Modify an MP3 slightly to change the data appearence
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I'm thinking about encrypting MP3s in a database, so that when user is downloading them with his software desktop player, only the software can decrypt them. This part is not a problem. The problem is I don't want a user to upload an mp3 to the database, then check which changes have been made to the file so he can reverse-engineer the file or at least see which algorithm  is used to encrypt the files.

So, user uploads MP3-A, then it becomes MP3-B because it has been modified, and I encrypt it to MP3-C. And when decrypted, it sounds 99.99% like MP3-A.

I know MP3 format is lossy, but I wonder if there's a way to convert audio with limited loss, or if I need to forget it right now.