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<div class="moz-cite-prefix">On 27.02.2015 02:23, Tom Mitchell
wrote:<br>
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cite="mid:CAAMy4UQZuEJWWUthYLT9SSuOXbJP_maHsAUb_1h1prU7H8UeoQ@mail.gmail.com"
type="cite">
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<div class="gmail_quote">On Wed, Feb 25, 2015 at 8:57 AM, Ralf
Senderek <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:crypto@senderek.ie" target="_blank">crypto@senderek.ie</a>></span>
wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
Are there any major problems with this threat model from
your point of view?<br>
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<div>One possible omission... verification.</div>
<div><br>
</div>
<div>The BBB does have a possible verification path.
Verification of the flash memory image and files</div>
<div>is possible by booting from a mSD card. <br>
Double check that connecting and disconnecting a mSD card
or other device does not reset the</div>
<div>system....</div>
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The system cannot be reset by accident for a number of reasons.
First, when in the initial step the<br>
secrets are being generated, a symbolic link (as root) is created to
indicate that this Crypto Bone is<br>
initialized. If an attacker is able to remove this link inside the
Crypto Bone from outside, then the system<br>
is reset. Obviously, using a root shell inside the Crypto Bone must
be made as impossible as possible.<br>
<br>
The most likely event for this to happen is the exploitation of
OpenBSD code via smtpd or fetchmail or<br>
cron, or ..., but it will never happen by inserting a SD media. The
user can get confused, if he uses<br>
several different Crypto Bone SD cards for different identities or
purposes, but the web interface will<br>
always tell him who he is at the moment.<br>
<br>
I don't have a solution for a complete system reset at the moment at
all, because I don't want to<br>
place a button in the web interface that removes the symbolic link.
I'm open for suggestions how<br>
to do this securely, other than to insert a virgin, verified new SD
image and start from scratch.<br>
<br>
In addition, OpenBSD does not support the use of "other devices",
the only path inside the Crypto<br>
Bone leads through the network interface. To prevent that an
attacker gets a root shell via the NIC<br>
is the main concern here.<br>
<br>
<br>
I'm really interested to find out how verification can be
implemented apart from signing the mSD card<br>
image file. When the system is in use a tripwire-like IDS may help,
but the user won't be able to make<br>
sense of the scan results. What are your suggestions?<br>
<br>
<br>
--Ralf<br>
<br>
<br>
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cite="mid:CAAMy4UQZuEJWWUthYLT9SSuOXbJP_maHsAUb_1h1prU7H8UeoQ@mail.gmail.com"
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<div>This is a good step iteration may be needed in the
future but good start.</div>
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