Motivation
Currently, EVE does not have capability to provide data security at rest. This is being designed and implemented [1]. With this, EVE will provide capabilities like file system encryption, but it is up to the EVE Controller to make use of these capabilities to to achieve a security goal. For this EVE needs to define its interface towards EVE controller, and provision a way to define security policies from the Controller. This proposal focuses more on the interaction between EVE and EVE controller in the context of realising a use case that the user might have to secure data processed on the EVE platform.
Sample Use Cases
Assuming that EVE provides a capability to store some files in an encrypted filesystem.
a) A user might want to run the Edge Containers out of this secure file system, so that data that is stored by these Edge Containers is stored in encrypted form at rest. A user might do this is to prevent an attacker from reading the application data if the EVE node is stolen or drive is taken out.
b) A user might also wish to store sensitive parts of EVE configuration (e.g. Image data store credentials), under this secure file system, so that it stays encrypted at rest.
c) A user might also want to be able to create secure file stores and be able to associate an arbitrary Edge Contrainer with such a secure file store.
d) He can choose to use a separate file store for each of his Edge Containers on an EVE node - so that compromising one vault does not lead to access to data of all the Edge Containers
e) A user might want to control security policies for such file stores using user-defined policies, e.g. whether key is protected by IP fencing, TPM attestation etc.
Proposed Interface between EVE and EVC
We are proposing to have a user visible construct called “Vault”. A Vault is a secure file system, protected by native file system encryption. Therefore the interface has 2 parts to it:
a) Lifecycle management of a “Vault” - How user can create, change, delete a given Vault and its associated policies.
b) Association of Edge Containers with a Vault - To control data at rest requirements of a Edge Container
Option 1: Separate REST API, completely handled by Vault Manager
Current Workflow in Provisioning EVE
The current user driven, device management event flow at a high level, is as follows,
New Stage in the Workflow - The Security Policy Enforcement
We propose a new stage/API in EVE Provisioning, where the controller can enforce the device policies on EVE, before EVE launches the pillar microservices. The reason we need this framework is because:
a) Mostly security policies have to be enforced at the time of EVE Provisioning or at the first handshake after a reboot, to setup the execution environment for launching other pillar services. e.g. one may setup disk encryption or unlock the encrypted directories for use by pillar services later on. Thus this can not be tied into regular config processing logic inside zedagent since we need access to these policies at a very early stage, immediately after "client" gets the UUID, and before any of the pillar services are launched. In other words, enforcement of security policies needs to precede launch of any business logic inside pillar.
b) This security polices contain sensitive information like encryption keys, which is best handled only in memory, and not stored on the persistent storage like other config items. Having a separate API endpoint helps handling of security policies be modular and more maintainable, without disturbing how config related to other pillar services are handled.
Therefore the proposed user driven, device management event flow, will be as follows.
Vault Manager to anchor handling of security policies
This module in EVE, will be responsible for periodic device policy fetch from controller and enforce them on the device. More details, are specified in [Ref.1].
Option 2: Same API that carries other config, handled by zedAgent
In this approach, security policies are pushed along with other config (by /api/v1/eddgedev/config), and parsed by zedagent. But zedagent will prioritise handling of security config over the rest of the config. Any file system interaction to setup/unlock the vault directory will have to be done according to the security config received, and then signal others that vault directory is now ready for use. Other services can listen to this to perform any task they need to do on top of the vault directory. Zedagent would interact with Vault Manager service for implementing file system encryption requirements.
Option 3: Same API, handled by Vault Manager at boot time, and ZedAgent at runtime
It is a mix of Option 1 and Option 2. It uses the same REST API that is used for pulling the device configuration (/api/v1/eddgedev/config). But Vault Manager will extract security config parts during pillar launch, to set up any filesystem encryption etc. Once ZedAgent takes over, any further change in security config can be driven from zedAgent, by passing the configuration to Vault Manager through pubsub mechanism.
Break-up of the proposed security config (Applicable to all the Approaches)
The policies are grouped into two major categories
- Data At Rest Policies
- Data In Transit Policies (mostly a placeholder for now, added for future use)
Data at Rest Policy
Data at rest security is applicable for the Application Instance mutable business sensitive data and storage for EVE sensitive configuration information.Application instance mutable business sensitive data will be stored in a reserved partition/directory and the security policy configuration will be applied on it.
The data at rest security policy will cover, the following aspects,
- encryption algorithm
- data handling policy
- data recovery policy
- key rotation policy
- key Information
Encryption Algorithm
This specifies, the encryption algorithm to be used for data at rest security. [Ref. 1].
- NONE
- AES256
- ADIANTUM
Data handling policy
Data handling policy will define, sensitive storage data handling, on encryption algorithm change,
- RETAIN
- DESTROY
- DESTROY_ON_SECURITY_BREACH
RETAIN: The application business sensitive data will be retained on encryption algorithm change.
DESTROY: The application business sensitive data will be destroyed on encryption algorithm change.
DESTROY_ON_SECURITY_BREACH: can be initiated by the user, on compromised device detection or, by
some user defined policy in the controller module.
Data Recovery Policy
When an EVE node faces network outage, it will keep operating, using the last known policy configuration.
On power recycle, followed by a network outage, the EVE node may require physical access/user intervention,
to decrypt the data vault, with the following options.
- None
- USBKEY
- KEYBOARD
The user has to ensure that, proper configuration is stored in the USB Stick or inputs them through to Keyboard.
Key rotation policy
Fscrypt provides a way to change the master key associated with an encrypted folder, without re-encrypting the contents. This is possible due to the protectors and policies constructs used by fscrypt (master key protects the protector, and protector in turn protects the final key used for encryption). Please see here for more details.
We can use this fscrypt feature to periodically rotate the master keys used for a given vault. The key rotation policy will be in the controller and will not be intimated to EVE.
Keys
This consists of set of Keys information( max. 2). For a key rotation scheme, a maximum of two keys will be intimated to the EVE node. Controller will store and publish, the last published key along with the most current key. This will cover cases, when the EVE node is not able to communicate with controller.
Data in transit policy (Mostly a placeholder for now, details added for brevity)
Currently, the data in transit is secured through TLS 1.2 framework, for configuration/ status/ information exchange between the controller and EVE. The data in transit security for Application instance data traffic will be prerogative of the application software and, is out of scope for the current proposal. The scope of data in transit security policy, will be applicable for the sensitive object level configuration data in transit between the controller software and the end user (downloader) inside EVE, viz., data store credentials. This will be done by using the device cert/key pair. The sensitive configuration for EVE, will be stored in encrypted form (cypher text), till it is ready for use by downloader.
References
- https://wiki.lfedge.org/display/EVE/Encrypting+Sensitive+Information+at+Rest+at+the+Edge
- The pull request corresponding to this proposal: https://github.com/lf-edge/eve/pull/186