



Limited Additional Mechanisms for PKIX and SMIME            G. Wang, Ed.
Internet-Draft                                                   Y. Yang
Intended status: Standards Track                     Huawei Int. Pte Ltd
Expires: 22 April 2026                                          J. Zhang
                                                        Huawei Tech. Ltd
                                                         19 October 2025


 Root CA Certificate Rekeying in the Scenario of Post Quantum Migration
               draft-wang-lamps-root-ca-cert-rekeying-03

Abstract

   In the public key infrastructures (PKIs), root certifcation authority
   (CA) certificate rekeying is crucial to guarantee business
   continuity.  Two approaches are given in [RFC4210] for entities which
   are belonging to different generations to verify each other's
   certificate chain.  However, these approaches rely on the assumption
   that the old entities can be updated.  In this draft, we propose a
   one-way link certificate based solution such that old entities are
   transparent to root CA certificate rekeying.  Namely, during the
   overlapping lifetime of two root CA certificates, without any update
   in old entities, old and new entities can verify each other's
   certificate chain smoothly.  Furthermore, the proposed solution works
   in both traditional PKIs, and post-quantum (PQ) PKIs, where the
   cerficate can be pure PQ ones or hybrid ones.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on 22 April 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   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.  Notes of Change . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Changes in v03  . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Changes in v02  . . . . . . . . . . . . . . . . . . . . .   2
     1.3.  Changes in v01  . . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements Language . . . . . . . . . . . . . . . . . . . .   5
   4.  Design Goals of a New Solution for Root CA Rekeying . . . . .   5
   5.  The Proposed Solution Based on One-way Link Certificate . . .   7
   6.  Testing Results . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  An Extension for Switching Root CA Certificate More
           Smoothly  . . . . . . . . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  14
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  14
   11. Informative References  . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Notes of Change

1.1.  Changes in v03

   *  Minor changes made from v02 to make the draft live.  Plan to have
      a major update in the next version.

1.2.  Changes in v02

   *  Added an extension that allows root CA certificate can be swithed
      more smoothly in Section 7, by assuming that there is a maximum
      time difference (MTD) T bewtween any two entities when one sending
      a certificate chain and the other receiving.

1.3.  Changes in v01

   *  Added the testing results using OpenSSL library in Section 6.






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2.  Introduction

   In the public key infrastructures (PKIs), root certification
   authority (CA) certificate management is crucial to guarantee
   business continuity, as the CA certificate is the trust anchor for
   certificate chains, which establish the trust paths in PKIs from end
   users to the trusted authority, i.e., the root CA.

   However, just like the certificates for end users, the root CA
   certificate has a limited time of liftime as well, which normally
   varies from a few years to several decades to satsify various
   applications.  Further more, while new end user certificates can be
   issued when old ones are nealy expiring, but a new root CA
   certificate should be issued normally when the old root CA
   certificate has been just used for half of its lifetime.  Here are
   the main reasonos behind this pratice.

   A root CA ceritifate is generally used to issue one or more
   suborniate CA (sub-CA) certificates (for different departments in a
   given organization, for exmpale), and then each of scuh sub-CA
   certificate is used to issue lower level sub-CA certificates or end
   user certificates.  The lifetime of ened user ceritificates are
   expected to be around a given period, say 5 years (for some specific
   products, for example).  Accoridg to [RFC4210], to issue end user
   certificates with validity of 5 years, the remaining lifetime of the
   sub-CA certificate must be 5 years or more, such that the lifetime of
   each end user certificate MUST be covered by that of the sub-CA
   certificate.  However, to avoid frequenly apply and mannage multiple
   or even many sub_CA certificates, the liftetime of each sub-CA
   certicate could be set as 10 years, which means for each 5 years sub-
   CA sub_CA certificates should be updated so that end ceritificates
   for new users or products can still be continously issued to
   guarratte business continuity.  Similarly, for continously issuing
   sub_CA certificates with validity of 10 years without frequently
   changing the root CA certificate, it can be expected that each root
   CA certificate may has lifetime of 20 years, which also implies that
   each root CA certificate should be updated for each 10 years, not
   nearly the expiry date of the root CA certificate.  Each such new
   root CA certificate can be called a new generation of root CA
   certificate, though all of them still belong to the same legal
   entity, a particular CA.










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   However, this also implies that different sub-CA certificates and end
   user certificates issued under different generations of root CA
   certificate co-exit during the overlapping period of those root CA
   certificastes.  So, it may be not easy to verify each other's
   certificate chain between entities that hold different generations of
   certificates issued by the same CA in the aspect of legal meaning but
   under different generations of root CA certificates.

   Say, for the above example, the sub-CA certifiates and end user
   certifiates issued under the first genarteation of root CA
   certificate may still be valid in the year of 12 when a given CA has
   been established, but the newly issued sub-CA certifiates and end
   user certifiates are actually under the second genarteation of root
   CA certificate.  For simpliciy, we call the owner of a sub-CA
   certifiate or such an end user as an entity or a device.  Moreover, a
   device or entity hold certificate chain issued by an old generation
   of root CA certificate are called as old device or old entity, while
   a device or entity hold certificate chain issued by a new generation
   of root CA certificate are called as new device or new entity.  These
   terms are in a relative way.

   Actually, to address the above issue, there are two solutions given
   in [RFC4210]:

   *  Old and new entities upload both old and new root CA certificates,

   *  Or upload two-way link certificates which introduce old CA to new
      CA and vice versa.

   However, these two solutions do not work if old entities cannot
   upload the new root certificates or the necessary link certificate,
   or old devices are even out of maintenance.  In fact, such worse
   cases are possible, due to either limited prediction fo product
   design such that old devices may do not support adding multiple root
   CA or link certificates (automatically), or still running old devices
   are not maintained well and automatically update is not supported.

   Back a little bit, basically, there are actullay two approaches to
   update root CA certifiate, i.e., renewing and rekeying.  The former
   means to extend the validity of an existing root CA certificate but
   the root CA key pair and the associated cryptographical algorithm is
   still the same.  In this case, the validity of the same (old) key
   pair of the root CA will be extended for a longer period.  So,
   attackers shall have longer time to cryptanalyze the same key pairs.
   Also, as time goes, the secuirty strenth of the associated
   cryptographical algorithm for the root CA certificate may become
   weaker and weaker.  So, soon or later, it still needs to issue a
   brand new CA certificate.



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   For the latter, namely rekeying approach, a brand new root CA
   certificate will be issued to replace the old key pair.  In this
   case,no just a new pair of keys, even different key length or new
   algorithm can be used for generating the new root CA certificate by
   considering the progress of cryptoanlysis and potentil security
   threads in the near future, like quantum computing.  However, in this
   situation, a big challenge is to manage two or even multiple root CA
   certificates during the overlapping periods, which could be 20 years
   or more, as mentioned in the above.  In particular, some old devices
   may be not able to install the new root CA or link certificates, such
   that the two solutions given in [RFC4210] do not work.  Therefore,
   old devices may not be able to verify the new certificate chain of a
   new device, though a new device can be intalled all necessary
   certifiates and verify the old certificate chains of old devices.


   Motivated by the above observation, this draft proposes a one-way
   link certificate based solution such that root CA certificate
   rekeying is transparent to old entities:

   *  During the overlapping period of two or multiple root CA
      certificates, without any update in old entities, old and new
      entities can verify each other's certificate chain smoothly.

   *  The proposed solution works in the scenario of traditional PKIs,
      pure post-quantum PKIs, and also hybrid PKIs [I-D.D24], as the
      rationale of the solution does not rely on the type of undelying
      cryptographic algorithms.

   *  Esentially, the solution can be viewed as an extension of the
      approach for root CA certificate issuing and managnement
      specififed in [RFC4210] and [RFC5280].

3.  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.

4.  Design Goals of a New Solution for Root CA Rekeying

   Basically speaking, to design the root CA rekeying solution based on
   one-way link certificate, the following principles are followed to
   maximize the potential employment of the solution in practice:





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   *  Requirements on old devices are minimized such that the solution
      is applicable to as many as possible scenarios.

   *  New devices are supposed to do more as they are normally more
      powerful and designed with better prediction.

   *  When possbile, the usage of the new root CA keys will be maximized
      as normally they associated with cryptographically sronger
      algorithms .

   *  The existing standards [RFC4210] and [RFC5280] will be followed as
      much as possible, so that the deployment of the new solution for
      root CA rekeying can be implemented as easy as possile.

   In Section 6.1 of [RFC5280] : the following is sepecified:

   "A prospective certification path (a sequence of n certificates)
   satisfies the following conditions:

   *  (a) for all x in {1, ..., n-1}, the subject of certificate x is
      the issuer of certificate x+1;

   *  (b) certificate 1 is issued by the trust anchor;

   *  (c) certificate n is the certificate to be validated (i.e., the
      target certificate); and

   *  (d) for all x in {1, ..., n}, the certificate was valid at the
      time in question. "

   While Link certificates was introduced in Section 4.4.1 for
   specifying CA operator actions to rekeying root CA certificate
   [RFC4210] as follows.

   " To change the key of the CA, the CA operator does the following:

   *  1.  Generate a new key pair;

   *  2.  Create a certificate containing the old CA public key signed
      with the new private key (the "old with new" certificate);

   *  3.  Create a certificate containing the new CA public key signed
      with the old private key (the "new with old" certificate);

   *  4.  Create a certificate containing the new CA public key signed
      with the new private key (the "new with new" certificate);





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   *  5.  Publish these new certificates via the repository and/or other
      means (perhaps using a CAKeyUpdAnn message);

   *  6.  Export the new CA public key so that end entities may acquire
      it using the "out-of-band" mechanism (if required).

   The old CA private key is then no longer required. "

   However, as we mentioned in Section 1, the above solution specified
   in [RFC4210] assumes that (new and old) end entities may acquire the
   new CA public key (using the "out-of-band" mechanism, if needed), as
   the above item 6 despicts.

5.  The Proposed Solution Based on One-way Link Certificate

   Here are the basic idea of the proposed root CA key rekeying based on
   One-way Link Certificate:

   *  Use the one-way link certificate, called newWithOld, which is the
      link certificate of the new public signed by the old private key
      of the root CA.

   *  The newWithOld certifies the new root CA key by the old one.

   *  So, during the overlapping period, old devices can verify a link
      certificate chain from a new device by using the old root CA
      certificate as the trust anchor.

   *  Other cases are simple …






















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      Old Device A                     New Device C
   *******************            ***************************
   *    oldCACet     *            * oldCACert     newCACert *
   *       ^         *            *      ^           ^      *
   *  oldSubCACert   *            *  newWithOld      ^      *
   *       ^         *            *          ^       ^      *
   *    oldCertA     *            *         newSubCAcert    *
   *******************            *              ^          *
               ^                  *           newCertC      *
               | B sends its      ***************************
               | link certificate     ^ B sends either of its two
               | chain to A           | certificate chains to C
               |                      |
             *****************************
             *  oldCACert     newCACert  *
             *         ^        ^        *
             *  newWithOld      ^        *
             *         ^        ^        *
             *        newSubCACert       *
             *              ^            *
             *           newCertB        *
             *****************************
                  New Device B


Figure 1. Illustraion to the Solution Based on One-way Link Certificate.

   Figure 1 shows how a new device B can send out its link certificate
   chain, (oldCACert, newWithOld, nweSubCACert, newCertB), to an old
   device A such that A can verify B's certificate chain by using the
   old root CA cerficate, which is A's trust anchor.  To repsond B, A
   just sends its old certificate chain, (oldCACert, oldSubCACert,
   oldCertA), to new device B, which can verify A's certificate chain by
   using the old root CA cerificate, which is one of B's two trust
   anchors, namely, the old or new root CA certificate.

   To communicate with another new device C, new device B can send out
   either its link certificate chain, (oldCACert, newWithOld,
   nweSubCACert, newCertB), or the new certificate chain, (newCAcert,
   newSubCACert, newCertB), to new device C, which can verify either of
   them by using one of its two trust anchors, namely, the old or new
   root CA certificate.  In this case, as both B and C are new devices,
   C can do as B does such that B can verify either of C's two
   certificate chains similarly.

   The case of one old device communicates with another old device is
   simple, as they just behaver as normaly by sending their own old
   certificate chain to the other.



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   More detailed description will be provided later.

6.  Testing Results

   The proposed solution has been tested using OpenSSL library.  Here
   are the testing enviroments:

   *  3 generations of PKIs with different root CA certificates.: G1
      (2016-2025), G2 (2018-2027), and G3 (2020-2029).

   *  G1 and G2 implements RSA, with RSA 4096 for root CA certificate,
      RSA 3092 for subject CA certifiacte, and RSA 2048 for end entity
      certificate.

   *  G3 implements ECDSA, with ECDSA 384 for root CA certificate, and
      ECDSA 256 for both subject CA certifiacte and end entity
      certificate.

   *  Cross verifying tests are experimented among implmentations of
      running OpenSSL 1.0.1c, OpenSSL 1.0.2u、OpenSSL 1.1.1g and JDK
      8u251.  More specicically, G1 implements RSA with all these four
      softeare packages, while G2 and G3 implement RSA and ECDA
      respectively in the last three softeare packages, but not OpenSSL
      1.0.1c.  This is becuase OpenSSL 1.0.1c is a relativley old
      version of openSSL, so new system may not employ it.

   Table 1 given below lists the life times of three generations of PKIs
   with different root CA certificates, namely, G1, G2 and G3.  That is,
   the life time of the first genarteation PKI G1 is valid from 2016 to
   2025.  More specifically, the root CA certificate of G1 is valid from
   the first moment of the year of 2016 to the last moment of the year
   of 2025.  Therefore, in 2015, G1 is invalid, namely, not issued yet.
   Similiarly, G1 is expired from the first moment of year 2026.  The
   root CA certificate of the 2nd generation PKI G2 is valid from 2018
   to 2027, while the root CA certificate of the 3rd generation PKI G3
   is valid from 2020 to 2029.

   +====+=======+=======+=======+========+========+=======+=======+=======+
   |    |  2015 | 2016  | 2018  | 2020   | 2025   | 2026  | 2028  | 2030  |
   +----+-------+-------+-------+--------+--------+-------+-------+-------+
   | G1 |Invalid| Valid | Valid | Valid  | Valid  |Expired|Expired|Expired|
   +----+-------+-------+-------+--------+--------+-------+-------+-------+
   | G2 |Invalid|Invalid| Valid | Valid  | Valid  | Valid |Expired|Expired|
   +----+---------------+-------+--------+--------+-------+-------+-------+
   | G3 |Invalid|Invalid|Invalid| Valid  | Valid  | Valid | Valid |Expired|
   +----+-------+-------+-------+--------+--------+-------+-------+-------+

          Table 1: Life Times of 3 Generations of Root CA Certificate



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   The testing results for eight selected years from 2015 to 20230 are
   given in the following four tables, namely, from Table 2 to Table 5.
   The ruslts show positve answers for all the cases considered, as
   explanied below in more detail.

   These tables show all representive cases needed to be considered.
   That is, for all three generateions of PKIs G1, G2 and G3, we have
   selected 8 years from 2015 to 2030 to include all possbile
   combinations of some of PKIs G1, G2, and G3 are not issued, valid
   and/or expired.  The complete list of these seven combinations is
   given as following: (G1 invalid, G2 invalid, G3 invaid), (G1 valid,
   G2 invalid, G3 invaid), (G1 valid, G2 valid, G3 invaid), (G1 valid,
   G2 valid, G3 vaid), (G1 expired, G2 valid, G3 vaid), (G1 expired, G2
   expired, G3 vaid), and (G1 expired, G2 expired, G3 expired).  Note
   that other combinations in theory do not exist in practice, like (G1
   valid, G2 expired, G3 vaid), as in the above test G1, G2, and G3 are
   issued and expired gradually in this order.  This means that it is
   not possible for G1 valid and G2 expired.  From Table 1, we actually
   can see that only for case (G1 valid, G2 valid, G3 vaid), twe years,
   namely 2020 and 2025, are selected.  This is because 2020 is the year
   when G3 is issued, while 2025 is the year when G1 is in service for
   the last year.  If fact, these eight years selected include all such
   critical years for these three generations of PKIs, namely the years
   when each G1, G2 or G3 is issued, and the years when each G1, G2 or
   G3 is in service for the last year.

   +=========+=============================+=============================+
   |         |              2015           |          2016               |
   +---------+---------+---------+---------+---------+---------+---------+
   |         |G1 Client|G2 Client|G3 Client|G1 Client|G2 Client|G3 Client|
   +---------+---------+---------+---------+---------+---------+---------+
   |         |Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|
   +---------+---------+---------+---------+---------+---------+---------+
   |G1 Server| -  | -  | -  | -  | -  | -  | OK | OK | -  | -  | -  | -  |
   +---------+---------+---------+---------+---------+---------+---------+
   |G2 Server| -  | -  | -  | -  | -  | -  | -  | -  | -  | -  | -  | -  |
   +---------+-----------------------------+-----------------------------+
   |G3 Server| -  | -  | -  | -  | -  | -  | -  | -  | -  | -  | -  | -  |
   +=========+=========+=========+=========+=========+=========+=========+

                Table 2: Testing Results for 2015 and 2016

   Each table from Table 2 Table 5 gives the testing rsults what a
   client and a server output for verifying the certificate chain of the
   other, for each case where during each of the eight years selected,
   both the server and the client can be any of G1, G2 or G3 server and
   client.  Namely, these sever and clients hold the certificate chains
   issued by the respective root CA, together with the one-way link



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   certifates NewWithOld which link the current root CA public key to
   the previous one or two old root CA public keys.  The verification
   results from the client and the server are listed in the colums of
   "Cli." and "Ser.", respectivley. "-" means that such a case actually
   doest not exist, while "OK" means that such a verificaiton of the
   other peer's certificate chain is possitive, and "No" means that such
   a verificaiton of the other peer's certificate chain is negative as
   one or more certificates in such a certificate chain are expired
   already.

   As the first example, in Table 2, the "-" shown in the six cells of
   the fifth row under "2016" mean that in the year of 2016, when a G2
   server interacts with a G1, G2 or G3 client, they cannot verify and
   accept each other's certificate chains, as such a G2 or G3 server, G2
   or G3 client should not exist.  As the second example, in Table 4,
   the "NO" shown in the six cells of the fourth row under "2026" mean
   that in the year of 2026, when a G1 server interacts with a G1, G2 or
   G3 client, they cannot verify and accept each other's certificate
   chains, as the root CA certificate of PKI G1 is expired already.  As
   the third example, in Table 3, the "OK" shown in the six cells from
   the fourth row to the sixth row under "2020" mean that in the year of
   2020, when any G1, G2 or G3 server interacts with any G1, G2 or G3
   client, both the server and the client can verify and accept each
   other's certificate chains, which includes the one-way link
   certificates specified in this draft.

   +=========+=============================+=============================+
   |         |              2018           |          2020               |
   +---------+---------+---------+---------+---------+---------+---------+
   |         |G1 Client|G2 Client|G3 Client|G1 Client|G2 Client|G3 Client|
   +---------+---------+---------+---------+---------+---------+---------+
   |         |Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|
   +---------+---------+---------+---------+---------+---------+---------+
   |G1 Server| OK | OK | OK | OK | -  | -  | OK | OK | OK | OK | OK | OK |
   +---------+---------+---------+---------+---------+---------+---------+
   |G2 Server| OK | OK | OK | OK | -  | -  | OK | OK | OK | OK | OK | OK |
   +---------+---------+---------+---------+---------+---------+---------+
   |G3 Server| -  | -  | -  | -  | -  | -  | OK | OK | OK | OK | OK | OK |
   +=========+=========+=========+=========+=========+=========+=========+

                 Table 3: Testing Results for 2018 and 2020










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   +=========+=============================+=============================+
   |         |              2025           |          2026               |
   +---------+---------+---------+---------+---------+---------+---------+
   |         |G1 Client|G2 Client|G3 Client|G1 Client|G2 Client|G3 Client|
   +---------+---------+---------+---------+---------+---------+---------+
   |         |Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|
   +---------+---------+---------+---------+---------+---------+---------+
   |G1 Server| OK | OK | OK | OK | OK | OK | NO | NO | NO | NO | NO | NO |
   +---------+---------+---------+---------+---------+---------+---------+
   |G2 Server| OK | OK | OK | OK | OK | OK | NO | NO | OK | OK | OK | OK |
   +---------+---------+---------+---------+---------+---------+---------+
   |G3 Server| OK | OK | OK | OK | OK | OK | NO | NO | OK | OK | OK | OK |
   +=========+=========+=========+=========+=========+=========+=========+

             Table 4: Testing Results for 2025 and 2026

   +=========+=============================+=============================+
   |         |              2028           |          2030               |
   +---------+---------+---------+---------+---------+---------+---------+
   |         |G1 Client|G2 Client|G3 Client|G1 Client|G2 Client|G3 Client|
   +---------+---------+---------+---------+---------+---------+---------+
   |         |Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|Cli.|Ser.|
   +---------+---------+---------+---------+---------+---------+---------+
   |G1 Server| NO | NO | NO | NO | NO | NO | NO | NO | NO | NO | NO | NO
   +---------+---------+---------+---------+---------+---------+---------+
   |G2 Server| NO | NO | NO | NO | NO | NO | NO | NO | NO | NO | NO | NO |
   +---------+---------+---------+---------+---------+---------+---------+
   |G3 Server| NO | NO | NO | NO | OK | OK | NO | NO | NO | NO | NO | NO |
   +=========+=========+=========+=========+=========+=========+=========+

             Table 5: Testing Results for 2028 and 2030

7.  An Extension for Switching Root CA Certificate More Smoothly

   There will be a time difference between when a device A sends its
   certificate chain and when another device B recives the certificate
   chain.  This time difference is due to a number of reasons, including
   communnicaiton delay, operation time (especially for PQ cryptographic
   operations) needed at the receiving device B, the clock drift between
   devices A and B.  In practice, the solution introduced in Section 5
   requires that a new device SHOULD switch its link certificate chain
   to its new certificate chain around the expiry time of the old root
   CA certificate.  Therfore, two abonormal cases may happen, as
   explained below.

   *  Case 1: A new decive A switches its certificate chain a little
      late.  In this case, for a new receiving device B, it may be not
      able to verify this link certificate chain from device A as the



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      old root certificate is expired when device B recieved the
      certificate chain, though such a connection is expected to be
      successful.  In fact, as a new device, if B could try to use the
      new root CA cerificate verifying the link certificate chain, the
      result SHALL be positive.  However, such a disturbance has been
      caused to new device B.

   *  Case 2: A new decive A switches its certificate chain a little
      early.  In this case, for an old device B, it may receive a new
      ccertificate chain from A beore the expiry time of the old root CA
      certificate.  Then, naturally, as an old device, B will be not
      able to verify this certificate chain when it received the
      certificate chain from device A, though such a connection is
      supposed to be successful as old device B does not retire yet.

   To address the above issue due to switching the link certificate
   chain early or late, this section desribes an exension to the
   solution proposed in Section 5.  The basic idea is to introduce a
   maximum time difference (MTD) T bewtween any two entities in a given
   domain when one entity sending a certificate chain and the other
   receiving it.  The extension works as follows.

   *  For any certificate issued by the old root CA certificate, its
      validity time MUST be at least 2T less than T3, the expected
      expiry time of the old root CA certificate and the newWithOld link
      certificate.

   *  Each new device is supposed to complete its certificate chain
      switching on T3-T.

   *  When a new device A sends out its link certificate chain before
      T3-T, it will be recieved by a device B by time T3 in B's local
      time.  At this moment, does not matter if B is a new or old old
      device, the old root CA certificate is still valid according to
      B's local time.  Therefore, B can verify A's link certificate
      chain and the exension works.

   *  When a new device A sends out its new certificate chain after
      T3-T, it will be recieved by a device B after time T3-2T in B's
      local time.  At this moment, if B is an old device, it retired or
      should be retired already.  If B is a new device, the new root CA
      certificate is valid alredy, so B can verify A's new certificate
      chain.

   Therefore, the exension works to avoid both anormal cases described
   in the above.





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8.  Security Considerations

   Security analysis will be given later.

9.  Acknowledgments

   To be added later.

10.  Normative References

   [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>.

   [RFC4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen,
              "Internet X.509 Public Key Infrastructure Certificate
              Management Protocol (CMP)", RFC 4210,
              DOI 10.17487/RFC4210, September 2005,
              <https://www.rfc-editor.org/info/rfc4210>.

   [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>.

11.  Informative References

   [I-D.D24]  F. Driscoll, F., "Terminology for Post-Quantum Traditional
              Hybrid Schemes", Work in Progress, Internet-Draft,,
              February 2024, <https://datatracker.ietf.org/doc/draft-
              ietf-pquip-pqt-hybrid-terminology/>.

Authors' Addresses

   Guilin Wang (editor)
   Huawei Int. Pte Ltd
   9 North Buona Vista Drive, #13-01
   The Metropolis Tower 1
   SINGAPORE 138588
   Singapore
   Email: wang.guilin@huawei.com




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   Yanjiang Yang
   Huawei Int. Pte Ltd
   Email: yang.yanjiang@huawei.com


   Jie Zhang
   Huawei Tech. Ltd
   Email: zhangjie184@huawei.com











































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