Cryptography

This document describes the cryptography used by Charmed Apache Kafka.

Resource checksums

Charmed Apache Kafka and Charmed Apache ZooKeeper operators use pinned revisions of their respective snaps to provide reproducible and secure environments.

The Charmed Apache Kafka snap and Charmed Apache ZooKeeper snap package the Apache Kafka and Apache ZooKeeper workloads, respectively, along with the necessary dependencies and utilities for operator lifecycle management. For details on the contents of these snaps, refer to the snapcraft.yaml file in the source code: Charmed Apache Kafka snap contents and Charmed Apache ZooKeeper snap contents.

Every artifact included in the snaps is verified against its SHA-256 or SHA-512 checksum after download.

Sources verification

Charmed Apache Kafka sources are stored in:

• GitHub repositories for snaps, rocks and charms
• LaunchPad repositories for the Apache Kafka and Apache ZooKeeper upstream fork used for building their respective distributions

LaunchPad

Distributions are built using private repositories only, hosted as part of the SOSS namespace to eventually integrate with Canonical’s standard process for fixing CVEs. Branches associated with releases are mirrored to a public repository, hosted in the Data Platform namespace to also provide the community with the patched source code.

GitHub

All Apache Kafka and Apache ZooKeeper artifacts built by Canonical are published and released programmatically using release pipelines implemented via GitHub Actions. Distributions are published as both GitHub and LaunchPad releases via the central-uploader repository, while charms, snaps and rocks are published using the workflows of their respective repositories.

All repositories in GitHub are set up with branch protection rules, requiring:

• new commits to be merged to main branches via pull request with at least 2 approvals from repository maintainers
• new commits to be signed (e.g. using GPG keys)
• developers to sign the Canonical Contributor License Agreement (CLA)

Encryption

Charmed Apache Kafka can be used to deploy a secure Apache Kafka cluster that provides encryption-in-transit capabilities out of the box for:

• Interbroker communications
• Apache ZooKeeper connection
• External client connection

To set up a secure connection Charmed Apache Kafka and Charmed Apache ZooKeeper applications need to be integrated with TLS Certificate Provider charms, e.g. self-signed-certificates operator. Certificate Singing Requests (CSRs) are generated for every unit using the tls_certificates_interface library that uses the cryptography Python library to create X.509 compatible certificates. The CSR is signed by the TLS Certificate Provider, returned to the units, and stored in a password-protected Keystore file. The password of the Keystore is stored in Juju secrets starting from revision 168 of Charmed Apache Kafka and revision 130 of Charmed Apache ZooKeeper. The relation also provides the CA certificate, which is loaded into a password-protected Truststore file.

When encryption is enabled, hostname verification is turned on for client connections, including inter-broker communication. The cipher suite can be customized by specifying a list of allowed cipher suites for external clients and Apache ZooKeeper connections. This is done using the charm configuration options ssl_cipher_suites and zookeeper_ssl_cipher_suites respectively (see reference documentation).

Encryption at rest is currently not supported, although it can be provided by the substrate (cloud or on-premises).

Authentication

In Charmed Apache Kafka, authentication layers can be enabled for:

1. Apache ZooKeeper connections
2. Apache Kafka inter-broker communication
3. Apache Kafka clients

Apache Kafka authentication to Apache ZooKeeper

Authentication to Apache ZooKeeper is based on Simple Authentication and Security Layer (SASL) using digested MD5 hashes of username and password and implemented both for client-server (with Apache Kafka) and server-server communication. Username and passwords are exchanged using peer relations among Apache ZooKeeper units and using normal relations between Apache Kafka and Apache ZooKeeper. Juju secrets are used for exchanging credentials starting from revision 168 of Charmed Apache Kafka and revision 130 of Charmed Apache ZooKeeper.

Usernames and passwords for different users are stored in Apache ZooKeeper servers in a JAAS configuration file in plain text format. Permissions on the file are restricted to the root user only.

Apache Kafka Inter-broker authentication

Authentication among brokers is based on the SCRAM-SHA-512 protocol. Usernames and passwords are exchanged via peer relations, using Juju secrets from revision 168 of Charmed Apache Kafka.

The Apache Kafka username and password, used by brokers to authenticate one another, are stored both in an Apache ZooKeeper zNode and in a JAAS configuration file on the Apache Kafka server in plain text format.

The file needs to be readable and writable by root (as it is created by the charm) and readable by the snap_daemon user running the Apache Kafka server snap commands.

Client authentication to Apache Kafka

Clients can authenticate to Apache Kafka using:

1. username and password exchanged using SCRAM-SHA-512 protocols
2. client certificates or CAs (mTLS)

When using SCRAM, usernames and passwords are stored in Apache ZooKeeper to be used by the Apache Kafka processes, in peer-relation data to be used by the Apache Kafka charm and in external relation to be shared with client applications. Starting from revision 168 of Charmed Apache Kafka, Juju secrets are used for storing the credentials instead of plain text.

When using mTLS, client certificates are loaded into a tls-certificates operator and provided to the Charmed Apache Kafka via the plain-text unencrypted relation. Certificates are stored in the password-protected Truststore file.