Secure DSA Signing

Question

Can someone put my mind at rest and see if this setup will verify that a file has come from me. An idea of how secure this is would be great and any potential attack vectors.

1. Create a public and private key with DSACryptoServiceProvider.
2. Add public key as application resource
3. Create an update
4. Get dsa hash of update using private key
5. Send hash and update to application(Presume these can be intercepted/changed)
6. Verify hash is correct using public key.
7. If verified apply update

The update is an exe and will be executed so I want to make sure it's not executed if someone replaces or tampers with it.

EDIT: Updated point 6 as the public key doesn't actually generate a hash, just verifies it. I think it's this part I'm struggling with the security of.

Answer 1

Your approach looks good. The question remaining is how secure is your application on the client. Is there a chance that someone could tamper with the executable? Maybe switch the public key in the application resource?

It is getting theoretical here, but I wold suggest a small modification to step 6: Be specific which exact public key you want to use. If some attacker could switch the key in the application resource he could send an altered package with a correct hash for another private key. This may be only a minor concern since the attacker already modified your software. But if he only could replace the application resource and nothing else he would have then the ability to let your application update itself with his malicious code.