Specifying server-side encryption with AWS KMS (SSE-KMS)

Important

Amazon S3 now applies server-side encryption with Amazon S3 managed keys (SSE-S3) as the base level of encryption for every bucket in Amazon S3. Starting January 5, 2023, all new object uploads to Amazon S3 are automatically encrypted at no additional cost and with no impact on performance. The automatic encryption status for S3 bucket default encryption configuration and for new object uploads is available in AWS CloudTrail logs, S3 Inventory, S3 Storage Lens, the Amazon S3 console, and as an additional Amazon S3 API response header in the AWS Command Line Interface and AWS SDKs. For more information, see Default encryption FAQ.

All Amazon S3 buckets have encryption configured by default and all new objects uploaded to an S3 bucket are automatically encrypted at rest. Server-side encryption with Amazon S3 managed keys (SSE-S3) is the base level of encryption configuration for every bucket in Amazon S3. If you want to use a different type of default encryption, you can also specify server-side encryption with AWS Key Management Service (AWS KMS) keys (SSE-KMS) or customer-provided keys (SSE-C) in your S3 PUT requests or set the default encryption configuration in the destination bucket to use SSE-KMS to encrypt your data.

You can apply encryption when you are either uploading a new object or copying an existing object.

You can specify SSE-KMS by using the Amazon S3 console, REST API operations, AWS SDKs, and the AWS Command Line Interface (AWS CLI). For more information, see the following topics.

Note

You can use multi-Region AWS KMS keys in Amazon S3. However, Amazon S3 currently treats multi-Region keys as though they were single-Region keys, and does not use the multi-Region features of the key. For more information, see Using multi-Region keys in AWS Key Management Service Developer Guide.

Note

If you want to use a KMS key that is owned by a different account, you must have permission to use the key. For more information about cross-account permissions for KMS keys, see Creating KMS keys that other accounts can use in the AWS Key Management Service Developer Guide.

Using the S3 console

This topic describes how to set or change the type of encryption of an object to use server-side encryption with AWS Key Management Service (AWS KMS) keys (SSE-KMS) by using the Amazon S3 console.

Note

If you change an object's encryption, a new object is created to replace the old one. If S3 Versioning is enabled, a new version of the object is created, and the existing object becomes an older version. The role that changes the property also becomes the owner of the new object (or object version).

To add or change encryption for an object

1. Sign in to the AWS Management Console and open the Amazon S3 console at https://console.aws.amazon.com/s3/.

2. In the left navigation pane, choose Buckets.

3. In the Buckets list, choose the name of the bucket that contains the object.

4. In the Objects list, choose the name of the object that you want to add or change encryption for.

   The object's details page appears, with several sections that display the properties for your object.

5. Choose the Properties tab.

6. Scroll down to the Server-side encryption settings section and choose Edit.

   The Edit server-side encryption page opens.

7. Under Server-side encryption, for Encryption settings, choose Override default encryption bucket settings.

8. Under Encryption key type, choose AWS Key Management Service key (SSE-KMS).

   Important

   If you use the SSE-KMS option for your default encryption configuration, you are subject to the requests per second (RPS) quotas of AWS KMS. For more information about AWS KMS quotas and how to request a quota increase, see Quotas in the AWS Key Management Service Developer Guide.

9. Under AWS KMS key, do one of the following to choose your KMS key:

   • To choose from a list of available KMS keys, choose Choose from your AWS KMS keys, and then choose your KMS key from the list of available keys.

     Both the AWS managed key (aws/s3) and your customer managed keys appear in this list. For more information about customer managed keys, see Customer keys and AWS keys in the AWS Key Management Service Developer Guide.

   • To enter the KMS key ARN, choose Enter AWS KMS key ARN, and then enter your KMS key ARN in the field that appears.

   • To create a new customer managed key in the AWS KMS console, choose Create a KMS key.

     For more information about creating an AWS KMS key, see Creating keys in the AWS Key Management Service Developer Guide.

   Important

   You can use only KMS keys that are available in the same AWS Region as the bucket. The Amazon S3 console lists only the first 100 KMS keys in the same Region as the bucket. To use a KMS key that is not listed, you must enter your KMS key ARN. If you want to use a KMS key that is owned by a different account, you must first have permission to use the key and then you must enter the KMS key ARN.

   Amazon S3 supports only symmetric encryption KMS keys, and not asymmetric KMS keys. For more information, see Identifying symmetric and asymmetric KMS keys in the AWS Key Management Service Developer Guide.

10. Choose Save changes.

Note

This action applies encryption to all specified objects. When you're encrypting folders, wait for the save operation to finish before adding new objects to the folder.

Using the REST API

When you create an object—that is, when you upload a new object or copy an existing object—you can specify the use of server-side encryption with AWS KMS keys (SSE-KMS) to encrypt your data. To do this, add the x-amz-server-side-encryption header to the request. Set the value of the header to the encryption algorithm aws:kms. Amazon S3 confirms that your object is stored using SSE-KMS by returning the response header x-amz-server-side-encryption.

If you specify the x-amz-server-side-encryption header with a value of aws:kms, you can also use the following request headers:

• x-amz-server-side-encryption-aws-kms-key-id

• x-amz-server-side-encryption-context

• x-amz-server-side-encryption-bucket-key-enabled

Amazon S3 REST API operations that support SSE-KMS

The following REST API operations accept the x-amz-server-side-encryption, x-amz-server-side-encryption-aws-kms-key-id, and x-amz-server-side-encryption-context request headers.

• PutObject – When you upload data by using the PUT API operation, you can specify these request headers.

• CopyObject – When you copy an object, you have both a source object and a target object. When you pass SSE-KMS headers with the COPY operation, they are applied only to the target object. When you're copying an existing object, regardless of whether the source object is encrypted or not, the destination object is not encrypted unless you explicitly request server-side encryption.

• POST Object – When you use a POST operation to upload an object, instead of the request headers, you provide the same information in the form fields.

• CreateMultipartUpload – When you upload large objects by using the multipart upload API operation, you can specify these headers. You specify these headers in the Initiate Multipart Upload request.

The response headers of the following REST API operations return the x-amz-server-side-encryption header when an object is stored by using server-side encryption.

• PutObject

• CopyObject

• POST Object

• CreateMultipartUpload

• UploadPart

• UploadPartCopy

• CompleteMultipartUpload

• GetObject

• HeadObject

Important

• All GET and PUT requests for an object protected by AWS KMS fail if you don't make them using Secure Sockets Layer (SSL), Transport Layer Security (TLS), or Signature Version 4.

• If your object uses SSE-KMS, don't send encryption request headers for GET requests and HEAD requests, or you’ll get an HTTP 400 BadRequest error.

Encryption context (x-amz-server-side-encryption-context)

If you specify x-amz-server-side-encryption:aws:kms, the Amazon S3 API supports an encryption context with the x-amz-server-side-encryption-context header. An encryption context is a set of key-value pairs that contain additional contextual information about the data.

Amazon S3 automatically uses the object or bucket Amazon Resource Name (ARN) as the encryption context pair. If you use SSE-KMS without enabling an S3 Bucket Key, you use the object ARN as your encryption context; for example, arn:aws:s3:::object_ARN. However, if you use SSE-KMS and enable an S3 Bucket Key, you use the bucket ARN for your encryption context; for example, arn:aws:s3:::bucket_ARN.

You can optionally provide an additional encryption context pair by using the x-amz-server-side-encryption-context header. However, because the encryption context is not encrypted, make sure it does not include sensitive information. Amazon S3 stores this additional key pair alongside the default encryption context.

For information about the encryption context in Amazon S3, see Encryption context. For general information about the encryption context, see AWS Key Management Service Concepts - Encryption context in the AWS Key Management Service Developer Guide.

AWS KMS key ID (x-amz-server-side-encryption-aws-kms-key-id)

You can use the x-amz-server-side-encryption-aws-kms-key-id header to specify the ID of the customer managed key that's used to protect the data. If you specify the x-amz-server-side-encryption:aws:kms header but don't provide the x-amz-server-side-encryption-aws-kms-key-id header, Amazon S3 uses the AWS managed key (aws/s3) to protect the data. If you want to use a customer managed key, you must provide the x-amz-server-side-encryption-aws-kms-key-id header of the customer managed key.

Important

When you use an AWS KMS key for server-side encryption in Amazon S3, you must choose a symmetric encryption KMS key. Amazon S3 supports only symmetric encryption KMS keys. For more information about these keys, see Symmetric encryption KMS keys in the AWS Key Management Service Developer Guide.

S3 Bucket Keys (x-amz-server-side-encryption-aws-bucket-key-enabled)

You can use the x-amz-server-side-encryption-aws-bucket-key-enabled request header to enable or disable an S3 Bucket Key at the object-level. S3 Bucket Keys reduce your AWS KMS request costs by decreasing the request traffic from Amazon S3 to AWS KMS. For more information, see Reducing the cost of SSE-KMS with Amazon S3 Bucket Keys.

If you specify the x-amz-server-side-encryption:aws:kms header but don't provide the x-amz-server-side-encryption-aws-bucket-key-enabled header, your object uses the S3 Bucket Key settings for the destination bucket to encrypt your object. For more information, see Configuring an S3 Bucket Key at the object level.

Using the AWS CLI

When you upload a new object or copy an existing object, you can specify the use of server-side encryption with AWS KMS keys to encrypt your data. To do this, add the --server-side-encryption aws:kms header to the request. Use the --ssekms-key-id example-key-id to add your customer managed AWS KMS key that you created. If you specify --server-side-encryption aws:kms, but do not provide an AWS KMS key ID, then Amazon S3 will use an AWS managed key.

aws s3api put-object --bucket DOC-EXAMPLE-BUCKET --key example-object-key --server-side-encryption aws:kms -–ssekms-key-id example-key-id --body filepath

You can additionally enable or disable Amazon S3 Bucket Keys on your PUT or COPY operations by adding -- bucket-key-enabled or --no-bucket-key-enabled. Amazon S3 Bucket Keys can reduce your AWS KMS request costs by decreasing the request traffic from Amazon S3 to AWS KMS. For more information, see Reducing the cost of SSE-KMS with Amazon S3 Bucket Keys.

aws s3api put-object --bucket DOC-EXAMPLE-BUCKET --key example-object-key --server-side-encryption aws:kms --bucket-key-enabled --body filepath

You can encrypt an unencrypted object to use SSE-KMS by copying the object back in place.

aws s3api copy-object --bucket DOC-EXAMPLE-BUCKET --key example-object-key --body filepath --bucket DOC-EXAMPLE-BUCKET --key example-object-key --sse aws:kms --sse-kms-key-id example-key-id --body filepath

Using the AWS SDKs

When using AWS SDKs, you can request Amazon S3 to use AWS KMS keys for server-side encryption. This section provides examples of using the AWS SDKs for Java and .NET. For information about other SDKs, go to Sample Code and Libraries.

Important

When you use an AWS KMS key for server-side encryption in Amazon S3, you must choose a symmetric encryption KMS key. Amazon S3 supports only symmetric encryption KMS keys. For more information about these keys, see Symmetric encryption KMS keys in the AWS Key Management Service Developer Guide.

Copy operation

When copying objects, you add the same request properties (ServerSideEncryptionMethod and ServerSideEncryptionKeyManagementServiceKeyId) to request Amazon S3 to use an AWS KMS key. For more information about copying objects, see Copying objects.

PUT operation

Java

When uploading an object by using the AWS SDK for Java, you can request Amazon S3 to use an AWS KMS key by adding the SSEAwsKeyManagementParams property as shown in the following request.

PutObjectRequest putRequest = new PutObjectRequest(bucketName,
   keyName, file).withSSEAwsKeyManagementParams(new SSEAwsKeyManagementParams());

In this case, Amazon S3 uses the AWS managed key (aws/s3) (see Protecting data using server-side encryption with AWS Key Management Service keys (SSE-KMS). You can optionally create a symmetric encryption KMS key and specify that in the request.

PutObjectRequest putRequest = new PutObjectRequest(bucketName,
   keyName, file).withSSEAwsKeyManagementParams(new SSEAwsKeyManagementParams(keyID));

For more information about creating customer managed keys, see Programming the AWS KMS API in the AWS Key Management Service Developer Guide.

For working code examples of uploading an object, see the following topics. To use these examples, you must update the code examples and provide encryption information as shown in the preceding code fragment.

• For uploading an object in a single operation, see Uploading objects.

• For a multipart upload, see the following topics:

  • Using the high-level multipart upload API, see Uploading an object using multipart upload.

  • Using the low-level multipart upload API, see Using the AWS SDKs (low-level API).

.NET

When uploading an object by using the AWS SDK for .NET, you can request Amazon S3 to use an AWS KMS key by adding the ServerSideEncryptionMethod property as shown in the following request.

PutObjectRequest putRequest = new PutObjectRequest
 {
     BucketName = DOC-EXAMPLE-BUCKET,
     Key = keyName,
     // other properties.
     ServerSideEncryptionMethod = ServerSideEncryptionMethod.AWSKMS
 };

In this case, Amazon S3 uses the AWS managed key. For more information, see Protecting data using server-side encryption with AWS Key Management Service keys (SSE-KMS). You can optionally create your own symmetric encryption customer managed key and specify that in the request.

PutObjectRequest putRequest1 = new PutObjectRequest
{
  BucketName = DOC-EXAMPLE-BUCKET,
  Key = keyName,
  // other properties.
  ServerSideEncryptionMethod = ServerSideEncryptionMethod.AWSKMS,
  ServerSideEncryptionKeyManagementServiceKeyId = keyId
};

For more information about creating customer managed keys, see Programming the AWS KMS API in the AWS Key Management Service Developer Guide.

For working code examples of uploading an object, see the following topics. To use these examples, you must update the code examples and provide encryption information as shown in the preceding code fragment.

• For uploading an object in a single operation, see Uploading objects.

• For multipart upload, see the following topics:

  • Using the high-level multipart upload API, see Uploading an object using multipart upload.

  • Using the low-level multipart upload API, see Uploading an object using multipart upload.

Presigned URLs

Java

When creating a presigned URL for an object encrypted with an AWS KMS key, you must explicitly specify Signature Version 4.

ClientConfiguration clientConfiguration = new ClientConfiguration();
clientConfiguration.setSignerOverride("AWSS3V4SignerType");
AmazonS3Client s3client = new AmazonS3Client(
        new ProfileCredentialsProvider(), clientConfiguration);
...

For a code example, see Sharing objects using presigned URLs.

.NET

When creating a presigned URL for an object encrypted with an AWS KMS key, you must explicitly specify Signature Version 4.

AWSConfigs.S3Config.UseSignatureVersion4 = true;

For a code example, see Sharing objects using presigned URLs.