Internet DRAFT - draft-ietf-lsvr-l3dl-signing
draft-ietf-lsvr-l3dl-signing
Network Working Group R. Bush
Internet-Draft Arrcus & IIJ
Intended status: Standards Track R. Housley
Expires: 17 July 2024 Vigil Security
R. Austein
Arrcus
14 January 2024
Layer-3 Discovery and Liveness Signing
draft-ietf-lsvr-l3dl-signing-06
Abstract
The Layer-3 Discovery and Liveness protocol OPEN PDU may contain a
public key and a certificate, 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 a trust anchor signture over the public key to provide
authentication as well as session integrity.
Requirements Language
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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 17 July 2024.
Bush, et al. Expires 17 July 2024 [Page 1]
Internet-Draft Layer-3 Discovery and Liveness Signing January 2024
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Signature Algorithm Identifiers . . . . . . . . . . . . . . . 3
3. Trust On First Use Method . . . . . . . . . . . . . . . . . . 3
3.1. Signing a PDU . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Verifying the OPEN PDU . . . . . . . . . . . . . . . . . 4
3.3. Verifying Other PDUs . . . . . . . . . . . . . . . . . . 5
4. Public Key Infrastructure Method . . . . . . . . . . . . . . 5
4.1. Signing OPEN PDU with PKI . . . . . . . . . . . . . . . . 6
4.2. Verifying OPEN PDU with PKI . . . . . . . . . . . . . . . 6
5. Local Policy . . . . . . . . . . . . . . . . . . . . . . . . 6
6. NEWKEY, Key Roll . . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Layer-3 Discovery and Liveness protocol [I-D.ietf-lsvr-l3dl] OPEN
PDU contains an algorithm identifier, a key, and a L3DL certificate,
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.
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 PDU may use one key for all links, a different key
for each link, or some mix(es) thereof.
Bush, et al. Expires 17 July 2024 [Page 2]
Internet-Draft Layer-3 Discovery and Liveness Signing January 2024
In the TOFU method the key sent in the OPEN PDU is generated on the
sending device, is believed without question by the receiver, and
used to verify all subsequent PDUs from the same sender with the same
public key and algorithm.
With the PKI method, an enrollment step is performed. The public key
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.
As part of enrollment or before hand, all relying parties must have
received the trust anchor in an authentic manner.
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.
In the PKI method the public key in the OPEN PDU MUST be verified
against the trust anchor for the operational domain. The OPEN PDU
public key is then used to verify all subsequent PDUs in the session.
A mechanism for 'rolling' from the current public key to a fresh one
is described in Section 6.
2. Signature Algorithm Identifiers
To avoid the creation of yet another IANA registry for digital
signature algorithm identifiers, this specification makes use of the
existing IANA registry for "DNS Security Algorithm Numbers" [IANA].
In this registry, each signature algorithm is identified by an 8-bit
value. The entries in this registry with "Y" in the "Zone Signing"
column are appropriate for use with this protocol.
For interoperability, all implementations of this protocol MUST
support the RSASHA256 algorithm (identified by the value 0x08).
Implementation MAY support any other registered "Zone Signing"
signature algorithms.
3. Trust On First Use Method
There are three parts to using a key: signing PDUs, verifying the
OPEN PDU, and verifying subsequent PDUs.
3.1. Signing a PDU
All signed PDUs are generated in the same way:
Bush, et al. Expires 17 July 2024 [Page 3]
Internet-Draft Layer-3 Discovery and Liveness Signing January 2024
* Compose the PDU, with all fields including "Sig Algo" and
"Signature Length" set, but omitting the trailing "Signature"
field itself. The Certificate Length should be zero and the
Certificate field should be empty. This is the "message to be
signed" for purposes of the signature algorithm.
* Generate the signature as specified for the chosen algorithm,
using the private key 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 signature algorithm. The result will be a sequence of
octets, the length of which MUST be equal to the value in the
"Signature Length" field.
* Construct the complete message by appending the signature octets
to the otherwise complete message composed above.
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.
3.2. Verifying the OPEN PDU
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.
* Verify that the PDU is syntactically correct, and extract the Auth
Type, Key, Sig Type, and Signature fields.
* Verify that Auth Type and Sig Type refer to the same algorithm
suite, and that said algorithm suite is one that the
implementation understands.
* 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).
* Verify the message constructed above against the public key using
the rules for the specific signature suite.
* Record Auth Type and Key as this sessions's authentication type
and session key, for use in verifying subseuqent PDUs.
If any of the above verification steps fail, generate an error using
error code 2 ("Authorization failure in OPEN").
Bush, et al. Expires 17 July 2024 [Page 4]
Internet-Draft Layer-3 Discovery and Liveness Signing January 2024
3.3. Verifying Other PDUs
The process for verifying non-OPEN PDUs is slightly simpler, but
follows the same basic pattern as for OPEN PDUs.
* Verify that the PDU is syntactically correct, and extract the Sig
Type and Signature fields.
* Verify that Sig Type refers to the same algorithm suite as the
Auth Type recorded during verification of the OPEN PDU.
* Construct the "message to be verified" by truncating the PDU to
remove the Signature field.
* Verify the message constructed above against the recorded session
key using the rules for the specific signature suite.
If any of the above verification steps fail, generate an error using
error code 3 ("Signature failure in PDU").
4. Public Key Infrastructure Method
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 OPEN
PDU signature, the receiver MUST verify the received key against the
PKI to confirm that it's an authorized key.
Generating an OPEN PDU using the PKI method requires a certificate,
which must be supplied via out of band configuration. The
certificate is a signature of the public key to be sent in the Key
field of the OPEN PDU, signed by the trust anchor private key.
Verifying an OPEN PDU using the PKI method requires the public key of
the trust anchor, which the receiver uses to verify the certificate,
thereby demonstrating that the supplied public key represents an
authorized L3DL speaker in this administrative domain.
We use the term "certificate" here in the generic sense, not as
defined in [RFC5280]. X.509 certificates are not used here; X.509
certificates are more complicated than needed for L3DL. The L3DL
certificates are just signatures of one key (the public key supplied
in the Key field of the OPEN PDU) that can be verified by another
trusted public key (the trust anchor).
Bush, et al. Expires 17 July 2024 [Page 5]
Internet-Draft Layer-3 Discovery and Liveness Signing January 2024
4.1. Signing OPEN PDU with PKI
Generating and signing the OPEN PDU with the PKI method is almost the
same as in Section 3.1. The only difference is that the PKI method
MUST supply the appropriate certificate in the Certificate field.
Note that the Auth Type field applies to both the Key and Certificate
fields. That is: the certificate uses the same certificate suite as
the session keys, L3DL does not support cross-algorithm-suite
certification.
4.2. Verifying OPEN PDU with PKI
Verifying the OPEN PDU with PKI is similar to verifying with TOFU as
described in Section 3.2, but includes one critical extra step:
After extracting the Key field from the PDU but before verifying the
Signature, extract the Certificate field and verfiy that the
Certificate is a valid signature of the Key field, according to the
rules for the signature suite specified by Auth Type. If this step
fails, handle as in Section 3.2.
5. Local Policy
Whether to use TOFU, PKI, or no signatures at all is a matter of
local policy, to be decided by the operator. The useful policy
combinations for Key and Certificate are probably:
* Not signing: sender need not sign, receiver does not check.
* Require TOFU: sender MUST supply key and receiver MUST check, but
L3DL certificates not needed and ignored if sent.
* Allow TOFU: sender MUST supply key and receiver MUST check,
receiver SHOULD check certificate if supplyed by sender.
* Require PKI: sender MUST supply key and L3DL certificate, receiver
MUST check signature and verify the L3DL certificate.
6. NEWKEY, Key Roll
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 PDU may cause a withdraw of
previously announced encapsulations. Therefore, a gentler rekeying
is needed.
Bush, et al. Expires 17 July 2024 [Page 6]
Internet-Draft Layer-3 Discovery and Liveness Signing January 2024
Prior to 'rolling' to a new key or new algorithm, a new public/
private key pair is generated. If PKI is being used, then the trust
anchor also signs the new public key to create a new L3DL
certificate.
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 ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | New Cert Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| New Certificate ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Old Key Type | Old Signature Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Old Signature ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The New Key Type, New Key Length, New Key, New Cert Length, and New
Certificate fields declare the replacement algorithm, key, and L3DL
certificate.
The NEWKEY PDU is signed using the current (soon to be old) algorithm
and key.
The sender and the receiver should be cautious of signature algorithm
downgrade attacks.
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.
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 PDU or by letting the receiver
eventually have a signature failure (error code 3) on a PDU.
The rekeying operation changes the session key and the associated
algorithm described in Section 3.3. The NEWKEY PDU itself is
verified using the old algorithm and session key. After the NEWKEY
PDU has been accepted, subsequent PDUs are verified with the new
algorithm and the new session key.
Bush, et al. Expires 17 July 2024 [Page 7]
Internet-Draft Layer-3 Discovery and Liveness Signing January 2024
7. Security Considerations
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.
The PKI method offers assurance that the L3DL certificate, and hence
the public key, provided in the OPEN PDU are authorized by a central
authority, e.g. the network's security team. The onward assurance of
talking to the same peer and data integrity are the same as in the
TOFU method.
With the PKI method, automated device provisioning could restrict
which L3DL 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.
The REKEY PDU is open to abuse to create a signature algorithm
downgrade attack.
8. IANA Considerations
This document requests the IANA create a new entry in the L3DL PDU
Type registry as follows:
PDU
Code PDU Name
---- -------------------
8 NEWKEY
This document requests the IANA add registry entries for "TOFU -
Trust On First Use" and "PKI" to the L3DL-Signature-Type registry as
follows:
Number Name
------ -------------------
1 TOFU - Trust On First Use
2 PKI
9. References
9.1. Normative References
Bush, et al. Expires 17 July 2024 [Page 8]
Internet-Draft Layer-3 Discovery and Liveness Signing January 2024
[I-D.ietf-lsvr-l3dl]
Bush, R., Austein, R., and K. Patel, "Layer-3 Discovery
and Liveness", Work in Progress, Internet-Draft, draft-
ietf-lsvr-l3dl-10, 25 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lsvr-
l3dl-10>.
[IANA] "DNS Security Algorithm Numbers",
<https://www.iana.org/assignments/dns-sec-alg-numbers/dns-
sec-alg-numbers.xhtml>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
Authors' Addresses
Randy Bush
Arrcus & IIJ
5147 Crystal Springs
Bainbridge Island, WA 98110
United States of America
Email: randy@psg.com
Russ Housley
Vigil Security, LLC
516 Dranesville Road
Herndon, VA 20170
United States of America
Email: housley@vigilsec.com
Rob Austein
Arrcus, Inc.
Bush, et al. Expires 17 July 2024 [Page 9]
Internet-Draft Layer-3 Discovery and Liveness Signing January 2024
Email: sra@hactrn.net
Bush, et al. Expires 17 July 2024 [Page 10]
