A KmsKey represents a customer-managed encryption key used for encrypting data at rest — EBS volumes, S3 buckets, RDS instances, and other resources. On AWS this is a KMS Key, on GCP a Cloud KMS CryptoKey. Hetzner and DigitalOcean do not have equivalent standalone key management services.
AWS KMS keys can be symmetric or asymmetric (default: symmetric). Rotation period sets automatic yearly rotation (when rotationPeriod is specified). Costs $1/month per key plus usage fees.
GCP Cloud KMS keys live in a key ring. The provider manages key ring creation automatically. Rotation period uses duration strings like 90d or 1y.
KMS keys are referenced by other resources (e.g. Bucket, Database) through provider-specific configuration. Future Kyku versions will add a direct reference field on resource configs.