Category: <span>Amazon Simple Storage Service (S3)</span>

Amazon S3 Encrypts New Objects By Default

At AWS, security is the top priority. Starting today, Amazon Simple Storage Service (Amazon S3) encrypts all new objects by default. Now, S3 automatically applies server-side encryption (SSE-S3) for each new object, unless you specify a different encryption option. SSE-S3 was first launched in 2011. As Jeff wrote at the time: “Amazon S3 server-side encryption handles all encryption, decryption, and key management in a totally transparent fashion. When you PUT an object, we generate a unique key, encrypt your data with the key, and then encrypt the key with a [root] key.”

This change puts another security best practice into effect automatically—with no impact on performance and no action required on your side. S3 buckets that do not use default encryption will now automatically apply SSE-S3 as the default setting. Existing buckets currently using S3 default encryption will not change.

As always, you can choose to encrypt your objects using one of the three encryption options we provide: S3 default encryption (SSE-S3, the new default), customer-provided encryption keys (SSE-C), or AWS Key Management Service keys (SSE-KMS). To have an additional layer of encryption, you might also encrypt objects on the client side, using client libraries such as the Amazon S3 encryption client.

While it was simple to enable, the opt-in nature of SSE-S3 meant that you had to be certain that it was always configured on new buckets and verify that it remained configured properly over time. For organizations that require all their objects to remain encrypted at rest with SSE-S3, this update helps meet their encryption compliance requirements without any additional tools or client configuration changes.

With today’s announcement, we have now made it “zero click” for you to apply this base level of encryption on every S3 bucket.

Verify Your Objects Are Encrypted
The change is visible today in AWS CloudTrail data event logs. You will see the changes in the S3 section of the AWS Management Console, Amazon S3 Inventory, Amazon S3 Storage Lens, and as an additional header in the AWS CLI and in the AWS SDKs over the next few weeks. We will update this blog post and documentation when the encryption status is available in these tools in all AWS Regions.

To verify the change is effective on your buckets today, you can configure CloudTrail to log data events. By default, trails do not log data events, and there is an extra cost to enable it. Data events show the resource operations performed on or within a resource, such as when a user uploads a file to an S3 bucket. You can log data events for Amazon S3 buckets, AWS Lambda functions, Amazon DynamoDB tables, or a combination of those.

Once enabled, search for PutObject API for file uploads or InitiateMultipartUpload for multipart uploads. When Amazon S3 automatically encrypts an object using the default encryption settings, the log includes the following field as the name-value pair: "SSEApplied":"Default_SSE_S3". Here is an example of a CloudTrail log (with data event logging enabled) when I uploaded a file to one of my buckets using the AWS CLI command aws s3 cp backup.sh s3://private-sst.

Cloudtrail log for S3 with default encryption enabled

Amazon S3 Encryption Options
As I wrote earlier, SSE-S3 is now the new base level of encryption when no other encryption-type is specified. SSE-S3 uses Advanced Encryption Standard (AES) encryption with 256-bit keys managed by AWS.

You can choose to encrypt your objects using SSE-C or SSE-KMS rather than with SSE-S3, either as “one click” default encryption settings on the bucket, or for individual objects in PUT requests.

SSE-C lets Amazon S3 perform the encryption and decryption of your objects while you retain control of the keys used to encrypt objects. With SSE-C, you don’t need to implement or use a client-side library to perform the encryption and decryption of objects you store in Amazon S3, but you do need to manage the keys that you send to Amazon S3 to encrypt and decrypt objects.

With SSE-KMS, AWS Key Management Service (AWS KMS) manages your encryption keys. Using AWS KMS to manage your keys provides several additional benefits. With AWS KMS, there are separate permissions for the use of the KMS key, providing an additional layer of control as well as protection against unauthorized access to your objects stored in Amazon S3. AWS KMS provides an audit trail so you can see who used your key to access which object and when, as well as view failed attempts to access data from users without permission to decrypt the data.

When using an encryption client library, such as the Amazon S3 encryption client, you retain control of the keys and complete the encryption and decryption of objects client-side using an encryption library of your choice. You encrypt the objects before they are sent to Amazon S3 for storage. The Java, .Net, Ruby, PHP, Go, and C++ AWS SDKs support client-side encryption.

You can follow the instructions in this blog post if you want to retroactively encrypt existing objects in your buckets.

Available Now
This change is effective now, in all AWS Regions, including on AWS GovCloud (US) and AWS China Regions. There is no additional cost for default object-level encryption.

— seb

Heads-Up: Amazon S3 Security Changes Are Coming in April of 2023

Starting in April of 2023 we will be making two changes to Amazon Simple Storage Service (Amazon S3) to put our latest best practices for bucket security into effect automatically. The changes will begin to go into effect in April and will be rolled out to all AWS Regions within weeks.

Once the changes are in effect for a target Region, all newly created buckets in the Region will by default have S3 Block Public Access enabled and access control lists (ACLs) disabled. Both of these options are already console defaults and have long been recommended as best practices. The options will become the default for buckets that are created using the S3 API, S3 CLI, the AWS SDKs, or AWS CloudFormation templates.

As a bit of history, S3 buckets and objects have always been private by default. We added Block Public Access in 2018 and the ability to disable ACLs in 2021 in order to give you more control, and have long been recommending the use of AWS Identity and Access Management (IAM) policies as a modern and more flexible alternative.

In light of this change, we recommend a deliberate and thoughtful approach to the creation of new buckets that rely on public buckets or ACLs, and believe that most applications do not need either one. If your application turns out to be one that does, then you will need to make the changes that I outline below (be sure to review your code, scripts, AWS CloudFormation templates, and any other automation).

What’s Changing
Let’s take a closer look at the changes that we are making:

S3 Block Public Access – All four of the bucket-level settings described in this post will be enabled for newly created buckets:

A subsequent attempt to set a bucket policy or an access point policy that grants public access will be rejected with a 403 Access Denied error. If you need public access for a new bucket you can create it as usual and then delete the public access block by calling DeletePublicAccessBlock (you will need s3:PutBucketPublicAccessBlock permission in order to call this function; read Block Public Access to learn more about the functions and the permissions).

ACLs Disabled – The Bucket owner enforced setting will be enabled for newly created buckets, making bucket ACLs and object ACLs ineffective, and ensuring that the bucket owner is the object owner no matter who uploads the object. If you want to enable ACLs for a bucket, you can set the ObjectOwnership parameter to ObjectWriter in your CreateBucket request or you can call DeleteBucketOwnershipControls after you create the bucket. You will need s3:PutBucketOwnershipControls permission in order to use the parameter or to call the function; read Controlling Ownership of Objects and Creating a Bucket to learn more.

Stay Tuned
We will publish an initial What’s New post when we start to deploy this change and another one when the deployment has reached all AWS Regions. You can also run your own tests to detect the change in behavior.

Jeff