Server-Side Object Encryption with Azure Key Vault Root KMS

MinIO Server-Side Encryption (SSE) protects objects as part of write operations, allowing clients to take advantage of server processing power to secure objects at the storage layer (encryption-at-rest). SSE also provides key functionality to regulatory and compliance requirements around secure locking and erasure.

MinIO SSE uses Key Encryption Service (KES) and an external root Key Management Service (KMS) for performing secured cryptographic operations at scale. The root KMS provides stateful and secured storage of External Keys (EK) while KES is stateless and derives additional cryptographic keys from the root-managed EK.

This procedure assumes a single local host machine running the MinIO and KES processes, with Azure Key Vault as the external root KMS.. As part of this procedure, you will:

  1. Deploy a KES server configured to use Azure Key Vault as the root KMS.

  2. Create a new EK on Vault for use with SSE.

  3. Deploy a MinIO server in Single-Node Single-Drive mode configured to use the KES container for supporting SSE.

  4. Configure automatic bucket-default SSE-KMS.

For production orchestrated environments, use the MinIO Kubernetes Operator to deploy a tenant with SSE enabled and configured for use with Azure Key Vault.

For production baremetal environments, see the MinIO on Linux documentation for tutorials on configuring MinIO with KES and Azure Key Vault.


Enabling SSE on a MinIO deployment automatically encrypts the backend data for that deployment using the default encryption key.

MinIO requires access to KES and the root KMS to decrypt the backend and start normally. You cannot disable KES later or “undo” the SSE configuration at a later point.


Azure Key Vault

This procedure assumes familiarity with Azure Key Vault. The Key Vault Quickstart provides a sufficient foundation for the purposes of this procedure.

MinIO specifically requires the following Azure settings or configurations:

  • Register an application for KES (e.g. minio-kes). Note the Application (client) ID, Directory (tenant) ID, and Client credentials. You may need to create the client credentials secret and copy the Secret Value for use in this procedure.

  • Create an Access Policy for use by KES. The policy must have the following Secret Permissions:

    • Get

    • List

    • Set

    • Delete

    • Purge

    Set the Principal for the new policy to the KES Application ID.

Deploy or Ensure Access to a MinIO Deployment

This procedure provides instructions for modifying the startup environment variables of a MinIO deployment to enable SSE via KES and the root KMS.

For instructions on new production deployments, see the Multi-Node Multi-Drive (Distributed) tutorial. For instructions on new local or evaluation deployments, see the Single-Node Single-Drive tutorial.

When creating the environment file for the deployment, pause and switch back to this tutorial to include the necessary environment variables to support SSE.

For existing MinIO Deployments, you can modify the existing environment file and restart the deployment as instructed during this procedure.

Deploy MinIO and KES with Server-Side Encryption using Azure Key Vault

Prior to starting these steps, create the following folders:

mkdir -P ~/minio-kes-azure/certs
mkdir -P ~/minio-kes-azure/config
mkdir -P ~/minio-kes-azure/minio

1) Download the KES Binary

Download the binary of the latest stable KES release (2023-02-15T14-54-37Z) from

Select the tab corresponding to the architecture for your MacOS hardware. The command downloads the 2023-02-15T14-54-37Z binary for that architecture, sets it to executable, and adds it to your system PATH.

curl -O
chmod +x ./kes-darwin-arm64
sudo mv ./kes-darwin-arm64 /usr/local/bin/kes
curl -O
chmod +x ./kes-darwin-amd64
sudo mv ./kes-darwin-amd64 /usr/local/bin/kes

2) Generate TLS Certificates for KES and MinIO

The following commands create two TLS certificates that expire within 30 days of creation:

  • A TLS certificate for KES to secure communications between it and the Vault deployment

  • A TLS certificate for MinIO to perform mTLS authentication to KES.

Use Caution in Production Environments

DO NOT use the TLS certificates generated as part of this procedure for any long-term development or production environments.

Defer to organization/industry best practices around TLS certificate generation and management. A complete guide to creating valid certificates (e.g. well-formed, current, and trusted) is beyond the scope of this procedure.

# These commands output keys to ~/minio-kes-azure/certs
# and ~/minio-kes-azure/certs respectively

kes identity new kes_server \
  --key  ~/minio-kes-azure/certs/kes-server.key  \
  --cert ~/minio-kes-azure/certs/kes-server.cert  \
  --ip   ""  \
  --dns  localhost

kes identity new minio_server \
  --key  ~/minio-kes-azure/certs/minio-kes.key  \
  --cert ~/minio-kes-azure/certs/minio-kes.cert  \
  --ip   ""  \
  --dns  localhost

The --ip and --dns parameters set the IP and DNS SubjectAlternativeName for the certificate. The above example assumes that all components (Vault, MinIO, and KES) deploy on the same local host machine accessible via localhost or You can specify additional IP or Hostnames based on the network configuration of your local host.

3) Create the KES and MinIO Configurations

  1. Create the KES Configuration File

    Create the configuration file using your preferred text editor. The following example uses nano:

    nano ~/minio-kes-azure/config/kes-config.yaml

    KES uses a YAML-formatted configuration file. The following example YAML specifies the minimum required fields for enabling SSE using AWS Secrets Manager:

    # Disable the root identity, as we do not need that level of access for
    # supporting SSE operations.
    root: disabled
    # Specify the TLS keys generated in the previous step here
    # For production environments, use keys signed by a known and trusted
    # Certificate Authority (CA).
      key:  ~/minio-kes-azure/certs/kes-server.key
      cert: ~/minio-kes-azure/certs/kes-server.cert
    # Create a policy named 'minio' that grants access to the
    # /create, /generate, and /decrypt KES APIs for any key name
    # KES uses mTLS to grant access to this policy, where only the client
    # whose TLS certificate hash matches one of the "identities" can
    # use this policy. Specify the hash of the MinIO server TLS certificate
    # hash here.
        - /v1/key/create/*
        - /v1/key/generate/*
        - /v1/key/decrypt/*
        - ${MINIO_IDENTITY_HASH} # Replace with the output of 'kes identity of minio-kes.cert'
    # Specify the connection information for the Key Vualt endpoint.
    # The endpoint should be resolvable from the host.
    # This example assumes that the specified Key Vault and Azure tenant/client
    # have the necessary permissions set.
          endpoint: "https://<keyvaultinstance>" # The Azure Keyvault Instance Endpoint
            tenant_id: "${TENANTID}" # The directory/tenant UUID
            client_id: "${CLIENTID}" # The application/client UUID
            client_secret: "${CLIENTSECRET}" # The Active Directory secret for the application
    • Set MINIO_IDENTITY_HASH to the identity hash of the MinIO mTLS certificate.

      The following command computes the necessary hash:

      kes identity of ~/minio-kes-azure/certs/minio-kes.cert
    • Replace the endpoint with the URL for the Keyvault instance.

    • Set TENANTID, CLIENTID, and CLIENTSECRET to match the credentials for a project user with the required permissions.

  2. Create the MinIO Environment File

    Create the environment file using your preferred text editor. The following example uses nano:

    nano ~/minio-kes-azure/config/minio

    Add the following lines to the MinIO Environment file on each MinIO host. See the tutorials for Deploy MinIO: Single-Node Single-Drive, Deploy MinIO: Single-Node Multi-Drive, or Deploy MinIO: Multi-Node Multi-Drive for more detailed descriptions of a base MinIO environment file.

    # Add these environment variables to the existing environment file
    # Allows validation of the KES Server Certificate (Self-Signed or Third-Party CA)
    # Change this path to the location of the KES CA Path
    # Sets the default KMS key for the backend and SSE-KMS/SSE-S3 Operations)
    # Optional, defines the name for the KES server enclave to use.

    Replace HOSTNAME with the IP address or hostname of the KES server. If the MinIO server host machines cannot resolve or reach the specified HOSTNAME, the deployment may return errors or fail to start.

    • If using a single KES server host, specify the IP or hostname of that host

    • If using multiple KES server hosts, specify a comma-separated list of IPs or hostnames of each host

    MinIO uses the MINIO_KMS_KES_KEY_NAME key for the following cryptographic operations:

    • Encrypting the MinIO backend (IAM, configuration, etc.)

    • Encrypting objects using SSE-KMS if the request does not include a specific EK.

    • Encrypting objects using SSE-S3.

    MinIO uses the MINIO_KMS_KES_ENCLAVE key to define the name of the KES enclave to use.

    • Replace <name> with the name of the enclave to use.

    • If not defined, MinIO does not send any enclave information. This may result in using the default enclave for stateful KES servers.

      A KES enclave provides an isolated space for its associated keys separate from other enclaves on a stateful KES server.

    The minio-kes certificates enable mTLS between the MinIO deployment and the KES server only. They do not otherwise enable TLS for other client connections to MinIO.

4) Start KES and MinIO

You must start KES before starting MinIO. The MinIO deployment requires access to KES as part of its startup.

  1. Start the KES Server

    Run the following commands in a terminal or shell to start the KES server as a foreground process:

    sudo setcap cap_ipc_lock=+ep $(readlink -f $(which kes))
    kes server --auth=off --config=~/minio-kes-azure/config/kes-config.yaml

    The first command allows KES to use the mlock system call without running as root. mlock ensures the OS does not write in-memory data to a drive (swap memory) and mitigates the risk of cryptographic operations being written to unsecured drive at any time. KES 0.21.0 and later automatically detect and enable mlock if supported by the host OS. Versions 0.20.0 and earlier required specifying the --mlock argument to KES.

    The second command starts the KES server in the foreground using the configuration file created in the last step. The --auth=off disables strict validation of client TLS certificates. Using self-signed certificates for either the MinIO client or the root KMS server requires specifying this option.

    KES listens on port 7373 by default. You can monitor the server logs from the terminal session. If you run KES without tying it to the current shell session (e.g. with nohup), use that method’s associated logging system (e.g. nohup.txt).

  2. Start the MinIO Server

    Run the following command in a terminal or shell to start the MinIO server as a foreground process.

    export MINIO_CONFIG_ENV_FILE=~/minio-kes-azure/config/minio
    minio server --console-address :9090

Foreground processes depend on the shell or terminal in which they run. Exiting or terminating the shell/terminal instance also kills the attached process. Defer to your operating system best practices for running processes in the background.

5) Generate a New Encryption Key

MinIO requires that the EK exist on the root KMS before performing SSE operations using that key. Use kes key create or mc admin kms key create to add a new EK for use with SSE.

The following command uses the kes key create command to add a new External Key (EK) stored on the root KMS server for use with encrypting the MinIO backend.

export KES_SERVER=
export KES_CLIENT_KEY=~/minio-kes-azure/certs/minio-kes.key
export KES_CLIENT_CERT=~/minio-kes-azure/certs/minio-kes.cert

kes key create -k encrypted-bucket-key

6) Enable SSE-KMS for a Bucket

You can use either the MinIO Console or the MinIO mc CLI to enable bucket-default SSE-KMS with the generated key:

Open the MinIO Console by navigating to in your preferred browser and logging in with the root credentials specified to the MinIO container. If you deployed MinIO using a different Console listen port, substitute 9090 with that port value.

Once logged in, create a new Bucket and name it to your preference. Select the Gear icon to open the management view.

Select the pencil icon next to the Encryption field to open the modal for configuring a bucket default SSE scheme.

Select SSE-KMS, then enter the name of the key created in the previous step.

Once you save your changes, try to upload a file to the bucket. When viewing that file in the object browser, note that in the sidebar the metadata includes the SSE encryption scheme and information on the key used to encrypt that object. This indicates the successful encrypted state of the object.

The following commands:

  • Create a new alias for the MinIO deployment

  • Create a new bucket for storing encrypted data

  • Enable SSE-KMS encryption on that bucket

mc alias set local ROOTUSER ROOTPASSWORD

mc mb local/encryptedbucket
mc encrypt set SSE-KMS encrypted-bucket-key ALIAS/encryptedbucket

Write a file to the bucket using mc cp or any S3-compatible SDK with a PutObject function. You can then run mc stat on the file to confirm the associated encryption metadata.

Configuration Reference for Azure Key Vault Root KMS

The following section describes each of the Key Encryption Service (KES) configuration settings for using Azure Key Vault as the root Key Management Service (KMS) for SSE:

The following YAML describes the minimum required fields for configuring Azure Key Vault as an external KMS for supporting SSE.

Any field with value ${VARIABLE} uses the environment variable with matching name as the value. You can use this functionality to set credentials without writing them to the configuration file.


  key: kes-server.key
  cert: kes-server.cert

      - /v1/key/create/*
      - /v1/key/generate/*
      - /v1/key/decrypt/*

  - name: "minio-encryption-key-alpha"
  - name: "minio-encryption-key-baker"
  - name: "minio-encryption-key-charlie"

      endpoint: "https://<keyvaultinstance>"
        tenant_id: "${TENANTID}" # The directory/tenant UUID
        client_id: "${CLIENTID}" # The application/client UUID
        client_secret: "${CLIENTSECRET}" # The Active Directory secret for the application




The network address and port the KES server listens to on startup. Defaults to port 7373 on all host network interfaces.


The identity for the KES superuser (root) identity. Clients connecting with a TLS certificate whose hash (kes identity of client.cert) matches this value have access to all KES API operations.

Specify disabled to remove the root identity and rely only on the policy configuration for controlling identity and access management to KES.


The TLS private key and certificate used by KES for establishing TLS-secured communications. Specify the full path for both the private .key and public .cert to the key and cert fields, respectively.


Specify one or more policies to control access to the KES server.

MinIO SSE requires access to the following KES cryptographic APIs:

  • /v1/key/create/*

  • /v1/key/generate/*

  • /v1/key/decrypt/*

Specifying additional keys does not expand MinIO SSE functionality and may violate security best practices around providing unnecessary client access to cryptographic key operations.

You can restrict the range of key names MinIO can create as part of performing SSE by specifying a prefix before the *. For example, minio-sse-* only grants access to create, generate, or decrypt keys using the minio-sse- prefix.

KES uses mTLS to authorize connecting clients by comparing the hash of the TLS certificate against the identities of each configured policy. Use the kes identity of command to compute the identity of the MinIO mTLS certificate and add it to the policy.<NAME>.identities array to associate MinIO to the <NAME> policy.


Specify an array of keys which must exist on the root KMS for KES to successfully start. KES attempts to create the keys if they do not exist and exits with an error if it fails to create any key. KES does not accept any client requests until it completes validation of all specified keys.

The configuration for the Azure Key Vault

  • endpoint - The hostname for the Key Vault service.

  • credentials - Replace the credentials with the credentials for the Active Directory application as which KES authenticates.

    The specified credentials must have the appropriate permissions