Bring Your Own Key (BYOK) allows organizations to encrypt data and have full control of their encryption keys.

Each cloud provider offers to Bring Your Own Key (BYOK), but with varying degrees of support. With client-side encryption, the application is typically responsible for encrypting and decrypting the data before sending and receiving it from the cloud service providers. 

With BYOK, organizations can import their own master key, which the cloud provider stores in the key management system (KMS). If the master keys are stored in an external Key Management System, the cloud provider never gets access to the master key.

The cloud provider protects the data encryption keys (DEKs) by using your master key. The organizations always have a copy of the master key in case it is lost or revoked.

"Bring Your Own Key" (BYOK) allows you to retain control over encryption keys even when using a public cloud provider. Instead of letting the cloud provider generate and store your keys, you generate them yourself and inject them into the cloud's KMS. That way, you're not unquestioningly trusting the provider with your data and the keys protecting it. 

You get the advantage of legal separation. Suppose you generate and manage the keys outside the cloud. In that case, you can argue that the provider is merely hosting encrypted content, not having custody of the data in any usable form. That distinction matters when subpoenas, regulatory inquiries, or third-party audits come are sanctioned. For example, a bank operating under GDPR can use BYOK to keep the root of trust within the EU, even if their workloads run in a US-based cloud. 

Another advantage is lifecycle control. When you bring your key, you decide when to rotate, revoke, or destroy it. If your contract with the provider ends or there's a breach, you don't have to request permission to cut off access. You simply delete or disable the key, and the data becomes unreadable. 

Some implementations still allow the cloud provider to hold cached versions of your keys or re-import them under certain conditions. A BYOK setup should include key attestation, strict key access policies, and preferably an external key management system that integrates via APIs such as Key Management Interoperability Protocol (KMIP) or EKM. 

No, BYOK is not fully do-it-yourself. It gives you control over key generation and import, but the moment your keys enter the cloud provider's KMS, you are working within their system, under their policies, and subject to their infrastructure. Sure, you create the key, but then it lives inside someone else's hardware. That's a shared responsibility, not full ownership.

Let's walk through what BYOK looks like. You might generate a key using a hardware security module (HSM) in your own environment. Then, you wrap it, upload it to the cloud provider's KMS, and define who or what can use it. From that point on, the cloud provider enforces the access controls, handles the cryptographic operations, and logs the usage. You're trusting them not to sidestep the rules you set. That's not anything, but it's not complete independence, either.

There's also no simple rollback. Once a key is in the cloud provider's system, deleting it or rotating it isn't always instant or reversible. Unless you have strong logging and attestation, you don't know whether copies were made, how it was cached, or whether it was accessed during a government request you were never told about.

For full control, what you need is external key management, often called "hold your own key" (HYOK) or "external key management" (EKM). In that model, the cloud service reaches out to your key manager every time it needs to use the key. The key never leaves your system. That's absolute control. BYOK is a step in the right direction, but it's only the middle ground.