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barbican/doc/source/contributor/plugin/crypto.rst

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barbican.plugin.crypto.base

Cryptographic Plugin Development

This guide describes how to develop a custom cryptographic plugin for use by Barbican.

Barbican supports two storage modes for secrets: a cryptographic mode (detailed on this page), and a secret store mode </contributor/plugin/secret_store>. The cryptographic mode stores encrypted secrets in Barbican's data store, utilizing a cryptographic process or appliance (such as a hardware security module (HSM)) to perform the encryption/decryption. Barbican includes a PKCS11-based interface to SafeNet HSMs.

Note that cryptographic plugins are not invoked directly from Barbican core, but rather via a secret store mode </contributor/plugin/secret_store> plugin adapter class, further described in plugin-secret-store-crypto-adapter-label.

crypto Module

The barbican.plugin.crypto module contains the classes needed to implement a custom plugin. These classes include the CryptoPluginBase abstract base class which custom plugins should inherit from, as well as several Data Transfer Object (DTO) classes used to transfer data between Barbican and the plugin.

Data Transfer Objects

The DTO classes are used to wrap data that is passed from Barbican to the plugin as well as data that is returned from the plugin back to Barbican. They provide a level of isolation between the plugins and Barbican's internal data models.

KEKMetaDTO

EncryptDTO

DecryptDTO

GenerateDTO

ResponseDTO

Plugin Base Class

Barbican cryptographic plugins should implement the abstract base class CryptoPluginBase. Concrete implementations of this class should be exposed to barbican using stevedore mechanisms explained in the configuration portion of this guide.

CryptoPluginBase

Barbican Core Plugin Sequence

Barbican invokes a different sequence of methods on the CryptoPluginBase plugin depending on the requested action. Note that these actions are invoked via the secret store adapter class StoreCryptoAdapterPlugin which is further described in plugin-secret-store-crypto-adapter-label.

For secret storage actions, Barbican core calls the following methods:

  1. supports() - Asks the plugin if it can support the barbican.plugin.crypto.base.PluginSupportTypes.ENCRYPT_DECRYPT operation type.
  2. bind_kek_metadata() - Allows a plugin to bind an internal key encryption key (KEK) to a project-ID, typically as a 'label' or reference to the actual KEK stored within the cryptographic appliance. This KEK information is stored into Barbican's data store on behalf of the plugin, and then provided back to the plugin for subsequent calls.
  3. encrypt() - Asks the plugin to perform encryption of an unencrypted secret payload, utilizing the KEK bound to the project-ID above. Barbican core will then persist the encrypted data returned from this method for later retrieval. The name of the plugin used to perform this encryption is also persisted into Barbican core, to ensure we decrypt this secret only with this plugin.

For secret decryptions and retrievals, Barbican core will select the same plugin as was used to store the secret, and then invoke its decrypt() method, providing it both the previously-persisted encrypted secret data as well as the project-ID KEK used to encrypt the secret.

For symmetric key generation, Barbican core calls the following methods:

  1. supports() - Asks the plugin if it can support the barbican.plugin.crypto.base.PluginSupportTypes.SYMMETRIC_KEY_GENERATION operation type.
  2. bind_kek_metadata() - Same comments as for secret storage above.
  3. generate_symmetric() - Asks the plugin to both generate a symmetric key, and then encrypted it with the project-ID KEK. Barbican core persists this newly generated and encrypted secret similar to secret storage above.

For asymmetric key generation, Barbican core calls the following methods:

  1. supports() - Asks the plugin if it can support the barbican.plugin.crypto.base.PluginSupportTypes.ASYMMETRIC_KEY_GENERATION operation type.
  2. bind_kek_metadata() - Same comments as for secret storage above.
  3. generate_asymmetric() - Asks the plugin to generate and encrypt asymmetric public and private key (and optional passphrase) information, which Barbican core will persist as a container of separate encrypted secrets.