GCP - Secret Manager vs Cloud KMS
The fundamental difference between GCP Secret Manager and Google Cloud KMS is what they are designed to protect.
- Secret Manager stores and manages the secrets themselves, like passwords or API keys.
- Cloud KMS creates and manages the cryptographic keys that are used to encrypt and decrypt data.
Think of it this way: Secret Manager is the secure vault where you put your valuable items. Cloud KMS is the service that manufactures and operates the un-copyable key that locks the vault.
GCP Secret Manager
The primary purpose of Secret Manager is to provide a central, secure place to store sensitive configuration data that your applications need at runtime. It is the right choice when your code needs to retrieve the actual content of a secret to function.
Its main use cases include:
- Storing database credentials that an application needs to connect to a database.
- Managing API keys for third-party services like Stripe or Twilio.
- Handling TLS certificates and their corresponding private keys.
Key features of Secret Manager revolve around managing the lifecycle of these secrets. It supports versioning, so you can update a password and easily roll back to a previous version if needed. It also allows you to set up rotation schedules to enforce good security hygiene. Access to secrets is tightly controlled through granular IAM permissions, ensuring only authorized applications or users can retrieve a secret's value.
Google Cloud KMS (Key Management Service)
Cloud KMS has a different job. It never stores your raw data or secrets. Instead, it manages the cryptographic keys you use to protect that data. The most important principle of KMS is that the actual key material can be used for cryptographic operations, but it can never be viewed or exported from the service.
You should use Cloud KMS when your primary goal is to perform encryption or decryption without ever handling the keys yourself.
Its main use cases include:
- Application-Level Encryption: Your application can send sensitive data (like a user's credit card number) to the KMS API and have it returned in an encrypted format. The application only ever handles the encrypted data.
- Customer-Managed Encryption Keys (CMEK): This is a major use case where you tell other GCP services, like Cloud Storage or BigQuery, to use a key that you control in KMS to encrypt their data at rest. This gives you authority over the data's security.
- Digital Signing: Using asymmetric keys in KMS to create and verify digital signatures, which proves data integrity and authenticity.
How They Work Together for Enhanced Security
Secret Manager and Cloud KMS are not mutually exclusive; they are designed to integrate for a more secure solution.
By default, every secret you put into Secret Manager is encrypted by Google. However, for maximum control, you can configure Secret Manager to use a key from your own Cloud KMS project to perform this encryption. This is an example of CMEK.
When you do this, you gain ultimate authority. If you disable or destroy the KMS key, the secret it was protecting in Secret Manager becomes permanently inaccessible and unusable, even by Google. This provides a powerful layer of security and control over your most sensitive application credentials.