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1

Yes it is possible and already in use in multiple way (LUKS for example). The way it works: Have a master key that encrypts the whole data Append a header in front that contains the master key encrypted by the password you want To add a password add a keyslot (master key encrypted by another password) To revoke a password remove said keyslot (the user ...


1

all those concerns have been studied a lot and still are. I'll try to give some keywords for them. a web app that stores all data on the server in a way that the server can't decrypt the data even if it wanted to. Solution for this is User-side encryption. That's why, forget about the server chosing the encryption key himself. It's quite well spread ...


0

First observe that the password is all that protects the user's data from the server. There is no security added by the public and private keys. Here's a simple solution that should work reasonably well. It may even be secure... Assumptions We rely on a secure symmetric cryptosystem $(E,D)$ that supports authenticated data, that is, $c = E(k, ad, m)$ and ...


1

The password P in the Microsoft implementation is first encoded using UTF-8. The iteration count c defaults to the value 100, and the hash algorithm Hash to SHA-1. The output is identical to PBKDF1 up to the maximum output size of PBKDF1, which is the output size of the hash. After that the first-to-last hash is prefixed with a counter (as a string ...


2

As CodesInChaos pointed out, the major flaw with this is that filenames aren't unique. If you did this on a large scale, anyone who's been given a key for a filename could decrypt any file with that filename. Even if the contents of the file are different, and they weren't intended to be given access to that file. Here's another solution that has one unique ...


2

Yes, it's safe, as you can't calculate the secret key from the HMAC result. HMAC would be useless without this feature No, Bob will not be able to use his key to calculate the other keys, as long as you use a reasonable hash function (SHA-2 should fit) It's the same as 1., Bob doesn't get more information by more derived keys But when Bob get the key for ...



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