S3 Error download file SSE

The error message you're encountering suggests that the object you're trying to download was stored using server-side encryption (SSE), and the correct parameters are required to retrieve it. This situation can occur even if you haven't explicitly set up encryption, as Amazon S3 uses default encryption for all new objects.

To resolve this issue, you can try the following steps:

1. Check the encryption settings for the specific object:

   • In the S3 console, navigate to the object's properties.
   • Look for the "Server-side encryption settings" section to see what type of encryption is being used.

2. If the object is using SSE-S3 (Amazon S3-managed keys), which is the default, you shouldn't need to provide additional parameters. Try downloading the object using the AWS CLI or SDK to see if it provides more detailed error information.

3. If the object is using SSE-KMS (AWS Key Management Service), ensure that you have the necessary permissions to use the KMS key associated with the object.

4. If the object is using SSE-C (Customer-provided keys), you'll need to provide the original encryption key to download the object. This is less likely if you haven't explicitly set up custom encryption.

5. If you're unable to determine the encryption type or still can't download the object, you may need to contact AWS Support for further assistance.

6. As a last resort, if the data isn't critical and you have the necessary permissions, you could try deleting the problematic object and reuploading it to the bucket.

Remember that changing encryption settings or deleting objects should be done cautiously, especially in production environments. Always ensure you have proper backups before making any changes.
Sources
Downloading objects - Amazon Simple Storage Service
Specifying server-side encryption with Amazon S3 managed keys (SSE-S3) - Amazon Simple Storage Service

The error message means that the object is encrypted on the server side by S3, but the encryption key wasn't generated by and isn't stored in S3, but instead was specified by the user when uploading the object. S3 is unable to decrypt the object when you request it, unless you provide the encryption key in the download (GetObject) request. That encryption key is the "correct parameter" that the error message is saying is missing.

This form of server-side encryption is called SSE-C, meaning server-side encryption with customer-provided keys: https://docs.aws.amazon.com/AmazonS3/latest/userguide/ServerSideEncryptionCustomerKeys.html

This can happen legitimately but inadvertently, if a developer or operator is testing different encryption options, for example, or if a third-party application or partner uploads object encrypted with SSE-C intentionally but without the knowledge of the AWS infrastructure staff. However, encrypting objects with SSE-C is also a reasonably well-known way for hackers to encrypt their victim's data in the hopes of holding the encryption key for ransom. The latter scenario has been discussed recently several times on re:Post. One recent discussion where I also provided sample CLI commands to reproduce the problem for testing purposes is here: https://repost.aws/questions/QUdzIgyxIkSCC00MtfabGsuA/s3-server-side-encryption-settings