What is the point of encrypting my files (on a server); if I can decrypt them why can't a hacker do that too?

Question

I help maintain a webserver that users use. They store data on our server. Most of the data is not sensitive, but some of it is highly sensitive. So, it seems like we want to encrypt it so that if someone compromises our server, they will only find encrypted data. However, to serve up the data to users on the website, the code is essentially like (pseudocode)

encryptedFile=getEncryptedFile();
decryptedFile=decrypt(encryptedFile);
serve up decrypted file

So, if our server is compromised, what is to stop the bad actor from finding this code and just running the decryption algorithm on their own? It seems like I am missing some step on how to prevent an attacker from finding the decryption key even if the server is compromised.

Essentially it boils down to: If I as a sysadmin creating the decryption system for the website can encrypt/decrypt files, what is to stop the hacker who compromises my server with root level access from the doing the same thing?

Answer 1

I don't know what decrypt() does, but you probably mean your OS-specific cryptography API. On Windows, this is protected with your account password. If the data gets downloaded or stolen, it will be much harder to read, even knowing you password. When your server is rooted, all bets are off, this just obfuscates it.

Answer 2

There's really two ways that one would encrypt all the data stored on a server:

1. Using a backed which encrypts the data in some way, ie. Any sort of vault that locks unlocks etc. If you don't automate the unlocking, or require some sort of authentication for every call to retrieve data and if this is not automated, then you should be able to force the ability to access your data away from the server (for example if only a client key could decrypt the response then you're safe because you can't decrypt it and therefore neither can an attacker

   2. Using something like LUKS to encrypt the server. This is a similar approach to the above but the initial unlock is basically just going to be booting the server.

Ideally you would always encrypt the disks so that your data can't be compromised by anyone with access to the server.

Depending on your role in serving sensitive data (ie. Do you own it?) Then it's probably worth also forcing clients to authorise their own access by either providing the keys as part of the request or providing the keys as part of their local application in order to decrypt the data you return.

Really, except for the case where a client needs to not only authenticate to access your system, but they also need to know some other secret to decrypt the data once they retrieve it (where the decryption key is not stored on the server, but is unique to each client), if someone gets root access to the box while it's online you're pretty much able to consider all the data compromised.