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encryptionkeyrsapassword-protection
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Reputation: 862

En/decrypt data using password without database admin being able to decrypt it

This is a more conceptual question, but I'm trying to have some content be made available only to a specific user at a time. To do so, I thought about using a users password as an encryption key. However, the problem with that is that if I encrypt it using the plaintext password, I won't be able to encrypt anything as I'm obviously storing a hashed version in my database. If I encrypt it using the hashed password, then any database admin will be able to read the content of every user.

So basically, I need some kind of public/private key concept where I can encrypt it with a users public key but only they have access to their private key to decrypt it. Using actual RSA keys will be annoying in terms of usability though, as a user would have to write down their private key somewhere.

Is there a clever way for me to store data in a way that only a specific user can see it, somehow accessible through a password they set without being able to see their data as a server admin?

Example, assuming a website:

Random person chooses a receiver person, writes a message. That message should be stored in encrypted form in the database, using some form of public key.

Receiver person enters their password (Not a huge RSA key, optimally, but a standard passphrase), on the server side this password will be treated as some form of private key in order to deencrypt the data and send it back to the client.

So basically, I want to treat a simple passphrase as a private key, and generate a corresponding public key for it.

Upvotes: 1

Views: 503

Answers (1)

Maxim Sagaydachny
Maxim Sagaydachny

Reputation: 2218

It looks like you want to use the same password for both authentication and for encryption.

Lets assume that only hashes of passwords are stored in a database (as it should be).

Issues:

  • "Remember me" function of web/mobile/desktop app will render encryption function impossible because user can log-in without password via token.
  • Admin can intercept login request to know user's password while it is transmitted in plain-text over https (simple infrastructure reconfiguration allows admin to sniff on traffic).

There is a way to secure transfers by using the same password in case:

  • you change your authentication procedure in a way that user sends to the server hashes only instead of plain-text password
  • and will save plain-text password at client side (for "remember me" scenario)

Then you could generate key pair during registration and save encrypted private key at server. This way you will have access to your private key even after client side reinstallation (web/mobile/desktop).

So upon login you request your private key from server and use password which was used for authentication to decrypt your private key.

If you trust that admin(or whoever else) will not be able to meddle with software (especially in key exchange phase) then you have a way to implement the feature you need.

This will be hacker-proof solution until someone patches your code and every user in system gets wrong public keys of other users.

Upvotes: 1

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