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<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3DUTF=
-8">
  </head>
  <body>
    <p>On 24.11.24 23:01, Giridhar Mandyam wrote:</p>
    <blockquote type=3D"cite"
cite=3D"mid:CAHAF5K0Ho_v5EgCSogMjhE5AsN6oYnnHgvVbAu7iyGp3stXzMw@mail.gmai=
l.com">
      <meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3DU=
TF-8">
      <div dir=3D"ltr">
        <div dir=3D"ltr">&gt;<span style=3D"white-space-collapse: preserv=
e;">I
            am struggling to understand what would be the benefit of the
            device generating a nonce itself? </span></div>
        <div dir=3D"ltr"><span style=3D"white-space-collapse: preserve;">=
<br>
          </span></div>
        <div><span style=3D"white-space-collapse: preserve;">When there i=
s
            no return channel from the verifier, then a nonce generated
            on the device could provide some level of assurance (as
            imperfect as it is). For instance, several years ago when we
            were developing ATSC 3.0 (an IP over Broadcast technology),
            we were looking into whether the rendering device could be
            attestable. Unfortunately, the transport (</span><a
            href=3D"https://datatracker.ietf.org/doc/rfc9223/"
            moz-do-not-send=3D"true" class=3D"moz-txt-link-freetext">http=
s://datatracker.ietf.org/doc/rfc9223/</a>)
          does not provide for a return channel.</div>
        <div><br>
        </div>
      </div>
    </blockquote>
    <p>Not sure if get the term "return channel" right. RFC9223 does not
      define it. RFC4949 does not define it either. Here is my thought:<b=
r>
    </p>
    <ul>
      <li>How would a device know when to send the attestation? The
        verifier would somehow request the attestation. The same channel
        over which it sends the request, it could also send the nonce
        within that request.=C2=A0</li>
    </ul>
    <ul>
      <li>The attester still has to send over the evidence; the same
        channel over which it sends the evidence, it could send the
        evidence containing that signed nonce.=C2=A0</li>
    </ul>
    <p>So why is a "return channel" required?</p>
    <blockquote type=3D"cite"
cite=3D"mid:CAHAF5K0Ho_v5EgCSogMjhE5AsN6oYnnHgvVbAu7iyGp3stXzMw@mail.gmai=
l.com">
      <div dir=3D"ltr">
        <div>A device-generated nonce provides the same kind of replay
          protection as a jti (<a
href=3D"https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.7"
            moz-do-not-send=3D"true" class=3D"moz-txt-link-freetext">http=
s://datatracker.ietf.org/doc/html/rfc7519#section-4.1.7</a>)
          in my opinion.</div>
        <div><br>
        </div>
      </div>
    </blockquote>
    <p>I disagree with the following statement in that section unless
      the Verifier keeps a state of all the jti's: <br>
    </p>
    <p>"<span style=3D"white-space: pre-wrap">The "jti" claim can be used=
</span></p>
    <pre class=3D"newpage"
style=3D"box-sizing: border-box; font-family: var(--bs-font-monospace); f=
ont-size: 16px; margin: -1.25em 0px 0px; display: block; overflow: visibl=
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1); font-style: normal; font-variant-ligatures: normal; font-variant-caps=
: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-alig=
n: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing=
: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 25=
5); text-decoration-thickness: initial; text-decoration-style: initial; t=
ext-decoration-color: initial;">   to prevent the JWT from being replayed=
=2E"=20

Is jti signed as well? Even then, nothing stops the adversary from reorde=
ring. Here is a sample issue (simple Attester-Verifier interaction):
</pre>
    <ul>
      <li> t=3D1: Verifier requests attestation <br>
      </li>
      <li>t=3D2: Attester in good state generates JWT1 with jti =3D "xyz"=
</li>
      <li>t=3D3: Adversary stores this JWT1 and does not forward to
        Verifier</li>
      <li>t=3D4: Adversary compromises the Attester <br>
      </li>
      <li>t=3D5: Verifier requests attestation again</li>
      <li>t=3D6: Adversary sends JWT1 from t=3D2.</li>
    </ul>
    <p>Verifier believes attester is in good state whereas it is not.=C2=A0=
</p>
    <p>I don't believe the security considerations of RFC7519 are good
      enough.<br>
    </p>
    <blockquote type=3D"cite"
cite=3D"mid:CAHAF5K0Ho_v5EgCSogMjhE5AsN6oYnnHgvVbAu7iyGp3stXzMw@mail.gmai=
l.com">
      <div dir=3D"ltr">
        <div>-Giri</div>
        <div><br>
        </div>
        <div>-Giri</div>
        <br>
        <div class=3D"gmail_quote">
          <div dir=3D"ltr" class=3D"gmail_attr">On Sun, Nov 24, 2024 at
            12:14=E2=80=AFPM Muhammad Usama Sardar &lt;<a
              href=3D"mailto:muhammad_usama.sardar@tu-dresden.de"
              moz-do-not-send=3D"true" class=3D"moz-txt-link-freetext">mu=
hammad_usama.sardar@tu-dresden.de</a>&gt;
            wrote:<br>
          </div>
          <blockquote class=3D"gmail_quote"
style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);=
padding-left:1ex">
            <div>
              <p>On 11.11.24 22:21, lgl <a
                  href=3D"http://island-resort.com" target=3D"_blank"
                  moz-do-not-send=3D"true">island-resort.com</a> wrote:</=
p>
              <blockquote type=3D"cite">There=E2=80=99s some framing in t=
he EAT
                introduction that contrasts attestation security with
                authentication security. It discusses key life cycles
                which are very different for attestation. That seems
                important to discuss in the context of using TLS for
                attestation security.</blockquote>
              <p>The second paragraph of intro was an interesting read.
                Since it states: "<span style=3D"white-space:pre-wrap">To=
 give an example of one aspect of the difference", I would naturally assu=
me there are more differences in the minds of editors. I would like to re=
ad more about it. Is there any issue/thread/meeting where this was discus=
sed? </span></p>
              <p><span style=3D"white-space:pre-wrap">Reading through the=
 privacy and security considerations, I have a couple of questions: </spa=
n></p>
              <ul>
                <li><span style=3D"white-space:pre-wrap">Sec. 8.4 states =
(emphasis my own)
</span></li>
              </ul>
              <pre
style=3D"box-sizing:border-box;font-size:0.875em;margin-top:0px;margin-bo=
ttom:0px;display:block;overflow:auto;white-space:pre-wrap;color:rgb(33,37=
,41);font-style:normal;font-variant-ligatures:normal;font-variant-caps:no=
rmal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0=
px;text-transform:none;word-spacing:0px;background-color:rgb(255,255,255)=
;text-decoration-style:initial;text-decoration-color:initial">&gt; The no=
nce claim is based on a value <b>usually</b> derived remotely (outside of=
 the entity).

</pre>
              <p><span style=3D"white-space:pre-wrap">I am struggling to =
understand what would be the benefit of the device generating a nonce its=
elf? How would the verifier/relying party make sense of this value? Moreo=
ver, t</span><span
                style=3D"white-space:pre-wrap">his directly contradicts S=
ec. 10.2 which states: (emphasis my own)</span></p>
              <p><span
style=3D"color:rgb(34,34,34);font-family:&quot;Noto Sans&quot;,Arial,Helv=
etica,sans-serif;font-size:14px;font-style:normal;font-variant-ligatures:=
normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;tex=
t-align:left;text-indent:0px;text-transform:none;word-spacing:0px;white-s=
pace:normal;background-color:rgb(255,255,255);text-decoration-style:initi=
al;text-decoration-color:initial;float:none;display:inline">&gt;
                  In this approach, an unpredictable nonce is sent by
                  the <b>appraising entity</b> and the nonce is then
                  signed and included along with the Claims in the
                  Evidence or Attestation Result.</span></p>
              <ul>
                <li>Sec. 9.3 states: (emphasis my own)<br>
                </li>
              </ul>
              <pre
style=3D"box-sizing:border-box;font-size:0.875em;margin-top:0px;margin-bo=
ttom:0px;display:block;overflow:auto;white-space:pre-wrap;color:rgb(33,37=
,41);font-style:normal;font-variant-ligatures:normal;font-variant-caps:no=
rmal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0=
px;text-transform:none;word-spacing:0px;background-color:rgb(255,255,255)=
;text-decoration-style:initial;text-decoration-color:initial">&gt; All EA=
T use MUST provide a freshness mechanism to prevent replay and <b>related=
 attacks</b>.

What are the related attacks?

Thanks,
Usama
</pre>
            </div>
            _______________________________________________<br>
            RATS mailing list -- <a href=3D"mailto:rats@ietf.org"
              target=3D"_blank" moz-do-not-send=3D"true"
              class=3D"moz-txt-link-freetext">rats@ietf.org</a><br>
            To unsubscribe send an email to <a
              href=3D"mailto:rats-leave@ietf.org" target=3D"_blank"
              moz-do-not-send=3D"true" class=3D"moz-txt-link-freetext">ra=
ts-leave@ietf.org</a><br>
          </blockquote>
        </div>
      </div>
    </blockquote>
  </body>
</html>

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