Securely storing (encrypting) data in an ASP.Net application

I have an asp.net application, accessed by people over the internet using web browsers. It runs on a web server and it talks to a backend database.

Some of the users would like to use the application to store some private data. The requirements of this are:

1) Only开发者_JS百科 the user who stored the data should be able to see it.

2) The developers/dbas should not be able to see the data.

3) If the web server and database server were compromised a hacker must not be able to decrypt the data.

So, it's obvious I'm going to have to encrypt this data. If I encrypt it there will be a key somewhere and probably a salt/IV. The question is where do I store the data which is used to perform the decryption? If I store it in the database or the web server then a developer, dba or hacker can access it and decrypt the data.

I think my ideal solution to this would be for the private key to be on the clients machine, that way they are entirely responsible for it. But I'm not sure of how to go about this with an asp.net web application.

I believe I can create a certificate which also stores a private key (PFX). The client companies could use group policy to deploy the certificate to their domain. But it is possible that the ASP.Net application can request the web browser to send the private key to it so that it can perform the decryption? Decrypting on the client would be best but other than creating something in javascript I don't see how this is possible.

Any advice welcome.

Store the key in the mind of the user. Use any password/passphrase based key derivation algorithm you like. The standard is PBKDF2. The optimum choice of algorithm will depend on precisely what your security requirements and threat mode is. Ideally, that decision and the implementation should at least be reviewed by a security expert.

Is it possible that you deploy a ClickOnce application as a part of your solution? The ClickOnce could easily access the cert store on a local machine thus allowing you to perform client-side encryption.