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Date: Sat, 15 Sep 2018 20:18:19 +0100
From: RW <rwmaillists@googlemail.com>
To: freebsd-geom@freebsd.org
Subject: Re: geli - why do I need a keyfile
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On Fri, 14 Sep 2018 17:55:58 -0700
Lee Brown wrote:

> I want to create a geli provider as authentication only, no password,
> no encryption.  I do:
...
> Instead:
> # echo " " > /tmp/key
> solves that issue, but I still don't get why I even need a key file
> with -e NULL?

Because HMAC itself needs an encrypted secret key, otherwise anyone
could write to the device without it being detectable. 

Without a securely entered passphase, or a passfile on removable media,
HMAC doesn't provide any authentication, it just detects bitrot and
naive attempts to modify the filesystem.