Anything that was encrypted by our software can only be decrypted by it, so currently there's no other option.

You can probably use something like Amazon AWS S3 KMS Encryption to encrypt objects in S3 and control the access to such objects using IAM controls, all without using our client-side encryption. All data in transit can be encrypted using SSL in CloudBerry Explorer. Have a look at these posts and see if it works for you: https://www.cloudberrylab.com/resources/blog/using-aws-kms-with-explorer/ https://docs.aws.amazon.com/kms/latest/developerguide/services-s3.html