7.8 KiB
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 Google's Cloud KMS, and Amazon's AWS KMS are supported. A still experimental version for YubiKeys is also available if you compile step-ca yourself.
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.
AWS KMS
AWS KMS is the Amazon's managed encryption and key management service. It creates and store the cryptographic keys, and use their infrastructure for signing operations. Amazon KMS operations are always backed by hardware security modules (HSMs).
To configure AWS KMS in your CA you need add the "kms"
property to you
ca.json
, and replace the property"key"
with the AWS KMS key name of your
intermediate key:
{
...
"key": "awskms:key-id=f879f239-feb6-4596-9ed2-b1606277c7fe",
...
"kms": {
"type": "awskms",
"region": "us-east-1"
}
}
By default it uses the credentials in ~/.aws/credentials
, but this can be
overridden using the credentialsFile
option, region
and profile
can also
be configured as options. These can also be configured using environment
variables as described by their session
docs.
To configure SSH certificate signing we do something similar, and replace the ssh keys with the ones in the KMS:
{
...
"ssh": {
"hostKey": "awskms:key-id=d48e502a-09bc-4bf7-9af8-ae1bccedc931",
"userKey": "awskms:key-id=cf28e942-1e10-4a08-b84c-5359af1b5f12"
},
}
The keys can also be just the Amazon's Key ID or the ARN, but using the format
based on the RFC7512 will allow more
flexibility for future releases of step
.
Currently step does not provide an automatic
way to initialize the public key infrastructure (PKI) using AWS KMS, but an
experimental tool named step-awskms-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-awskms-init
make sure to have to have your environment
configured
running aws configure
and then just run:
$ bin/step-awskms-init --ssh --region us-east-1
Creating PKI ...
✔ Root Key: awskms:key-id=f53fb767-4029-40ff-b650-0dd35fb661df
✔ Root Certificate: root_ca.crt
✔ Intermediate Key: awskms:key-id=f879f239-feb6-4596-9ed2-b1606277c7fe
✔ Intermediate Certificate: intermediate_ca.crt
Creating SSH Keys ...
✔ SSH User Public Key: ssh_user_ca_key.pub
✔ SSH User Private Key: awskms:key-id=cf28e942-1e10-4a08-b84c-5359af1b5f12
✔ SSH Host Public Key: ssh_host_ca_key.pub
✔ SSH Host Private Key: awskms:key-id=cf28e942-1e10-4a08-b84c-5359af1b5f12
The --region
parameter is only required if your aws configuration does not
define a region. See step-awskms-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"
},
...
}
SSHAgentKMS
SSHAgentKMS is a KMS that wrapps a ssh-agent which has access to the keys to sign ssh certificates. This was primarly written to be able to use gpg-agent to provide the keys stored in a YubiKeys openpgp interface.
{
"kms": {
"type": "sshagentkms"
},
"ssh": {
"hostKey": "sshagentkms:cardno:000123456789",
"userKey": "sshagentkms:cardno:000123456789",
},
...
}
This KMS requires that "root", "crt" and "key" are stored in plain files as for SoftKMS.