Creating a Private CA - AWS Certificate Manager Private Certificate Authority

Creating a Private CA

This section describes how you create a private certificate authority (CA) using ACM Private CA. You can use these procedures to create both root CAs and subordinate CAs, resulting in an auditable hierarchy of trust relationships that matches your organizational needs.

For information about using a CA to sign end-entity certificates for your users, devices, and applications, see Issuing a Private End-Entity Certificate.

Note

Your account is charged a monthly price for each private CA starting from the time that you create it.

To create a private CA using the AWS console

  1. Sign in to your AWS account and open the ACM Private CA console at https://console.aws.amazon.com/acm-pca/home. The introductory page will appear if your console opens to a region in which you do not have a CA. Choose Get started beneath Private certificate authority. Choose Get started again. If the console opens to a region in which you already have one or more CAs, the introductory page will not be shown. Choose Private CAs and then choose Create CA.

  2. On the Select the certificate authority (CA) type page, select the type of the private certificate authority that you want to create.

    • Choosing Root CA establishes a new CA hierarchy. This CA is backed by a self-signed certificate. It serves as the ultimate signing authority for other CAs and end-entity certificates in the hierarchy.

    • Choosing Subordinate CA creates a CA that must be signed by a parent CA above it in the hierarchy. Subordinate CAs are typically be used to create other subordinate CAs or to issue end-entity certificates to users, computers, and applications.

    After selecting a CA type, choose Next.

  3. On the Configure the certificate authority (CA) subject name, configure the subject name of your private CA. You must enter at least one of the following values:

    • Organization (O)

    • Organization Unit (OU)

    • Country name (C)

    • State or province name

    • Locality name

    • Common Name (CN)

    Because the backing certificate is self-signed, the subject information you provide for a private CA is probably sparser than what a public CA would contain. For more information about each of the values that make up a subject distinguished name, see X.500 Distinguished Name.

    When done, choose Next.

  4. On the Configure the certificate authority (CA) key type page, select the key algorithm and the bit-size of the key. The default value is an RSA algorithm with a 2048-bit key length. If you expand the Advanced options, you can select from the following algorithms:

    • RSA 2048

    • RSA 4096

    • ECDSA P256

    • ECDSA P384

    Make a selection and then choose Next.

  5. On the Configure certificate revocation page, you have the option of creating a certificate revocation list (CRL) managed by ACM Private CA. Clients such as web browsers query CRLs to determine whether an end-entity or subordinate CA certificate can be trusted. For more information, see Revoking a Private Certificate.

    ACM Private CA automatically deposits the CRL in the Amazon S3 bucket you designate and updates it periodically.

    Note

    The CRL will only be deposited in Amazon S3 once a certificate has been issued that refers to it. Prior to that, there will only be an acm-pca-permission-test-key file visible in the Amazon S3 bucket.

    For information about adding encryption protection to your CRLs, see Encrypting Your CRLs .

    Each CRL is a DER encoded file. To download the file and use OpenSSL to view it, use a command like to the following:

    openssl crl -inform DER -in path-to-crl-file -text -noout

    CRLs have the following format:

    Certificate Revocation List (CRL): Version 2 (0x1) Signature Algorithm: sha256WithRSAEncryption Issuer: /C=US/ST=WA/L=Seattle/O=Example Company CA/OU=Corporate/CN=www.example.com Last Update: Feb 26 19:28:25 2018 GMT Next Update: Feb 26 20:28:25 2019 GMT CRL extensions: X509v3 Authority Key Identifier: keyid:AA:6E:C1:8A:EC:2F:8F:21:BC:BE:80:3D:C5:65:93:79:99:E7:71:65 X509v3 CRL Number: 1519676905984 Revoked Certificates: Serial Number: E8CBD2BEDB122329F97706BCFEC990F8 Revocation Date: Feb 26 20:00:36 2018 GMT CRL entry extensions: X509v3 CRL Reason Code: Key Compromise Serial Number: F7D7A3FD88B82C6776483467BBF0B38C Revocation Date: Jan 30 21:21:31 2018 GMT CRL entry extensions: X509v3 CRL Reason Code: Key Compromise Signature Algorithm: sha256WithRSAEncryption 82:9a:40:76:86:a5:f5:4e:1e:43:e2:ea:83:ac:89:07:49:bf: c2:fd:45:7d:15:d0:76:fe:64:ce:7b:3d:bb:4c:a0:6c:4b:4f: 9e:1d:27:f8:69:5e:d1:93:5b:95:da:78:50:6d:a8:59:bb:6f: 49:9b:04:fa:38:f2:fc:4c:0d:97:ac:02:51:26:7d:3e:fe:a6: c6:83:34:b4:84:0b:5d:b1:c4:25:2f:66:0a:2e:30:f6:52:88: e8:d2:05:78:84:09:01:e8:9d:c2:9e:b5:83:bd:8a:3a:e4:94: 62:ed:92:e0:be:ea:d2:59:5b:c7:c3:61:35:dc:a9:98:9d:80: 1c:2a:f7:23:9b:fe:ad:6f:16:7e:22:09:9a:79:8f:44:69:89: 2a:78:ae:92:a4:32:46:8d:76:ee:68:25:63:5c:bd:41:a5:5a: 57:18:d7:71:35:85:5c:cd:20:28:c6:d5:59:88:47:c9:36:44: 53:55:28:4d:6b:f8:6a:00:eb:b4:62:de:15:56:c8:9c:45:d7: 83:83:07:21:84:b4:eb:0b:23:f2:61:dd:95:03:02:df:0d:0f: 97:32:e0:9d:38:de:7c:15:e4:36:66:7a:18:da:ce:a3:34:94: 58:a6:5d:5c:04:90:35:f1:8b:55:a9:3c:dd:72:a2:d7:5f:73: 5a:2c:88:85

    When you have associated a CRL with a CA, ACM Private CA includes the CRL Distribution Points extension in certificates issued by the CA. This extension provides the URL to the CRL so that client devices can check certificate revocation status.

    To create a CRL, complete the following steps:

    1. Choose Enable CRL distribution.

    2. To create a new Amazon S3 bucket for your CRL entries, choose Yes for the Create a new S3 bucket option and type a unique bucket name. (You do not need to include the path to the bucket.) Otherwise, choose No and select an existing bucket from the list.

      If you choose Yes, ACM Private CA creates the necessary bucket policy for you. If you choose No, make sure the following policy is attached to your bucket. For more information, see Adding a Bucket Policy.

      { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Principal": { "Service": "acm-pca.amazonaws.com" }, "Action": [ "s3:PutObject", "s3:PutObjectAcl", "s3:GetBucketAcl", "s3:GetBucketLocation" ], "Resource": [ "arn:aws:s3:::your-bucket-name/*", "arn:aws:s3:::your-bucket-name" ] } ] }
      Note

      Your private CA may fail to create a CRL bucket if Amazon S3 block public access settings are enforced on your account. Check your Amazon S3 settings if this occurs. For more information, see Using Amazon S3 Block Public Access.

    3. Expand Advanced for additional configuration options.

      • Add a Custom CRL Name to create an alias for your Amazon S3 bucket. This name is contained in certificates issued by the CA in the “CRL Distribution Points” extension that is defined by RFC 5280.

      • Type the number of days your CRL will remain valid. The default value is 7 days. For online CRLs, a validity period of two to seven days is common. ACM Private CA tries to regenerate the CRL at the midpoint of the specified period.

    Choose Next.

  6. On the Add tags page, you can optionally tag your CA. Tags are key/value pairs that serve as metadata for identifying and organizing AWS resources. For a list of ACM Private CA tag parameters and for instructions on how to add tags to CAs after creation, see Add Tags to your Private Certificate Authority.

    Choose Next.

  7. Configure CA permissions

    Optionally delegate automatic renewal permissions to the ACM service principal. ACM can only automatically renew private end-entity certificates generated by this CA if this permission is granted. You can assign renewal permissions at any time with the ACM Private CA API.

    The default is to enable these permissions.

    Choose Next.

  8. On the Review and create page, confirm that your configuration is correct, check the box to acknowledge pricing information, and choose Confirm and create.

    If you want to continue on to creating and installing a CA certificate, choose Get started in the Success dialog box and follow the instructions at Creating and Installing the Certificate for a Private CA. Otherwise choose You can also finish this later, which takes you to a list of your Private CAs.

To create a private CA using the AWS CLI

Use the create-certificate-authority command to create a private CA. You must specify the CA configuration, the revocation configuration, and the CA type. You can optionally add an idempotency token or tags. The CA configuration specifies the following:

  • The name of the algorithm

  • The key size to be used to create the CA private key

  • The type of signing algorithm that the CA uses to sign

  • X.500 subject information

The CRL configuration specifies the following:

  • The CRL expiration period in days (the validity period of the CRL)

  • The Amazon S3 bucket that will contain the CRL

  • A CNAME alias for the S3 bucket that is included in certificates issued by the CA

You can modify the following example files to use with this command.

C:\ca_config.txt { "KeyAlgorithm": "RSA_2048", "SigningAlgorithm": "SHA256WITHRSA", "Subject": {"Country": "US", "Organization": "Example Corp", "OrganizationalUnit": "Sales", "State": "WA", "Locality": "Seattle", "CommonName": "www.example.com"} }
C:\revoke_config.txt { "CrlConfiguration": {"Enabled": true, "ExpirationInDays": 7, "CustomCname": "some_name.crl", "S3BucketName": "your-bucket-name"} }
aws acm-pca create-certificate-authority \ --certificate-authority-configuration file://C:\ca_config.txt \ --revocation-configuration file://C:\revoke_config.txt \ --certificate-authority-type "ROOT" \ --idempotency-token 98256344 \ --tags Key=Name,Value=MyPCA

If successful, this command outputs the ARN (Amazon Resource Name) of the CA.

{ "CertificateAuthorityArn": "arn:aws:acm-pca:region:account: certificate-authority/12345678-1234-1234-123456789012" }

To create a private CA using AWS CloudFormation

For information about creating a private CA using AWS CloudFormation, see ACM PCA Resource Type Reference in the AWS CloudFormation User Guide.

Encrypting Your CRLs

You can optionally configure encryption on the Amazon S3 bucket containing your CRLs. ACM Private CA supports two encryption modes for assets in S3:

  • Automatic server-side encryption with Amazon S3-managed AES-256 keys.

  • Customer-managed encryption using AWS Key Management Service and customer master keys (CMKs) configured to your specifications.

Note

ACM Private CA does not support using default CMKs generated automatically by S3.

The following procedures describe how to set up each of the encryption options.

To configure automatic encryption

Complete the following steps to enable S3 server-side encryption.

  1. Open the Amazon S3 console at https://console.aws.amazon.com/s3/.

  2. In the Buckets table, choose the bucket that will hold your ACM Private CA assets.

  3. On the page for your bucket, choose the Properties tab.

  4. Choose the Default encryption card.

  5. Choose AES-256.

  6. Optionally view the bucket permissions policy, then choose Save.

To configure custom encryption

Complete the following steps to enable encryption using a custom CMK.

  1. (Optional) If you do not have an AWS KMS CMK already, create one using the following AWS CLI create-key command:

    aws kms create-key

    The output contains the key ID and Amazon Resource Name (ARN) of the CMK. The following is example output:

    { "KeyMetadata": { "KeyId": "6f815f63-e628-448c-8251-e40cb0d29f59", "Description": "", "Enabled": true, "KeyUsage": "ENCRYPT_DECRYPT", "KeyState": "Enabled", "CreationDate": 1478910250.94, "Arn": "arn:aws:kms:us-west-2:123456789012:key/6f815f63-e628-448c-8251-e40cb0d29f59", "AWSAccountId": "123456789012" } }
  2. By default, all AWS KMS CMKs are private; only the resource owner can use it to encrypt and decrypt data. However, the resource owner can grant permissions to access the CMK to other users and resources. Using the following steps, you give the ACM Private CA service principal permission to use the CMK. This service principal must be in the same region as where the CMK is stored.

    1. First, save the default policy for your CMK as policy.json using the following get-key-policy command:

      aws kms get-key-policy --key-id key-id --policy-name default --output text > ./policy.json
    2. Open the policy.json file in a text editor and add the following statement:

      { "Sid":"Allow ACM-PCA use of the key", "Effect":"Allow", "Principal":{ "Service":"acm-pca.amazonaws.com" }, "Action":[ "kms:GenerateDataKey", "kms:Decrypt" ], "Resource":"*", "Condition":{ "StringLike":{ "kms:EncryptionContext:aws:s3:arn":[ "arn:aws:s3:::bucket_name/acm-pca-permission-test-key", "arn:aws:s3:::bucket_name/acm-pca-permission-test-key-private", "arn:aws:s3:::bucket_name/audit-report/*", "arn:aws:s3:::bucket_name/crl/*" ] } } }
    3. Finally, add the updated policy using the following put-key-policy command:

      aws kms put-key-policy --key-id key-id --policy-name default --policy file://policy.json