smallstep-certificates/docs/kms.md

Key Management Services

This document describes how to use a key management service or KMS to store the private keys and sign certificates.

Support for multiple KMS are planned, but currently the only supported one is Google's Cloud KMS.

Google's Cloud KMS

Cloud KMS is the Google's cloud-hosted KMS that allows you to store the cryptographic keys, and sign certificates using their infrastructure. Cloud KMS supports two different protection levels, SOFTWARE and HSM.

To configure Cloud KMS in your CA you need add the "kms" property to you ca.json, and replace the property"key" with the Cloud KMS key name of your intermediate key:

{
    ...
    "key": "projects/<project-id>/locations/global/keyRings/<ring-id>/cryptoKeys/<key-id>/cryptoKeyVersions/<version-number>",
    ...
    "kms": {
        "type": "cloudkms",
        "credentialsFile": "path/to/credentials.json"
    }
}

In a similar way, for SSH certificate, the SSH keys must be Cloud KMS names:

{
    ...
    "ssh": {
        "hostKey": "projects/<project-id>/locations/global/keyRings/<ring-id>/cryptoKeys/<key-id>/cryptoKeyVersions/<version-number>",
        "userKey": "projects/<project-id>/locations/global/keyRings/<ring-id>/cryptoKeys/<key-id>/cryptoKeyVersions/<version-number>"
    },
}

Currently step does not provide an automatic way to initialize the public key infrastructure (PKI) using Cloud KMS, but an experimental tool named step-cloudkms-init is available for this use case. At some point this tool will be integrated into step and it will be deleted.

To use step-cloudkms-init just enable Cloud KMS in your project and run:

$ export GOOGLE_APPLICATION_CREDENTIALS=/path/to/credentials.json
$ step-cloudkms-init --project your-project-id --ssh
Creating PKI ...
✔ Root Key: projects/your-project-id/locations/global/keyRings/pki/cryptoKeys/root/cryptoKeyVersions/1
✔ Root Certificate: root_ca.crt
✔ Intermediate Key: projects/your-project-id/locations/global/keyRings/pki/cryptoKeys/intermediate/cryptoKeyVersions/1
✔ Intermediate Certificate: intermediate_ca.crt

Creating SSH Keys ...
✔ SSH User Public Key: ssh_user_ca_key.pub
✔ SSH User Private Key: projects/your-project-id/locations/global/keyRings/pki/cryptoKeys/ssh-user-key/cryptoKeyVersions/1
✔ SSH Host Public Key: ssh_host_ca_key.pub
✔ SSH Host Private Key: projects/your-project-id/locations/global/keyRings/pki/cryptoKeys/ssh-host-key/cryptoKeyVersions/1

See step-cloudkms-init --help for more options.

YubiKey

And incomplete and experimental support for YubiKeys is also available. Support for YubiKeys is not enabled by default and only TLS signing can be configured.

The YubiKey implementation requires cgo, and our build system does not produce binaries with it. To enable YubiKey download the source code and run:

make build GOFLAGS=""

The implementation uses piv-go, and it requires PCSC support, this is available by default on macOS and Windows operating systems, but on Linux piv-go requires PCSC lite.

To install on Debian-based distributions, run:

sudo apt-get install libpcsclite-dev

On Fedora:

sudo yum install pcsc-lite-devel

On CentOS:

sudo yum install 'dnf-command(config-manager)'
sudo yum config-manager --set-enabled PowerTools
sudo yum install pcsc-lite-devel

The initialization of the public key infrastructure (PKI) for YubiKeys, is not currently integrated into step, but an experimental tool named step-yubikey-init is available for this use case. At some point this tool will be integrated into step and it will be deleted.

To configure your YubiKey just run:

$ bin/step-yubikey-init
What is the YubiKey PIN?:
Creating PKI ...
✔ Root Key: yubikey:slot-id=9a
✔ Root Certificate: root_ca.crt
✔ Intermediate Key: yubikey:slot-id=9c
✔ Intermediate Certificate: intermediate_ca.crt

See step-yubikey-init --help for more options.

Finally to enable it in the ca.json, point the root and crt to the generated certificates, set the key with the yubikey URI generated in the previous step and configure the kms property with the type and your pin in it.

{
    "root": "/path/to/root_ca.crt",
    "crt": "/path/to/intermediate_ca.crt",
    "key": "yubikey:slot-id=9c",
    "kms": {
        "type": "yubikey",
        "pin": "123456"
    },
    ...
}