for volume encryption.

Proxy encryption

The last encryption option uses an inline software encryption proxy to encrypt and decrypt data. This option doesn’t work for boot volumes, but may allow you to encrypt a wider range of storage types, and offers an alternate technical architecture for connecting to external volumes.

The proxy is a virtual appliance running in the same zone as the instance accessing the data and the storage volume. We are talking about IaaS volumes in this section, so that will be our focus.

The storage volume attaches to the proxy, which performs all cryptographic operations. Keys can be managed in the proxy or extended to external key management using the options we already discussed. The proxy uses memory protection techniques to resist memory parsing attacks, and never stores unencrypted keys in its own persistent storage.

The instance accessing the data then connects to the proxy using a network file system/sharing protocol like iSCSI. Depending on the pieces used this could, for example, allow multiple instances to connect to a single encrypted storage volume.

Protecting object storage

Object storage such as Amazon S3, Openstack Swift, and Rackspace Cloud Files, is fairly straightforward to encrypt, with three options:

  • Server-side encryption
  • Client/agent encryption
  • Proxy encryption

As with our earlier examples overall security is dependent on where you place the encryption agent, key management, and data. Before we describe these options we need to address the two types of object storage. Object storage itself, like our examples above, is accessed and managed only via APIs and forms the foundation of cloud data storage (although it might use traditional SAN/NAS underneath).

There are also a number of popular cloud storage services including Dropbox, Box.com, and Copy.com – as well as applications to build private internal systems – which include basic object storage but layer on PaaS and SaaS features. Some of these even rely on Amazon, Rackspace, or another “root” service to handle the actual storage. The main difference is that these services tend to add their own APIs and web interfaces, and offer clients for different operating systems – including mobile platforms.

Server-side encryption

With this option all data is encrypted in storage by the cloud platform itself. The encryption engine, keys, and data all run within the cloud platform and are managed by the cloud administrators. This option is extremely common at many public cloud object storage providers, sometimes without additional cost.

Server-side encryption really only protects against a single threat: lost media. It is more of a compliance tool than an actual security tool because the cloud administrators have the keys. It may offer minimal additional security in private cloud storage but still fails to disrupt most of the dangerous attack paths for access to the data.

So server-side encryption is good for compliance and may be good useful in private clouds; but it offers no protection against cloud administrators and depending on configuration it may provide little protection for your data in case of management plane compromise.

Client/agent encryption

If you don’t trust the storage environment your best option is to encrypt the data before sending it up. We call this Virtual Private Storage because, as with a Virtual Private Network, we turn a shared public resource into a private one by encrypting the information on it while retaining the keys. The first way to do this is with an encryption agent on the host connecting to the cloud service.

This is architecturally equivalent to externally-managed encryption for storage volumes. You install a local agent to encrypt/decrypt the data before it moves to the cloud, but manage the keys in an external appliance, service, or server. Technically you could manage locally, as with instance-managed encryption, but it is even less useful here than for volume encryption because object storage is normally accessed by multiple systems, so we always need to manage keys in multiple locations.

The minimum architecture is comprised of encryption agents and a key management server. Agents implement the cloud’s native object storage API, and provide logical volumes or directories with decrypted access to the encrypted volume, so applications do not need to handle cloud storage or encryption APIs. This option is most often used with cloud storage and backup services rather than for direct access to root object storage.

Some agents are advances on file/folder encryption, especially for tools like Dropbox or Box.com which are accessed as a normal directory on client systems. But stock agents need to be tuned to work with the specific platform in question – which is outside our object storage focus.

Proxy encryption

One of the best options for business-scale use of object storage, especially public object storage, is an inline or cloud-hosted proxy.

There are two main topologies:

  • The proxy resides on your network, and all data access runs through it for encryption and decryption. The proxy uses the cloud’s native object storage APIs.
  • The proxy runs as a virtual appliance in either a public or private cloud.

You also set two key management options: internal to the proxy or external; and the usual deployment options: hardware/appliance, virtual appliance, or software.

Proxies are especially useful for object storage because they are a very easy way to implement Virtual Private Storage. You route all approved connections through the proxy, which encrypts the data and then passes it on to the object storage service.

Object storage encryption proxies are evolving very quickly to meet user needs. For example, some tie into the Amazon Web Services Storage Gateway to keep some data local and some in the cloud for faster performance. Others not only proxy to the cloud storage service, but function as a normal network file share for local users.

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