serverSideEncryption

The server-side encryption algorithm that was used when you store this object in Amazon S3 or Amazon FSx.

• **General purpose buckets ** - You have four mutually exclusive options to protect data using server-side encryption in Amazon S3, depending on how you choose to manage the encryption keys. Specifically, the encryption key options are Amazon S3 managed keys (SSE-S3), Amazon Web Services KMS keys (SSE-KMS or DSSE-KMS), and customer-provided keys (SSE-C). Amazon S3 encrypts data with server-side encryption by using Amazon S3 managed keys (SSE-S3) by default. You can optionally tell Amazon S3 to encrypt data at rest by using server-side encryption with other key options. For more information, see Using Server-Side Encryption in the Amazon S3 User Guide.

• **Directory buckets ** - For directory buckets, there are only two supported options for server-side encryption: server-side encryption with Amazon S3 managed keys (SSE-S3) (AES256) and server-side encryption with KMS keys (SSE-KMS) (aws:kms). We recommend that the bucket's default encryption uses the desired encryption configuration and you don't override the bucket default encryption in your CreateSession requests or PUT object requests. Then, new objects are automatically encrypted with the desired encryption settings. For more information, see Protecting data with server-side encryption in the Amazon S3 User Guide. For more information about the encryption overriding behaviors in directory buckets, see Specifying server-side encryption with KMS for new object uploads. In the Zonal endpoint API calls (except CopyObject and UploadPartCopy) using the REST API, the encryption request headers must match the encryption settings that are specified in the CreateSession request. You can't override the values of the encryption settings (x-amz-server-side-encryption, x-amz-server-side-encryption-aws-kms-key-id, x-amz-server-side-encryption-context, and x-amz-server-side-encryption-bucket-key-enabled) that are specified in the CreateSession request. You don't need to explicitly specify these encryption settings values in Zonal endpoint API calls, and Amazon S3 will use the encryption settings values from the CreateSession request to protect new objects in the directory bucket. When you use the CLI or the Amazon Web Services SDKs, for CreateSession, the session token refreshes automatically to avoid service interruptions when a session expires. The CLI or the Amazon Web Services SDKs use the bucket's default encryption configuration for the CreateSession request. It's not supported to override the encryption settings values in the CreateSession request. So in the Zonal endpoint API calls (except CopyObject and UploadPartCopy), the encryption request headers must match the default encryption configuration of the directory bucket.

• **S3 access points for Amazon FSx ** - When accessing data stored in Amazon FSx file systems using S3 access points, the only valid server side encryption option is aws:fsx. All Amazon FSx file systems have encryption configured by default and are encrypted at rest. Data is automatically encrypted before being written to the file system, and automatically decrypted as it is read. These processes are handled transparently by Amazon FSx.