linux-ext4 - Re: [PATCH] fscrypt: add a documentation file for filesystem-level encryption

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Message-Id: <8EA94C5A-A3F7-48BC-91BE-3C0BD17D7927@dilger.ca>
Date:   Fri, 18 Aug 2017 15:06:52 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     linux-fscrypt@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Richard Weinberger <richard@....at>,
        Michael Halcrow <mhalcrow@...gle.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH] fscrypt: add a documentation file for filesystem-level
 encryption

On Aug 18, 2017, at 1:47 PM, Eric Biggers <ebiggers3@...il.com> wrote:
> +Key hierarchy
> +=============
> +
> +Master Keys
> +-----------
> +
> +Userspace should generate master keys either using a cryptographically
> +secure random number generator, e.g. by reading from ``/dev/urandom``
> +or calling getrandom(), or by using a KDF (Key Derivation Function).
> +Note that whenever a KDF is used to "stretch" a lower-entropy secret
> +such as a passphrase, it is critical that a KDF designed for this
> +purpose be used, such as scrypt, PBKDF2, or Argon2.

One minor suggestion - when generating a master key for a filesystem,
I'd think it is preferable to use /dev/random instead of /dev/urandom
to ensure there is enough entropy.

Cheers, Andreas






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