Encrypting files in AWS S3 using Java API

aws

If you use AWS S3 Java API, and would like to see how you can encrypt files on S3, this post is for you.

First of all, there are two ways you can encrypt files in S3. One is to encrypt files on the server side, and one is to encrypt files on the client side. With using the server side option, you don’t have to worry about too much. S3 encrypts the files for you when they are written to disk, and decrypts them when they are read, seamlessly. With the client side option, the client (your application) has to encrypt files before transmitting them to S3, and decrypt them after receiving the file from S3.

In this post I’ll cover server side encryption. We opted to use this one because it’s just simpler, and seamless. You don’t have to worry about encrypting/decrypting files yourself, nor do you have to worry about the key.

I’m assuming that you’re already familiar with the AWS Java API. For most things related to S3, AWS provides a class called AmazonS3Client. Once you have AmazonS3Client instantiated with your configuration, you will need to enable encryption in the matadata for each file you upload.

Example:

File fileForUpload = new File(...);
AmazonS3Client amazonS3Client = new AmazonS3Client(...);
ObjectMetadata meta = new ObjectMetadata();
meta.setContentType(URLConnection.guessContentTypeFromName(fileForUpload.getName()));
meta.setSSEAlgorithm(ObjectMetadata.AES_256_SERVER_SIDE_ENCRYPTION);
amazonS3Client.putObject(s3Bucket, s3FullDestinationPath, new FileInputStream(fileForUpload), meta);

Let’s examine. First you instantiate the File you want to upload, and AmazonS3Client. Next you set the metadata on the file. This includes setting the content type of the file (important because having the wrong content-type can cause issues down the line), and sets the encryption flag for the file. Then when you upload the file using AmazonS3Client.putObject(…), the file will be encrypted by S3 before it is stored, and automatically decrypted when it is retrieved, all by S3’s servers. And that’s it!

Note that according to AWS Java API documentation, AmazonS3Client uses SSL under the hood so you don’t have to worry about transmitting unencrypted files over the network.

Leave a Reply