Automate and Manage AWS KMS from Centralized AWS Account

By March 26, 2020 AWS, Blogs

Written by Priyanka Sharma, DevOps Architect, Powerupcloud Technologies

As we have discussed in our previous blog that we use the AWS Landing Zone concept for many of our customers which consists of separate AWS accounts so they can meet the different needs of their organization. One of the accounts is the Security account where the security-related components reside. KMS Keys are one of the security-related key components that helps in the encryption of data. 

A Customer Master Key (CMK) is a logical representation of a master key which includes the following details:

  • metadata, such as the key ID, creation date, description
  • key state
  • key material used to encrypt and decrypt data.

There are three types of AWS KMS:

  • Customer Managed CMK: CMKs that you create, own, and manage. You have full control over these CMKs.
  • AWS Managed CMK: CMKs that are created, managed, and used on your behalf by an AWS service that is integrated with AWS KMS. Some AWS services support only an AWS managed CMK.
  • AWS Owned CMK:  CMKs that an AWS service owns and manages for use in multiple AWS accounts. You do not need to create or manage the AWS owned CMKs.

This blog covers the automation of Customer Managed CMKs i.e. how we can use the Cloudformation templates to create the Customer Managed CMKs. It also discusses the strategy that we follow for our enterprise customers for enabling encryption in cross accounts. 

KMS Encryption Strategy

We are covering the KMS strategy that we follow for most of our customers.

In each of the Accounts, create a set of KMS Keys for the encryption of data. For example,

  • UAT/EC2
    • For enabling the default EC2 encryption, go to Ec2 dashboard settings in the right-hand side as shown in the below screenshot:

Select “Always encrypt the EBS volumes” and Change the default key. Paste the ARN of the UAT/EC2 KMS Key ARN.

  • UAT/S3
    • Copy the ARN of UAT/S3 KMS Key ARN.
    • Go to Bucket Properties and Enable Default Encryption with Custom AWS-KMS. Provide the KMS ARN from the security account.
    • This Key can be used while provisioning the RDS DB instance.
    • Ensure to provide the Key ARN if using via cross-account

Automated KMS Keys Creation

Below Cloudformation template can be used to create a set of KMS Keys as follows:

Ensure to replace the SECURITY_ACCOUNT_ID variable with the 12-digit AWS security account ID where KMS keys will be created.

The CF Template does the following:

  • Creates the below KMS Keys in the Target Account:
    • PROD/EC2
      • It is used to encrypt the EBS Volumes.
    • PROD/S3
      • Used to encrypt the S3 buckets.
    • PROD/RDS
      • Used to encrypt the RDS data.
      • It can be used to encrypt the AWS resources other than EC2, S3, and RDS. For example, if EFS requires to be created in the production account, PROD/OTHERS KMS key can be used for the encryption of EFS.
  • In our case, we are using the Landing Zone concept, so the “OrganizationAccountAccessRole” IAM Role used for Switch Role access from Master account is one of the Key Administrator.
  • Also, We have enabled the Single sign-on in our account, the IAM Role created by SSO “AWSReservedSSO_AdministratorAccess_3687e92578266b74″ has also the Key Administrator access.

The Key administrators can be changed as required in the Key Policy.

The “ExternalAccountID” in the Cloudformation parameters is used to enable the cross-account access via KMS Key policy.

Hope you found it useful.

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