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132 lines
8.4 KiB
Markdown
132 lines
8.4 KiB
Markdown
# Key management and cryptographic primitives
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Constellation protects and isolates your cluster and workloads.
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To that end, cryptography is the foundation that ensures the confidentiality and integrity of all components.
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Evaluating the security and compliance of Constellation requires a precise understanding of the cryptographic primitives and keys used.
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The following gives an overview of the architecture and explains the technical details.
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## Confidential VMs
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Confidential VM (CVM) technology comes with hardware and software components for memory encryption, isolation, and remote attestation.
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For details on the implementations and cryptographic soundness, refer to the hardware vendors' documentation and advisories.
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## Master secret
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The master secret is the cryptographic material used for deriving the [*clusterID*](#cluster-identity) and the *key encryption key (KEK)* for [storage encryption](#storage-encryption).
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It's generated during the bootstrapping of a Constellation cluster.
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It can either be managed by [Constellation](#constellation-managed-key-management) or an [external key management system](#user-managed-key-management).
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In case of [recovery](#recovery-and-migration), the master secret allows to decrypt the state and recover a Constellation cluster.
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## Cluster identity
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The identity of a Constellation cluster is represented by cryptographic [measurements](attestation.md#runtime-measurements):
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The **base measurements** represent the identity of a valid, uninitialized Constellation node.
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They depend on the node image, but are otherwise the same for every Constellation cluster.
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On node boot, they're determined using the CVM's attestation mechanism and [measured boot up to the read-only root filesystem](images.md).
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The **clusterID** represents the identity of a single initialized Constellation cluster.
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It's derived from the master secret and a cryptographically random salt and unique for every Constellation cluster.
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The [Bootstrapper](components.md#bootstrapper) measures the *clusterID* into its own PCR before executing any code not measured as part of the *base measurements*.
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See [Node attestation](attestation.md#node-attestation) for details.
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The remote attestation statement of a Constellation cluster combines the *base measurements* and the *clusterID* for a verifiable, unspoofable, unique identity.
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## Network encryption
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Constellation encrypts all cluster network communication using the [container network interface (CNI)](https://github.com/containernetworking/cni).
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See [network encryption](networking.md) for more details.
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The Cilium agent running on each node establishes a secure [WireGuard](https://www.wireguard.com/) tunnel between it and all other known nodes in the cluster.
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Each node creates its own [Curve25519](http://cr.yp.to/ecdh.html) encryption key pair and distributes its public key via Kubernetes.
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A node uses another node's public key to decrypt and encrypt traffic from and to Cilium-managed endpoints running on that node.
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Connections are always encrypted peer-to-peer using [ChaCha20](http://cr.yp.to/chacha.html) with [Poly1305](http://cr.yp.to/mac.html).
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WireGuard implements [forward secrecy with key rotation every 2 minutes](https://lists.zx2c4.com/pipermail/wireguard/2017-December/002141.html).
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Cilium supports [key rotation](https://docs.cilium.io/en/stable/gettingstarted/encryption-ipsec/#key-rotation) for the long-term node keys via Kubernetes secrets.
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## Storage encryption
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Constellation supports transparent encryption of persistent storage.
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The Linux kernel's device mapper-based encryption features are used to encrypt the data on the block storage level.
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Currently, the following primitives are used for block storage encryption:
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* [dm-crypt](https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/dm-crypt.html)
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* [dm-integrity](https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/dm-integrity.html)
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Adding primitives for integrity protection in the CVM attacker model are under active development and will be available in a future version of Constellation.
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See [encrypted storage](encrypted-storage.md) for more details.
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As a cluster administrator, when creating a cluster, you can use the Constellation [installation program](orchestration.md) to select one of the following methods for key management:
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* Constellation-managed key management
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* User-managed key management
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### Constellation-managed key management
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#### Key material and key derivation
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During the creation of a Constellation cluster, the cluster's master secret is used to derive a KEK.
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This means creating two clusters with the same master secret will yield the same KEK.
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Any data encryption key (DEK) is derived from the KEK via HKDF.
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Note that the master secret is recommended to be unique for every cluster and shouldn't be reused (except in case of [recovering](../workflows/recovery.md) a cluster).
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#### State and storage
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The KEK is derived from the master secret during the initialization.
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Subsequently, all other key material is derived from the KEK.
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Given the same KEK, any DEK can be derived deterministically from a given identifier.
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Hence, there is no need to store DEKs. They can be derived on demand.
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After the KEK was derived, it's stored in memory only and never leaves the CVM context.
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#### Availability
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Constellation-managed key management has the same availability as the underlying Kubernetes cluster.
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Therefore, the KEK is stored in the [distributed Kubernetes etcd storage](https://kubernetes.io/docs/tasks/administer-cluster/configure-upgrade-etcd/) to allow for unexpected but non-fatal (control-plane) node failure.
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The etcd storage is backed by the encrypted and integrity protected [state disk](images.md#state-disk) of the nodes.
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#### Recovery
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Constellation clusters can be recovered in the event of a disaster, even when all node machines have been stopped and need to be rebooted.
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For details on the process see the [recovery workflow](../workflows/recovery.md).
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### User-managed key management
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User-managed key management is under active development and will be available soon.
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In scenarios where constellation-managed key management isn't an option, this mode allows you to keep full control of your keys.
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For example, compliance requirements may force you to keep your KEKs in an on-prem key management system (KMS).
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During the creation of a Constellation cluster, you specify a KEK present in a remote KMS.
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This follows the common scheme of "bring your own key" (BYOK).
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Constellation will support several KMSs for managing the storage and access of your KEK.
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Initially, it will support the following KMSs:
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* [AWS KMS](https://aws.amazon.com/kms/)
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* [GCP KMS](https://cloud.google.com/security-key-management)
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* [Azure Key Vault](https://azure.microsoft.com/en-us/services/key-vault/#product-overview)
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* [KMIP-compatible KMS](https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=kmip)
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Storing the keys in Cloud KMS of AWS, GCP, or Azure binds the key usage to the particular cloud identity access management (IAM).
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In the future, Constellation will support remote attestation-based access policies for Cloud KMS once available.
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Note that using a Cloud KMS limits the isolation and protection to the guarantees of the particular offering.
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KMIP support allows you to use your KMIP-compatible on-prem KMS and keep full control over your keys.
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This follows the common scheme of "hold your own key" (HYOK).
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The KEK is used to encrypt per-data "data encryption keys" (DEKs).
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DEKs are generated to encrypt your data before storing it on persistent storage.
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After being encrypted by the KEK, the DEKs are stored on dedicated cloud storage for persistence.
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Currently, Constellation supports the following cloud storage options:
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* [AWS S3](https://aws.amazon.com/s3/)
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* [GCP Cloud Storage](https://cloud.google.com/storage)
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* [Azure Blob Storage](https://azure.microsoft.com/en-us/services/storage/blobs/#overview)
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The DEKs are only present in plaintext form in the encrypted main memory of the CVMs.
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Similarly, the cryptographic operations for encrypting data before writing it to persistent storage are performed in the context of the CVMs.
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#### Recovery and migration
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In the case of a disaster, the KEK can be used to decrypt the DEKs locally and subsequently use them to decrypt and retrieve the data.
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In case of migration, configuring the same KEK will provide seamless migration of data.
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Thus, only the DEK storage needs to be transferred to the new cluster alongside the encrypted data for seamless migration.
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