442 lines
15 KiB
XML
442 lines
15 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
|
|
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
|
|
<?rfc comments="yes"?>
|
|
<?rfc compact="yes"?>
|
|
<?rfc subcompact="no"?>
|
|
<?rfc inline="yes"?>
|
|
<?rfc sortrefs="yes"?>
|
|
<?rfc symrefs="yes"?>
|
|
<?rfc toc="yes"?>
|
|
<?rfc tocdepth="6"?>
|
|
<?rfc tocindent="yes"?>
|
|
<?rfc tocompact="yes"?>
|
|
|
|
<rfc category="std" docName="draft-ymbk-lsvr-l3dl-signing-00" ipr="trust200902">
|
|
|
|
<front>
|
|
|
|
<title>Layer 3 Discovery and Liveness Signing</title>
|
|
|
|
<author fullname="Randy Bush" initials="R." surname="Bush">
|
|
<organization>Arrcus & IIJ</organization>
|
|
<address>
|
|
<postal>
|
|
<street>5147 Crystal Springs</street>
|
|
<city>Bainbridge Island</city>
|
|
<region>WA</region>
|
|
<code>98110</code>
|
|
<country>United States of America</country>
|
|
</postal>
|
|
<email>randy@psg.com</email>
|
|
</address>
|
|
</author>
|
|
|
|
<!--
|
|
<author fullname="Russ Housley" initials="R" surname="Housley">
|
|
<organization abbrev="Vigil Security">Vigil Security, LLC</organization>
|
|
<address>
|
|
<postal>
|
|
<street>516 Dranesville Road</street>
|
|
<city>Herndon</city>
|
|
<region>VA</region>
|
|
<code>20170</code>
|
|
<country>USA</country>
|
|
</postal>
|
|
<email>housley@vigilsec.com</email>
|
|
</address>
|
|
</author>
|
|
-->
|
|
|
|
<author initials="R." surname="Austein" fullname="Rob Austein">
|
|
<organization abbrev="Arrcus">Arrcus, Inc.</organization>
|
|
<address>
|
|
<email>sra@hactrn.net</email>
|
|
</address>
|
|
</author>
|
|
|
|
<date />
|
|
|
|
<abstract>
|
|
|
|
<t>The Layer 3 Discovery and Liveness protocol OPEN PDU contains a
|
|
key which can be used to verify signatures on subsequent PDUs. This
|
|
document describes two mechanisms based on digital signatures, one
|
|
that is Trust On First Use (TOFU), and one that uses certificates to
|
|
provide authentication as well as session integrity.</t>
|
|
|
|
</abstract>
|
|
|
|
<note title="Requirements Language">
|
|
|
|
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
|
|
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
|
|
"OPTIONAL" in this document are to be interpreted as described in
|
|
BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when,
|
|
and only when, they appear in all capitals, as shown here.</t>
|
|
|
|
</note>
|
|
|
|
</front>
|
|
|
|
<middle>
|
|
|
|
<section anchor="intro" title="Introduction">
|
|
|
|
<t>The Layer 3 Discovery and Liveness protocol [old ref because new
|
|
draft not yet pushed] <xref target="I-D.ietf-lsvr-lsoe"/> OPEN PDU
|
|
contains an algorithm specifier and a key which can be used to
|
|
verify signatures on subsequent PDUs. This document describes two
|
|
methods of key generation and signing for use by L3DL, Trust On
|
|
First Use (TOFU) and a PKI-based mechanism to provide authentication
|
|
as well as session integrity.</t>
|
|
|
|
<t>The Key in the OPEN PDU SHOULD be the public key of an asymmetric
|
|
key pair. The sender signs with the private key, of course. The
|
|
device sending the OPEN may use one key for all links, a different
|
|
key for each link, or some aggregation(s) thereof.</t>
|
|
|
|
<t>In the TOFU method the OPEN key is generated on the sending
|
|
device, believed without question by the receiver, and used to
|
|
verify all subsequent PDUs from the same sender with the same Key
|
|
Type.</t>
|
|
|
|
<t>With the PKI-mechanism, an enrollment step is performed. The
|
|
public key and an identifier of the subject are put into a
|
|
certificate, which is signed by the the operational environment's
|
|
trust anchor. In this way, the relying party can be confident that
|
|
the public key is under control of the identified L3DL protocol
|
|
entity.</t>
|
|
|
|
<t>To the receiver verifying signatures on PDUs, the two methods are
|
|
indistinguishable; the key provided in the OPEN PDU is used to
|
|
verify the signatures of subsequent PDUs. The difference that
|
|
PKI-based keys may be verified against the trust anchor when the
|
|
OPEN PDU is received.</t>
|
|
|
|
<t>In the PKI method the OPEN key MUST be verified against the trust
|
|
anchor for the operational domain. It is then used to verify all
|
|
subsequent PDUs from the same peer with the same Key Type.</t>
|
|
|
|
</section>
|
|
|
|
<section anchor="tofu" title="Trust On First Use Method">
|
|
|
|
<t>There are three parts to using a key: signing PDUs, verifying
|
|
the OPEN PDU, and verifying subsequent PDUs.</t>
|
|
|
|
<section anchor="signing" title="Signing a PDU">
|
|
|
|
<t>All signed PDUs are generated in the same way:</t>
|
|
|
|
<list style="symbols">
|
|
|
|
<t>
|
|
Compose the PDU, with all fields including "Sig Type" and
|
|
"Signature Length" set, but omitting the trailing
|
|
"Signature" field itself. This is the "message to be
|
|
signed" for purposes of the signature algorithm.
|
|
</t>
|
|
|
|
<t>
|
|
Generate the signature as specified for the chosen signature
|
|
suite, using the private member of the asymmetric key pair.
|
|
In general this will involve first hashing the "message to
|
|
be signed" then signing the hash, but the precise details
|
|
may vary with the specific algorithm. The result will be a
|
|
sequence of octets, the length of which MUST be equal to the
|
|
setting of the "Signature Length" field.
|
|
</t>
|
|
|
|
<t>
|
|
Construct the complete message by appending the signature
|
|
octets to the otherwise complete message composed above.
|
|
</t>
|
|
|
|
</list>
|
|
|
|
<t>
|
|
In the case of the OPEN PDU, the message to be signed will
|
|
include the public member of the asymmetric keypair, but as
|
|
far as the signature algorithm is concerned that's just
|
|
payload, no different from any other PDU content.
|
|
</t>
|
|
|
|
</section>
|
|
|
|
<section anchor="verify-open" title="Verifying the OPEN PDU">
|
|
|
|
<t>
|
|
The process for verifying an OPEN PDU is slightly different
|
|
from the process for verifying other PDU types, because the
|
|
OPEN PDU also establishes the session key.
|
|
</t>
|
|
|
|
<list style="symbols">
|
|
|
|
<t>
|
|
Verify that the PDU is syntactically correct, and extract
|
|
the Auth Type, Key, Sig Type, and Signature fields.
|
|
</t>
|
|
|
|
<t>
|
|
Verify that Auth Type and Sig Type refer to the same
|
|
algorithm suite, and that said algorithm suite is one that
|
|
the implementation understands.
|
|
</t>
|
|
|
|
<t>
|
|
Construct the "message to be verified" by truncating the PDU
|
|
to remove the Signature field (in practice this should not
|
|
require copying any data, just subtract the signature length
|
|
from the PDU length).
|
|
</t>
|
|
|
|
<t>
|
|
Verify the message constructed above against the public key
|
|
using the rules for the specific signature suite.
|
|
</t>
|
|
|
|
<t>
|
|
Record Auth Type and Key as this sessions's authentication
|
|
type and session key, for use in verifying subseuqent PDUs.
|
|
</t>
|
|
|
|
</list>
|
|
|
|
<t>
|
|
If any of the above verification steps fail, generate an error
|
|
using error code 2 ("Authorization failure in OPEN").
|
|
</t>
|
|
|
|
<!--
|
|
Why are we using a different error code for failures in OPEN
|
|
PDUs than we do in other PDUs? We don't want to provide an
|
|
oracle, so we want to return the same error code for any
|
|
verification failure for a particular PDU, so the only effect
|
|
would be to have all failures in OPEN PDUs return a different
|
|
single error code than all failures in any other PDU would
|
|
use, which doens't seem useful.
|
|
-->
|
|
|
|
</section>
|
|
|
|
<section anchor="verify-other" title="Verifying Other PDUs">
|
|
|
|
<t>
|
|
The process for verifying non-OPEN PDUs is slightly simpler,
|
|
but follows the same basic pattern as for OPEN PDUs.
|
|
</t>
|
|
|
|
<list style="symbols">
|
|
|
|
<t>
|
|
Verify that the PDU is syntactically correct, and extract
|
|
the Sig Type and Signature fields.
|
|
</t>
|
|
|
|
<t>
|
|
Verify that Sig Type refers to the same algorithm suite as
|
|
the Auth Type recorded during verification of the OPEN PDU.
|
|
</t>
|
|
|
|
<t>
|
|
Construct the "message to be verified" by truncating the PDU
|
|
to remove the Signature field.
|
|
</t>
|
|
|
|
<t>
|
|
Verify the message constructed above against the recorded
|
|
session key using the rules for the specific signature
|
|
suite.
|
|
</t>
|
|
|
|
</list>
|
|
|
|
<t>
|
|
If any of the above verification steps fail, generate an error
|
|
using error code 3 ("Signature failure in PDU").
|
|
</t>
|
|
|
|
<!--
|
|
See note in previous section regarding error codes.
|
|
-->
|
|
|
|
</section>
|
|
|
|
</section>
|
|
|
|
<section anchor="pki" title="Public Key Infrastructure Method">
|
|
|
|
<t>
|
|
Using a PKI is almost the same as using TOFU, but with one
|
|
additional step: during verification of an OPEN PDU, after
|
|
extracting the Key field from the PDU but before attempting to
|
|
use it to verify the PDU's signature, the receiver MUST verify
|
|
the received key against the PKI to confirm that it's an
|
|
authorized key.
|
|
</t>
|
|
|
|
<t>
|
|
Use of a PKI requires, at minimum, configuration of a trust
|
|
anchor and an End-Entity certificate corresponding to each peer
|
|
with which this l3dl instance is expected to establish sessions.
|
|
Optionally, a PKI MAY also allow configuration of zero or more
|
|
intermediate CA certificates and certificate revocation lists,
|
|
as needed to support an operator's preferred PKI architecture.
|
|
In general, however, we strongly recommend keeping the PKI as
|
|
simple as possible, because all of the configured PKI data must
|
|
be provided via out-of-band means, and will require maintenance.
|
|
</t>
|
|
|
|
<!--
|
|
This would be easier if we were providing certificates rather
|
|
than raw public keys in the OPEN PDU, but that would create a
|
|
significant difference between the TOFU and PKI cases. Not
|
|
happy about having to preconfigure all the peer EE certs, though,
|
|
so we might want to consider this.
|
|
|
|
Have deliberately not yet said "X.509v3" in so many words
|
|
because suspect LSVR people would run screaming from the room,
|
|
but that's another thing like TLS that it's probably just
|
|
not worth reinventing.
|
|
-->
|
|
|
|
</section>
|
|
|
|
<section anchor="roll" title="NEWKEY, Key Roll">
|
|
|
|
<t>Modern key management allows for agility in 'rolling' to a new
|
|
key or even algorithm in case of key expiry, key compromise, or
|
|
merely prudence. Declaring a new key with an L3DL OPEN PDU would
|
|
cause serious churn in topology as a new OPEN causes a withdraw of
|
|
previously announced encapsulations. Therefore, a gentler rekeying
|
|
is needed.</t>
|
|
|
|
<!--
|
|
protocol "Type = 8:8,Payload Length:16,New Key Type:8,New Key Length:16,New Key ...:40,Old Sig Type:8,Old Signature Length:16,Old Signature ...:40"
|
|
-->
|
|
|
|
<figure>
|
|
<artwork>
|
|
0 1 2 3
|
|
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| Type = 8 | Payload Length | New Key Type |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| New Key Length | ~
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|
|
~ New Key ... | Old Sig Type |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
| Old Signature Length | ~
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|
|
~ Old Signature ... |
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
</artwork>
|
|
</figure>
|
|
|
|
<t>The New Key Type, New Key Length, and New Key fields declare the
|
|
replacement algorithm suite and key.</t>
|
|
|
|
<t>The NEWKEY PDU is signed using the current (soon to be old)
|
|
algorithm suite and key.</t>
|
|
|
|
<t>The sender and the receiver should be cautious of algorithm suite
|
|
downgrade attacks.</t>
|
|
|
|
<t>To avoid possible race conditions, the receiver SHOULD accept
|
|
signatures using either the new or old key for a configurable time
|
|
(default 30 seconds). This is intended to accommodate situations
|
|
such as senders with high peer out-degree and a single per-device
|
|
asymmetric key.</t>
|
|
|
|
<t>If the sender does not receive an ACK in the normal window,
|
|
including retransmission, then the sender MAY choose to allow a
|
|
session reset by either issuing a new OPEN or by letting the
|
|
receiver eventually have a signature failure (error code 3) on a
|
|
PDU.</t>
|
|
|
|
<t>
|
|
The rekeying operation changes the session key and algorithm
|
|
suite described in <xref target="verify-other"/>. The NEWKEY
|
|
PDU itself is verified using the old algorithm and session key,
|
|
subsequent PDUs are verified with the new algorithm and session
|
|
key recorded after the NEWKEY PDU has been accepted.
|
|
</t>
|
|
|
|
</section>
|
|
|
|
<section anchor="security" title="Security Considerations">
|
|
|
|
<t>The TOFU method requires a leap of faith to accept the key in the
|
|
OPEN PDU, as it can not be verified against any authority. Hence it
|
|
is jokingly referred to as Married On First Date. The assurance it
|
|
does provide is that subsequent signed PDUs are from the same peer.
|
|
And data integrity is a positive side effect of the signature
|
|
covering the payload.</t>
|
|
|
|
<t>The PKI-based method offers assurance that the certificate, and
|
|
hence the keying material, provided in the OPEN PDU are authorized
|
|
by a central authority, e.g. the Clos's network security team. The
|
|
onward assurance of talking to the same peer and data integrity are
|
|
the same as in the TOFU method.</t>
|
|
|
|
<t>With the PKI-based method, automated device provisioning could
|
|
restrict which subsidiary certificates are allowed from which peers
|
|
on a per interface basis. This would complicate key rolls. Where
|
|
one draws the line between rigidity, flexibility, and security
|
|
varies.</t>
|
|
|
|
<t>The REKEY PDU is open to abuse to create an algorithm suite
|
|
downgrade attack.</t>
|
|
|
|
</section>
|
|
|
|
<section anchor="iana" title="IANA Considerations">
|
|
|
|
<t>This document requests the IANA create a new entry in the L3DL PDU
|
|
Type registry as follows:</t>
|
|
<figure>
|
|
<artwork>
|
|
PDU
|
|
Code PDU Name
|
|
---- -------------------
|
|
8 NEWKEY
|
|
</artwork>
|
|
</figure>
|
|
|
|
<t>This document requests the IANA add a registry entry for "TOFU -
|
|
Trust On First Use" to the L3DL-Signature-Type registry as follows:</t>
|
|
<figure>
|
|
<artwork>
|
|
Number Name
|
|
------ -------------------
|
|
1 TOFU - Trust On First Use
|
|
2 PKI
|
|
</artwork>
|
|
</figure>
|
|
|
|
</section>
|
|
|
|
<section anchor="acks" title="Acknowledgments">
|
|
|
|
<t>The authors than Russ Housley for advice and review.</t>
|
|
|
|
</section>
|
|
|
|
</middle>
|
|
|
|
<back>
|
|
|
|
<references title="Normative References">
|
|
<?rfc include="reference.RFC.2119"?>
|
|
<?rfc include="reference.RFC.8174"?>
|
|
<?rfc include="reference.I-D.ietf-lsvr-lsoe"?>
|
|
</references>
|
|
<!--
|
|
<references title="Informative References">
|
|
</references>
|
|
-->
|
|
|
|
</back>
|
|
|
|
</rfc>
|