Cloud External Key Manager

This page provides an overview of Cloud External Key Manager (Cloud EKM).

Terminology

  • External key manager (EKM)

    The key manager used outside of Google Cloud to manage your keys.

  • Cloud External Key Manager (Cloud EKM)

    A Google Cloud service for using your external keys that are managed within a supported EKM.

  • Cloud EKM through the internet

    A version of Cloud EKM where Google Cloud communicates with your external key manager over the internet.

  • Cloud EKM through a VPC

    A version of Cloud EKM where Google Cloud communicates with your external key manager over a Virtual Private Cloud (VPC). For more information, see VPC network overview.

  • EKM key management from Cloud KMS

    When using Cloud EKM through a VPC with an external key management partner that supports the Cloud EKM control plane, you can use the Cloud KMS EKM management mode to simplify the process of maintaining external keys in your external key management partner and in Cloud EKM. For more information, see Coordinated external keys and EKM key management from Cloud KMS on this page.

  • Crypto space

    A container for your resources within your external key management partner. Your crypto space is identified by a unique crypto space path. The format of the crypto space path varies by external key management partner—for example, v0/cryptospaces/YOUR_UNIQUE_PATH.

  • Partner-managed EKM

    An arrangement where your EKM is managed for you by a trusted partner. For more information, see Partner-managed EKM on this page.

  • Key Access Justifications

    When you use Cloud EKM with Key Access Justifications, each request to your external key management partner includes a field that identifies the reason for each request. You can configure your external key management partner to allow or deny requests based on the Key Access Justifications code provided. For more information about Key Access Justifications, see Key Access Justifications overview.

Overview

With Cloud EKM, you can use keys that you manage within a supported external key management partner to protect data within Google Cloud. You can protect data at rest in supported CMEK integration services, or by calling the Cloud Key Management Service API directly.

Cloud EKM provides several benefits:

  • Key provenance: You control the location and distribution of your externally managed keys. Externally managed keys are never cached or stored within Google Cloud. Instead, Cloud EKM communicates directly with the external key management partner for each request.

  • Access control: You manage access to your externally managed keys in your external key manager. You can't use an externally managed key in Google Cloud without first granting the Google Cloud project access to the key in your external key manager. You can revoke this access at any time.

  • Centralized key management: You can manage your keys and access policies from a single user interface, whether the data they protect resides in the cloud or on your premises.

In all cases, the key resides on the external system, and is never sent to Google.

You can communicate with your external key manager via the internet or via a Virtual Private Cloud (VPC).

How Cloud EKM works

Cloud EKM key versions consist of these parts:

  • External key material: The external key material of a Cloud EKM key is cryptographic material created and stored in your EKM. This material does not leave your EKM and it is never shared with Google.
  • Key reference: Each Cloud EKM key version contains either a key URI or a key path. This is a unique identifier for the external key material that Cloud EKM uses when requesting cryptographic operations using the key.
  • Internal key material: When a symmetric Cloud EKM key is created, Cloud KMS creates additional key material in Cloud KMS, which never leaves Cloud KMS. This key material is used as an extra layer of encryption when communicating with your EKM. This internal key material does not apply to asymmetric signing keys.

To use your Cloud EKM keys, Cloud EKM sends requests for cryptographic operations to your EKM. For example, to encrypt data with a symmetric encryption key, Cloud EKM first encrypts the data using the internal key material. The encrypted data is included in a request to the EKM. The EKM wraps the encrypted data in another layer of encryption using the external key material, and then returns the resulting ciphertext. Data encrypted using a Cloud EKM key can't be decrypted without both the external key material and the internal key material.

If your organization has enabled Key Access Justifications, your external key management partner records the provided access justification and completes the request only for justification reason codes that are allowed by your Key Access Justifications policy on the external key management partner.

Creating and managing Cloud EKM keys requires corresponding changes in both Cloud KMS and the EKM. These corresponding changes are handled differently for manually managed external keys and for coordinated external keys. All external keys accessed over the internet are manually managed. External keys accessed over a VPC network can be manually managed or coordinated, depending on the EKM management mode of the EKM via VPC connection. The Manual EKM management mode is used for manually managed keys. The Cloud KMS EKM management mode is used for coordinated external keys. For more information about EKM management modes, see Manually managed external keys and Coordinated external keys on this page.

The following diagram shows how Cloud KMS fits into the key management model. This diagram uses Compute Engine and BigQuery as two examples; you can also see the full list of services that support Cloud EKM keys.

Diagram illustrating encryption and decryption with Cloud EKM

You can learn about the considerations and restrictions when using Cloud EKM.

Manually managed external keys

This section provides a broad overview of how Cloud EKM works with a manually managed external key.

  1. You create or use an existing key in a supported external key management partner system. This key has a unique URI or key path.
  2. You grant your Google Cloud project access to use the key, in the external key management partner system.
  3. In your Google Cloud project, you create a Cloud EKM key version, using the URI or key path for the externally managed key.
  4. Maintenance operations like key rotation must be manually managed between your EKM and Cloud EKM. For example, key version rotation or key version destruction operations need to be completed both directly in your EKM and in Cloud KMS.

Within Google Cloud, the key appears alongside your other Cloud KMS and Cloud HSM keys, with protection level EXTERNAL or EXTERNAL_VPC. The Cloud EKM key and the external key management partner key work together to protect your data. The external key material is never exposed to Google.

Coordinated external keys

This section provides an overview of how Cloud EKM works with a coordinated external key.

  1. You set up an EKM via VPC connection, setting the EKM management mode to Cloud KMS. During setup, you must authorize your EKM to access your VPC network and authorize your Google Cloud project service account to access your crypto space in your EKM. Your EKM connection uses the hostname of your EKM and a crypto space path that identifies your resources within your EKM.

  2. You create an external key in Cloud KMS. When you create a Cloud EKM key using an EKM via VPC connection with the Cloud KMS EKM management mode enabled, the following steps take place automatically:

    1. Cloud EKM sends a key creation request to your EKM.
    2. Your EKM creates the requested key material. This external key material remains in the EKM and is never sent to Google.
    3. Your EKM returns a key path to Cloud EKM.
    4. Cloud EKM creates your Cloud EKM key version using the key path provided by your EKM.

  3. Maintenance operations on coordinated external keys can be initiated from Cloud KMS. For example, coordinated external keys used for symmetric encryption can be automatically rotated on a set schedule. The creation of new key versions is coordinated in your EKM by Cloud EKM. You can also trigger the creation or destruction of key versions in your EKM from Cloud KMS using the Google Cloud console, the gcloud CLI, the Cloud KMS API, or Cloud KMS client libraries.

Within Google Cloud, the key appears alongside your other Cloud KMS and Cloud HSM keys, with protection level EXTERNAL_VPC. The Cloud EKM key and the external key management partner key work together to protect your data. The external key material is never exposed to Google.

EKM key management from Cloud KMS

Coordinated external keys are made possible by EKM via VPC connections that use EKM key management from Cloud KMS. If your EKM supports the Cloud EKM control plane, then you can enable EKM key management from Cloud KMS for your EKM via VPC connections to create coordinated external keys. With EKM key management from Cloud KMS enabled, Cloud EKM can request the following changes in your EKM:

  • Create a key: When you create an externally managed key in Cloud KMS using a compatible EKM via VPC connection, Cloud EKM sends your key creation request to your EKM. When successful, your EKM creates the new key and key material and returns the key path for Cloud EKM to use to access the key.

  • Rotate a key: When you rotate an externally-managed key in Cloud KMS using a compatible EKM via VPC connection, Cloud EKM sends your rotation request to your EKM. When successful, your EKM creates new key material and returns the key path for Cloud EKM to use to access the new key version.

  • Destroy a key: When you destroy a key version for an externally-managed key in Cloud KMS using a compatible EKM via VPC connection, Cloud KMS schedules the key version for destruction in Cloud KMS. If the key version is not restored before the scheduled for destruction period ends, Cloud EKM destroys its part of the key's cryptographic material and sends a destruction request to your EKM.

    Data encrypted with this key version cannot be decrypted after the key version is destroyed in Cloud KMS, even if the EKM has not yet destroyed the key version. You can see whether the EKM has successfully destroyed the key version by viewing the key's details in Cloud KMS.

When keys in your EKM are managed from Cloud KMS, the key material still resides in your EKM. Google can't make any key management requests to your EKM without explicit permission. Google can't change permissions or Key Access Justifications policies in your external key management partner system. If you revoke Google's permissions in your EKM, key management operations attempted in Cloud KMS fail.

Compatibility

Supported key managers

You can store external keys in the following external key management partner systems:

Services that support CMEK with Cloud EKM

The following services support integration with Cloud KMS for external (Cloud EKM) keys:

Considerations

  • When you use a Cloud EKM key, Google has no control over the availability of your externally managed key in the external key management partner system. If you lose keys that you manage outside of Google Cloud, Google can't recover your data.

  • Review the guidelines about external key management partners and regions when choosing the locations for your Cloud EKM keys.

  • Review the Cloud EKM Service Level Agreement (SLA).

  • Communicating with an external service over the internet can lead to problems with reliability, availability, and latency. For applications with low tolerance for these types of risks, consider using Cloud HSM or Cloud KMS to store your key material.

    • If an external key is unavailable, Cloud KMS returns a FAILED_PRECONDITION error and provides details in the PreconditionFailure error detail.

      Enable data audit logging to maintain a record of all errors related to Cloud EKM. Error messages contain detailed information to help pinpoint the source of the error. An example of a common error is when an external key management partner does not respond to a request within a reasonable timeframe.

    • You need a support contract with the external key management partner. Google Cloud support can only help with issues in Google Cloud services and cannot directly assist with issues on external systems. Sometimes, you must work with support on both sides to troubleshoot interoperability issues.

  • Cloud EKM can be used with Bare Metal Rack HSM to create a single-tenant HSM solution integrated with Cloud KMS. To learn more, choose a Cloud EKM partner that supports single-tenant HSMs and review the requirements for Bare Metal Rack HSMs.

  • Enable audit logging in your external key manager to capture access and usage to your EKM keys.

Restrictions

  • Automatic rotation is not supported.
  • When you create a Cloud EKM key using the API or the Google Cloud CLI, it must not have an initial key version. This does not apply to Cloud EKM keys created using the Google Cloud console.
  • Cloud EKM operations are subject to specific quotas in addition to the quotas on Cloud KMS operations.

Symmetric encryption keys

Asymmetric signing keys

External key managers and regions

Cloud EKM needs to be able to reach your keys quickly to avoid an error. When creating a Cloud EKM key, choose a Google Cloud location that is geographically near the location of the external key management partner key. See your external key management partner's documentation to determine which locations they support.

  • Cloud EKM via the internet: available in most Google Cloud locations where Cloud KMS is available, including regional and multi-regional locations.
  • Cloud EKM via a VPC: available in most regional locations where Cloud KMS is available. Cloud EKM via a VPC isn't available in multi-regional locations.

Some locations including global and nam-eur-asia1 aren't available for Cloud EKM. To learn which locations support Cloud EKM, see Cloud KMS locations.

Multi-region use

When you use an externally managed key with a multi-region, the metadata of the key is available in multiple data centers within the multi-region. This metadata includes the information needed to communicate with the external key management partner. If your application fails over from one data center to another within the multi-region, the new data center initiates key requests. The new data center may have different network characteristics from the previous data center, including distance from the external key management partner and the likelihood of timeouts. We recommend only using a multi-region with Cloud EKM if your chosen external key manager provides low latency to all areas of that multi-region.

Partner-managed EKM

Partner-managed EKM lets you use Cloud EKM through a trusted sovereign partner that manages your EKM system for you. With partner-managed EKM, your partner creates and manages the keys that you use in Cloud EKM. The partner ensures that your EKM complies with sovereignty requirements.

When you onboard with your sovereign partner, the partner provisions resources in the Google Cloud and your EKM. These resources include a Cloud KMS project to manage your Cloud EKM keys and an EKM via VPC connection configured for EKM key management from Cloud KMS. Your partner creates resources in Google Cloud locations according to your data residency requirements.

Each Cloud EKM key includes Cloud KMS metadata, which lets Cloud EKM send requests to your EKM to perform cryptographic operations using the external key material that never leaves your EKM. Symmetric Cloud EKM keys also include Cloud KMS internal key material that never leaves Google Cloud. For more information about the internal and external sides of Cloud EKM keys, see How Cloud EKM works on this page.

For more information about partner-managed EKM, see Configure partner-managed Cloud KMS.

Monitor Cloud EKM usage

You can use Cloud Monitoring to monitor your EKM connection. The following metrics can help you understand your EKM usage:

  • cloudkms.googleapis.com/ekm/external/request_latencies
  • cloudkms.googleapis.com/ekm/external/request_count

For more information about these metrics, see cloudkms metrics. You can create a dashboard to track these metrics. To learn how to set up a dashboard to monitor your EKM connection, see Monitor EKM usage.

Getting support

If you experience an issue with Cloud EKM, contact Support.

What's next