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AWS KMS LUKS

Use AWS KMS to encrypt Linux block devices with LUKS.

Encryption keys are not stored anywhere in an unencrypted form.

Setup

AWS

In the same AWS region create:

  • S3 bucket - this is the backup archive of encrypted keys.
  • KMS CMK - this is the CMK that data keys will be created off and encrypted by.
  • IAM user - this will be used by the tool to access the AWS APIs.

AWS IAM Permissions

Apply the policy found in iam/policy.json to the IAM user. The values of the CMK ARN and bucket name need to be replaced in the policy document.

Create an AWS key pair for this user.

Host

Prerequisites

There is a dependency on installing the cryptsetup package.

AWS Credentials

On the host that will have the encrypted volume configure the AWS credentials under the root user. This is described at (https://docs.aws.amazon.com/cli/latest/userguide/cli-config-files.html). The default region is also needs to be set to the region in which the backup archive bucket and KMS CMK has been created.

awskmsluks

Create the directory: mkdir /etc/awskmsluks/bin

Build and copy the awskmsluks binary to this directory

awskmsluks Configuration

Copy the config.json file to /etc/awskmsluks/config.json and set the following values:

  • CMKARN: This is the full ARN of the CMK you want to create data keys from for encrypting devices on this host.
  • Production: This is a boolean to indicate if this host is considered a production host.
  • KeyArchiveBucket: This is the bucket name (not the full ARN) of the bucket to use for keeping an off host backup archive of encrypted data keys.

Systemd Unit Files

Copy thesystemd/awskmsluks.service file to /etc/systemd/system

Enable this with systemctl enable awskmsluks.service

Creating an Encrypted Volume

Ecrypt the block device with LUKS using an AWS KMS data key:

/etc/awskmsluks/bin/awskmsluks -encrypt=/dev/sdb

Open the device:

/etc/awskmsluks/bin/awskmsluks -open

Format the device with the filesystem of your choice. The open device will be in /dev/mapper with the name of the device appended with _crypt For example:

mkfs.ext4 /dev/mapper/sdb_crypt

Create a systemd mount. Set the values in the [Mount] section of the example below as required. It is important to have the After=awskmsluks.service configuration

[Unit]
After=awskmsluks.service

[Mount]
What=/dev/mapper/sdb_crypt
Where=/mnt/data
Type=ext4
Options=defaults

[Install]
WantedBy=multi-user.target

Building

go build -ldflags "-X main.version=v1.0.0 -X main.buildtime=`date -u '+%FT%TZ'` -X main.buildhash=`git rev-parse HEAD`"