The following FAQ does not apply to KMS in the AWS China (Beijing) Region, operated by Sinnet and the AWS China (Ningxia) Region, operated by NWCD. Please visit this FAQ link for content relevant to these two China regions.  

General

Q: What is AWS Key Management Service (KMS)?
AWS KMS is a managed service that enables you to easily encrypt your data. AWS KMS provides a highly available key storage, management, and auditing solution for you to encrypt data within your own applications and control the encryption of stored data across AWS services.

Q: Why should I use AWS KMS?
If you are a developer who needs to encrypt data in your applications, you should use the AWS Encryption SDK with AWS KMS support to easily use and protect encryption keys. If you’re an IT administrator looking for a scalable key management infrastructure to support your developers and their growing number of applications, you should use AWS KMS to reduce your licensing costs and operational burden. If you’re responsible for proving data security for regulatory or compliance purposes, you should use AWS KMS to verify that data is encrypted consistently across the applications where it is used and stored.

Q: How do I get started with AWS KMS?
The easiest way is to get started using AWS KMS is to choose to encrypt your data within supported AWS services using AWS managed master keys that are automatically created in your account for each service. If you want full control over the management of your keys, including the ability to share access to keys across accounts or services, you can create your own master keys in KMS. You can also use the master keys that you create in KMS directly within your own applications. AWS KMS can be accessed from the KMS console that is grouped under Security, Identity and Compliance on the AWS Services home page of the AWS Console. KMS APIs can also be accessed directly through the AWS KMS Command Line Interface or AWS SDK for programmatic access. KMS APIs can be used indirectly to encrypt data within your own applications by using the AWS Encryption SDK. Visit the Getting Started page to learn more.

Q: In what Regions is KMS available?
Availability is listed on our global Products and Services by Region page.

Q: What key management features are available in AWS KMS?
You can perform the following key management functions in AWS KMS:

  • Create keys with a unique alias and description
  • Import your own key material
  • Define which IAM users and roles can manage keys
  • Define which IAM users and roles can use keys to encrypt and decrypt data
  • Choose to have AWS KMS automatically rotate your keys on an annual basis
  • Temporarily disable keys so they cannot be used by anyone
  • Re-enable disabled keys
  • Delete keys that you no longer use
  • Audit use of keys by inspecting logs in AWS CloudTrail
  • Create custom key stores*
  • Connect and disconnect custom key stores*
  • Delete custom key stores*

* The use of custom key stores requires CloudHSM resources to be available in your account.

Q: How does AWS KMS work?
AWS KMS allows you to centrally manage and securely store your keys. These are known as customer master keys or CMKs. You can generate CMKs in KMS, in an AWS CloudHSM cluster, or import them from your own key management infrastructure. These master keys are protected by hardware security modules (HSMs) and are only ever used within those modules. You can submit data directly to KMS to be encrypted or decrypted using these master keys. You set usage policies on these keys that determine which users can use them to encrypt and decrypt data under which conditions.

AWS KMS is integrated with AWS services and client-side toolkits that use a method known as envelope encryption to encrypt your data. Under this method, KMS generates data keys which are used to encrypt data and are themselves encrypted using your master keys in KMS. Data keys are not retained or managed by KMS. AWS services encrypt your data and store an encrypted copy of the data key along with the data it protects. When a service needs to decrypt your data they request KMS to decrypt the data key using your master key. If the user requesting data from the AWS service is authorized to decrypt under your master key policy, the service will receive the decrypted data key from KMS with which it can decrypt the your data and return it in plaintext. All requests to use your master keys are logged in AWS CloudTrail so you can understand who used which key under which context and when they used it.

Q: Where is my data encrypted if I use AWS KMS?
There are typically three scenarios for how data is encrypted using AWS KMS. Firstly, you can use KMS APIs directly to encrypt and decrypt data using your master keys stored in KMS. Secondly, you can choose to have AWS services encrypt your data using your master keys stored in KMS. In this case data is encrypted using data keys that are protected by your master keys in KMS. Thirdly, you can use the AWS Encryption SDK that is integrated with AWS KMS to perform encryption within your own applications, whether they operate in AWS or not.

Q: Which AWS cloud services are integrated with AWS KMS?
AWS KMS is seamlessly integrated with most other AWS services to make encrypting data in those services as easy as checking a box. In some cases data is encrypted by default using keys that are stored in KMS but owned and managed by the AWS service in question. In many cases the master keys are owned and managed by you within your account. Some services give you the choice of managing the keys yourself or allowing the service to manage the keys on your behalf. See the list of AWS services currently integrated with KMS. See the AWS KMS Developer’s Guide for more information on how integrated services use AWS KMS.

Q: Why use envelope encryption? Why not just send data to AWS KMS to encrypt directly?
While AWS KMS does support sending data less than 4 KB to be encrypted directly, envelope encryption can offer significant performance benefits. When you encrypt data directly with AWS KMS it must be transferred over the network. Envelope encryption reduces the network load since only the request and delivery of the much smaller data key go over the network. The data key is used locally in your application or encrypting AWS service, avoiding the need to send the entire block of data to KMS and suffer network latency.

Q: What’s the difference between a master key I create and master keys created automatically for me by other AWS services?
You have the option of selecting a specific customer master key (CMK) to use when you want an AWS service to encrypt data on your behalf. These are known as customer managed CMKs and you have full control over them. You define the access control and usage policy for each key and you can grant permissions to other accounts and services to use them. If you don’t specify a CMK, the service in question will create an AWS managed CMK the first time you try to create an encrypted resource within that service. AWS will manage the policies associated with AWS managed CMKs on your behalf. You can track AWS managed keys in your account and all usage is logged in AWS CloudTrail, but you have no direct control over the keys themselves.

Q: Why should I create my own customer master keys?
Creating your own CMK in AWS KMS gives you more control than you have with AWS managed CMKs. When you create a customer managed CMK, you can choose to use key material generated by AWS KMS, generated within an AWS CloudHSM cluster, or import your own key material. You can define an alias and description for the key and opt-in to have the key automatically rotated once per year if it was generated by AWS KMS. You also define all the permissions on the key to control who can use or manage the key.

Q: Can I import keys into AWS KMS?
Yes. You can import a copy of your key from your own key management infrastructure to AWS KMS and use it with any integrated AWS service or from within your own applications.

Q: When would I use an imported key?
You can use an imported key to get greater control over the creation, lifecycle management, and durability of your key in AWS KMS. Imported keys are designed to help you meet your compliance requirements which may include the ability to generate or maintain a secure copy of the key in your infrastructure, and the ability to immediately delete the imported copy of the key from AWS infrastructure.

Q: What type of keys can I import?
You can import 256-bit symmetric keys.

Q: How is the key that I import into AWS KMS protected in transit?
During the import process, your key must be wrapped by an AWS KMS-provided public key using one of two RSA PKCS#1 schemes. This ensures that your encrypted key can only be decrypted by AWS KMS.

Q: What’s the difference between a key I import and a key I generate in AWS KMS?
There are two main differences:

  1. You are responsible for maintaining a copy of your imported keys in your key management infrastructure so that you can re-import them at any time. AWS, however, ensures the availability, security, and durability of keys generated by AWS KMS on your behalf until you schedule the keys for deletion.
  2. You may set an expiration period for an imported key. AWS KMS will automatically delete the key material after the expiration period. You may also delete imported key material on demand. In both cases the key material itself is deleted but the CMK reference in KMS and associated metadata are retained so that the key material can be re-imported in the future. Keys generated by AWS KMS do not have an expiration time and cannot be deleted immediately; there is a mandatory 7 to 30 day wait period. All customer managed CMKs, irrespective of whether the key material was imported, can be manually disabled or scheduled for deletion. In this case the CMK itself is deleted, not just the underlying key material.

Q: Can I rotate my keys?
Yes. You can choose to have AWS KMS automatically rotate CMKs every year, provided that those keys were generated by AWS KMS. Automatic key rotation is not supported for imported keys or keys generated in an AWS CloudHSM cluster using the KMS custom key store feature. If you choose to import keys to AWS KMS or use a custom key store, you can manually rotate them whenever you want by creating a new CMK and mapping a key alias from the old key to the new key.

Q: Do I have to re-encrypt my data after keys in AWS KMS are rotated?
If you choose to have AWS KMS automatically rotate keys, you don’t have to re-encrypt your data. AWS KMS automatically keeps previous versions of keys to use for decryption of data encrypted under an old version of a key. All new encryption requests against a key in AWS KMS are encrypted under the newest version of the key.

If you manually rotate your imported or custom key store keys, you may have to re-encrypt your data depending on whether you decide to keep old versions of keys available.

Q: Can I delete a key from AWS KMS?
Yes. You can schedule a customer master key and associated metadata that you created in AWS KMS for deletion, with a configurable waiting period from 7 to 30 days. This waiting period allows you to verify the impact of deleting a key on your applications and users that depend on it. The default waiting period is 30 days. You can cancel key deletion during the waiting period. The key cannot be used if it is scheduled for deletion until you cancel the deletion during the waiting period. The key gets deleted at the end of the configurable waiting period if you don’t cancel the deletion. Once a key is deleted, you can no longer use it. All data protected under a deleted master key is inaccessible.

For customer master keys with imported key material, you can delete the key material without deleting the customer master key id or metadata in two ways. First, you can delete your imported key material on demand without a waiting period. Second, at the time of importing the key material into the customer master key, you may define an expiration time for how long AWS can use your imported key material before it is deleted. You can re-import your key material into the customer master key if you need to use it again.

Q: What should I do if my imported key material has expired or I accidentally deleted it?
You can re-import your copy of the key material with a valid expiration period to AWS KMS under the original customer master key so it can be used.

Q: Can I be alerted that I need to re-import the key?
Yes. Once you import your key to a customer master key, you will receive an Amazon CloudWatch Metric every few minutes that counts down the time to expiration of the imported key. You will also receive an Amazon CloudWatch Event once the imported key under your customer master key expires. You can build logic that acts on these metrics or events and automatically re-imports the key with a new expiration period to avoid an availability risk.

Q: Can I use AWS KMS to help manage encryption of data outside of AWS cloud services?
Yes. AWS KMS is supported in AWS SDKs, AWS Encryption SDK, the Amazon DynamoDB Client-side Encryption, and the Amazon S3 Encryption Client to facilitate encryption of data within your own applications wherever they run. Visit the AWS Crypto Tools and Developing on AWS website for more information.

Q: Is there a limit to the number of keys I can create in AWS KMS?
You can create up to 1000 customer master keys per account per region. As both enabled and disabled customer master keys count towards the limit, we recommend deleting disabled keys that you no longer use. AWS managed master keys created on your behalf for use within supported AWS services do not count against this limit. There is no limit to the number of data keys that can be derived using a master key and used in your application or by AWS services to encrypt data on your behalf. You may request a limit increase for customer master keys by visiting the AWS Support Center.

Q: Does AWS KMS offer a Service Level Agreement (SLA)?
Yes. The AWS KMS SLA provides for a service credit if a customer's monthly uptime percentage is below our service commitment in any billing cycle.

Custom Key Store

Q: What is a custom key store?
The AWS KMS custom key store feature combines the controls provided by AWS CloudHSM with the integration and ease of use of AWS KMS. You can configure your own CloudHSM cluster and authorize KMS to use it as a dedicated key store for your keys rather than the default KMS key store. When you create keys in KMS you can chose to generate the key material in your CloudHSM cluster. Master keys that are generated in your custom key store never leave the HSMs in the CloudHSM cluster in plaintext and all KMS operations that use those keys are only performed in your HSMs. In all other respects master keys stored in your custom key store are consistent with other KMS CMKs.

Additional guidance for deciding if using a custom key store it is right for you can be found in this blog.

Q: Why would I need to use a custom key store?
Since you control your AWS CloudHSM cluster, you have the option to manage the lifecycle of your AWS KMS master keys independently of KMS. There are four reasons why you might find a custom key store useful. Firstly, you might have keys that are explicitly required to be protected in a single tenant HSM or in an HSM over which you have direct control. Secondly, you might have keys that are required to be stored in an HSM that has been validated to FIPS 140-2 level 3 overall (the HSMs used in the standard KMS key store are validated to level 2 with level 3 in multiple categories). Thirdly, you might need the ability to immediately remove key material from KMS and to prove you have done so by independent means. Finally, you might have a requirement to be able to audit all use of your keys independently of KMS or AWS CloudTrail.

Q: Do custom key stores affect how keys are managed?
There are two differences when managing keys in a custom key store compared to the default AWS KMS key store. You cannot import key material into your custom key store and you cannot have KMS automatically rotate keys. In all other respects, including the type of keys that can be generated, the way that keys use aliases and how policies are defined, keys that are stored in a custom key store are managed in the same way as any other KMS customer managed CMK.

Q: Can I use a custom key store to store an AWS managed customer master key?
No, only customer managed CMKs can be stored and managed in an AWS KMS custom key store. AWS managed CMKs that are created on your behalf by other AWS services to encrypt your data are always generated and stored in the KMS default key store.

Q: Do custom key stores affect how keys are used?
No, API requests to AWS KMS to use a CMK to encrypt and decrypt data are handled in the same way. Authentication and authorization processes operate independently of where the key is stored. All activity using a key in a custom key store is also logged to AWS CloudTrail in the same way. However, the actual cryptographic operations happen exclusively in either the custom key store or the default KMS key store.

Q: How can I audit the use of keys in a custom key store?
In addition to the activity that is logged to AWS CloudTrail by AWS KMS the use of a custom key store provides three further auditing mechanisms. First, AWS CloudHSM also logs all API activity to CloudTrail, for example to create clusters and to add or remove HSMs. Second, each cluster also captures its own local logs to record user and key management activity. Third, each CloudHSM instance copies the local user and key management activity logs to AWS CloudWatch.

Q: What impact does using a custom key store have on availability of keys?
The use of an AWS KMS custom key store makes you responsible for ensuring that your keys are available for use by KMS. Errors in configuration of CloudHSM and accidental deletion of key material within an AWS CloudHSM cluster could impact availability. The number of HSMs you use and your choice of availability zones (AZs) can also affect the resilience of your cluster. As in any key management system, it is important to understand how the availability of keys can impact the recovery of your encrypted data.

Q: What are the performance limitations associated with a custom key store?
The rate at which keys stored in an AWS KMS custom key store can be used via AWS KMS API calls are lower than for keys stored in the default AWS KMS key store. See the KMS Developer Guide for the current performance limits.

Q: What are the costs associated with using a custom key store?
AWS KMS prices are unaffected by the use of a custom key store. However, each custom key store does require that your AWS CloudHSM cluster contains at least two HSMs. These HSMs are charged at the standard AWS CloudHSM prices. There are no additional charges for using a custom key store.

Q: What additional skills and resources are required to configure a custom key stores?
AWS KMS users that wish to use a custom key store will need to set up an AWS CloudHSM cluster, add HSMs, manage HSMs users and potentially restore HSMs from backup. These are security sensitive tasks and you should ensure that you have the appropriate resources and organizational controls in place.

Q: Can I import keys into a custom key store?
No, the ability to import your own key material into an AWS KMS custom key store is not supported. Keys that are stored in a custom key store can only be generated in the HSMs that form your AWS CloudHSM cluster.

Q: Can I migrate keys between the default KMS keys store and a custom key store?
No, the ability to migrate keys between the different types of AWS KMS key store is not currently supported. All keys must be created in the key store in which they will be used, except in situations where you import you own key material into the default KMS key store.

Q: Can I rotate keys stored in a custom key store?
The ability to automatically rotate key material in an AWS KMS custom key store is not supported. Key rotation must be performed manually by creating new keys and re-mapping KMS key aliases used by your application code to use the new keys for future encryption operations.

Q: Can I use my AWS CloudHSM cluster for other applications?
Yes, AWS KMS does not require exclusive access to your AWS CloudHSM cluster. If you already have a cluster you can use it as a custom key store and continue to use it for your other applications. However, if your cluster is supporting high, non-KMS, workloads you may experience reduced throughput for operations using KMS master keys in your custom key store. Similarly, a high KMS request rate to your custom key store could impact your other applications.

Q: How can I learn more about AWS CloudHSM?
Visit the AWS CloudHSM web site for an overview of the service and for more details on configuring and using the service read the AWS CloudHSM User Guide.  

Billing

Q: How will I be charged and billed for my use of AWS KMS?
With AWS KMS, you pay only for what you use, there is no minimum fee. There are no set-up fees or commitments to begin using the service. At the end of the month, your credit card will automatically be charged for that month’s usage.

You are charged for all customer master keys (CMKs) you create, and for API requests made to the service each month above a free tier.

For current pricing information, please visit the AWS KMS pricing page.

Q: Is there a free tier?
Yes. With the AWS Free Usage Tier you can get started with AWS KMS for free in all regions. AWS managed master keys that are created on your behalf by AWS services are free to store in your account. There is a free tier for usage that provides a free number of requests to AWS KMS each month. For current information on pricing, including the free tier, please visit the AWS KMS pricing page.

Q: Do your prices include taxes?
Except as otherwise noted, our prices are exclusive of applicable taxes and duties, including VAT and applicable sales tax. For customers with a Japanese billing address, use of AWS services is subject to Japanese Consumption Tax. You can learn more here.

Security

Q: Who can use and manage my keys in AWS KMS?
AWS KMS enforces usage and management policies that you define. You choose to allow AWS Identity and Access Management (IAM) users and roles from your account or other accounts to use and manage your keys.

Q: How does AWS secure the master keys that I create inside AWS KMS?
AWS KMS is designed so that no one, including AWS employees, can retrieve your plaintext master keys from the service. The service uses FIPS 140-2 validated hardware security modules (HSMs) to protect the confidentiality and integrity of your keys regardless of whether you use AWS KMS or AWS CloudHSM to create your keys or you import them into the service yourself. Your plaintext keys never leave the HSMs, are never written to disk and are only ever used in the volatile memory of the HSMs for the time needed to perform your requested cryptographic operation. AWS KMS keys are never transmitted outside of the AWS regions in which they were created. Updates to software on the service hosts and to the AWS KMS HSM firmware is controlled by multi-party access control that is audited and reviewed by an independent group within Amazon as well as a NIST-certified lab in compliance with FIPS 140-2.

More details about these security controls can be found in the AWS KMS Cryptographic Details whitepaper. You can also review the FIPS 140-2 certificate for AWS KMS HSM along with the associated Security Policy to get more details about how AWS KMS HSM meets the security requirements of FIPS 140-2. In addition, you can download a copy of the Service Organization Controls (SOC) report from AWS Artifact to learn more about security controls used by AWS KMS to protect your master keys.

Q: How do I migrate my existing AWS KMS master keys to use FIPS 140-2 validated HSMs?
All master keys in AWS KMS regardless of their creation date or origin are automatically protected using FIPS 140-2 validated HSMs. No action is required on your part to use the FIPS 140-2 validated HSMs.

Q: Which AWS regions have FIPS 140-2 validated HSMs?
FIPS 140-2 validated HSMs are available in all AWS regions where AWS KMS is offered.

Q: What is the difference between the FIPS 140-2 validated endpoints and the FIPS 140-2 validated HSMs in AWS KMS?
AWS KMS is a two-tier service. The API endpoints receive client requests over an HTTPS connection using only TLS ciphersuites that support perfect forward secrecy. These API endpoints authenticate and authorize the request before passing the request for a cryptographic operation to the AWS KMS HSMs or your AWS CloudHSM cluster if you’re using the KMS custom key store feature.

Q: How do I make API requests to AWS KMS using the FIPS 140-2 validated endpoints?
You configure your applications to connect to the unique regional FIPS 140-2 validated HTTPS endpoints. AWS KMS FIPS 140-2 validated HTTPS endpoints are powered by the OpenSSL FIPS Object Module. You can review the security policy of the OpenSSL module at https://www.openssl.org/docs/fips/SecurityPolicy-2.0.13.pdf. FIPS 140-2 validated API endpoints are available in all commercial regions where AWS KMS is available.

Q: Can I use AWS KMS to help me comply with the encryption and key management requirements in the Payment Card Industry Data Security Standard (PCI DSS 3.1)?
Yes. AWS KMS has been validated as having the functionality and security controls to help you meet the encryption and key management requirements (primarily referenced in sections 3.5 and 3.6) of the PCI DSS 3.1.

For more details on PCI DSS compliant services in AWS, you can read the PCI DSS FAQs.

Q: How does AWS KMS secure the data keys I export and use in my application?
You can request that AWS KMS generate data keys and return them for use in your own application. The data keys are encrypted under a master key you define in AWS KMS so that you can safely store the encrypted data key along with your encrypted data. Your encrypted data key (and therefore your source data) can only be decrypted by users with permissions to use the original master key to decrypt your encrypted data key.

Q: What length of keys does AWS KMS generate?
Master keys in AWS KMS are 256-bits in length. Data keys can be generated at 128-bit or 256-bit lengths and encrypted under a master key you define. AWS KMS also provides the ability to generate random data of any length you define suitable for cryptographic use.

Q: Can I export a master key from AWS KMS and use it in my own applications?
No. Master keys are created and used only within AWS KMS to help ensure their security, enable your policies to be consistently enforced, and provide a centralized log of their use.

Q: What geographic region are my keys stored in?
Keys generated by AWS KMS are only stored and used in the region in which they were created. They cannot be transferred to another region. For example; keys created in the EU-Central (Frankfurt) region are only stored and used within the EU-Central (Frankfurt) region.

Q: How can I tell who used or changed the configuration of my keys in AWS KMS?
Logs in AWS CloudTrail will show all KMS API requests, including both management requests (e.g. create, rotate, disable, policy edits) and cryptographic requests (e.g. encrypt/decrypt). Turn on AWS CloudTrail in your account to view these logs.

Q: How does AWS KMS compare to AWS CloudHSM?
AWS CloudHSM provides you with a FIPS 140-2 Level 3 overall validated single-tenant HSM cluster in your Amazon Virtual Private Cloud (VPC) to store and use your keys. You have exclusive control over how your keys are used via an authentication mechanism independent from AWS. You interact with keys in your AWS CloudHSM cluster similar to the way you interact with your applications running in Amazon EC2. You can use AWS CloudHSM to support a variety of use cases, such as Digital Rights Management (DRM), Public Key Infrastructure (PKI), document signing, and cryptographic functions using PKCS#11, Java JCE, or Microsoft CNG interfaces.

AWS KMS allows you to create and control the encryption keys used by your applications and supported AWS services in multiple regions around the world from a single console. The service uses a FIPS 140-2 validated HSM to protect the security of your keys. Centralized management of all your keys in AWS KMS lets you enforce who can use your keys under which conditions, when they get rotated, and who can manage them. AWS KMS integration with AWS CloudTrail gives you the ability to audit the use of your keys to support your regulatory and compliance activities. You interact with AWS KMS from your applications using the AWS SDK if you want to call the service APIs directly, via other AWS services that are integrated with KMS or by using the AWS Encryption SDK if you want to perform client-side encryption.

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