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Versions: (draft-tbruijnzeels-sidrops-signed-tal) 00 01 02 03

Network Working Group                                     T. Bruijnzeels
Internet-Draft                                                NLnet Labs
Intended status: Standards Track                             C. Martinez
Expires: April 19, 2019                                           LACNIC
                                                              R. Austein
                                                    Dragon Research Labs
                                                        October 16, 2018


                RPKI Signed Object for Trust Anchor Keys
                    draft-ietf-sidrops-signed-tal-02

Abstract

   Trust Anchor Locators (TALs) [I-D.ietf-sidrops-https-tal] are used by
   Relying Parties in the RPKI to locate and validate Trust Anchor
   certificates used in RPKI validation.  This document defines an RPKI
   signed object for Trust Anchor Keys (TAK), that can be used by Trust
   Anchors to signal their set of current keys and the location(s) of
   the accompanying CA certiifcates to Relying Parties, as well as
   changes to this set in the form of revoked keys and new keys, in
   order to support both planned and unplanned key rolls without
   impacting RPKI validation.

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 April 19, 2019.

Copyright Notice

   Copyright (c) 2018 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



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   (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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Requirements notation . . . . . . . . . . . . . . . . . . . .   3
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  TAK Object definition . . . . . . . . . . . . . . . . . . . .   4
     3.1.  The TAK Object Content Type . . . . . . . . . . . . . . .   5
     3.2.  The TAK Object eContent . . . . . . . . . . . . . . . . .   5
       3.2.1.  version . . . . . . . . . . . . . . . . . . . . . . .   5
       3.2.2.  current . . . . . . . . . . . . . . . . . . . . . . .   5
       3.2.3.  revoked . . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  TAK Object Validation . . . . . . . . . . . . . . . . . .   6
   4.  Maintaining multiple TA keys  . . . . . . . . . . . . . . . .   7
     4.1.  Prepare a new TA key  . . . . . . . . . . . . . . . . . .   7
     4.2.  Publishing for Multiple TA Keys . . . . . . . . . . . . .   7
   5.  TAK Object Generation and Publication . . . . . . . . . . . .   8
   6.  Performing TA Key Rolls . . . . . . . . . . . . . . . . . . .   9
     6.1.  Opting in to Key Rolls  . . . . . . . . . . . . . . . . .  10
       6.1.1.  Trust Anchor  . . . . . . . . . . . . . . . . . . . .  10
       6.1.2.  Relying Parties . . . . . . . . . . . . . . . . . . .  12
     6.2.  Pre-stage a New Key . . . . . . . . . . . . . . . . . . .  12
       6.2.1.  Trust Anchor  . . . . . . . . . . . . . . . . . . . .  12
       6.2.2.  Relying Parties . . . . . . . . . . . . . . . . . . .  14
     6.3.  Planned Key Revocation  . . . . . . . . . . . . . . . . .  14
       6.3.1.  Trust Anchor  . . . . . . . . . . . . . . . . . . . .  14
       6.3.2.  Relying Parties . . . . . . . . . . . . . . . . . . .  17
     6.4.  Unplanned revocation  . . . . . . . . . . . . . . . . . .  17
       6.4.1.  Trust Anchor  . . . . . . . . . . . . . . . . . . . .  17
   7.  Deployment Considerations . . . . . . . . . . . . . . . . . .  18
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
     8.1.  OID . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
     8.2.  File Extension  . . . . . . . . . . . . . . . . . . . . .  19
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     11.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21






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1.  Requirements notation

   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.

2.  Overview

   Trust Anchor Locators (TALs) [I-D.ietf-sidrops-https-tal] are used by
   Relying Parties in the RPKI to locate and validate Trust Anchor (TA)
   certificates used in RPKI validation.  However, until now there has
   been no formal way of notifying Relying Parties (RP) of updates to a
   TAL.  Such updates may be needed in particular in case a Trust Anchor
   needs to perform a planned, or unplanned, key roll.

   This document defines a new RPKI signed object that can be used to
   document the current set of keys and the loctaion(s) of the
   accompanying CA certificates, as well as any changes to this set.
   This allows RPs to be notified automatically of such changes, and
   enables Trust Anchors to pre-stage a number of operational keys so
   that planned and unplanned key rolls can be performed without risking
   the invalidation of the RPKI tree under the TA.  We call this object
   the Trust Anchor Keys (TAK) object.

   When Relying Parties (RPs) are first bootstrapped, they use any
   current TAL to discover a key and location(s) of the TA
   certificate(s) for a TA.  The RP can then retreive and validating the
   TA certificate, and subsequently validate the manifest [RFC6486] and
   CRL [section 5 of @!RFC6487].  However, before processing any other
   objects it will then first validate the TAK object, if present.  All
   enumarated new keys (and locations) are then added to a new list of
   current TA keys for this TA.  The RP will then recursively fetch and
   validate the TA certificates, manifest, CRL and TAK objects for each
   of these keys.  As a part of this process the RP will also compile a
   list of revoked keys enumarated by any of the validly signed TAK
   objects.  As the final step the RP will then filter out any revoked
   TA keys from its new set.  This new set now replaces the previous
   set.

   If the key used to start this process is still considered current,
   then validation continues.  But if the key was revoked, then
   validation is restarted using one of the remaining keys in the set.

   This process allows Trust Anchors to operate a set of N current keys,
   where any key can effectively revoke any or all of the other keys to
   perform either a planned, or an unplanned, key roll.  This also



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   allows Trust Anchors to produce long lived TAK objects as forward
   pointers to RPs, and retire its old key when doing a key roll.

   While the generic process is quite involved, the amount of work
   needed to support an envisioned normal key roll is fairly limited.
   Under normal circumstances a TA will typically have two current keys,
   so that is can perform an emergency roll over in case one of the keys
   is lost.  This means that the RP will need to validate two TAK
   objects.  However, typically these files will agree that both keys
   are current and validation continues.

   When a key roll is executed a TA will remove one old key, and
   introduce one new (back-up) key.  The RP will remove the old key from
   its set, and it will not be queried again, and it will add the new
   key and its TA certifcate location(s).

   Only in a situation where an RP is very outdated can it be expected
   that the RP will have to discover several chained TAK object.  But,
   since it will remove the outdated TALs in this process, this presents
   a one time cost only.

   Note that in theory a TA can revoke all of its keys and make itself
   obsolete.  In practice however, a well operated TA will have measures
   in place to prevent this.  Furthermore they can protect themselves
   against key loss to adversaries through the use of such as the use of
   a Hardware Security Module (HSM) to protect keys.  Protecting against
   this mis-operation would incur complexity and guesswork on the RPs.
   Therefore it is believed that it is best to keep the process
   straightforward, and offer a solution for the more likely issues of
   loss of a key, e.g.  because an HSM or card set is broken, and
   planned key rolls.

3.  TAK Object definition

   The TAK object makes use of the template for RPKI digitally signed
   objects [RFC6488], which defines a Crytopgraphic Message Syntax (CMS)
   [RFC5652] wrapper for the Signed TALs content as well as a generic
   validation procedure for RPKI signed objects.  Therefore, to complete
   the specification of the TAK object (see Section 4 of [RFC6488]),
   this document defines:

   o  The OID defined in Section 3.1 that identifies the signed object
      as being a TAK.  (This OID appears within the eContentType in the
      encapContentInfo object as well as the content-type signed
      attribute in the signerInfo object).

   o  The ASN.1 syntax for the TAK eContent defined in Section 3.2.




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   o  Additional steps to the validation steps specified in [RFC6488]
      required to validate the TAK, defined in Section 3.3.

3.1.  The TAK Object Content Type

   This document requests an OID for TAK objects as follows:

       signed-Tal OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
                  rsadsi(113549) pkcs(1) pkcs9(9) 16 id-smime (1) TBD }

   This OID MUST appear both within the eContentType in the
   encapContentInfo object as well as the content-type signed attribute
   in the signerInfo object (see [RFC6488])

3.2.  The TAK Object eContent

   The content of a TAK object is ASN.1 encoded using the Distinguished
   Encoding Rules (DER) [X.690], and is defined as follows:

      TAK ::= SEQUENCE {
         version   INTEGER DEFAULT 0,
         current   ::= SEQUENCE SIZE (1..MAX) OF CurrentKey,
         revoked   ::= SEQUENCE OF SubjectPublicKeyInfo
      }

      CurrentKey ::= SEQUENCE {
         certificateURIs       SEQUENCE SIZE (1..MAX) OF CertificateURI,
         subjectPublicKeyInfo  SubjectPublicKeyInfo
      }

      CertificateURI ::= IA5String

      SubjectPublicKeyInfo ::= SEQUENCE {
           algorithm            AlgorithmIdentifier,
           subjectPublicKey     BIT STRING
      }

3.2.1.  version

   The version number of the TAK object MUST be 0.

3.2.2.  current

   This field defines the set of current keys (CurrentKey) according to
   the signer of this Signed TALs object.






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3.2.2.1.  CurrentKey

   This field defines a current TA Key, equivalent to [I-D.ietf-sidrops-
   https-tal].  This structure contains a sequence of one or more URIs
   and a SubjectPublicKeyInfo.

3.2.2.1.1.  certificateURIs

   This field is equivalent to the URI section in section 2.1 of
   [I-D.ietf-sidrops-https-tal].  It MUST contain at least one
   CertificateURI element.  Each CertificateURI element contains the
   IA5String representation of either an rsync URI [RFC5781], or an
   HTTPS URI [RFC7230].

3.2.2.1.2.  subjectPublicKeyInfo

   This field contains a SubjectPublicKeyInfo [section 4.1.2.7 or
   @!RFC5280] in DER format [X.690].

3.2.3.  revoked

   This field contains the list of keys, identified by
   SubjectPublicKeyInfo, that are no longer to be used according to the
   signer of this document.

3.3.  TAK Object Validation

   To determine whether a TAK object is valid, the RP MUST perform the
   following steps in addition to those specified in [RFC6488]:

   o  The eContentType OID matches the OID described in Section 3.1

   o  The TAK object appears as the product of a Trust Anchor CA
      certificate.

   o  This Trust Anchor CA has published only one TAK object in its
      repository for this key, and this object appears on the Manifest
      as the only entry using the ".tak" extension (see [RFC6481]).  In
      case more than one TAK object is found, all such objects MUST be
      considered invalid.

   o  The EE certificate of this TAK object describes its Internet
      Number Resources (INRs) using the "inherit" attribute

   o  The decoded TAK content conforms to the format defined in
      Section 3.2.





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   If the above procedure indicates that the manifest is invalid, then
   the TAK object MUST be discarded and treated as though no TAK object
   were present.

4.  Maintaining multiple TA keys

   As described in Section 6 a TA will most likely choose to operate two
   keys at any one time in order to be prepared for an emergency key
   roll.  When a TA operates multiple keys, each key MUST use its own CA
   repository publication point as described in [RFC6481].  The CRL and
   Manifest [RFC6486] for each of these keys will be unique to each key,
   but the TA MUST ensure that equivalent CA certificates and RPKI
   signed objects are issued under each key.  Note that this is similar
   to how such certificates and RPKI signed objects are re-issued as
   part of a lower level CA key roll, described in section 4 of
   [RFC6489].

4.1.  Prepare a new TA key

   The Trust Anchors MUST generate a new key pair and generate a new TA
   Certificate.  For the Subject Information Access (see section 4.8.8.1
   of [RFC6487]) this MUST use URIs that will be used by the new key to
   publish objects.  These URIs MUST be uniqe for use by this new key
   only.  The Internet Number Resources on this new certificate MUST be
   equivalent to those found on the current certificate.

   The new TA certificate MUST be published under one or more new
   Certificate URIs for use by this new key only.

   As decribed above, the TA MUST issue and publish equivalent CA
   certificates and RPKI signed objects under this new key.

   It is RECOMMENDED that the TA now generates a new TAL
   [I-D.ietf-sidrops-https-tal] and verifies that the new Trust Anchor
   certificate can be retrieved from all locations, and that it
   generates the same results when it is used for top-down validation
   instead of (any of) the current TA key(s).

   Note that the TA MAY choose to make this TAL available to Relying
   Parties, in particular to those that do not support TAK objects, and
   for inclusion in the distribution of RP software in order to minimise
   the overhead in bootstrapping fresh installations.

4.2.  Publishing for Multiple TA Keys

   If a TA uses a single remote publication server for its keys using
   the RPKI publication protocol [RFC8181], then it MUST include all
   <publish/> and <withdraw/> PDUs for the products of each of its keys



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   in a single query in order to ensure that they will reflect the same
   content at all times.

   If a TA uses multiple publication servers then it is by definition
   inevitable that the content of different keys will be out of sync at
   times.  In such cases the TA SHOULD ensure that the duration of these
   moments are limited to the shortest possible time.  Furthermore the
   following should be observed:

   o  It is strongly RECOMMENDED that TAs do not issue any RPKI Signed
      Objects, such as ROAs [RFC6482], but limit their operations to
      maintaining a CRL, Manifest and CA certificates only.  If an
      organisation maintaining a TA has an operational need for such
      objects then it is strongly RECOMMENDED that they operate a
      separate non-TA CA as a child of their TA for these operations.
      If this approach is used the remaining issues regarding temporary
      inconsistencies between multiple TA key repository publication
      points is greatly reduced.

   o  In cases where a CA certificate is revoked completely, or replaced
      by a certifcate with a reduced set of resources, these changes
      will not take effect fully until all the TA keys repository
      publication points have been updated.  Given that TA key
      operations are normally performed infrequently we don't expect
      that this is a problem.  I.e. if the revocation or shrinking of an
      issued CA certificate is staged for days, or weeks anyway, then
      experiencing a delay of several minutes for the repository
      publication points to all be updated is fairly insignificant.

   o  In cases where a CA certificate is replaced by a certifcate with
      an extend set of resources the TA MUST inform the receiving CA
      only after all its repository publication points have been
      updated.  This ensures that the receiveing CA will not issue any
      products that could be invalid if an RP uses a TA key just before
      the CA certificate was due to be updated.

5.  TAK Object Generation and Publication

   A TA MAY choose to use TAK objects to communicate its set of current,
   and revoked keys.  If a TA chooses to use TAK objects, then it SHOULD
   generate and publish TAK objects under each of its current keys.  An
   exception to this rule exists when a TA has lost permanent access to
   one of its keys or the accompanying repository publication point.  In
   such cases however, the key in question MUST be revoked as described
   below in Section 6.

   A non-normative guideline for naming this object is that the filename
   chosen for the Signed TAL Object in the publication repository be a



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   value derived from the public key part of the entity's key pair,
   using the algorithm described for CRLs in section 2.2 of [RFC6481]
   for generation of filenames.  The filename extension of ".tak" MUST
   be used to denote the object as a TAK.  Note that this is in-line
   with filename extensions defined in section 7.2 of [RFC6481]

   In order to generate the TAK Objects, the TA MUST perform the
   following actions:

   o  The TA MUST generate a key pair for a "one-time-use" EE
      certificate to use for the TAK

   o  The TA MUST generate a one-time-use EE certificate for the TAK

   o  This EE certificate MUST have an SIA extension access description
      field with an accessMethod OID value of id-ad-signedobject, where
      the associated accessLocation references the publication point of
      the TAK as an object URL.

   o  As described in [RFC6487], an [RFC3779] extension is required in
      the EE certificate used for this object.  However, because the
      resource set is irrelevant to this object type, this certificate
      MUST describe its Internet Number Resources (INRs) using the
      "inherit" attribute, rather than explicit description of a
      resource set.

   o  This EE certificate MUST have a "notBefore" time that matches, or
      predates the moment that the TAK will be published.

   o  This EE certificate MUST have a "notAfter" time that reflects the
      intended duration for which this TAK will be published.  If the EE
      certificate for a Signed TAL is expired, it MUST no longer be
      published, but it MAY be replaced by a newly generated TAK object
      with equivalent content and an updated "notAfter" time.

   o  The same set of current keys (see Section 3.2.2) MUST be included
      on each TAK object for each current key.

   o  The TAK object MUST include all revoked keys (see Section 3.2.3)
      that became revoked while the key signing the TAK in question was
      current.

6.  Performing TA Key Rolls








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6.1.  Opting in to Key Rolls

6.1.1.  Trust Anchor

   For simplicitly let's start with a situation where a TA has only one
   key.  The TA wants to start using TAK objects to perform key rolls in
   future, so it introduces a TAK object under its single key 'A'.  The
   repository structure looks as follows (irrelevant details omitted):











































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                          +--------------------+
                          |        A.MFT       |
                          +--------------------+
                          | A.CRL      <hash>  |
                          | A.TAK      <hash>  |
                          | C1-A.CER   <hash>  |
                          | C2-A.CER   <hash>  |
                          +--------------------+

                          +--------------------+
                          |        A.CRL       |
                          +--------------------+
                          | revocations..      |
                          +--------------------+

                          +--------------------+
                          |        A.TAK       |
                          +--------------------+
                          | current: A         |
                          | revoked: none      |
                          +--------------------+

                          +--------------------+
                          |      C1-A.CER      |
                          +--------------------+
                          | resources: C1 res  |
                          | subject:   C1 name |
                          | pub key:   C1 key  |
                          | SIA:       C1 SIAs |
                          | AKI:       A       |
                          +--------------------+

                          +--------------------+
                          |      C2-A.CER      |
                          +--------------------+
                          | resources: C2 res  |
                          | subject:   C2 name |
                          | pub key:   C2 key  |
                          | SIA:       C2 SIAs |
                          | AKI:       A       |
                          +--------------------+

   So, the TA publishes a CRL and MFT under its key A, listing a TAK
   object and in this case two certificates issued to children 'C1' and
   'C2' signed using key A.  The TAK object lists key 'A' as the only
   current key, and has no revoked keys.





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6.1.2.  Relying Parties

   Relying Parties who have a TAL for key 'A' configured will discover
   the TAK object.  If the RP does not support this object, it will
   reject this object but continue to validate the remaining RPKI tree
   as usual.  If the RP does support TAK objects it will conclude that
   key 'A' is the one and only current key, and will proceed to validate
   the remaining RPKI tree as usual.

6.2.  Pre-stage a New Key

6.2.1.  Trust Anchor

   Now the TA prestages a new key 'B' and produces equivalent CA
   certificates for children 'C1' and 'C2', i.e. the resources, subject
   name, public key and SIA etc are all equivalent, but these
   certificates are signed under key 'B'.  (See Section 4 for a more
   thorough description of this).  The TAK object for key 'B' recognises
   both keys 'A' and 'B' as current.

   The repostory structure and TAK object for key B are then as follows:






























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                          +--------------------+
                          |        B.MFT       |
                          +--------------------+
                          | B.CRL      <hash>  |
                          | B.TAK      <hash>  |
                          | C1-B.CER   <hash>  |
                          | C2-B.CER   <hash>  |
                          +--------------------+

                          +--------------------+
                          |        B.CRL       |
                          +--------------------+
                          | revocations..      |
                          +--------------------+

                          +--------------------+
                          |        B.TAK       |
                          +--------------------+
                          | current: A, B      |
                          | revoked: none      |
                          +--------------------+

                          +--------------------+
                          |      C1-B.CER      |
                          +--------------------+
                          | resources: C1 res  |
                          | subject:   C1 name |
                          | pub key:   C1 key  |
                          | SIA:       C1 SIAs |
                          | AKI:       B       |
                          +--------------------+

                          +--------------------+
                          |      C2-B.CER      |
                          +--------------------+
                          | resources: C2 res  |
                          | subject:   C2 name |
                          | pub key:   C2 key  |
                          | SIA:       C2 SIAs |
                          | AKI:       B       |
                          +--------------------+

   When the TA is certain that the content for key 'B' is correct, it
   can also update the TAK object for key 'A' to include 'B':







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                          +--------------------+
                          |        A.TAK       |
                          +--------------------+
                          | current: A, B      |
                          | revoked: none      |
                          +--------------------+

   One way to do this is by generating a TAL
   [I-D.ietf-sidrops-https-tal] for key B and verifying that validation
   using this yields the same results as validation using the TAL for
   key A would.  However, note, that it is preferred that this is done
   as part of an automated process that is sufficiently well tested, and
   that the contents of the repositories for keys 'A' and 'B' are
   updated as a single delta if the publication protocol [RFC8181] is
   used (see also: Section 5).

6.2.2.  Relying Parties

   Relying Parties who have a TAL for key 'A' configured will discover
   the TAK object.  If the RP does not support this object, it will
   reject this object but continue to validate the remaining RPKI tree
   as usual.  If the RP does support TAK objects it will conclude that
   there are now two keys 'A' and 'B', and no revoked keys that it
   should be aware of.  Since key 'A' is still current, the RP will
   continue to validate the RPKI tree structure using the repository for
   key 'A', ignoring the non-TAK objects in the repository for key 'B'.

   The result will be the same for Relying Parties who have a TAL for
   key 'B' configured, because both keys are equivalent at this time.

6.3.  Planned Key Revocation

6.3.1.  Trust Anchor

   The TA has now decided that key 'A' must be revoked.  It still has
   access to this key and the repository, so it can perform a planned
   key roll.  In addition to revoking key 'A', the TA will also generate
   new key 'C' to ensure that it has at least two current keys at all
   times for redundancy.

   Keys 'B' and 'C' will become current keys on the TAK objects for all
   keys: 'A', 'B' and 'C'.  Key 'A' will become part of the revoked keys
   on the TAK objects for keys 'A' and 'B'.  Note that it is not needed
   to list key 'A' as revoked on the TAK file for key 'C', because RPs
   will only learn about key 'C' at the same time as learning about the
   revocation of key 'A' (see also below).





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   The TA will publish a long-lived TAK file and MFT and CRL only for
   key 'A' and publish these objects as waypointers for RPs that have a
   TAL pointing at key 'A' before destroying key 'A'.

   The resulting structure for key 'A' will be as follows:

                          +--------------------+
                          |        A.MFT       |
                          +--------------------+
                          | A.CRL      <hash>  |
                          | A.TAK      <hash>  |
                          +--------------------+

                          +--------------------+
                          |        A.CRL       |
                          +--------------------+
                          | revocations..      |
                          +--------------------+

                          +--------------------+
                          |        A.TAK       |
                          +--------------------+
                          | current: B, C      |
                          | revoked: A         |
                          +--------------------+

   The resulting structures for keys 'B' and 'C' will be as follows:
























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           +--------------------+         +--------------------+
           |        B.MFT       |         |        C.MFT       |
           +--------------------+         +--------------------+
           | B.CRL      <hash>  |         | B.CRL      <hash>  |
           | B.TAK      <hash>  |         | B.TAK      <hash>  |
           | C1-B.CER   <hash>  |         | C1-C.CER   <hash>  |
           | C2-B.CER   <hash>  |         | C2-C.CER   <hash>  |
           +--------------------+         +--------------------+

           +--------------------+         +--------------------+
           |        B.CRL       |         |        C.CRL       |
           +--------------------+         +--------------------+
           | revocations..      |         | revocations..      |
           +--------------------+         +--------------------+

           +--------------------+         +--------------------+
           |        B.TAK       |         |        C.TAK       |
           +--------------------+         +--------------------+
           | current: B, C      |         | current: B, C      |
           | revoked: A         |         | revoked: <none>    |
           +--------------------+         +--------------------+

           +--------------------+         +--------------------+
           |      C1-B.CER      |         |      C1-C.CER      |
           +--------------------+         +--------------------+
           | resources: C1 res  |         | resources: C1 res  |
           | subject:   C1 name |         | subject:   C1 name |
           | pub key:   C1 key  |         | pub key:   C1 key  |
           | SIA:       C1 SIAs |         | SIA:       C1 SIAs |
           | AKI:       B       |         | AKI:       C       |
           +--------------------+         +--------------------+

           +--------------------+         +--------------------+
           |      C2-B.CER      |         |      C2-B.CER      |
           +--------------------+         +--------------------+
           | resources: C2 res  |         | resources: C2 res  |
           | subject:   C2 name |         | subject:   C2 name |
           | pub key:   C2 key  |         | pub key:   C2 key  |
           | SIA:       C2 SIAs |         | SIA:       C2 SIAs |
           | AKI:       B       |         | AKI:       B       |
           +--------------------+         +--------------------+

   In addition to this the TA SHOULD reach out to RP vendors so that
   they can update the TAL included in the RP software distribution to
   use key 'B'.






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6.3.2.  Relying Parties

   Relying Parties who have a TAL for key 'A' configured will discover
   the TAK object.  If the RP does not support this object, it will
   reject this object but continue to validate the remaining RPKI tree
   as usual.  In this case that means that validation will stop, because
   there are no more objects under key 'A'.  Therefore it is important
   that RPs that do not support TAK files are updated to use the TAL for
   key 'B' through some other process.

   If the RP uses a TAL for key 'A' and it supports TAK objects, it will
   discover that the TAL for key 'A' has keys 'B' and 'C' as current,
   and revokes itself.  It will then proceed to process keys 'B' and 'C'
   and find TALs which list the same current keys.  So, it will now
   replace its notion of the current key set for this TA based on its
   TAL (key 'A') with what it learned.  To keep things simple the RP
   will now conclude that it should re-start validation using a
   remaining current key, in this case key either 'B' or 'C' may be
   used.

   If the RP already had a TAL for key 'B' and it supports TAK objects,
   or it simply started with key 'B' because it added it to its set of
   current keys when this key was pre-staged (see Section 6.2), it will
   learn that key 'A' is revoked and therefore will not attempt to
   verify the TAK file for key 'A'.  It will also learn about key 'C'
   and inspect this key's TAL, and discover that only keys 'B' and 'C'
   are considered current.  Since it started the validation process with
   a key that is still current, it can proceed to validate the RPKI tree
   using the repository under key 'B'.

6.4.  Unplanned revocation

6.4.1.  Trust Anchor

   Now keys 'B' and 'C' are current.  The TA may have intended to revoke
   key 'B', essentially rolling over to key 'C' and a new key 'D', but
   let us suppose that the TA lost access to key 'C'.  In this case the
   TA will simply revoke key 'C' instead, and still introduce a new key
   'D'.

   The major difference with the process described above for planned
   rolls, is that now the TA will not be able to update the TAK object,
   MFT or CRL for key 'C'.  However, because all TAL objects for current
   keys are evaluated before tree validation is performed, it is safe to
   leave these objects in a repository.  Keys 'B' and 'D' will simply
   mark key 'C' as being revoked.





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   If an RP still has a TAL pointing at key 'C' it will discover that
   key 'D' is added, and that key 'B' has been revoked through the TAK
   object published for keys 'B' and 'D'.  At least, as long as the the
   MFT and TAK EE certificates have not expired, and the CRL and MFT are
   not stale.

   If the TA is absolutely sure that the TAL for key 'C' never shipped
   with any RP distribution, then it would also be safe to delete the
   repository key 'C' altogether.  RPs will learn that 'C' is revoked,
   and therefore will not even attempt to download the TAK object.
   However, it is hard to be certain of this and there this is NOT
   RECOMMENDED.

7.  Deployment Considerations

   Including Signed TAL objects while RP tools do not support this
   standard will result in these RPs rejecting these objects.  It is not
   expected that this will result in the invalidation of any other
   object under a Trust Anchor.

   That said, the flagging mechanism introduced here can only be relied
   on once a majority of RPs support it.  Defining when that moment
   arrives is by definition something that cannot be established at the
   time of writing this document.  Until such time, TAs SHOULD continue
   to generate unsigned TAL files [I-D.ietf-sidrops-https-tal], and
   indicate which should be considered their current TAL, and
   communicate them to RPs through other means.

   However, once a majority of RPs support this mechanism it would be
   RECOMMENDED that Trust Anchor operators perform key rolls regularly.
   The most assured way to know that such key rolls will work is by
   making them a part of normal operations.  Determining when this
   moment arrives is by definition out of scope for this document, as it
   should be based on operational experience.

8.  IANA Considerations

8.1.  OID

   IANA is to add the following to the "RPKI Signed Objects" registry:

          Decimal | Description                    | References
          --------+--------------------------------+---------------
          TBD     | Trust Anchor Keys              | [section 3.1]







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8.2.  File Extension

   IANA is to add an item for the Signed TAL file extension to the "RPKI
   Repository Name Scheme" created by [RFC6481] as follows:

          Extension  |   RPKI Object              | References
          -----------+-------------------------------------------
           .tak      |   Trust Anchor Keys        | [this document]

9.  Security Considerations

   TBD

10.  Acknowledgements

   The authors wish to thank Martin Hoffmann for a thourough review of
   this document.

11.  References

11.1.  Normative References

   [I-D.ietf-sidrops-https-tal]
              Huston, G., Weiler, S., Michaelson, G., Kent, S., and T.
              Bruijnzeels, "Resource Public Key Infrastructure (RPKI)
              Trust Anchor Locator", draft-ietf-sidrops-https-tal-05
              (work in progress), October 2018.

   [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>.

   [RFC3779]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
              Addresses and AS Identifiers", RFC 3779,
              DOI 10.17487/RFC3779, June 2004,
              <https://www.rfc-editor.org/info/rfc3779>.

   [RFC5781]  Weiler, S., Ward, D., and R. Housley, "The rsync URI
              Scheme", RFC 5781, DOI 10.17487/RFC5781, February 2010,
              <https://www.rfc-editor.org/info/rfc5781>.

   [RFC6481]  Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              Resource Certificate Repository Structure", RFC 6481,
              DOI 10.17487/RFC6481, February 2012,
              <https://www.rfc-editor.org/info/rfc6481>.





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   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482,
              DOI 10.17487/RFC6482, February 2012,
              <https://www.rfc-editor.org/info/rfc6482>.

   [RFC6486]  Austein, R., Huston, G., Kent, S., and M. Lepinski,
              "Manifests for the Resource Public Key Infrastructure
              (RPKI)", RFC 6486, DOI 10.17487/RFC6486, February 2012,
              <https://www.rfc-editor.org/info/rfc6486>.

   [RFC6487]  Huston, G., Michaelson, G., and R. Loomans, "A Profile for
              X.509 PKIX Resource Certificates", RFC 6487,
              DOI 10.17487/RFC6487, February 2012,
              <https://www.rfc-editor.org/info/rfc6487>.

   [RFC6488]  Lepinski, M., Chi, A., and S. Kent, "Signed Object
              Template for the Resource Public Key Infrastructure
              (RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012,
              <https://www.rfc-editor.org/info/rfc6488>.

   [RFC6489]  Huston, G., Michaelson, G., and S. Kent, "Certification
              Authority (CA) Key Rollover in the Resource Public Key
              Infrastructure (RPKI)", BCP 174, RFC 6489,
              DOI 10.17487/RFC6489, February 2012,
              <https://www.rfc-editor.org/info/rfc6489>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [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>.

   [RFC8181]  Weiler, S., Sonalker, A., and R. Austein, "A Publication
              Protocol for the Resource Public Key Infrastructure
              (RPKI)", RFC 8181, DOI 10.17487/RFC8181, July 2017,
              <https://www.rfc-editor.org/info/rfc8181>.

   [X.690]    ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002,
              "Information technology - ASN.1 encoding rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER)", 2002.






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11.2.  Informative References

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <https://www.rfc-editor.org/info/rfc5652>.

Authors' Addresses

   Tim Bruijnzeels
   NLnet Labs

   Email: tim@nlnetlabs.nl
   URI:   https://www.nlnetlabs.nl/


   Carlos Martinez
   LACNIC

   Email: carlos@lacnic.net
   URI:   https://www.lacnic.net/


   Rob Austein
   Dragon Research Labs

   Email: sra@hactrn.net

























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