This is the third in a three-part series on evolving encryption key management best practices. The first post is available here. This research is also posted at GitHub for public review and feedback. My thanks to Hewlett Packard Enterprise for licensing this research, in accordance with our strict Totally Transparent Research policy, which enables us to release our independent and objective research for free.

Use Cases

Now that we’ve discussed best practices, it’s time to cover common use cases. Well, mostly common – one of our goals for this research is to highlight emerging practices, so a couple of our use cases cover newer data-at-rest key management scenarios, while the rest are more traditional options.

Traditional Data Center Storage

It feels a bit weird to use the word ‘traditional’ to describe a data center, but people give us strange looks when we call the most widely deployed storage technologies ‘legacy’. We’d say “old school”, but that sounds a bit too retro. Perhaps we should just say “big storage stuff that doesn’t involve the cloud or other weirdness”.

We typically see three major types of data storage encrypted at rest in traditional data centers: SAN/NAS, backup tapes, and databases. We also occasionally we also see file servers encrypted, but they are in the minority. Each of these is handled slightly differently, but normally one of three ‘meta-architectures’ is used:

  • Silos: Some storage tools include their own encryption capabilities, managed within the silo of the application/storage stack. For example a backup tape system with built-in encryption. The keys are managed by the tool within its own stack. In this case an external key manager isn’t used, which can lead to a risk of application dependency and key loss, unless it’s a very well-designed product.
  • Centralized key management: Rather than managing keys locally, a dedicated central key management tool is used. Many organizations start with silos, and later integrate them with central key management for advantages such as improved separation of duties, security, auditability, and portability. Increasing support for KMIP and the PKCS 11 standards enables major products to leverage remote key management capabilities, and exchange keys.
  • Distributed key management: This is very common when multiple data centers are either actively sharing information or available for disaster recovery (hot standby). You could route everything through a single key manager, but this single point of failure would be a recipe for disaster. Enterprise-class key management products can synchronize keys between multiple key managers. Remote storage tools should connect to the local key manager to avoid WAN dependency and latency. The biggest issue with this design is typically ensuring the different locations synchronize quickly enough, which tends to be more of an issue for distributed applications balanced across locations than for a hot standby sites, where data changes don’t occur on both sides simultaneously. Another major concern is ensuring you can centrally manage the entire distributed deployment, rather than needing to log into each site separately.

Each of those meta-architectures can manage keys for all of the storage options we see in use, assuming the tools are compatible, even using different products. The encryption engine need not come from the same source as the key manager, so long as they are able to communicate.

That’s the essential requirement: the key manager and encryption engines need to speak the same language, over a network connection with acceptable performance. This often dictates the physical and logical location of the key manager, and may even require additional key manager deployments within a single data center. But there is never a single key manager. You need more than one for availability, whether in a cluster or using a hot standby.

As we mentioned under best practices, some tools support distributing only needed keys to each ‘local’ key manager, which can strike a good balance between performance and security.


There are as many different ways to encrypt an application as there are developers in the world (just ask them). But again we see most organizations coalescing around a few popular options:

  • Custom: Developers program their own encryption (often using common encryption libraries), and design and implement their own key management. These are rarely standards-based, and can become problematic if you later need to add key rotation, auditing, or other security or compliance features.
  • Custom with external key management: The encryption itself is, again, programmed in-house, but instead of handling key management itself, the application communicates with a central key manager, usually using an API. Architecturally the key manager needs to be relatively close to the application server to reduce latency, depending on the particulars of how the application is programmed. In this scenario, security depends strongly on how well the application is programmed.
  • Key manager software agent or SDK: This is the same architecture, but the application uses a software agent or pre-configured SDK provided with the key manager. This is a great option because it generally avoids common errors in building encryption systems, and should speed up integration, with more features and easier management. Assuming everything works as advertised.
  • Key manager based encryption: That’s an awkward way of saying that instead of providing encryption keys to applications, each application provides unencrypted data to the key manager and gets encrypted data in return, and vice-versa.

We deliberately skipped file and database encryption, because they are variants of our “traditional data center storage” category, but we do see both integrated into different application architectures.

Based on our client work (in other words, a lot of anecdotes), application encryption seems to be the fastest growing option. It’s also agnostic to your data center architecture, assuming the application has adequate access to the key manager. It doesn’t really care whether the key manager is in the cloud, on-premise, or a hybrid.

Hybrid Cloud

Speaking of hybrid cloud, after application encryption (usually in cloud deployments) this is where we see the most questions. There are two main use cases:

  • Extending existing key management to the cloud: Many organizations already have a key manager they are happy with. As they move into the cloud they may either want to maintain consistency by using the same product, or need to support a migrating application without having to gut their key management to build something new. One approach is to always call back over the network to the on-premise key manager. This reduces architectural changes (and perhaps additional licensing), but often runs into latency and performance issues, even with a direct network connection. Alternatively you can deploy a virtual appliance version of your key manager as a ‘bastion’ host, and synchronize keys so assets in the cloud connect to the distributed virtual server for better performance.
  • Building a root of trust for cloud deployments: Even if you are fully comfortable deploying your key manager in the cloud, you may still want an on-premise key manager to retain backups of keys or support interoperability across cloud providers.

Generally you will want to run a virtual version of your key manager within the cloud to satisfy performance requirements, even though you could route all requests back to your data center. It’s still essential to synchronize keys, backups, and even logs back on-premise or to multiple, distributed cloud-based key managers, because no single instance or virtual machine can provide sufficient reliability.

Bring Your Own Key

This is a very new option with some cloud providers who allow you to use an encryption service or product within their cloud, while you retain ownership of your keys. For example you might provide your own file encryption key to your cloud provider, who then uses it to encrypt your data, instead of using a key they manage.

The name of the game here is ‘proprietary’. Each cloud provider offers different ways of supporting customer-managed keys. You nearly always need to meet stringent network and location requirements to host your key manager yourself, or you need to use your cloud provider’s key management service, configured so you can manage your keys yourself.