Confidential Data Disk Encryption brings guest-side encryption and attestation-based key release to attached data disks on Azure confidential VMs.
Sensitive workloads need protection beyond the operating system. Azure confidential VM workloads rely on OS, temporary, and attached data disks, and protecting all three is essential to extending confidentiality. Existing storage- and host-based encryption protect data at rest, but host-based encryption retains the Azure host within the trust boundary. Building on confidential OS disk encryption, Confidential Data Disk Encryption extends protection to temporary and attached data disks by encrypting inside the confidential guest, before data reaches the host.
Confidential Data Disk Encryption (CDDE), currently in private preview, combines encryption inside the confidential VM with customer-managed keys and attestation-based key release, authorization govern access to encrypted data disks, aligning disk protection with the confidential computing threat model rather than requiring trust in the host. This empowers organizations to bring their persistent application data within their confidential computing security architecture.
Why data disk protection matters
Azure confidential VMs create a hardware-enforced boundary between workloads and the underlying virtualization infrastructure. Confidential OS disk encryption complements that boundary by protecting the operating system disk and its keys.
Attached data disks need their own protection. Azure Storage server-side encryption already encrypts managed disks at rest, including configurations that use customer-managed keys. CDDE adds a different layer: encryption performed inside the confidential guest, with access to key material governed by authorization and attestation policy.
The distinction is where encryption happens and what must be verified before keys become available. CDDE brings those controls closer to the workload consuming the data, rather than relying on storage encryption alone.
How CDDE works
CDDE connects Azure managed disks, a Disk Encryption Set (DES), a customer-managed key, and a guest extension running inside the confidential VM. The documented setup uses mHSM and a dedicated user-assigned managed identity for confidential data disk encryption.
At a high level, the workflow has three stages:
- Configure the disk and key relationship: Create the customer-managed key with the required Secure Key Release policy, reference it through a confidential DES, and associate the data disk with that DES. The data-disk design uses a separate DES from the confidential OS disk because their key policies differ.
- Authorize and attest the guest: The guest extension uses the configured managed identity and obtains attestation evidence. Secure Key Release evaluates the required authorization and attestation claims against the key's release policy before releasing key material to the approved environment.
- Encrypt and unlock inside the VM: The extension performs data disk encryption in the guest, using LUKS2 on Linux or BitLocker on Windows. The architecture also includes an unlock flow for encrypted volumes and seamless customer managed key rotation.
This design combines two complementary controls: identity establishes who may request access, while attestation provides evidence about the environment receiving the key. Confidential VM isolation helps protect released key material in memory from the host.
Customer-controlled keys, with policy-based release
Customer-managed keys are central to the documented CDDE configuration. Customers configure the key, the identities permitted to use it, and the release policy that governs access to key material. Secure Key Release adds an environmental condition to that access decision. Possession of an authorized identity is not the only requirement: the requesting environment must also satisfy the configured attestation policy.
For organizations evaluating confidential computing for sensitive or regulated workloads, this provides a concrete architectural control to assess alongside application security, access management, and operational procedures.
Getting started with the private preview
Begin by confirming CDDE enablement for your subscription and target region with your Microsoft account team.
Bringing persistent data into your confidential computing architecture
CDDE extends the role of confidential computing beyond memory and the operating system disk to the attached disks that hold application data. By combining guest-side encryption, customer-managed keys, and attestation-based release, it gives organizations another building block for protecting sensitive workloads on Azure.
To evaluate CDDE, work with your Microsoft account team to confirm private-preview access and obtain the current deployment and validation guidance.
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