Storing and retaining sensitive data discovery results - Amazon Macie

Storing and retaining sensitive data discovery results

When you run a sensitive data discovery job or Amazon Macie performs automated sensitive data discovery, Macie creates an analysis record for each Amazon Simple Storage Service (Amazon S3) object that's included in the scope of the analysis. These records, referred to as a sensitive data discovery results, log details about the analysis that Macie performs on individual S3 objects. This includes objects that Macie doesn't detect sensitive data in, and therefore don't produce findings, and objects that Macie can't analyze due to errors or issues. If Macie detects sensitive data in an object, the record includes data from the corresponding finding as well as additional information. Sensitive data discovery results provide you with analysis records that can be helpful for data privacy and protection audits or investigations.

Macie stores your sensitive data discovery results for only 90 days. To access your results and enable long-term storage and retention of them, configure Macie to encrypt the results with an AWS Key Management Service (AWS KMS) key and store them in an S3 bucket. The bucket can serve as a definitive, long-term repository for all of your sensitive data discovery results. You can then optionally access and query the results in that repository.

This topic guides you through the process of using the AWS Management Console to configure a repository for your sensitive data discovery results. The configuration is a combination of an AWS KMS key that encrypts the results, an S3 general purpose bucket that stores the results, and Macie settings that specify which key and bucket to use. If you prefer to configure the Macie settings programmatically, you can use the PutClassificationExportConfiguration operation of the Amazon Macie API.

When you configure the settings in Macie, your choices apply only to the current AWS Region. If you're the Macie administrator for an organization, your choices apply only to your account. They don't apply to any associated member accounts. If you enable automated sensitive data discovery or run sensitive data discovery jobs to analyze data for member accounts, Macie stores the sensitive data discovery results in the repository for your administrator account.

If you use Macie in multiple AWS Regions, configure the repository settings for each Region in which you use Macie. You can optionally store sensitive data discovery results for multiple Regions in the same S3 bucket. However, note the following requirements:

  • To store the results for a Region that AWS enables by default for AWS accounts, such as the US East (N. Virginia) Region, you have to choose a bucket in a Region that's enabled by default. The results can't be stored in a bucket in an opt-in Region (Region that's disabled by default).

  • To store the results for an opt-in Region, such as the Middle East (Bahrain) Region, you have to choose a bucket in that same Region or a Region that's enabled by default. The results can't be stored in a bucket in a different opt-in Region.

To determine whether a Region is enabled by default, see Enable or disable AWS Regions in your account in the AWS Account Management User Guide. In addition to the preceding requirements, also consider whether you want to retrieve samples of sensitive data that Macie reports in individual findings. To retrieve sensitive data samples from an affected S3 object, all of the following resources and data must be stored in the same Region: the affected object, the applicable finding, and the corresponding sensitive data discovery result.

Before you begin: Learn key concepts

Amazon Macie automatically creates a sensitive data discovery result for each Amazon S3 object that it analyzes or attempts to analyze when you run a sensitive data discovery job or it performs automated sensitive data discovery. This includes:

  • Objects that Macie detects sensitive data in, and therefore also produce sensitive data findings.

  • Objects that Macie doesn't detect sensitive data in, and therefore don't produce sensitive data findings.

  • Objects that Macie can't analyze due to errors or issues such as permissions settings or use of an unsupported file or storage format.

If Macie detects sensitive data in an S3 object, the sensitive data discovery result includes data from the corresponding sensitive data finding. It provides additional information too, such as the location of as many as 1,000 occurrences of each type of sensitive data that Macie found in the object. For example:

  • The column and row number for a cell or field in a Microsoft Excel workbook, CSV file, or TSV file

  • The path to a field or array in a JSON or JSON Lines file

  • The line number for a line in a non-binary text file other than a CSV, JSON, JSON Lines, or TSV file—for example, an HTML, TXT, or XML file

  • The page number for a page in an Adobe Portable Document Format (PDF) file

  • The record index and the path to a field in a record in an Apache Avro object container or Apache Parquet file

If the affected S3 object is an archive file, such as a .tar or .zip file, the sensitive data discovery result also provides detailed location data for occurrences of sensitive data in individual files that Macie extracted from the archive. Macie doesn’t include this information in sensitive data findings for archive files. To report location data, sensitive data discovery results use a standardized JSON schema.

A sensitive data discovery result doesn't include the sensitive data that Macie found. Instead, it provides you with an analysis record that can be helpful for audits or investigations.

Macie stores your sensitive data discovery results for 90 days. You can’t access them directly on the Amazon Macie console or with the Amazon Macie API. Instead, follow the steps in this topic to configure Macie to encrypt your results with an AWS KMS key that you specify, and store the results in an S3 general purpose bucket that you also specify. Macie then writes the results to JSON Lines (.jsonl) files, adds the files to the bucket as GNU Zip (.gz) files, and encrypts the data using SSE-KMS encryption. As of November 8, 2023, Macie also signs the resulting S3 objects with a Hash-based Message Authentication Code (HMAC) AWS KMS key.

After you configure Macie to store your sensitive data discovery results in an S3 bucket, the bucket can serve as a definitive, long-term repository for the results. You can then optionally access and query the results in that repository.

Tips

For a detailed, instructional example of how you might query and use sensitive data discovery results to analyze and report potential data security risks, see the following blog post on the AWS Security Blog: How to query and visualize Macie sensitive data discovery results with Amazon Athena and Amazon QuickSight.

For samples of Amazon Athena queries that you can use to analyze sensitive data discovery results, visit the Amazon Macie Results Analytics repository on GitHub. This repository also provides instructions for configuring Athena to retrieve and decrypt your results, and scripts for creating tables for the results.

Step 1: Verify your permissions

Before you configure a repository for your sensitive data discovery results, verify that you have the permissions that you need to encrypt and store the results. To verify your permissions, use AWS Identity and Access Management (IAM) to review the IAM policies that are attached to your IAM identity. Then compare the information in those policies to the following list of actions that you must be allowed to perform to configure the repository.

Amazon Macie

For Macie, verify that you're allowed to perform the following action:

macie2:PutClassificationExportConfiguration

This action allows you to add or change the repository settings in Macie.

Amazon S3

For Amazon S3, verify that you're allowed to perform the following actions:

  • s3:CreateBucket

  • s3:GetBucketLocation

  • s3:ListAllMyBuckets

  • s3:PutBucketAcl

  • s3:PutBucketPolicy

  • s3:PutBucketPublicAccessBlock

  • s3:PutObject

These actions allow you to access and configure an S3 general purpose bucket that can serve as the repository.

AWS KMS

To use the Amazon Macie console to add or change the repository settings, also verify that you're allowed to perform the following AWS KMS actions:

  • kms:DescribeKey

  • kms:ListAliases

These actions allow you to retrieve and display information about the AWS KMS keys for your account. You can then choose one of these keys to encrypt your sensitive data discovery results.

If you plan to create a new AWS KMS key to encrypt the data, you also need to be allowed to perform the following actions: kms:CreateKey, kms:GetKeyPolicy, and kms:PutKeyPolicy.

If you're not allowed to perform the requisite actions, ask your AWS administrator for assistance before you proceed to the next step.

Step 2: Configure an AWS KMS key

After you verify your permissions, determine which AWS KMS key you want Macie to use to encrypt your sensitive data discovery results. The key must be a customer managed, symmetric encryption KMS key that's enabled in the same AWS Region as the S3 bucket where you want to store the results.

The key can be an existing AWS KMS key from your own account, or an existing AWS KMS key that another account owns. If you want to use a new KMS key, create the key before proceeding. If you want to use an existing key that another account owns, obtain the Amazon Resource Name (ARN) of the key. You'll need to enter this ARN when you configure the repository settings in Macie. For information about creating and reviewing the settings for KMS keys, see the AWS Key Management Service Developer Guide.

Note

The key can be an AWS KMS key in an external key store. However, the key might then be slower and less reliable than a key that’s managed entirely within AWS KMS. You can reduce this risk by storing your sensitive data discovery results in an S3 bucket that’s configured to use the key as an S3 Bucket Key. Doing so reduces the number of AWS KMS requests that must be made to encrypt your sensitive data discovery results.

For information about using KMS keys in external key stores, see External key stores in the AWS Key Management Service Developer Guide. For information about using S3 Bucket Keys, see Reducing the cost of SSE-KMS with Amazon S3 Bucket Keys in the Amazon Simple Storage Service User Guide.

After you determine which KMS key you want Macie to use, give Macie permission to use the key. Otherwise, Macie won't be able to encrypt or store your results in the repository. To give Macie permission to use the key, update the key policy for the key. For detailed information about key policies and managing access to KMS keys, see Key policies in AWS KMS in the AWS Key Management Service Developer Guide.

To update the key policy
  1. Open the AWS KMS console at https://console.aws.amazon.com/kms.

  2. To change the AWS Region, use the Region selector in the upper-right corner of the page.

  3. Choose the key that you want Macie to use to encrypt your sensitive data discovery results.

  4. On the Key policy tab, choose Edit.

  5. Copy the following statement to your clipboard, and then add it to the policy:

    { "Sid": "Allow Macie to use the key", "Effect": "Allow", "Principal": { "Service": "macie.amazonaws.com" }, "Action": [ "kms:GenerateDataKey", "kms:Encrypt" ], "Resource": "*", "Condition": { "StringEquals": { "aws:SourceAccount": "111122223333" }, "ArnLike": { "aws:SourceArn": [ "arn:aws:macie2:Region:111122223333:export-configuration:*", "arn:aws:macie2:Region:111122223333:classification-job/*" ] } } }
    Note

    When you add the statement to the policy, make sure that the syntax is valid. Policies use JSON format. This means that you need to also add a comma before or after the statement, depending on where you add the statement to the policy. If you add the statement as the last statement, add a comma after the closing curly brace for the preceding statement. If you add it as the first statement or between two existing statements, add a comma after the closing curly brace for the statement.

  6. Update the statement with the correct values for your environment:

    • In the Condition fields, replace the placeholder values, where:

      • 111122223333 is the account ID for your AWS account.

      • Region is the AWS Region in which you're using Macie and you want to allow Macie to use the key.

        If you use Macie in multiple Regions and want to allow Macie to use the key in additional Regions, add aws:SourceArn conditions for each additional Region. For example:

        "aws:SourceArn": [ "arn:aws:macie2:us-east-1:111122223333:export-configuration:*", "arn:aws:macie2:us-east-1:111122223333:classification-job/*", "arn:aws:macie2:us-west-2:111122223333:export-configuration:*", "arn:aws:macie2:us-west-2:111122223333:classification-job/*" ]

        Alternatively, you can allow Macie to use the key in all Regions. To do this, replace the placeholder value with the wildcard character (*). For example:

        "aws:SourceArn": [ "arn:aws:macie2:*:111122223333:export-configuration:*", "arn:aws:macie2:*:111122223333:classification-job/*" ]
    • If you're using Macie in an opt-in Region, add the appropriate Region code to the value for the Service field. For example, if you're using Macie in the Middle East (Bahrain) Region, which has the Region code me-south-1, replace macie.amazonaws.com with macie.me-south-1.amazonaws.com. For a list of Regions where Macie is currently available and the Region code for each one, see Amazon Macie endpoints and quotas in the AWS General Reference.

    Note that the Condition fields use two IAM global condition keys:

    • aws:SourceAccount – This condition allows Macie to perform the specified actions only for your account. More specifically, it determines which account can perform the specified actions for the resources and actions specified by the aws:SourceArn condition.

      To allow Macie to perform the specified actions for additional accounts, add the account ID for each additional account to this condition. For example:

      "aws:SourceAccount": [111122223333,444455556666]
    • aws:SourceArn – This condition prevents other AWS services from performing the specified actions. It also prevents Macie from using the key while performing other actions for your account. In other words, it allows Macie to encrypt S3 objects with the key only if: the objects are sensitive data discovery results, and the results are for automated sensitive data discovery or sensitive data discovery jobs created by the specified account in the specified Region.

      To allow Macie to perform the specified actions for additional accounts, add ARNs for each additional account to this condition. For example:

      "aws:SourceArn": [ "arn:aws:macie2:us-east-1:111122223333:export-configuration:*", "arn:aws:macie2:us-east-1:111122223333:classification-job/*", "arn:aws:macie2:us-east-1:444455556666:export-configuration:*", "arn:aws:macie2:us-east-1:444455556666:classification-job/*" ]

    The accounts specified by the aws:SourceAccount and aws:SourceArn conditions should match.

    These conditions help prevent Macie from being used as a confused deputy during transactions with AWS KMS. Although we don’t recommend it, you can remove these conditions from the statement.

  7. When you finish adding and updating the statement, choose Save changes.

Step 3: Choose an S3 bucket

After you verify your permissions and configure the AWS KMS key, you're ready to specify which S3 bucket you want to use as the repository for your sensitive data discovery results. You have two options:

  • Use a new S3 bucket that Macie creates – If you choose this option, Macie automatically creates a new S3 general purpose bucket in the current AWS Region for your discovery results. Macie also applies a bucket policy to the bucket. The policy allows Macie to add objects to the bucket. It also requires the objects to be encrypted with the AWS KMS key that you specify, using SSE-KMS encryption. To review the policy, choose View policy on the Amazon Macie console after you specify a name for the bucket and the KMS key to use.

  • Use an existing S3 bucket that you create – If you prefer to store your discovery results in a particular S3 bucket that you create, create the bucket before you proceed. The bucket must be a general purpose bucket. In addition, the bucket's settings and policy must allow Macie to add objects to the bucket. This topic explains which settings to check and how to update the policy. It also provides examples of the statements to add to the policy.

The following sections provide instructions for each option. Choose the section for the option that you want.

If you prefer to use a new S3 bucket that Macie creates for you, the final step in the process is to configure the repository settings in Macie.

To configure the repository settings in Macie
  1. Open the Amazon Macie console at https://console.aws.amazon.com/macie/.

  2. In the navigation pane, under Settings, choose Discovery results.

  3. Under Repository for sensitive data discovery results, choose Create bucket.

  4. In the Create a bucket box, enter a name for the bucket.

    The name must be unique across all S3 buckets. In addition, the name can consist only of lowercase letters, numbers, dots (.), and hyphens (-). For additional naming requirements, see Bucket naming rules in the Amazon Simple Storage Service User Guide.

  5. Expand the Advanced section.

  6. (Optional) To specify a prefix to use in the path to a location in the bucket, enter the prefix in the Data discovery result prefix box.

    When you enter a value, Macie updates the example below the box to show the path to the bucket location where it will store your discovery results.

  7. For Block all public access, choose Yes to enable all block public access settings for the bucket.

    For information about these settings, see Blocking public access to your Amazon S3 storage in the Amazon Simple Storage Service User Guide.

  8. Under Encryption settings, specify the AWS KMS key that you want Macie to use to encrypt the results:

    • To use a key from your own account, choose Select a key from your account. Then, in the AWS KMS key list, choose the key to use. The list displays customer managed, symmetric encryption KMS keys for your account.

    • To use a key that another account owns, choose Enter the ARN of a key from another account. Then, in the AWS KMS key ARN box, enter the Amazon Resource Name (ARN) of the key to use—for example, arn:aws:kms:us-east-1:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab.

  9. When you finish entering the settings, choose Save.

    Macie tests the settings to verify that they're correct. If any settings are incorrect, Macie displays an error message to help you address the issue.

After you save the repository settings, Macie adds existing discovery results for the preceding 90 days to the repository. Macie also starts adding new discovery results to the repository.

If you prefer to store your sensitive data discovery results in a particular S3 bucket that you create, create and configure the bucket before you configure the settings in Macie. When you create the bucket, note the following requirements:

  • The bucket must be a general purpose bucket. It can't be a directory bucket.

  • If you enable Object Lock for the bucket, you have to disable the default retention setting for that feature. Otherwise, Macie won't be able to add your discovery results to the bucket. For information about this setting, see Using S3 Object Lock in the Amazon Simple Storage Service User Guide.

  • To store your discovery results for a Region that's enabled by default for AWS accounts, such as the US East (N. Virginia) Region, the bucket has to be in a Region that's enabled by default. The results can't be stored in a bucket in an opt-in Region (Region that's disabled by default).

  • To store your discovery results for an opt-in Region, such as the Middle East (Bahrain) Region, the bucket has to be in the same Region or a Region that's enabled by default. The results can't be stored in a bucket in a different opt-in Region.

To determine whether a Region is enabled by default, see Enable or disable AWS Regions in your account in the AWS Account Management User Guide.

After you create the bucket, update the bucket's policy to allow Macie to retrieve information about the bucket and add objects to the bucket. You can then configure the settings in Macie.

To update the bucket policy for the bucket
  1. Open the Amazon S3 console at https://console.aws.amazon.com/s3/.

  2. Choose the bucket that you want to store your discovery results in.

  3. Choose the Permissions tab.

  4. In the Bucket policy section, choose Edit.

  5. Copy the following example policy to your clipboard:

    { "Version": "2012-10-17", "Statement": [ { "Sid": "Allow Macie to use the GetBucketLocation operation", "Effect": "Allow", "Principal": { "Service": "macie.amazonaws.com" }, "Action": "s3:GetBucketLocation", "Resource": "arn:aws:s3:::amzn-s3-demo-bucket", "Condition": { "StringEquals": { "aws:SourceAccount": "111122223333" }, "ArnLike": { "aws:SourceArn": [ "arn:aws:macie2:Region:111122223333:export-configuration:*", "arn:aws:macie2:Region:111122223333:classification-job/*" ] } } }, { "Sid": "Allow Macie to add objects to the bucket", "Effect": "Allow", "Principal": { "Service": "macie.amazonaws.com" }, "Action": "s3:PutObject", "Resource": "arn:aws:s3:::amzn-s3-demo-bucket/[optional prefix/]*", "Condition": { "StringEquals": { "aws:SourceAccount": "111122223333" }, "ArnLike": { "aws:SourceArn": [ "arn:aws:macie2:Region:111122223333:export-configuration:*", "arn:aws:macie2:Region:111122223333:classification-job/*" ] } } }, { "Sid": "Deny unencrypted object uploads. This is optional", "Effect": "Deny", "Principal": { "Service": "macie.amazonaws.com" }, "Action": "s3:PutObject", "Resource": "arn:aws:s3:::amzn-s3-demo-bucket/[optional prefix/]*", "Condition": { "StringNotEquals": { "s3:x-amz-server-side-encryption": "aws:kms" } } }, { "Sid": "Deny incorrect encryption headers. This is optional", "Effect": "Deny", "Principal": { "Service": "macie.amazonaws.com" }, "Action": "s3:PutObject", "Resource": "arn:aws:s3:::amzn-s3-demo-bucket/[optional prefix/]*", "Condition": { "StringNotEquals": { "s3:x-amz-server-side-encryption-aws-kms-key-id": "arn:aws:kms:Region:111122223333:key/KMSKeyId" } } }, { "Sid": "Deny non-HTTPS access", "Effect": "Deny", "Principal": "*", "Action": "s3:*", "Resource": "arn:aws:s3:::amzn-s3-demo-bucket/*", "Condition": { "Bool": { "aws:SecureTransport": "false" } } } ] }
  6. Paste the example policy in the Bucket policy editor on the Amazon S3 console.

  7. Update the example policy with the correct values for your environment:

    • In the optional statement that denies incorrect encryption headers:

      • Replace amzn-s3-demo-bucket with the name of the bucket. To also specify a prefix for a path to a location in the bucket, replace [optional prefix/] with the prefix. Otherwise, remove the [optional prefix/] placeholder value.

      • In the StringNotEquals condition, replace arn:aws:kms:Region:111122223333:key/KMSKeyId with the Amazon Resource Name (ARN) of the AWS KMS key to use for encryption of your discovery results.

    • In all other statements, replace the placeholder values, where:

      • amzn-s3-demo-bucket is the name of the bucket.

      • [optional prefix/] is the prefix for a path to a location in the bucket. Remove this placeholder value if you don't want to specify a prefix.

      • 111122223333 is the account ID for your AWS account.

      • Region is the AWS Region in which you're using Macie and want to allow Macie to add discovery results to the bucket.

        If you use Macie in multiple Regions and want to allow Macie to add results to the bucket for additional Regions, add aws:SourceArn conditions for each additional Region. For example:

        "aws:SourceArn": [ "arn:aws:macie2:us-east-1:111122223333:export-configuration:*", "arn:aws:macie2:us-east-1:111122223333:classification-job/*", "arn:aws:macie2:us-west-2:111122223333:export-configuration:*", "arn:aws:macie2:us-west-2:111122223333:classification-job/*" ]

        Alternatively, you can allow Macie to add results to the bucket for all Regions in which you use Macie. To do this, replace the placeholder value with the wildcard character (*). For example:

        "aws:SourceArn": [ "arn:aws:macie2:*:111122223333:export-configuration:*", "arn:aws:macie2:*:111122223333:classification-job/*" ]
    • If you're using Macie in an opt-in Region, add the appropriate Region code to the value for the Service field in each statement that specifies the Macie service principal. For example, if you're using Macie in the Middle East (Bahrain) Region, which has the Region code me-south-1, replace macie.amazonaws.com with macie.me-south-1.amazonaws.com in each applicable statement. For a list of Regions where Macie is currently available and the Region code for each one, see Amazon Macie endpoints and quotas in the AWS General Reference.

    Note that the example policy includes statements that allow Macie to determine which Region the bucket resides in (GetBucketLocation) and add objects to the bucket (PutObject). These statements define conditions that use two IAM global condition keys:

    • aws:SourceAccount – This condition allows Macie to add sensitive data discovery results to the bucket only for your account. It prevents Macie from adding discovery results for other accounts to the bucket. More specifically, the condition specifies which account can use the bucket for the resources and actions specified by the aws:SourceArn condition.

      To store results for additional accounts in the bucket, add the account ID for each additional account to this condition. For example:

      "aws:SourceAccount": [111122223333,444455556666]
    • aws:SourceArn – This condition restricts access to the bucket based on the source of the objects that are being added to the bucket. It prevents other AWS services from adding objects to the bucket. It also prevents Macie from adding objects to the bucket while performing other actions for your account. More specifically, the condition allows Macie to add objects to the bucket only if: the objects are sensitive data discovery results, and the results are for automated sensitive data discovery or sensitive data discovery jobs created by the specified account in the specified Region.

      To allow Macie to perform the specified actions for additional accounts, add ARNs for each additional account to this condition. For example:

      "aws:SourceArn": [ "arn:aws:macie2:us-east-1:111122223333:export-configuration:*", "arn:aws:macie2:us-east-1:111122223333:classification-job/*", "arn:aws:macie2:us-east-1:444455556666:export-configuration:*", "arn:aws:macie2:us-east-1:444455556666:classification-job/*" ]

    The accounts specified by the aws:SourceAccount and aws:SourceArn conditions should match.

    Both conditions help prevent Macie from being used as a confused deputy during transactions with Amazon S3. Although we don’t recommend it, you can remove these conditions from the bucket policy.

  8. When you finish updating the bucket policy, choose Save changes.

You can now configure the repository settings in Macie.

To configure the repository settings in Macie
  1. Open the Amazon Macie console at https://console.aws.amazon.com/macie/.

  2. In the navigation pane, under Settings, choose Discovery results.

  3. Under Repository for sensitive data discovery results, choose Existing bucket.

  4. For Choose a bucket, select the bucket that you want to store your discovery results in.

  5. To specify a prefix for a path to a location in the bucket, expand the Advanced section. Then, for Data discovery result prefix, enter the prefix.

    When you enter a value, Macie updates the example below the box to show the path to the bucket location where it will store your discovery results.

  6. Under Encryption settings, specify the AWS KMS key that you want Macie to use to encrypt the results:

    • To use a key from your own account, choose Select a key from your account. Then, in the AWS KMS key list, choose the key to use. The list displays customer managed, symmetric encryption KMS keys for your account.

    • To use a key that another account owns, choose Enter the ARN of a key from another account. Then, in the AWS KMS key ARN box, enter the ARN of the key to use—for example, arn:aws:kms:us-east-1:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab.

  7. When you finish entering the settings, choose Save.

    Macie tests the settings to verify that they're correct. If any settings are incorrect, Macie displays an error message to help you address the issue.

After you save the repository settings, Macie adds existing discovery results for the preceding 90 days to the repository. Macie also starts adding new discovery results to the repository.

Note

If you subsequently change the Data discovery result prefix setting, also update the bucket policy in Amazon S3. Policy statements that specify the previous prefix must specify the new prefix. Otherwise, Macie won't be allowed to add your discovery results to the bucket.

Tip

To reduce server-side encryption costs, also configure the S3 bucket to use an S3 Bucket Key, and specify the AWS KMS key that you configured for encryption of your sensitive data discovery results. Use of an S3 Bucket Key reduces the number of calls to AWS KMS, which can reduce AWS KMS request costs. If the KMS key is in an external key store, use of an S3 Bucket Key can also minimize the performance impact of using the key. To learn more, see Reducing the cost of SSE-KMS with Amazon S3 Bucket Keys in the Amazon Simple Storage Service User Guide.