AWS Key Management Service

Developer Guide

AWS Documentation » AWS KMS » Developer Guide » Limits

Limits

AWS KMS resources have limits that apply to each region and each AWS account. Some limits apply to all resources. Others apply only to resources that you create, but not to resources that AWS services create in your account. Resources that you use, but that aren't in your AWS account, such as AWS owned CMKs, do not count against these limits.

Customer Master Keys (CMKs): 10,000

You can have up to 10,000 customer managed CMKs in each Region of your AWS account. This limit applies to all customer managed CMKs regardless of their key state. AWS managed CMKs and AWS owned CMKs do not count against this limit.

You can create a support case to request more CMKs in a region. However, managing a large number of CMKs from the AWS Management Console may be slower than acceptable. If you have a large number of CMKs in a region, we recommend managing them programmatically with the AWS SDKs or AWS Command Line Tools.

Aliases: 10,000

You can create up to 10,000 aliases in each region of your account. Aliases that AWS creates in your account, such as aws/<service-name>, do not count against this limit.

An alias is a display name that you can map to a CMK. Each alias is mapped to exactly one CMK and multiple aliases can map to the same CMK.

If you use a support case to increase your CMK limit, you might also need to request an increase in the number of aliases.

Grants per CMK: 10,000

Each customer managed CMK can have up to 10,000 grants, including the grants created by AWS services that are integrated with AWS KMS. This limit does not apply to AWS managed CMKs.

One effect of this limit is that you cannot create more than 10,000 resources that use the same CMK. For example, you cannot create more than 10,000 encrypted EBS volumes that use the same CMK.

Grants are an alternative to key policy. They are advanced mechanisms for specifying permissions.

You or an AWS service integrated with AWS KMS can use a grant to limit how and when the grantee can use a CMK. Grants are attached to a CMK. Each grant includes the principal who receives permission to use the CMK, the ID of the CMK, and a list of operations that the grantee can perform.

Grants for a Given Principal per CMK: 500

For a given CMK, no more than 500 grants can specify the same grantee principal. This limit applies to all CMKs, including AWS managed CMKs.

For example, you might want to encrypt multiple Amazon EBS volumes and attach them to a single Amazon Elastic Compute Cloud (Amazon EC2) instance. A unique grant is created for each encrypted volume and all of these grants have the same grantee principal (an IAM assumed-role user associated with the EC2 instance). Each grant gives permission to use the specified CMK to decrypt an EBS volume's unique data encryption key. For each CMK, you can have up to 500 grants that specify the same EC2 instance as the grantee principal. This effectively means that you can have no more than 500 encrypted EBS volumes per EC2 instance for a given CMK.

Key Policy Document Size: 32 KB

The maximum length of each key policy document is 32 KB (32,768 bytes). If the document exceeds this length, operations that use the key policy document to set or change the key policy fail. If you must exceed this limit, create a support case.

A key policy document is a collection of policy statements in JSON format. The statements in the key policy document determine who has permission to use the CMK and how they can use it. You may also use IAM policies and grants to control access to the CMK, but every CMK must have a key policy document.

You can create a key policy document by using the default view or policy view in the AWS Management Console, or by using the PutKeyPolicy API operation. All of these techniques involve an underlying key policy document.

Requests per Second: Varies

AWS KMS throttles API requests at different limits depending on the API operation. Throttling means that AWS KMS rejects an otherwise valid request because the request exceeds the limit for the number of requests per second. When a request is throttled, AWS KMS returns a ThrottlingException error. The following table lists each API operation and the point at which AWS KMS throttles requests for that operation.

This limit applies to all CMKs, including AWS managed CMKs.

Shared Limit

The API operations in the first row of the following table share a limit of 5,500 (or 10,000) requests per second. For example, with a shared limit of 5,500 requests per second, when you make 3,000 GenerateDataKey requests per second and 1,000 Decrypt requests per second, AWS KMS doesn't throttle your requests. However, when you make 5,000 GenerateDataKey and 1,000 Encrypt and requests per second, AWS KMS throttles your requests because you are making more than 5,500 requests per second for operations with the shared limit.

The remaining API operations have a unique limit for requests per second, which means the limit is not shared.

API Requests Made on Your Behalf

You can make API requests directly or by using an integrated AWS service that makes API requests to AWS KMS on your behalf. The limit applies to both kinds of requests.

For example, you might store data in Amazon S3 using server-side encryption with AWS KMS (SSE-KMS). Each time you upload or download an S3 object that's encrypted with SSE-KMS, Amazon S3 makes a GenerateDataKey (for uploads) or Decrypt (for downloads) request to AWS KMS on your behalf. These requests count toward your limit, so AWS KMS throttles the requests if you exceed a combined total of 5,500 (or 10,000) uploads or downloads per second of S3 objects encrypted with SSE-KMS.

Cross-Account Requests

When an application in one AWS account uses a CMK owned by a different account, that's known as a cross-account request. For cross-account requests, AWS KMS throttles the account that makes the requests, not the account that owns the CMK. For example, you might have applications in accounts A and B that both use a CMK in account C. In this scenario, the limit for requests per second applies separately to accounts A and B, not to account C.

Custom Key Store Limits

Cryptographic operations that use CMKs in a custom key store share a throttle limit of 1,800 operations per second for each custom key store. However, not all operations use the limit equally. The GenerateDataKey, GenerateDataKeyWithoutPlaintext, and GenerateRandom operations use approximately three times as much of the per-second limit as the Encrypt, Decrypt, and ReEncrypt operations.

For example, if you are requesting only Encrypt and Decrypt operations, you can perform approximately 1,800 operations per second. If, instead, you request repeated GenerateDataKey operations, your performance might be closer to 600 operations per second. For applications patterns that consist of roughly equal numbers of GenerateDataKey and Decrypt operations, you can expect about 1,200 operations per second.

Unlike other limits, you cannot raise this limit by creating a case in the AWS Support Center.

Requests-per-Second Limit for Each AWS KMS API Operation

On this page:

• Customer Master Keys (CMKs): 10,000
• Aliases: 10,000
• Grants per CMK: 10,000
• Grants for a Given Principal per CMK: 500
• Key Policy Document Size: 32 KB
• Requests per Second: Varies