Encrypting 3rd party credentials

Question

I have an application where I need to store 3rd party credentials to services like Amazon S3, FTP, SFTP, etc..

I know that it is possible to access some of those sys

Answer 1

Have the user supply a (strong) password when they set up an account (before they provide their passwords). Then encrypt all data for that account within your database using a key derived from a strong hash (SHA256 or something like that) of the user's password. That way if your servers get compromised, no data will be revealed because it is encrypted with the user's password (well, a hash of the user's password) and that password is not stored anywhere on your server.