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SubjectRe: eCryptfs Design Document
Michael Halcrow wrote:
> * A mount-wide passphrase is stored in the user session
> keyring in the form of an authentication token.

I'm a bit confused because you appear to be contradicting yourself. You
say several times that a mount-wide passphrase is used for the master
key. If that is the case, then it would be given at mount time and be
bound to the super block. You also then say that the master key is
stored in the kernel keyring. If that is the case, then you don't have
to know the key at mount time, rather the key is associated with a given
process or group of processes and will be required when such a process
attempts to open a file on that mount point. This would also allow
different users to use different keys.


So which is it? Is the master key bound to the superblock, or to the
session keyring? Or am I just confused about the meaning of the kernel
keyring?

> passphrase into a key follows the S2K process as described in RFC
> 2440, in that the passphrase is concatenated with a salt; that data
> block is then iteratively MD5-hashed 65,536 times to generate the key
> that encrypts the file encryption key.


Are you saying that you salt the passphrase, hash that, then hash the
hash, then hash that hash, and so on? What good does repeatedly hashing
the hash do? Simply hashing the salted passphrase should be sufficient
to obtain a key.


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