Configure Amazon KMS key policies for CloudTrail - Amazon CloudTrail
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Configure Amazon KMS key policies for CloudTrail

You can create an Amazon KMS key in three ways:

  • The CloudTrail console

  • The Amazon Management console

  • The Amazon CLI

Note

If you create a KMS key in the CloudTrail console, CloudTrail adds the required KMS key policy for you. You do not need to manually add the policy statements. See Default KMS key policy created in CloudTrail console.

If you create a KMS key in the Amazon Management or the Amazon CLI, you must add policy sections to the key so that you can use it with CloudTrail. The policy must allow CloudTrail to use the key to encrypt your log files and event data stores, and allow the users you specify to read log files in unencrypted form.

See the following resources:

Required KMS key policy sections for use with CloudTrail

If you created a KMS key with the Amazon Management console or the Amazon CLI, then you must, at minimum, add the following statements to your KMS key policy for it to work with CloudTrail.

Required KMS key policy elements for trails

  1. Enable CloudTrail log encrypt permissions. See Granting encrypt permissions.

  2. Enable CloudTrail log decrypt permissions. See Granting decrypt permissions. If you are using an existing S3 bucket with an S3 Bucket Key, kms:Decrypt permissions are required to create or update a trail with SSE-KMS encryption enabled.

  3. Enable CloudTrail to describe KMS key properties. See Enable CloudTrail to describe KMS key properties.

As a security best practice, add an aws:SourceArn condition key to the KMS key policy. The IAM global condition key aws:SourceArn helps ensure that CloudTrail uses the KMS key only for a specific trail or trails. The value of aws:SourceArn is always the trail ARN (or array of trail ARNs) that is using the KMS key. Be sure to add the aws:SourceArn condition key to KMS key policies for existing trails.

The aws:SourceAccount condition key is also supported, but not recommended. The value of aws:SourceAccount is the account ID of the trail owner, or for organization trails, the management account ID.

Important

When you add the new sections to your KMS key policy, do not change any existing sections in the policy.

If encryption is enabled on a trail, and the KMS key is disabled, or the KMS key policy is not correctly configured for CloudTrail, CloudTrail cannot deliver logs.

Required KMS key policy elements for event data stores

  1. Enable CloudTrail log encrypt permissions. See Granting encrypt permissions.

  2. Enable CloudTrail log decrypt permissions. See Granting decrypt permissions.

  3. Grant users and roles permission to encrypt and decrypt event data store data with the KMS key.

    When you create an event data store and encrypt it with a KMS key, or run queries on an event data store that you're encrypting with a KMS key, you should have write access to the KMS key. The KMS key policy must have access to CloudTrail, and the KMS key should be manageable by users who run operations (such as queries) on the event data store.

  4. Enable CloudTrail to describe KMS key properties. See Enable CloudTrail to describe KMS key properties.

The aws:SourceArn and aws:SourceAccount condition keys are not supported in KMS key policies for event data stores.

Important

When you add the new sections to your KMS key policy, do not change any existing sections in the policy.

If encryption is enabled on an event data store, and the KMS key is disabled or deleted, or the KMS key policy is not correctly configured for CloudTrail, CloudTrail cannot deliver events to your event data store.

Granting encrypt permissions

Example Allow CloudTrail to encrypt logs on behalf of specific accounts

CloudTrail needs explicit permission to use the KMS key to encrypt logs on behalf of specific accounts. To specify an account, add the following required statement to your KMS key policy and replace account-id, region, and trailName with the appropriate values for your configuration. You can add additional account IDs to the EncryptionContext section to enable those accounts to use CloudTrail to use your KMS key to encrypt log files.

As a security best practice, add an aws:SourceArn condition key to the KMS key policy for a trail. The IAM global condition key aws:SourceArn helps ensure that CloudTrail uses the KMS key only for a specific trail or trails.

{ "Sid": "Allow CloudTrail to encrypt logs", "Effect": "Allow", "Principal": { "Service": "cloudtrail.amazonaws.com.cn" }, "Action": "kms:GenerateDataKey*", "Resource": "arn:aws-cn:kms:Region:account_ID:key/key_ID", "Condition": { "StringLike": { "kms:EncryptionContext:aws:cloudtrail:arn": [ "arn:aws-cn:cloudtrail:*:account-id:trail/*" ] }, "StringEquals": { "aws:SourceArn": "arn:aws:cloudtrail:region:account-id:trail/trailName" } } }

The following example policy statement illustrates how another account can use your KMS key to encrypt CloudTrail logs.

Scenario
  • Your KMS key is in account 111111111111.

  • Both you and account 222222222222 will encrypt logs.

In the policy, you add one or more accounts that will encrypt with your key to the CloudTrail EncryptionContext. This restricts CloudTrail to using your key to encrypt logs only for those accounts that you specify. Giving the root of account 222222222222 permission to encrypt logs delegates the administrator of that account to allocate encrypt permissions as required to other users in account 222222222222 by changing their IAM user policies.

As a security best practice, add an aws:SourceArn condition key to the KMS key policy. The IAM global condition key aws:SourceArn helps ensure that CloudTrail uses the KMS key only for a specific trail or trails. This condition is not supported in KMS key policies for event data stores.

KMS key policy statement:

{ "Sid": "Enable CloudTrail Encrypt Permissions", "Effect": "Allow", "Principal": { "Service": "cloudtrail.amazonaws.com.cn" }, "Action": "kms:GenerateDataKey*", "Resource": "arn:aws-cn:kms:Region:account_ID:key/key_ID", "Condition": { "StringLike": { "kms:EncryptionContext:aws:cloudtrail:arn": [ "arn:aws-cn:cloudtrail:*:111111111111:trail/*", "arn:aws-cn:cloudtrail:*:222222222222:trail/*" ] }, "StringEquals": { "aws:SourceArn": "arn:aws:cloudtrail:region:account-id:trail/trailName" } } }

For more information about editing a KMS key policy for use with CloudTrail, see Editing a Key Policy in the Amazon Key Management Service Developer Guide.

Granting decrypt permissions

Before you add your KMS key to your CloudTrail configuration, it is important to give decrypt permissions to all users who require them. Users who have encrypt permissions but no decrypt permissions cannot read encrypted logs. If you are using an existing S3 bucket with an S3 Bucket Key, kms:Decrypt permissions are required to create or update a trail with SSE-KMS encryption enabled.

Enable CloudTrail log decrypt permissions

Users of your key must be given explicit permissions to read the log files that CloudTrail has encrypted. To enable users to read encrypted logs, add the following required statement to your KMS key policy, modifying the Principal section to add a line for every principal (role or user) that you want to be able decrypt by using your KMS key.

{ "Sid": "Enable CloudTrail log decrypt permissions", "Effect": "Allow", "Principal": { "AWS": "arn:aws-cn:iam::account-id:user/username" }, "Action": "kms:Decrypt", "Resource": "*", "Condition": { "Null": { "kms:EncryptionContext:aws:cloudtrail:arn": "false" } } }

The following is an example policy that is required to allow the CloudTrail service principal to decrypt trail logs.

{ "Sid": "Allow CloudTrail to decrypt a trail", "Effect": "Allow", "Principal": { "Service": "cloudtrail.amazonaws.com" }, "Action": "kms:Decrypt" "Resource": "*" }

Allow users in your account to decrypt trail logs with your KMS key

Example

This policy statement illustrates how to allow an IAM user or role in your account to use your key to read the encrypted logs in your account's S3 bucket.

Example Scenario
  • Your KMS key, S3 bucket, and IAM user Bob are in account 111111111111.

  • You give IAM user Bob permission to decrypt CloudTrail logs in the S3 bucket.

In the key policy, you enable CloudTrail log decrypt permissions for IAM user Bob.

KMS key policy statement:

{ "Sid": "Enable CloudTrail log decrypt permissions", "Effect": "Allow", "Principal": { "AWS": "arn:aws-cn:iam::111111111111:user/Bob" }, "Action": "kms:Decrypt", "Resource": "arn:aws-cn:kms:Region:account_ID:key/key_ID", "Condition": { "Null": { "kms:EncryptionContext:aws:cloudtrail:arn": "false" } } }

Topics

    Allow users in other accounts to decrypt trail logs with your KMS key

    You can allow users in other accounts to use your KMS key to decrypt trail logs, but not event data store logs. The changes required to your key policy depend on whether the S3 bucket is in your account or in another account.

    Allow users of a bucket in a different account to decrypt logs

    Example

    This policy statement illustrates how to allow an IAM user or role in another account to use your key to read encrypted logs from an S3 bucket in the other account.

    Scenario
    • Your KMS key is in account 111111111111.

    • The IAM user Alice and S3 bucket are in account 222222222222.

    In this case, you give CloudTrail permission to decrypt logs under account 222222222222, and you give Alice's IAM user policy permission to use your key KeyA, which is in account 111111111111.

    KMS key policy statement:

    { "Sid": "Enable encrypted CloudTrail log read access", "Effect": "Allow", "Principal": { "AWS": [ "arn:aws-cn:iam::222222222222:root" ] }, "Action": "kms:Decrypt", "Resource": "arn:aws-cn:kms:Region:account_ID:key/key_ID", "Condition": { "Null": { "kms:EncryptionContext:aws:cloudtrail:arn": "false" } } }

    Alice's IAM user policy statement:

    { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": "kms:Decrypt", "Resource": "arn:aws-cn:kms:us-west-2:111111111111:key/KeyA" } ] }

    Allow users in a different account to decrypt trail logs from your bucket

    Example

    This policy illustrates how another account can use your key to read encrypted logs from your S3 bucket.

    Example Scenario
    • Your KMS key and S3 bucket are in account 111111111111.

    • The user who reads logs from your bucket is in account 222222222222.

    To enable this scenario, you enable decrypt permissions for the IAM role CloudTrailReadRole in your account, and then give the other account permission to assume that role.

    KMS key policy statement:

    { "Sid": "Enable encrypted CloudTrail log read access", "Effect": "Allow", "Principal": { "AWS": [ "arn:aws-cn:iam::11111111111:role/CloudTrailReadRole" ] }, "Action": "kms:Decrypt", "Resource": "arn:aws-cn:kms:Region:account_ID:key/key_ID", "Condition": { "Null": { "kms:EncryptionContext:aws:cloudtrail:arn": "false" } } }

    CloudTrailReadRole trust entity policy statement:

    { "Version": "2012-10-17", "Statement": [ { "Sid": "", "Effect": "Allow", "Principal": { "AWS": "arn:aws-cn:iam::222222222222:root" }, "Action": "sts:AssumeRole" } ] }

    For information about editing a KMS key policy for use with CloudTrail, see Editing a Key Policy in the Amazon Key Management Service Developer Guide.

    Enable CloudTrail to describe KMS key properties

    CloudTrail requires the ability to describe the properties of the KMS key. To enable this functionality, add the following required statement as is to your KMS key policy. This statement does not grant CloudTrail any permissions beyond the other permissions that you specify.

    As a security best practice, add an aws:SourceArn condition key to the KMS key policy. The IAM global condition key aws:SourceArn helps ensure that CloudTrail uses the KMS key only for a specific trail or trails.

    { "Sid": "Allow CloudTrail access", "Effect": "Allow", "Principal": { "Service": "cloudtrail.amazonaws.com.cn" }, "Action": "kms:DescribeKey", "Resource": "arn:aws-cn:kms:Region:account_ID:key/key_ID", "Condition": { "StringEquals": { "aws:SourceArn": "arn:aws:cloudtrail:region:account-id:trail/trailName" } } }

    For more information about editing KMS key policies, see Editing a Key Policy in the Amazon Key Management Service Developer Guide.