Required KMS key policy sections for use with CloudTrail Granting encrypt permissions Granting decrypt permissions Enable CloudTrail to describe KMS key properties

Configure AWS KMS key policies for CloudTrail

You can create an AWS KMS key in three ways:

The CloudTrail console
The AWS Management console
The AWS 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 AWS Management or the AWS 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:

To create a KMS key with the AWS CLI, see create-key.
To edit a KMS key policy for CloudTrail, see Editing a Key Policy in the AWS Key Management Service Developer Guide.
For technical details on how CloudTrail uses AWS KMS, see How AWS CloudTrail Uses AWS KMS in the AWS Key Management Service Developer Guide.

Required KMS key policy sections for use with CloudTrail

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

Topics

Required KMS key policy elements for trails
Required KMS key policy elements for event data stores

Required KMS key policy elements for trails

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

Enable CloudTrail log encrypt permissions. See Granting encrypt permissions.
Enable CloudTrail log decrypt permissions. See Granting decrypt permissions.
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.
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"
    },
    "Action": "kms:GenerateDataKey*",
    "Resource": "*",
    "Condition": {
        "StringEquals": {
            "aws:SourceArn": "arn:aws:cloudtrail:region:account-id:trail/trail-name"
         },
         "StringLike": {
             "kms:EncryptionContext:aws:cloudtrail:arn": "arn:aws:cloudtrail:*:account-id:trail/*"
         }
    }
}

A policy for a KMS key used to encrypt CloudTrail Lake event data store logs cannot use the condition keys aws:SourceArn or aws:SourceAccount. The following is an example of a KMS key policy for an event data store.


{
    "Sid": "Allow CloudTrail to encrypt event data store",
    "Effect": "Allow",
    "Principal": {
        "Service": "cloudtrail.amazonaws.com"
     },
     "Action": [
        "kms:GenerateDataKey",
        "kms:Decrypt"
      ],
      "Resource": "*"
}

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 encrypt with your key to the CloudTrail EncryptionContext. This restricts CloudTrail to using your key to encrypt logs only for the accounts that you specify. When you give the root of account 222222222222 permission to encrypt logs, it delegates permission to the account administrator to encrypt the necessary permissions to other users in that account. The account administrator does this by changing the policies associated with those IAM users.

KMS key policy statement:


{
  "Sid": "Enable CloudTrail encrypt permissions",
  "Effect": "Allow",
  "Principal": {
    "Service": "cloudtrail.amazonaws.com"
  },
  "Action": "kms:GenerateDataKey*",
  "Resource": "*",
  "Condition": {
    "StringLike": {
      "kms:EncryptionContext:aws:cloudtrail:arn": [
        "arn:aws:cloudtrail:*:111111111111:trail/*",
        "arn:aws:cloudtrail:*:222222222222:trail/*"
      ]
    },
    "StringEquals": {
        "aws:SourceArn": "arn:aws:cloudtrail:region:account-id:trail/trail-name"
    }
  }
}

For more information about editing a KMS key policy for use with CloudTrail, see Editing a key policy in the AWS 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 that you want to be able decrypt by using your KMS key.


{
  "Sid": "Enable CloudTrail log decrypt permissions",
  "Effect": "Allow",
  "Principal": {
    "AWS": "arn:aws: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": "*"
}

A decrypt policy for a KMS key that is used with a CloudTrail Lake event data store is similar to the following. The user or role ARNs specified as values for Principal need decrypt permissions to create or update event data stores, run queries, or get query results.


{
      "Sid": "Enable user key permissions for event data stores"
      "Effect": "Allow",
      "Principal": {
          "AWS": "arn:aws:iam::account-id:user/username"
      },
      "Action": [
          "kms:Decrypt",
          "kms:GenerateDataKey"
      ],
      "Resource": "*"
  }

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


{
      "Sid": "Allow CloudTrail to decrypt an event data store",
      "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 a 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:iam::111111111111:user/Bob"
  },
  "Action": "kms:Decrypt",
  "Resource": "arn:aws: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:iam::222222222222:root"
    ]
  },
  "Action": "kms:Decrypt",
  "Resource": "arn:aws: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: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:iam::11111111111:role/CloudTrailReadRole"
    ]
  },
  "Action": "kms:Decrypt",
  "Resource": "arn:aws: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": "Allow CloudTrail access",
     "Effect": "Allow",
     "Principal": {
       "AWS": "arn:aws: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 AWS 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.


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

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

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Document Conventions

Granting permissions to create a KMS key

Default KMS key policy created in CloudTrail console