Three common cloud encryption questions and their answers on AWS

August 31, 2021: AWS KMS is replacing the term customer master key (CMK) with AWS KMS key and KMS key. The concept has not changed. To prevent breaking changes, AWS KMS is keeping some variations of this term. More info.

At Amazon Web Services (AWS), we encourage our customers to take advantage of encryption to help secure their data. Encryption is a core component of a good data protection strategy, but people sometimes have questions about how to manage encryption in the cloud to meet the growth pace and complexity of today’s enterprises. Encryption can seem like a difficult task—people often think they need to master complicated systems to encrypt data—but the cloud can simplify it.

In response to frequently asked questions from executives and IT managers, this post provides an overview of how AWS makes encryption less difficult for everyone. In it, I describe the advantages to encryption in the cloud, common encryption questions, and some AWS services that can help.

Cloud encryption advantages

The most important thing to remember about encryption on AWS is that you always own and control your data. This is an extension of the AWS shared responsibility model, which makes the secure delivery and operation of your applications the responsibility of both you and AWS. You control security in the cloud, including encryption of content, applications, systems, and networks. AWS manages security of the cloud, meaning that we are responsible for protecting the infrastructure that runs all of the services offered in the AWS Cloud.

Encryption in the cloud offers a number of advantages in addition to the options available in on-premises environments. This includes on-demand access to managed services that enable you to more easily create and control the keys used for cryptographic operations, integrated identity and access management, and automating encryption in transit and at rest. With the cloud, you don’t manage physical security or the lifecycle of hardware. Instead of the need to procure, configure, deploy, and decommission hardware, AWS offers you a managed service backed by hardware that meets the security requirements of FIPS 140-2. If you need to use that key tens of thousands of times per second, the elastic capacity of AWS services can scale to meet your demands. Finally, you can use integrated encryption capabilities with the AWS services that you use to store and process your data. You pay only for what you use and can instead focus on configuring and monitoring logical security, and innovating on behalf of your business.

Addressing three common encryption questions

For many of the technology leaders I work with, agility and risk mitigation are top IT business goals. An enterprise-wide cloud encryption and data protection strategy helps define how to achieve fine-grained access controls while maintaining nearly continuous visibility into your risk posture. In combination with the wide range of AWS services that integrate directly with AWS Key Management Service (AWS KMS), AWS encryption services help you to achieve greater agility and additional control of your data as you move through the stages of cloud adoption.

The configuration of AWS encryption services is part of your portion of the shared responsibility model. You’re responsible for your data, AWS Identity and Access Management (IAM) configuration, operating systems and networks, and encryption on the client-side, server-side, and network. AWS is responsible for protecting the infrastructure that runs all of the services offered in AWS.

That still leaves you with responsibilities around encryption—which can seem complex, but AWS services can help. Three of the most common questions we get from customers about encryption in the cloud are:

How can I use encryption to prevent unauthorized access to my data in the cloud?
How can I use encryption to meet compliance requirements in the cloud?
How do I demonstrate compliance with company policies or other standards to my stakeholders in the cloud?

Let’s look closely at these three questions and some ways you can address them in AWS.

How can I use encryption to prevent unauthorized access to my data in the cloud?

Start with IAM

The primary way to protect access to your data is access control. On AWS, this often means using IAM to describe which users or roles can access resources like Amazon Simple Storage Service (Amazon S3) buckets. IAM allows you to tightly define the access for each user—whether human or system—and set the conditions in which that access is allowed. This could mean requiring the use of multi-factor authentication, or making the data accessible only from your Amazon Virtual Private Cloud (Amazon VPC).

Encryption allows you to introduce an additional authorization condition before granting access to data. When you use AWS KMS with other services, you can get further control over access to sensitive data. For example, with S3 objects that are encrypted by KMS, each IAM user must not only have access to the storage itself but also have authorization to use the KMS key that protects the data. This works similarly for Amazon Elastic Block Store (Amazon EBS). For example, you can allow an entire operations team to manage Amazon EBS volumes and snapshots, but, for certain Amazon EBS volumes that contain sensitive data, you can use a different KMS key with different permissions that are granted only to the individuals you specify. This ability to define more granular access control through independent permission on encryption keys is supported by all AWS services that integrate with KMS.

When you configure IAM for your users to access your data and resources, it’s critical that you consider the principle of least privilege. This means you grant only the access necessary for each user to do their work and no more. For example, instead of granting users access to an entire S3 bucket, you can use IAM policy language to specify the particular Amazon S3 prefixes that are required and no others. This is important when thinking about the difference between using a service—data plane events—and managing a service—management plane events. An application might store and retrieve objects in an S3 bucket, but it’s rarely the case that the same application needs to list all of the buckets in an account or configure the bucket’s settings and permissions.

Making clear distinctions between who can use resources and who can manage resources is often referred to as the principle of separation of duties. Consider the circumstance of having a single application with two identities that are associated with it—an application identity that uses a key to encrypt and decrypt data and a manager identity that can make configuration changes to the key. By using AWS KMS together with services like Amazon EBS, Amazon S3, and many others, you can clearly define which actions can be used by each persona. This prevents the application identity from making configuration or permission changes while allowing the manager to make those changes but not use the services to actually access the data or use the encryption keys.

Use AWS KMS and key policies with IAM policies

AWS KMS provides you with visibility and granular permissions control of a specific key in the hierarchy of keys used to protect your data. Controlling access to the keys in KMS is done using IAM policy language. The AWS KMS key has its own policy document, known as a key policy. AWS KMS key policies can work together with IAM identity policies or you can manage the permissions for a KMS key exclusively with key policies. This gives you greater flexibility to separately assign permissions to use the key or manage the key, depending on your business use case.

Encryption everywhere

AWS recommends that you encrypt as much as possible. This means encrypting data while it’s in transit and while it’s at rest.

For customers seeking to encrypt data in transit for their public facing applications, our recommended best practice is to use AWS Certificate Manager (ACM). This service automates the creation, deployment, and renewal of public TLS certificates. If you’ve been using SSL/TLS for your websites and applications, then you’re familiar with some of the challenges related to dealing with certificates. ACM is designed to make certificate management easier and less expensive.

One way ACM does this is by generating a certificate for you. Because AWS operates a certificate authority that’s already trusted by industry-standard web browsers and operating systems, public certificates created by ACM can be used with public websites and mobile applications. ACM can create a publicly trusted certificate that you can then deploy into API Gateway, Elastic Load Balancing, or Amazon CloudFront (a globally distributed content delivery network). You don’t have to handle the private key material or figure out complicated tooling to deploy the certificates to your resources. ACM helps you to deploy your certificates either through the AWS Management Console or with automation that uses AWS Command Line Interface (AWS CLI) or AWS SDKs.

One of the challenges related to certificates is regularly rotating and renewing them so they don’t unexpectedly expire and prevent your users from using your website or application. Fortunately, ACM has a feature that updates the certificate before it expires and automatically deploys the new certificate to the resources associated with it. No more needing to make a calendar entry to remind your team to renew certificates and, most importantly, no more outages because of expired certificates.

Many customers want to secure data in transit for services by using privately trusted TLS certificates instead of publicly trusted TLS certificates. For this use case, you can use AWS Certificate Manager Private Certificate Authority (ACM PCA) to issue certificates for both clients and servers. ACM PCA provides an inexpensive solution for issuing internally trusted certificates and it can be integrated with ACM with all of the same integrative benefits that ACM provides for public certificates, including automated renewal.

For encrypting data at rest, I strongly encourage using AWS KMS. There is a broad range of AWS storage and database services that support KMS integration so you can implement robust encryption to protect your data at rest within AWS services. This lets you have the benefit of the KMS capabilities for encryption and access control to build complex solutions with a variety of AWS services without compromising on using encryption as part of your data protection strategy.

How can I use encryption to meet compliance requirements in the cloud?

The first step is to identify your compliance requirements. This can often be done by working with your company’s risk and compliance team to understand the frameworks and controls that your company must abide by. While the requirements vary by industry and region, the most common encryption compliance requirements are to encrypt your data and make sure that the access control for the encryption keys (for example by using AWS KMS key policies) is separate from the access control to the encrypted data itself (for example through Amazon S3 bucket policies).

Another common requirement is to have separate encryption keys for different classes of data, or for different tenants or customers. This is directly supported by AWS KMS as you can have as many different keys as you need within a single account. If you need to use even more than the 10,000 keys AWS KMS allows by default, contact AWS Support about raising your quota.

For compliance-related concerns, there are a few capabilities that are worth exploring as options to increase your coverage of security controls.

Amazon S3 can automatically encrypt all new objects placed into a bucket, even when the user or software doesn’t specify encryption.
You can use batch operations in Amazon S3 to encrypt existing objects that weren’t originally stored with encryption.
You can use the Amazon S3 inventory report to generate a list of all S3 objects in a bucket, including their encryption status.

AWS services that track encryption configurations to comply with your requirements

Anyone who has pasted a screenshot of a configuration into a word processor at the end of the year to memorialize compliance knows how brittle traditional on-premises forms of compliance attestation can be. Everything looked right the day it was installed and still looked right at the end of the year—but how can you be certain that everything was correctly configured at all times?

AWS provides several different services to help you configure your environment correctly and monitor its configuration over time. AWS services can also be configured to perform automated remediation to correct any deviations from your desired configuration state. AWS helps automate the collection of compliance evidence and provides nearly continuous, rather than point in time, compliance snapshots.

AWS Config is a service that enables you to assess, audit, and evaluate the configurations of your AWS resources. AWS Config continuously monitors and records your AWS resource configurations and helps you to automate the evaluation of recorded configurations against desired configurations. One of the most powerful features of AWS Config is AWS Config Rules. While AWS Config continuously tracks the configuration changes that occur among your resources, it checks whether these changes violate any of the conditions in your rules. If a resource violates a rule, AWS Config flags the resource and the rule as noncompliant. AWS Config comes with a wide range of prewritten managed rules to help you maintain compliance for many different AWS services. The managed rules include checks for encryption status on a variety of resources, ACM certificate expiration, IAM policy configurations, and many more.

For additional monitoring capabilities, consider Amazon Macie and AWS Security Hub. Amazon Macie is a service that helps you understand the contents of your S3 buckets by analyzing and classifying the data contained within your S3 objects. It can also be used to report on the encryption status of your S3 buckets, giving you a central view into the configurations of all buckets in your account, including default encryption settings. Amazon Macie also integrates with AWS Security Hub, which can perform automated checks of your configurations, including several checks that focus on encryption settings.

Another critical service for compliance outcomes is AWS CloudTrail. CloudTrail enables governance, compliance, operational auditing, and risk auditing of your AWS account. With CloudTrail, you can log, continuously monitor, and retain account activity related to actions across your AWS infrastructure. AWS KMS records all of its activity in CloudTrail, allowing you to identify who used the encryption keys, in what context, and with which resources. This information is useful for operational purposes and to help you meet your compliance needs.

How do I demonstrate compliance with company policy to my stakeholders in the cloud?

You probably have internal and external stakeholders that care about compliance and require that you document your system’s compliance posture. These stakeholders include a range of possible entities and roles, including internal and external auditors, risk management departments, industry and government regulators, diligence teams related to funding or acquisition, and more.

Unfortunately, the relationship between technical staff and audit and compliance staff is sometimes contentious. AWS believes strongly that these two groups should work together—they want the same things. The same services and facilities that engineering teams use to support operational excellence can also provide output that answers stakeholders’ questions about security compliance.

You can provide access to the console for AWS Config and CloudTrail to your counterparts in audit and risk management roles. Use AWS Config to continuously monitor your configurations and produce periodic reports that can be delivered to the right stakeholders. The evolution towards continuous compliance makes compliance with your company policies on AWS not just possible, but often better than is possible in traditional on-premises environments. AWS Config includes several managed rules that check for encryption settings in your environment. CloudTrail contains an ongoing record of every time AWS KMS keys are used to either encrypt or decrypt your resources. The contents of the CloudTrail entry include the KMS key ID, letting your stakeholders review and connect the activity recorded in CloudTrail with the configurations and permissions set in your environment. You can also use the reports produced by Security Hub automated compliance checks to verify and validate your encryption settings and other controls.

Your stakeholders might have further requirements for compliance that are beyond your scope of control because AWS is operating those controls for you. AWS provides System and Organization Controls (SOC) Reports that are independent, third-party examination reports that demonstrate how AWS achieves key compliance controls and objectives. The purpose of these reports is to help you and your auditors understand the AWS controls established to support operations and compliance. You can consult the AWS SOC2 report, available through AWS Artifact, for more information about how AWS operates in the cloud and provides assurance around AWS security procedures. The SOC2 report includes several AWS KMS-specific controls that might be of interest to your audit-minded colleagues.

Summary

Encryption in the cloud is easier than encryption on-premises, powerful, and can help you meet the highest standards for controls and compliance. The cloud provides more comprehensive data protection capabilities for customers looking to rapidly scale and innovate than are available for on-premises systems. This post provides guidance for how to think about encryption in AWS. You can use IAM, AWS KMS, and ACM to provide granular access control to your most sensitive data, and support protection of your data in transit and at rest. Once you’ve identified your compliance requirements, you can use AWS Config and CloudTrail to review your compliance with company policy over time, rather than point-in-time snapshots obtained through traditional audit methods. AWS can provide on-demand compliance evidence, with tools such as reporting from CloudTrail and AWS Config, and attestations such as SOC reports.

I encourage you to review your current encryption approach against the steps I’ve outlined in this post. While every industry and company is different, I believe the core concepts presented here apply to all scenarios. I want to hear from you. If you have any comments or feedback on the approach discussed here, or how you’ve used it for your use case, leave a comment on this post.

And for more information on encryption in the cloud and on AWS, check out the following resources, in addition to our collection of encryption blog posts.

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