smallstep_full_white

Configuring step-ca

When the step ca init command sets up your PKI, it creates an initial configuration file for your CA and stores it in $(step path)/config/ca.json.

This document describes how to configure every aspect of step-ca. You'll learn how to configure your CA to:

  • bind to a non-default address
  • generate ACME certificates
  • adjust the default lifetime of certificates
  • store certificates in memory, on the file system, or in a database
  • set the root and intermediate PKI chain used to sign new certificates
  • and much more

Overview

Specify a Configuration File

When you run step-ca, you must provide a path to a configuration file (ca.json). It is the only required argument. After you've run step ca init to create a default configuration, use step path to discover the path to ca.json:

$ step-ca $(step path)/config/ca.json

The output of step path varies based on the $STEPPATH environment variable, and whether you use the step command with multiple CAs.

For non-interactive use (eg. as a systemd service), the --password-file flag accepts the name of a file containing the password for the CA's keys.

Environment Variables

  • STEPDEBUG When set to 1, step-ca provides extra diagnostic information for debugging. This variable can also be used with step.

Basic Configuration Options

Example Configuration

{
  "root": "examples/pki/secrets/root_ca.crt",
  "federatedRoots": ["examples/pki/secrets/federated_root_ca.crt"],
  "crt": "examples/pki/secrets/intermediate_ca.crt",
  "key": "examples/pki/secrets/intermediate_ca_key",
  "address": ":9000",
  "dnsNames": [
    "localhost"
  ],
  "logger": {
    "format": "text"
  },
  "ssh": {
    "hostKey": "/examples/pki/secrets/secrets.host.key",
    "userKey": "/examples/pki/secrets/secrets.user.key"
  },
  "db": {
    "type": "badgerv2",
    "dataSource": "/Users/carl/.step/authorities/config-example/db"
  }, 
  "crl": {
    "enabled": false
  }, 
  "authority": {
    "claims": {
      "minTLSCertDuration": "5m",
      "maxTLSCertDuration": "24h",
      "defaultTLSCertDuration": "24h",
      "disableRenewal": false,
      "allowRenewalAfterExpiry": false,
      "minHostSSHCertDuration": "5m",
      "maxHostSSHCertDuration": "1680h",
      "defaultHostSSHCertDuration": "720h",
      "minUserSSHCertDuration": "5m",
      "maxUserSSHCertDuration": "24h",
      "defaultUserSSHCertDuration": "16h"
    },
    "policy": {
      "x509": {
        "allow": {
          "dns": ["*.local"]
        }
      },
      "ssh": {
        "user": {
          "allow": {
            "email": ["@local"]
          }
        },
        "host": {
          "allow": {
            "dns": ["*.local"]
          }
        }
      }
    },
    "provisioners": [
      {
        "type": "jwk",
        "name": "mike@smallstep.com",
        "key": {
          "use": "sig",
          "kty": "EC",
          "kid": "YYNxZ0rq0WsT2MlqLCWvgme3jszkmt99KjoGEJJwAKs",
          "crv": "P-256",
          "alg": "ES256",
          "x": "LsI8nHBflc-mrCbRqhl8d3hSl5sYuSM1AbXBmRfznyg",
          "y": "F99LoOvi7z-ZkumsgoHIhodP8q9brXe4bhF3szK-c_w"
        },
        "encryptedKey": "eyJhbGciOiJQQkVTMi1IUzI1NitBMTI4S1ciLCJjdHkiOiJqd2sranNvbiIsImVuYyI6IkEyNTZHQ00iLCJwMmMiOjEwMDAwMCwicDJzIjoiVERQS2dzcEItTUR4ZDJxTGo0VlpwdyJ9.2_j0cZgTm2eFkZ-hrtr1hBIvLxN0w3TZhbX0Jrrq7vBMaywhgFcGTA.mCasZCbZJ-JT7vjA.bW052WDKSf_ueEXq1dyxLq0n3qXWRO-LXr7OzBLdUKWKSBGQrzqS5KJWqdUCPoMIHTqpwYvm-iD6uFlcxKBYxnsAG_hoq_V3icvvwNQQSd_q7Thxr2_KtPIDJWNuX1t5qXp11hkgb-8d5HO93CmN7xNDG89pzSUepT6RYXOZ483mP5fre9qzkfnrjx3oPROCnf3SnIVUvqk7fwfXuniNsg3NrNqncHYUQNReiq3e9I1R60w0ZQTvIReY7-zfiq7iPgVqmu5I7XGgFK4iBv0L7UOEora65b4hRWeLxg5t7OCfUqrS9yxAk8FdjFb9sEfjopWViPRepB0dYPH8dVI.fb6-7XWqp0j6CR9Li0NI-Q",
        "claims": {
          "minTLSCertDuration": "1m0s",
          "defaultTLSCertDuration": "2m0s"
        },
        "options": {
          "x509": {
            "templateFile": "templates/certs/x509/default.tpl"
          },
          "ssh": {
            "templateFile": "templates/certs/ssh/default.tpl"
          }
        }
      },
      {
        "type": "OIDC",
        "name": "Google",
        "clientID": "1087160488420-8qt7bavg3qesdhs6it824mhnfgcfe8il.apps.googleusercontent.com",
        "clientSecret": "udTrOT3gzrO7W9fDPgZQLfYJ",
        "configurationEndpoint": "https://accounts.google.com/.well-known/openid-configuration",
        "admins": ["you@smallstep.com"],
        "domains": ["smallstep.com"],
        "listenAddress": ":10000",
        "claims": {
          "maxTLSCertDuration": "8h",
          "defaultTLSCertDuration": "2h",
          "enableSSHCA": true,
          "disableRenewal": true
        },
        "options": {
          "x509": {
            "templateFile": "templates/certs/x509/default.tpl"
          },
          "ssh": {
            "templateFile": "templates/certs/ssh/default.tpl"
          }
        }
      },
      {
        "type": "SSHPOP",
        "name": "sshpop-smallstep",
        "claims": {
          "enableSSHCA": true
        }
      },
      {
        "type": "ACME",
        "name": "my-acme-provisioner"
      }
    ]
  },
  "tls": {
    "cipherSuites": [
      "TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256",
      "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256"
    ],
    "minVersion": 1.2,
    "maxVersion": 1.3,
    "renegotiation": false
  },
  "password": "p@55w0rd"
}

Configuration Options

  • root: location of the root certificate PEM file on the filesystem. The root certificate is used to mutually authenticate all API clients of the CA. This can be a string containing one root PEM file, or an array containing multiple root CA files (useful for root rotation).

  • federatedRoots: location of the federated root certificates on the filesystem. The federated roots are used to authenticate client and servers using TLS certificates from multiple CAs.

  • crt: location of the intermediate certificate on the filesystem. The intermediate certificate is returned alongside each new certificate, allowing the client to complete the certificate chain. Multiple intermediates are allowed here. When multiple intermediates are supplied, the first certificate in the PEM bundle must be the one used for signing.

  • key: location of the intermediate private key on the filesystem. The intermediate key signs all new certificates generated by the CA.

  • kms: enables and configures cryptographic protection using cloud key management services or hardware security modules. See Cryptographic Protection.

    • type: required. one of azurekms, awskms, cloudkms, pkcs11, or yubikey

    • uri: this field can be used to specify other fields in this section, and its value takes precedence over those values. See cryptographic protection for examples.

    • region: for awskms, the AWS region

    • profile: for awskms, the AWS profile

    • credentialsFile: for cloudkms, the path to a Google Cloud Platform credentials JSON file for a role that can access cloudkms

    • pin: for yubikey, the PIN of the YubiKey PIV application

  • address: ex. 127.0.0.1:8080 - address and port on which the CA bind and respond to requests.

  • dnsNames: comma separated list of DNS name(s) for the CA.

  • logger: the default logging format for the CA is text. The other option is json.

  • ssh: enables the provisioning of SSH certificates by the CA. Add this section to an existing ca.json to enable SSH for an existing CA. SSH keys can be created by running step crypto keypair host.pub host.key and step crypto keypair user.pub user.key.

    • userKey: the signing key for user SSH certificates.

    • hostKey: the signing key for host SSH certificates.

  • db: data persistence layer. See databases, below.

  • crl: Certificate Revocation List (CRL) settings. (experimental)

    • enabled: enables CRL generation (true to generate, false to disable). Default is false.

    • generateOnRevoke: a revoke will generate a new CRL if the crl is enabled. Default is false.

    • cacheDuration: the duration until next update of the CRL. Defaults to 24h.

    • renewPeriod: the time between CRL regeneration. Defaults to ~2/3 of the cacheDuration.

  • tls: settings for negotiating communication with the CA; includes acceptable ciphersuites, min/max TLS version, etc.

  • authority: controls the request authorization and signature processes.

    • type: the type of backing CA service that issues certificates for this step-ca instance. The default is an internal certificate authority service. Other options can turn step-ca into a Registration Authority: stepcas uses a remote step-ca instance as the backend, cloudcas uses Google CloudCAS, vaultcas uses Hashicorp Vault.

    • template: default ASN1DN values for new certificates. See Templates.

    • claims: default validation for requested attributes in the certificate request. Can be overridden by similar claims objects defined by individual provisioners.

      • minTLSCertDuration: do not allow certificates with a duration less than this value.

      • maxTLSCertDuration: do not allow certificates with a duration greater than this value.

      • defaultTLSCertDuration: if no certificate validity period is specified, use this value.

      • disableRenewal: do not allow any certificates to be renewed. The default is false.

      • allowRenewalAfterExpiry: ☠️ allow expired certificates to be renewed. The default is false. This option adds security risk; proceed with caution and consider alternatives.

      • minUserSSHCertDuration: do not allow certificates with a duration less than this value.

      • maxUserSSHCertDuration: do not allow certificates with a duration greater than this value.

      • defaultUserSSHCertDuration: if no certificate validity period is specified, use this value.

      • minHostSSHCertDuration: do not allow certificates with a duration less than this value.

      • maxHostSSHCertDuration: do not allow certificates with a duration greater than this value.

      • defaultHostSSHCertDuration: if no certificate validity period is specified, use this value.

      • enableSSHCA: enable this provisioner to generate SSH Certificates. The default value is false.

      • disableIssuedAtCheck: ☠️ disable a check verifying that provisioning tokens must be issued after the CA has booted. This claim is one prevention against token reuse. The default value is false. Do not change this unless you know what you are doing.

    • provisioners: list of certificate Provisioners. Each provisioner has a name, associated authentication attributes, and an optional claims attribute that overrides any values set in the global claims directly underneath authority. The step ca provisioner command group can add, modify, and remove provisioners. See Provisioners.

      • claims: Each provisioner can override the authority-wide claims settings. See the authority's claims section above for a complete list of options.

      • options: This optional attribute allows an operator to set templates applied to all X.509 or SSH certificates generated using the provisioner. See Templates.

    • password: ☠️ plain text password for starting the CA. Used to decrypt the intermediate CA private key.

Provisioners

Provisioners offer many ways to issue certificates to endpoints and people. By default, step ca init creates a JWK provisioner, for administrative use.

step-ca supports ACME, SCEP, X.509, OpenID, and several other provisioner types.

See Provisioners to learn more.

Policy

Policies can be used to enforce which Subjects, SANs and Principals the CA is allowed to issue a certificate for. They can be configured for X.509 certificates, SSH user, and SSH host certificates. Policies are evaluated before a certificate is signed. Some examples of policies are:

  • A dns rule for www.example.com, only matching the domain www.example.com
  • A dns rule for *.internal.example.com, matching all subdomains of internal.example.com.
  • An ip rule for the 192.168.0.0/24 CIDR, matching all IPs in the range from 192.168.0.0-192.168.0.255.
  • An email rule for @devops, matching all SSH user principals in the @devops domain.
  • A uri rule for *.example.com, matching all URIs for subdomains of example.com, ignoring the URI scheme, path, query and fragment parts.

See Policies to learn more.

Templates

Using X.509 and SSH certificate templates administrators can configure information that gets processed and added to certificates. These include things like:

  • Custom SANs or extensions for X.509 certificates
  • Create longer certificate chains, including multiple intermediate CAs
  • Embed SSH force-command or source-address extensions
  • Evaluate basic logic operations on certificate's parameters, and fail if requirements are not met

See Templates to learn more.

Databases

To store state, step-ca uses a simple NoSQL key-value interface over popular database systems.

The database stores things like:

  • Issued certificates and certificate metadata, to facilitate passive revocation
  • ACME accounts
  • Used one-time-use tokens

The database for step-ca is configured in a top-level db stanza in your ca.json.

Because Badger and BoltDB are embedded, only MySQL and PostgreSQL are appropriate for load balanced, high availability deployments of step-ca.

Badger

Badger is a key-value database embedded in step-ca.

{
  ...
  "db": {
    "type": "badger",
    "dataSource": "./.step/db",
    "valueDir": "./.step/valuedb",
    "badgerFileLoadingMode": "MemoryMap"
  },
  ...
},

Options

  • type

    • badger: currently refers to Badger V1. This is subject to change.
    • badgerV1: explicitly select Badger V1.
    • badgerV2: explicitly select Badger V2.

  • dataSource: path, database directory.

  • valueDir [optional]: path, value directory, only if different from dataSource.

  • badgerFileLoadingMode [optional]: can be set to FileIO (instead of the default MemoryMap) to avoid memory-mapping log files. This can be useful in environments with low RAM. Make sure to use badgerV2 as the database type if using this option.

    • MemoryMap: default.
    • FileIO: This can be useful in environments with low RAM.

BoltDB

Bolt (etcd fork) is a key-value database embedded in step-ca.

{
  ...
  "db": {
    "type": "bbolt",
    "dataSource": "./stepdb"
  },
  ...
}

Options

  • type: bbolt
  • dataSource: path, database directory.

MySQL

step-ca uses MySQL as a simple key-value store, not as a relational database.

{
  ...
  "db": {
    "type": "mysql",
    "dataSource": "user:password@tcp(127.0.0.1:3306)/",
    "database": "myDBName"
  },
  ...
},

Options

  • type: mysql
  • dataSource: path, database directory.

PostgreSQL

step-ca uses PostgreSQL as a simple key-value store, not as a relational database.

{
  ...
  "db": {
    "type": "postgresql",
    "dataSource": "postgresql://user:password@127.0.0.1:5432/",
    "database": "myDBName"
  },
  ...
},

Options

  • type: postgresql
  • dataSource: a PostgreSQL DSN.
  • database: database name. Takes precedence over name in the DSN if provided.

Use TLS with PostgreSQL

The PostgreSQL DSN can be used to configure TLS settings for connecting to the server. An example database configuration that enables TLS server hostname verification is shown below:

{
  ...
  "db": {
    "type": "postgresql",
    "dataSource": "postgresql://user:password@127.0.0.1:5432/dbname?sslmode=verify-full"
  },
  ...
},

The database driver looks in $HOME/.postgresql/root.crt for a PEM bundle of root CAs to trust. When that file is not found, it uses the system's default trust store. Similarly, $HOME/.postgresql/postgresql.crt and the corresponding $HOME/.postgresql/postgresql.key is used for mutual TLS authentication if these files exist, and if the PostgreSQL server requests a client certificate. You can override the locations for these files by providing them in the DSN:

{
  ...
  "db": {
    "type": "postgresql",
    "dataSource": "postgresql://user:password@127.0.0.1:5432/dbname?sslmode=verify-full&sslrootcert=/path/to/roots.pem&sslcert=/path/to/client.pem&sslkey=/path/to/client.key"
  },
  ...
},

The behavior of the PostgreSQL database driver mimics that of libpq and also encompasses handling of other default settings and environment variables.

The libpq docs cover TLS options and the DSN query parameters for libpq in more detail.

Schema

As the interface is a key-value store, the schema is very simple. We support tables, keys, and values. An entry in the database is a []byte value that is indexed by []byte table and []byte key.

Exporting Data

At this time step-ca does not have any API or interface for easily exporting data. Because the data is stored in a noSQL like manner, it is difficult to explore the data even when using a SQL backend like MySQL. We do have a scripted example for accessing the DB to give users a jumping off point for writing their own reporting and logging tools.

Cryptographic Protection

By default, step-ca stores its signing keys encrypted on disk.

For security hardening, you may desire more advanced cryptographic protection (or hardware protection) of your CA's signing keys.

For these scenarios, step-ca integrates with the following key management systems:

For a complete, end-to-end example using a YubiKey, see our blog post Build a Tiny Certificate Authority For Your Homelab.

Before You Begin

The step ca init command has very limited support for keys not stored on disk. We've created the step kms plugin for managing the keys and certificates on cloud KMSs and on hardware devices. Please install this plugin before continuing with any of the examples below.

Google Cloud KMS

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

Creating your PKI in Google Cloud KMS

Please install the step kms plugin before you begin. You'll need it to create your PKI.

Also, make sure you have installed the gcloud CLI and have configured Google Cloud application default credentials in your local environment, eg. by running gcloud auth application-default login.

Next, let's generate a private key for your Root CA. The step kms create command will also create a Cloud KMS key ring for you, if it doesn't exist. Run:

$ step kms create --json --kms 'cloudkms:' \
    'projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/root'

To constructe the key name parameter above, use the resource name of the CryptoKey object you want to create, following the format:

projects/<project-id>/locations/<location>/keyRings/<key-ring-id>/cryptoKeys/<key-id>

Once the key is generated, step outputs the key's name (including a version number), and the public key PEM:

{
  "name": "projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/root/cryptoKeyVersions/1",
  "publicKey": "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAERcTjeMNjBs29ReA1nf6Odyn2l4Yt\nXPo4CUOcCrn6yw7LJmzaDiqIErhuS9r6BNg92kJvFUiuiU8+w+WZOyhZdw==\n-----END PUBLIC KEY-----\n"
}

You'll need this key name for the next step.

Now, let's sign a root CA certificate based on the the key you just created. Substitute the key name output from step kms create here:

$ step certificate create --profile root-ca \
   --kms 'cloudkms:' \
   --key 'projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/root/cryptoKeyVersions/1' \
   "Smallstep Root CA" root_ca.crt

Output:

Your certificate has been saved in root_ca.crt.

Great. Next, repeat the process for the Intermediate CA:

$ step kms create --json --kms 'cloudkms:' \
    'projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/intermediate'
$ step certificate create --profile intermediate-ca \
   --kms 'cloudkms:' \
   --ca-kms 'cloudkms:' \
   --ca root_ca.crt \
   --ca-key 'projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/root/cryptoKeyVersions/1' \
   --key 'projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/intermediate/cryptoKeyVersions/1' \
   "Smallstep Intermediate CA" intermediate_ca.crt

Output:

Your certificate has been saved in intermediate_ca.crt.

Now you should have both root_ca.crt and intermediate_ca.crt certificate PEM files. Use these files in your CA configuration, below.

If you want to run an SSH CA, you also need to create SSH CA key pairs:

$ step kms create --json --kms 'cloudkms:' \
    'projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/ssh-user'
$ step kms create --json --kms 'cloudkms:' \
    'projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/ssh-host'

Configuring step-ca to use Google Cloud KMS

Next, to configure Cloud KMS in step-ca, start with a basic CA configuration created using step ca init. Add the kms object to your ca.json file and replace the property key with the Cloud KMS resource name of your intermediate key:

{
    "root": "/etc/step-ca/certs/root_ca.crt",
    "crt": "/etc/step-ca/certs/intermediate_ca.crt",
    "key": "projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/intermediate/cryptoKeyVersions/1",
    "kms": {
        "type": "cloudkms",
        "uri": "cloudkms:credentials-file=/path/to/gcloud-kms-credentials.json"
    }
}

Finally, copy the root_ca.crt and intermediate_ca.crt files into the root and crt locations:

$ cp root_ca.crt intermediate_ca.crt $(step path)/certs

Your X.509 CA is ready.

To add SSH support, change the SSH key locations to Cloud KMS resource names for the SSH host and user CA keys:

{
    "ssh": {
        "hostKey": "projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/ssh-host/cryptoKeyVersions/1",
        "userKey": "projects/smallstep/locations/global/keyRings/step-ca/cryptoKeys/ssh-user/cryptoKeyVersions/1"
    }
}

When you start step-ca, it prints your X.509 root fingerprint, and the SSH user and host CA keys in SSH key format:

2022/09/20 16:28:45 The primary server URL is https://localhost:443
2022/09/20 16:28:45 Root certificates are available at https://localhost:443/roots.pem
2022/09/20 16:28:45 X.509 Root Fingerprint: b061dfca1013c074244b0f376e5be70b6eb0bd7f21d5438aa3af71fe62b0acf5
2022/09/20 16:28:45 SSH Host CA Key: ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBIwmL7aDOJId/9UOVJGhVux6Rlvea+q2017aLsfze+/EwGQ5BdZ4k2Qh+5VekebBKZYLNO0LkSf9bZb4o9GSxIs=
2022/09/20 16:28:45 SSH User CA Key: ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFE0VY9eLxkoHrXoWk5VxeOQTUt53U5xIo89pfsgYHh450cdE4c3mYw5YeOueESyu/lFUHfJoNS6twVR1wuCOdc=
2022/09/20 16:28:45 Serving HTTPS on :443 ...

Notes on Google Cloud KMS Permissions

Following the principle of least privilege, you'll want to define an IAM operational role for step-ca that limits its access. See Google Cloud KMS: Access Control with IAM for an overview.

Here are some notes on granting a custom IAM role that provides step-ca with access to Google Cloud KMS:

  • You can constrain the role to the key ring that you created for step-ca.
  • For day-to-day operation, grant step-ca the following default roles:
  • More specifically, a running step-ca needs access to the following KMS APIs:
    • resourcemanager.projects.get
    • cloudkms.locations.get
    • cloudkms.keyRings.get
    • cloudkms.cryptoKeys.get
    • cloudkms.cryptoKeyVersions.get
    • cloudkms.cryptoKeyVersions.useToSign
    • cloudkms.cryptoKeyVersions.useToVerify
    • cloudkms.cryptoKeyVersions.useToDecrypt

AWS KMS

AWS KMS is Amazon's managed encryption and key management service. It creates and stores the cryptographic keys and uses AWS infrastructure for signing operations. Amazon KMS operations are always backed by HSMs.

Creating your PKI in AWS KMS

Please install the step kms plugin before you begin. You'll need it to create your PKI.

Also, make sure you have installed the aws CLI and have configured AWS credentials in your local environment.

Next, let's generate a private key for your root CA inside AWS KMS. Run:

$ step kms create --json --kms 'awskms:region=us-east-2' root-ca

Once the key is generated, step outputs the key ID and the public key PEM:

{
  "name": "awskms:key-id=78980acd-a42d-4d84-97ba-1e50d3082214",
  "publicKey": "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEH2ls6h1y2jsXV+IeuhDVkb68zkMe\nKPtI7L6vBIa5ThxOyFaZFnUrGWU6B+KQjProAntgKyNTqOnAh7Eyr3RmgQ==\n-----END PUBLIC KEY-----\n"
}

When creating the key, step kms create will also add an AWS key alias root-ca-78980acd for the key. The alias is concatenates the key name and the first segment of the key's ID.

You'll need this key name for the next step.

Now, let's sign a root CA certificate based on the the key you just created. Substitute the key name output from step kms create here:

$ step certificate create --profile root-ca \
   --kms 'awskms:region=us-east-2' \
   --key 'awskms:key-id=78980acd-a42d-4d84-97ba-1e50d3082214' \
   "Smallstep Root CA" root_ca.crt

Output:

Your certificate has been saved in root_ca.crt.

Great. Next, we'll repeat the process for the Intermediate CA:

$ step kms create --json --kms 'awskms:region=us-east-2' intermediate-ca
$ step certificate create --profile intermediate-ca \
   --kms 'awskms:region=us-east-2' \
   --ca-kms 'awskms:region=us-east-2' \
   --ca root_ca.crt \
   --ca-key 'awskms:key-id=78980acd-a42d-4d84-97ba-1e50d3082214' \
   --key 'awskms:key-id=9432458d-1e67-4a74-9a23-8f94708b45fe' \
   "Smallstep Intermediate CA" intermediate_ca.crt

Here, the --ca-key is the root CA key id; the --key is the intermediate CA key id.

Output:

Your certificate has been saved in intermediate_ca.crt.

Now you should have both root_ca.crt and intermediate_ca.crt certificate PEM files. You'll need these files for your CA configuration, below.

If you want to run an SSH CA, you'll also need to create SSH CA key pairs:

$ step kms create --json --kms 'awskms:region=us-east-2' ssh-user-ca
$ step kms create --json --kms 'awskms:region=us-east-2' ssh-host-ca

Hold onto the key IDs from these commands; you'll need them below.

Configuring step-ca to use AWS KMS

To use step-ca with AWS KMS, create a scoped IAM role that has kms:GetPublicKey permissions on all of your CA keys, and kms:Sign permission on your intermediate CA key.

To configure AWS KMS in your certificate authority, add the kms object to ca.json and replace the key property with the AWS KMS key ID of your intermediate CA key:

{
    "root": "/etc/step-ca/certs/root_ca.crt",
    "crt": "/etc/step-ca/certs/intermediate_ca.crt",
    "key": "awskms:key-id=f879f239-feb6-4596-9ed2-b1606277c7fe",
    "kms": {
        "type": "awskms",
        "uri": "awskms:region=us-east-2;profile=foo;credentials-file=/path/to/credentials"
    }
}

By default, step-ca (and, more broadly, AWS's SDK) looks for credentials stored in ~/.aws/credentials. Use the credentials-file option to override. The region and profile options specify the AWS region and configuration profiles respectively. These options can also be configured using environment variables as described in the AWS SDK for Go session documentation.

Finally, copy the root_ca.crt and intermediate_ca.crt files into the root and crt locations:

$ cp root_ca.crt intermediate_ca.crt $(step path)/certs

Your X.509 CA is ready.

To configure an SSH CA, replace the SSH key locations with the SSH CA keys you created above:

{
    "ssh": {
        "hostKey": "awskms:key-id=d48e502a-09bc-4bf7-9af8-ae1bccedc931",
        "userKey": "awskms:key-id=cf28e942-1e10-4a08-b84c-5359af1b5f12"
    }
}

When you start step-ca, it prints your X.509 root fingerprint, and the SSH user and host CA keys in SSH key format:

2022/09/20 16:28:45 The primary server URL is https://localhost:443
2022/09/20 16:28:45 Root certificates are available at https://localhost:443/roots.pem
2022/09/20 16:28:45 X.509 Root Fingerprint: b061dfca1013c074244b0f376e5be70b6eb0bd7f21d5438aa3af71fe62b0acf5
2022/09/20 16:28:45 SSH Host CA Key: ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBIwmL7aDOJId/9UOVJGhVux6Rlvea+q2017aLsfze+/EwGQ5BdZ4k2Qh+5VekebBKZYLNO0LkSf9bZb4o9GSxIs=
2022/09/20 16:28:45 SSH User CA Key: ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFE0VY9eLxkoHrXoWk5VxeOQTUt53U5xIo89pfsgYHh450cdE4c3mYw5YeOueESyu/lFUHfJoNS6twVR1wuCOdc=
2022/09/20 16:28:45 Serving HTTPS on :443 ...

Notes on AWS KMS Permissions

Following the principle of least privilege, you'll want to define an IAM operational role for step-ca that limits its access. See Using IAM Policies With AWS KMS for an overview.

Here are some notes on granting a custom IAM role that provides step-ca with access to AWS KMS:

  • You can constrain the role to specific keys that you created for step-ca, by listing each key's ARN in the Resource block of the JSON policy.
  • For day-to-day operation, grant step-ca the following permissions:
    • kms:GetPublicKey
    • kms:Sign

Azure Key Vault

Azure Key Vault is Microsoft's managed key management service.

Authentication

When using Azure Key Vault with step-ca, first authenticate to Azure.

Authentication to Azure is handled via environment variables; we recommend using either file-based authentication via the AZURE_AUTH_LOCATION environment variable, or using a managed identity and setting the AZURE_TENANT_ID and AZURE_CLIENT_ID variables when starting step-ca. Alternatively, you can create a service principal and set the AZURE_TENANT_ID, AZURE_CLIENT_ID, and AZURE_CLIENT_SECRET variables. See Option 1 under Authentication Methods for Azure SDK for Go for examples of authentication methods and environment variables.

For local development and testing, Azure CLI credentials are used if no authentication environment variables are set.

Initialize a PKI

To initialize a PKI backed by Azure Key Vault, start by authenticating to Azure using one of the above approaches. Set the environment variables necessary for authentication to your tenant.

Then, run:

$ step ca init --kms azurekms

This walks you through the process of creating root and intermediate CA signing keys in Key Vault, and configuring the CA to use them. If you're creating an SSH CA, SSH host and user CA keys are created in Key Vault as well.

Manual Configuration

To configure an existing CA for Azure Key Vault, or to import an existing Azure Key Vault signing key, add the kms object to your ca.json, and replace the key properties with the key name, vault name, and version of your intermediate (signing) key in Azure Key Vault:

{
    "root": "/etc/step-ca/certs/root_ca.crt",
    "crt": "/etc/step-ca/certs/intermediate_ca.crt",
    "key": "azurekms:name=intermediate-ca-key;vault=example-vault-0?version=15faf8b8b80d4f1ead067c6383a38b8f&hsm=true",
    "kms": {
        "type": "azurekms"
    }
}
  • In the key URI, the name and vault refer to the key name and vault name of your intermediate key in Azure Key Vault.
  • In the key URI, the version is the version of the Azure Key Vault key name. Though it is optional, we recommend setting this value explicitly. If omitted, the latest version is used.
  • In the key URI, the optional hsm property can be set to true if HSM protection is desired. This is only used when the key is being created by step-ca. The default is to use software-protected (non-HSM-backed) keys. See Key Vault's About Keys page for more details.
  • In kms, an optional uri property can be added to provide client credentials (eg. azurekms:client-id=fooo;client-secret=bar;tenant-id=9de53416-4431-4181-7a8b-23af3EXAMPLE) instead of using the environment variables described above.

Notes on Azure Key Vault IAM Permissions

Following the principle of least privilege, you'll want to define an IAM operational role for step-ca that limits its access. See Provide access to Key Vault keys, certificates, and secrets with an Azure role-based access control for an overview.

Here are some notes on granting a custom IAM role that provides step-ca with access to Azure Key Vault:

  • You can constrain the role to the vault that you created for step-ca.
  • For day-to-day operation, grant step-ca the following default RBAC roles on the vault:
    • Key Vault Crypto User
    • Key Vault Reader
  • More specifically, a running step-ca needs access to the following APIs:
    • GetKey
    • Sign

PKCS #11

A Hardware Security Module (HSM) is a specialized piece of hardware that is designed to generate and store private keys, and sign messages using those keys. The private keys on an HSM cannot be exported from the device. One can only run signing operations using the key. This is an excellent way to protect private keys for a Certificate Authority, which in normal operation simply needs to be able to sign Certificate Signing Requests.

Public-Key Cryptography Standards #11 (PKCS #11) is the most common platform-independent API used to access HSM hardware. It's supported by most HSM hardware, like Yubico's YubiHSM2, and the Nitrokey HSM 2. There's also a software-based "HSM," SoftHSMv2, which offers a PKCS #11 interface without the hardware. Finally, you can use PKCS#11 with a Trusted Platform Module (TPM) 2.0 chip on Linux. This requires the libtpm2_pkcs11.so library.

0. Before you begin

Your HSM or TPM2 may need to be prepared before you can initialize a PKI on it. Preparation steps depend on the device and are beyond the scope of this documentation. For example,

  • With YubiHSM2, first create an authentication key with appropriate capabiliites.
  • With TPM2, initialize the TPM and create a PKCS#11 token on it.

Plan how you will backup and restore your CA keys, for offline storage.

The step kms plugin will create CA keys and sign certificates on your device. To use it, you'll need to provide a PKCS #11 URI for accessing the device, using the --kms flag.

Here are some examples of PKCS #11 URIs for accessing various devices in Linux:

HSMURI format
YubiHSM2pkcs11:module-path=/usr/lib/x86_64-linux-gnu/pkcs11/yubihsm_pkcs11.so;token=YubiHSM
AWS CloudHSMpkcs11:module-path=/opt/cloudhsm/lib/libcloudhsm_pkcs11.so;token=cavium?pin-value=$HSM_USER:$HSM_PASSWORD
SoftHSMpkcs11:module-path=/usr/lib/softhsm/libsofthsm2.so;token=token1?pin-value=$HSM_PASSWORD
nCipher nShieldpkcs11:module-path=/opt/nfast/toolkits/pkcs11/libcknfast.so;token=rjk?pin-source=/etc/step-ca/hsm-pin.txt
TPM2 (via libtpm2_pkcs11)pkcs11:module-path=/usr/local/lib/libtpm2_pkcs11.so;token=step-ca?pin-value=$HSM_PASSWORD

Substitute $HSM_USER and $HSM_PASSWORD with your own values.

In this URI,

  • module-path points to your PKCS #11 .dll, .so, or .dylib library file,
  • token is the label (CKA_LABEL) of the HSM you're using,
  • pin-value contains hardcoded HSM credentials. It may be a PIN, username and password, password, or a filename. The YubiHSM2 is special in that the PIN value is the concatenation of the four-digit authorization key ID (eg. 0001) and the PIN.
  • Or, pin-source is a filename containing HSM credentials.

1. Create your PKI

Once you've constructed the right URI for accessing your device, use it in place of $PKCS_URI in the commands below.

First, please install the step kms plugin before you begin. You'll need it to create your PKI.

Next, let's ask the device to generate a private key for your root CA. Run:

$ step kms create --json --kms "$PKCS_URI" "pkcs11:id=7331;object=root-ca"

Once the key is generated, step will output the key ID and the public key PEM:

{
  "name": "pkcs11:id=7331;object=root-ca",
  "publicKey": "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEH2ls6h1y2jsXV+IeuhDVkb68zkMe\nKPtI7L6vBIa5ThxOyFaZFnUrGWU6B+KQjProAntgKyNTqOnAh7Eyr3RmgQ==\n-----END PUBLIC KEY-----\n"
}

You'll need this key name for the next step.

Now, let's sign a root CA certificate based on the the key you just created. Substitute the key name output from step kms create here:

$ step certificate create --profile root-ca \
   --kms "$PKCS_URI"
   --key "pkcs11:id=7331;object=root-ca" \
   "Smallstep Root CA" root_ca.crt

Output:

Your certificate has been saved in root_ca.crt.

Great. Next, we'll repeat the process for the Intermediate CA:

$ step kms create --json --kms "$PKCS_URI" "pkcs11:id=7332;object=intermediate-ca"
$ step certificate create --profile intermediate-ca \
   --kms "$PKCS_URI" \
   --ca-kms "$PKCS_URI" \
   --ca root_ca.crt \
   --ca-key "pkcs11:id=7331;object=root-ca" \
   --key "pkcs11:id=7332;object=intermediate-ca" \
   "Smallstep Intermediate CA" intermediate_ca.crt

Here, the --ca-key is the root CA key id; the --key is the intermediate CA key id.

Output:

Your certificate has been saved in intermediate_ca.crt.

Now you should have both root_ca.crt and intermediate_ca.crt certificate PEM files. You'll need these files for your CA configuration, below.

If you want to run an SSH CA, you'll also need to create SSH CA key pairs:

$ step kms create --json --kms "$PKCS_URI" "pkcs11:id=7333;object=ssh-host-ca"
$ step kms create --json --kms "$PKCS_URI" "pkcs11:id=7334;object=ssh-user-ca"

Hold onto the key IDs from these commands; you'll need them below.

Configuring step-ca to use PKCS #11

One you've created your PKI on the HSM using step-kms-plugin, you'll need to configure step-ca to use the HSM.

To configure your certificate authority, add the kms object to ca.json and replace the key property with the object ID of your intermediate CA key:

{
    "root": "/etc/step-ca/certs/root_ca.crt",
    "crt": "/etc/step-ca/certs/intermediate_ca.crt",
    "key": "pkcs11:id=7332;object=intermediate-ca",
    "kms": {
        "type": "pkcs11",
        "uri": "$PKCS_URI"
    }
}

Finally, copy the root_ca.crt and intermediate_ca.crt files into the root and crt locations:

$ cp root_ca.crt intermediate_ca.crt $(step path)/certs

Your X.509 CA is ready.

To configure an SSH CA, replace the SSH key locations with the SSH CA keys you created above:

{
    "ssh": {
        "hostKey": "pkcs11:id=7333;object=ssh-host-ca",
        "userKey": "pkcs11:id=7334;object=ssh-user-ca"
    }
}

When you start step-ca, you will see your X.509 root fingerprint, and the SSH user and host CA keys in SSH key format:

2022/09/20 16:28:45 The primary server URL is https://localhost:443
2022/09/20 16:28:45 Root certificates are available at https://localhost:443/roots.pem
2022/09/20 16:28:45 X.509 Root Fingerprint: b061dfca1013c074244b0f376e5be70b6eb0bd7f21d5438aa3af71fe62b0acf5
2022/09/20 16:28:45 SSH Host CA Key: ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBIwmL7aDOJId/9UOVJGhVux6Rlvea+q2017aLsfze+/EwGQ5BdZ4k2Qh+5VekebBKZYLNO0LkSf9bZb4o9GSxIs=
2022/09/20 16:28:45 SSH User CA Key: ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFE0VY9eLxkoHrXoWk5VxeOQTUt53U5xIo89pfsgYHh450cdE4c3mYw5YeOueESyu/lFUHfJoNS6twVR1wuCOdc=
2022/09/20 16:28:45 Serving HTTPS on :443 ...

YubiKey PIV

You can leverage a hardware YubiKey—and the YubiKey PIV application—to store your CA keys and sign TLS and SSH certificates.

Prerequisites and Caveats

Please install the step kms plugin before you begin. You'll need it to create your PKI.

Now, insert your YubiKey. Let's generate a private key for your root CA in slot 82 on the YubiKey. Run:

$ step kms create --json 'yubikey:slot-id=82'

Once the key is generated, step outputs the key name and public key PEM:

{
  "name": "yubikey:slot-id=82",
  "publicKey": "-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAED3T/7q+p+6239Ri35TBVoChM6VNq\n1buLfql1acRl7F2qf/L96x9XHY5GHoqYNCAm/ocL9hTl8ytWJao+JSNE+Q==\n-----END PUBLIC KEY-----\n"
}

Now, let's sign a root CA certificate based on the the key you just created. Substitute the key name output from step kms create here:

$ step certificate create --profile root-ca \
   --kms 'yubikey:pin-value=123456' \
   --key 'yubikey:slot-id=82' \
   "Smallstep Root CA" root_ca.crt

Here we're using the default PIN code of 123456 to access the YubiKey.

Output:

Your certificate has been saved in root_ca.crt.

Great. Next, we'll repeat the process for the Intermediate CA:

$ step kms create --json 'yubikey:slot-id=83'
$ step certificate create --profile intermediate-ca \
   --kms 'yubikey:pin-value=123456' \
   --ca-kms 'yubikey:pin-value=123456' \
   --ca root_ca.crt \
   --ca-key 'yubikey:slot-id=82' \
   --key 'yubikey:slot-id=83' \
   "Smallstep Intermediate CA" intermediate_ca.crt

Here, the --ca-key is the root CA key id; the --key is the intermediate CA key id.

Output:

Your certificate has been saved in intermediate_ca.crt.

Now you should have both root_ca.crt and intermediate_ca.crt certificate PEM files. You'll need these files for your CA configuration, below.

for safekeeping, you may wish to import the certificates into the YubiKey. To do this, you'll need Yubico's ykman CLI utility. Run:

$ ykman piv certificates import 82 root_ca.crt
$ ykman piv certificates import 83 intermediate_ca.crt

(While step-ca won't use these copies of the certificates, you can always use ykman piv certificates export to download the certificates later.)

Next, if you want to run an SSH CA, you'll also need to create two SSH CA keys:

$ step kms create --json 'yubikey:slot-id=84'
$ step kms create --json 'yubikey:slot-id=85'

Finally, to enable your CA in ca.json, point the root and crt options to the generated certificates, replace the key option with the YubiKey URI generated in the previous part, and configure the kms option with the appropriate type and pin.

{
    "root": "/etc/step-ca/certs/root_ca.crt",
    "crt": "/etc/step-ca/certs/intermediate_ca.crt",
    "key": "yubikey:slot-id=83",
    "kms": {
        "type": "yubikey",
        "uri": "yubikey:management-key=01020304...?pin-value=123456"
    }
}

Finally, copy the root_ca.crt and intermediate_ca.crt files into the root and crt locations:

$ cp root_ca.crt intermediate_ca.crt $(step path)/certs

Your X.509 CA is ready.

To configure an SSH CA, replace the SSH key locations with the SSH CA keys you created in AWS KMS:

{
    "ssh": {
        "hostKey": "yubikey:slot-id=84",
        "userKey": "yubikey:slot-id=85"
    }
}

When you start step-ca, it prints your X.509 root fingerprint, and the SSH host and user CA keys in SSH key format:

2022/09/20 16:28:45 The primary server URL is https://localhost:443
2022/09/20 16:28:45 Root certificates are available at https://localhost:443/roots.pem
2022/09/20 16:28:45 X.509 Root Fingerprint: b061dfca1013c074244b0f376e5be70b6eb0bd7f21d5438aa3af71fe62b0acf5
2022/09/20 16:28:45 SSH Host CA Key: ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBIwmL7aDOJId/9UOVJGhVux6Rlvea+q2017aLsfze+/EwGQ5BdZ4k2Qh+5VekebBKZYLNO0LkSf9bZb4o9GSxIs=
2022/09/20 16:28:45 SSH User CA Key: ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFE0VY9eLxkoHrXoWk5VxeOQTUt53U5xIo89pfsgYHh450cdE4c3mYw5YeOueESyu/lFUHfJoNS6twVR1wuCOdc=
2022/09/20 16:28:45 Serving HTTPS on :443 ...