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EXPERIMENTAL

Network Working Group                                        D. Chadwick
Request for Comments: 2120                         University of Salford
Category: Experimental                                        March 1997


                 Managing the X.500 Root Naming Context

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  This memo does not specify an Internet standard of any
   kind.  Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Abstract

   The X.500 Standard [X.500 93] has the concept of first level DSAs,
   whose administrators must collectively manage the root naming context
   through bi-lateral agreements or other private means which are
   outside the scope of the X.500 Standard.

   The NameFLOW-Paradise X.500 service has an established procedure for
   managing the root naming context, which currently uses Quipu
   proprietary replication mechanisms and a root DSA. The benefits that
   derive from this are twofold:

      - firstly it is much easier to co-ordinate the management of the
      root context information, when there is a central point of
      administration,

      - secondly the performance of one-level Search operations is
      greatly improved because the Quipu distribution and replication
      mechanism does not have a restriction that exists in the 1988 and
      1993 X.500 Standard.

   The NameFLOW-Paradise project is moving towards 1993 ISO X.500
   Standard replication protocols and wants to standardise the protocol
   and procedure for managing the root naming context which will be
   based on 1993 X.500 Standard protocols. Such a protocol and procedure
   will be useful to private X.500 domains as well as to the Internet
   X.500 public domain. It is imperative that overall system performance
   is not degraded by this transition.

   This document describes the use of 1993 ISO X.500 Standard protocols
   for managing the root context. Whilst the ASN.1 is compatible with
   that of the X.500 Standard, the actual settings of the parameters are
   supplementary to that of the X.500 Standard.




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Table of Contents

   1 Introduction.............................................   2
   2 Migration Plan...........................................   3
   3 Technical Solutions......................................   3
   4 The Fast Track Solution..................................   4
   5 The Slower Track Solution................................   6
   6 The Long Term Solution...................................   7
   7 Security Considerations..................................   8
   8 Acknowledgments..........................................   9
   9 References...............................................   9
   10 Author's Address........................................  10
   Annex 1 Solution Text of Defect Reports submitted to ISO/ITU-
        T by the UK...........................................  11
   Annex 2 Defect Report on 1993 X.500 Standard for Adding
        full ACIs to DISP for Subordinate References, so that
        Secure List Operation can be performed in Shadow DSAs.  12
   Annex 3 Defect Report on 1997 X.500 Standard Proposing
        an Enhancement to the Shadowing Agreement in order to
        support 1 Level Searches in Shadow DSAs...............  14

1     Introduction

   The NameFLOW-Paradise service has a proprietary way of managing the
   set of first level DSAs and the root naming context. There is a
   single root DSA (Giant Tortoise) which holds all of the country
   entries, and the country entries are then replicated to every country
   (first level) DSA and other DSAs by Quipu replication [RFC 1276] from
   the root DSA. In June 1996 there were 770 DSAs replicating this
   information over the Internet. The root DSA is not a feature of the
   X.500 Standard [X.500 93]. It was introduced because of the non-
   standard nature of the original Quipu knowledge model (also described
   in RFC 1276). However, it does have significant advantages both in
   managing the root naming context and in the performance of one-level
   Searches of the root.  Performance is increased because each country
   DSA holds all the entry information of every country.

   By comparison, the 1988 X.500 Standard root context which is
   replicated to all the country DSAs, only holds knowledge information
   and a boolean (to say if the entry is an alias or not) for each
   country entry. This is sufficient to perform an insecure List
   operation, but not a one-level Search operation. When access controls
   were added to the 1993 X.500 Standard, the root context information
   was increased (erroneously as it happens - this is the subject of
   defect report 140 - see Annex 1) to hold the access controls for each
   country entry, but a note in the X.500 Standard restricted its use to
   the List operation, in order to remain compatible with the 1988
   edition of the X.500 Standard.



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2     Migration Plan

   The NameFLOW-Paradise service is now migrating to X.500 Standard
   [X.500 93] conforming products, and it is essential to replace the
   Quipu replication protocol with the 1993 shadowing and operational
   binding protocols, but without losing the performance improvement
   that has been gained for one-level Searches.

   It is still the intention of the NameFLOW-Paradise service to have
   one master root DSA. This root DSA will not support user Directory
   operations via the LDAP, the DAP or the DSP, but each country (first
   level) DSA will be able to shadow the root context from this root
   DSA, using the DISP. Each first level DSA then only needs to have one
   bi-lateral agreement, between itself and the root DSA. This agreement
   will ensure that the first level DSA keeps the root DSA up to date
   with its country level information, and in turn, that the root DSA
   keeps the first level DSA up to date with the complete root naming
   context. When a new first level DSA comes on line, it only needs to
   establish a bi-lateral agreement with the root DSA, in order to
   obtain the complete root context.

   This is a much easier configuration to manage than simply a set of
   first level DSAs without a root DSA, as suggested in the ISO X.500
   Standard. In the X.500 Standard case each first level DSA must have
   bi-lateral agreements with all of the other first level DSAs. When a
   new first level DSA comes on line, it must establish agreements with
   all the existing first level DSAs. As the number of first level DSAs
   grows, the process becomes unmanageable.

   However, it is also important to increase the amount of information
   that is held about every country entry, so that a one-level Search
   operation can be performed in each first level DSA, without it
   needing to chain or refer the operation to all the other first level
   DSAs (as is currently the case with a X.500 Standard conforming
   system.)

3     Technical Solutions

   3.1 The solution at first appears to be relatively straight forward,
   and involves two steps. Firstly, create a root DSA, and establish
   hierarchical operational bindings using the DOP, between it and each
   master first level DSA. Secondly, each master first level DSA enters
   into a shadowing agreement with the root DSA, to shadow the enlarged
   root context information. In this way each first level DSA is then
   capable of independently performing List and one-level Search
   operations, and name resolving to all other first level DSAs.





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   3.2 Unfortunately there are a number of complications that inhibit a
   quick implementation of this solution. Firstly, few DSA suppliers
   have implemented the DOP. Secondly there are several defects in the
   X.500 Standard that currently stop the above solution from working.

   3.3 At a meeting chaired by DANTE in the UK on 18 June 1996[Mins], at
   which several DSA suppliers were present, the following pragmatic
   technical solution was proposed. This comprises a fast track partial
   solution and a slower track fuller solution. Both the fast and slower
   tracks use the shadowing protocol (DISP) for both steps of the
   solution, and do not rely on the DOP to establish HOBs. The fast
   track solution, described in section 4, will support knowledge
   distribution of the root context, and the (insecure) List operation
   of the root's subordinates. The List operation will be insecure
   because access control information will not be present in the shadow
   DSEs. (However, since it is generally thought that first level
   entries, in particular country entries, are publicly accessible, this
   is not considered to be a serious problem.) Suppliers expect to have
   the fast track solution available before the end of 1996. The slower
   track solution, described in section 5, will in addition support
   fully secure one level Search and List operations of the root
   (without the need to chain to the master DSAs). Suppliers at the
   DANTE meeting did not realistically expect this to be in their
   products much sooner than mid 1998.

   3.4 The long term solution, which relies on the DOP to establish
   HOBs, is described in section 6 of this document.

   (Note. It is strongly recommended that non-specific subordinate
   references should not be allowed in the root context for efficiency
   reasons. This is directed by the European functional X.500 Standard
   [ENV 41215] and the NADF standing document [NADF 7]. It is also
   preferred by the International X.500 Standardized Profile [ISP
   10615-6].)

4     The Fast Track Solution

   4.1 The fast track solution provides root knowledge collection and
   insecure List operations for first level DSAs, and will be of use to
   systems which do not yet support the DOP for managing hierarchical
   operational bindings. The fast track solution relies upon the DISP
   with very few changes to the 1993 edition of the X.500 Standard.









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   4.2 Each master first level DSA administrator will make available to
   the administrator of the root DSA, sufficient information to allow
   the root DSA to configure a subordinate reference to their DSA. In
   the simplest case, this can be via a telephone call, and the
   information comprises the access point of their DSA and the RDNs of
   the first level entries that they master.

   4.3 Each master first level DSA enters into a shadowing agreement
   with the root DSA, for the purpose of shadowing the root naming
   context.

   The 1993 edition of the X.500 Standard explicitly recognises that
   there can be master and shadow first level DSAs (X.501 Section 18.5).
   (The 1988 edition of the X.500 Standard does not explicitly recognise
   this, since it does not recognise shadowing.) A shadow first level
   DSA holds a copy of the root context, provided by a master first
   level DSA. In addition it holds shadow copies of the (one or more)
   country entries that the master first level DSA holds. There is
   currently an outstanding defect report [UK 142] on the 1993 X.500
   Standard to clarify how a shadowing agreement is established between
   first level DSAs. Once this has been ratified, the only additional
   text needed in order to establish a shadowing agreement between the
   root DSA and a master first level DSA is as follows:

   "When clause 9.2 of ISO/IEC 9594-9:1993 is applied to the
   shadowing of the root context by a first level DSA from the root
   DSA of a domain, then UnitOfReplication shall be set as follows:

   contextPrefix of AreaSpecification shall be null,

   replicationArea of AreaSpecification shall be set to
                       SEQUENCE {
        specificExclusions  [1]  SET OF {
             chopBefore          [0]  FirstLevelEntry},
        maximum             [3]  1 }

   where FirstLevelEntry is the RDN of a first level entry (e.g.
   country, locality or international organisation) held by the
   master first level DSA. specificExclusions shall contain one

   FirstLevelEntry for each first level entry mastered by this DSA,

   attributes of UnitofReplication shall be an empty SET OF SEQUENCE,

   knowledge of UnitofReplication shall be set to both (shadow and
   master).





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   In other words, the information that will be replicated will be an
   empty root entry plus all the attributes of the complete set of
   subordinate DSEs of the root that are held in the root DSA excluding
   the DSEs that the first level DSA already masters, plus a complete
   set of subordinate reference."

   Note that the maximum component of replicationArea, although not
   strictly necessary, is there for pragmatic reasons, for example,
   where a community of users wish to use the root DSA to hold some
   country specific entries.

5     The Slower Track Solution

   5.1 The slower track solution provides support for fully secure one
   level Search and List operations of the root in first level DSAs, and
   comprises of two steps for HOB establishment between the root DSA and
   master first level DSAs, using the DISP instead of the DOP. Step one,
   described in 5.3, allows the root DSA to shadow first level entries
   from a master first level DSA. Step two, described in 5.4, requires
   either the root DSA administrator or the root DSA implementation to
   massage the shadow first level entries so that they appear to have
   been created by a HOB.  Managing the root context then continues as
   in 4.3 above.

   5.2 This solution requires two significant defects in the ISO X.500
   Standard to be corrected. Firstly, access control information needs
   to be added to subordinate references in the DISP to allow the List
   operation to work securely in a shadowed DSA. (The ACI are held in
   both the subr DSE and in its subentry.) This requires a defect report
   on the 93 X.500 Standard to be submitted. The text of this defect
   report (that has been submitted to ISO) is given in Annex 2.

   Secondly, a new type of shadowing agreement will need to be
   established between the supplier and consumer DSAs, to copy
   subordinate entries rather than simply subordinate references, so
   that one level Search operations can work in the shadowing DSA.  This
   procedure should have been part of the 1997 edition of the X.500
   Standard, but due to an omission is not. Consequently  a defect
   report on the 1997 X.500 Standard has been submitted. The text of
   this defect report is given in Annex 3.











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   5.3 The hierarchical operational binding between the root DSA and a
   master first level DSA can be replaced by a set of "spot" shadowing
   agreements, in which the first level DSA acts as the supplier, and
   the root DSA as the consumer. Each "spot" shadowing agreement
   replicates a first level entry which is mastered by the first level
   DSA. The UnitOfReplication shall be set as follows:

   contextPrefix of AreaSpecification shall be FirstLevelEntry,

   replicationArea of AreaSpecification shall be set to
                       SEQUENCE {
        specificExclusions  [1]  SET OF {
                       chopAfter [1]  {null} } }

   where FirstLevelEntry is the Distinguished Name of a first level
   entry (e.g. country, locality or international organisation) held by
   the master first level DSA.

   attributes of UnitofReplication shall be an empty SET OF SEQUENCE,

   knowledge of UnitofReplication shall be absent.

   5.4 The root DSA administrator, or the root DSA implementation
   (suitably tailored) must then administratively update each shadowed
   first level entry, so that they appear to have been created by a HOB,
   i.e. it is necessary to add a subordinate reference to each one of
   them. The subordinate reference will point to the respective master
   first level DSA, and will comprise of a specific knowledge attribute,
   and the DSE bit of type subr being set. The contents of the specific
   knowledge attribute can be created from the contents of the supplier
   knowledge attribute already present in the first level entry and
   created by the "spot" shadowing agreement.

6     The Long Term Solution

   6.1 Each master first level DSA will have a hierarchical operational
   binding with the root DSA of the domain. Each master first level DSA
   will master one or more first level entries. The hierarchical
   operational binding will keep the appropriate subordinate
   reference(s) (of category shadow and master) up to date, as well as
   the other entry information that is needed for one-level Search
   operations (such as access controls, and attributes used in
   filtering).








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   Whilst hierarchical agreements are standardised, this particular
   novel use of a HOB is not specifically recognised in the X.500
   Standard.  Although the ASN.1 will support it, there is no supporting
   text in the X.500 Standard. The following text supplements that in
   the X.500 Standard, and describes how a first level DSA may have a
   hierarchical operational binding with the root DSA of its domain.

   "Clause 24 of ISO/IEC 9594-4:1993 shall also apply when a first level
   DSA is a subordinate DSA, and the root DSA of the domain is the
   superior DSA. The naming context held by the superior (root) DSA is
   the root naming context (or root context - the terms are synonymous)
   of the domain. The root context consists of the root entry of the DIT
   (which is empty) plus a complete set of subordinate DSEs (i.e. first
   level DSEs), one for each first level naming context in the domain,
   and their corresponding subentries.  The first level DSEs and their
   subentries will contain, in addition to specific knowledge attribute
   values of category master and shadow, sufficient attributes and
   collective attributes, including access control information, to allow
   List and one-level Search operations to be performed on them.

   In clause 24.1.2, the DistinguishedName of the immediateSuperior
   component of HierarchicalAgreement shall be null."

   6.2 The ASN.1 of hierarchical operational bindings already allows any
   attributes to be passed from the subordinate DSA to the superior DSA
   (SubordinateToSuperior parameter in clause 24.1.4.2 of X.518).
   However, a note in the 1993 edition of the X.500 Standard limits this
   to those which are required to perform a List operation. In the 1997
   edition of the X.500 Standard [DAM User] this restriction has been
   removed, so that the attributes may also be used for a one-level
   Search operation.

   1993 implementations of X.500 conforming to this RFC, shall also
   remove this restriction.

7     Security Considerations

   Security considerations are discussed in this memo in relation to
   List and one-level Search operations. Each DSE has access control
   information associated with it, and these must be adhered to when the
   operations are performed.










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8     Acknowledgments

   The author would like to thank DANTE, without whose funding this work
   would not have been possible.

   The author would also like to thank Nexor, who reviewed the first
   version of this document in detail and provided valuable comments,
   and who first suggested the use of the DISP as a pragmatic solution
   for HOB establishment until the DOP becomes widely implemented.

   The author would also like to thank John Farrell from the ISODE
   Consortium, Andrew Palk   from Digital and Keith Richardson from ICL
   who attended the DANTE meeting, and contributed to the technical
   contents of the defect reports in Annexes 2 and 3.

9     References

   [DAM User] Draft Amendments on Minor Extensions to OSI Directory
   Service to support User Requirements, August 1995.

   [ENV 41215] "Behaviour of DSAs for Distributed Operations",
   European X.500 Pre-Standard, Dec 1992

   [ISP 10615-6] "DSA Support of Distributed Operations", 5th draft
   pDISP, Oct 1994

   [Mins] "Notes of DANTE meeting to discuss Managing the Root Naming
   Context. 18 June 1996." D W Chadwick, circulated to IDS mailing
   list

   [NADF 7] SD-7 "Mapping the North American DIT onto Directory
   Management Domains", North American Directory Forum, V 8.0, Jan
   1993

   [RFC 1276] Kille, S., "Replication and Distributed Operations
   extensions to provide an Internet Directory using X.500", UCL,
   November 1991.














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   [UK 142] Defect report number 142, submitted by the UK to ISO,
   March 1995. (Proposed solution text included in Annex 1)

   [X.500 93] X.500 | 9594.Part 1 Overview of Concepts, Models and
   Services
   X.501 | 9594.Part 2 Models
   X.511 | 9594.Part 3 Abstract Service Definition
   X.518 | 9594.Part 4 Procedures for Distributed Operations
   X.519 | 9594.Part 5 Protocol Specifications
   X.520 | 9594.Part 6 Selected Attribute Types
   X.521 | 9594.Part 7 Selected Object Classes
   X.509 | 9594.Part 8 Authentication Framework
   X.525 | 9594.Part 9 Replication

10     Author's Address

   D W Chadwick
   IT Institute
   University of Salford
   Salford
   M5 4WT
   England
   Phone: +44 161 745 5351
   Fax: +44 161 745 8169
   E-mail: D.W.Chadwick@iti.salford.ac.uk


























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Annex 1 Solution Text of Defect Reports submitted to ISO/ITU-T by
   the UK

Defect Report 140

   Nature of Defect

   In section 24.1.4.2 it is defined that the SubordinateToSuperior
   parameter of a HOB can pass an entryInfo parameter. This should
   contain entryACI which may be used in the resolution of the List
   operation.

   This is not correct as the prescriptive ACI from the relevant
   subentries is also required in the superior DSA.

   Solution Proposed by Source

   It is proposed that the following is added to the
   SubordinateToSuperior SEQUENCE of section 24.1.4.2 of X.518:

        subentries     [2] SET OF SubentryInfo OPTIONAL

   This is used to pass the relevant subentries from the subordinate to
   the superior. This is similar to the way subentry information is
   passed in the SuperiorToSubordinate parameter defined in 24.1.4.1.

Defect Report 142

   Nature of Defect

   The text which describes AreaSpecification in clause 9.2 of X.525 is
   completely general. However, for the special case of replicating
   first level knowledge references between first level DSAs, a
   clarifying sentence should be added.

   Solution Proposed by Source

   In Section 9.2, under the ASN.1, after the description of area, and
   before the description of SubtreeSpecification, add the sentence:

      "For the case where a DSA is shadowing first level knowledge from
      a first level DSA, the contextPrefix component is empty."









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Annex 2 Defect Report on 1993 X.500 Standard for Adding full ACIs to
      DISP for Subordinate References, so that Secure List Operation can
      be performed in Shadow DSAs

   Nature of Defect:

   The List operation may be carried out in a superior DSA using
   subordinate reference information, providing that the fromEntry flag
   is set to false in the response. However, in order to do this
   securely, complete access control information is needed for the RDN
   of the subordinate entry. The existing text assumes that this is held
   in entry ACI (e.g. see 9.2.4.1 c) or in prescriptive ACI held in
   subentries above the DSE (e.g. see 9.2.4.1 b). In the case of a
   subordinate reference, the prescriptive ACI may be held below the
   DSE, if the subordinate reference points to a new administrative
   point. The shadowing document needs to make it clear that this can be
   the case, and needs to allow for this additional access control
   information to be shadowed.

   A related defect report (140) has already suggested that this same
   omission should be added to operational bindings.

   Solution Proposed by the Source:

   All the following changes are to X.525|ISO 9594-9.

   I) Insert the following text into 7.2.2.3, at the end of both the
   second paragraph and the first sentence of the third paragraph (after
   "appropriate knowledge"): "and access control information."

   II) Insert a new third paragraph into 7.2.2.3: "If  subordinate
   knowledge is supplied, and the supplying DSE (of type subr) is also
   of type admPoint, then the SDSE shall additionally be of type
   admPoint and the administrativeRole attribute shall be supplied.  If
   such a DSE has any immediately subordinate subentries containing
   PrescriptiveACI relating to the administrative point, then they shall
   also be supplied as SDSEs in the shadowed information.

   Note. A DSE can be of type subr and admPoint in a superior DSA, when
   the naming context in the subordinate DSA is the start of a new
   administrative area."

   III) Update figure 3 to show a subentry immediately below a
   subordinate reference. The subentry contains prescriptiveACI and is
   part of the shadowed information.






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                            .
    Etc.                   / \
                          /   \
                         /  o  \
                        /  / \  \
   Replicated          /  /   \  \
   Area --------------/--/->   \  \
                     /  /       \  \
                    /  /         \  \
                   /  /           \  \
   Subordinate    /__/_____________\__\
   knowledge--------/-> o   o    o  \
                   /   /          \  \
   Prescriptive---/-> o            o  \
   ACI Subentries/                     \
                   Unit of Replication


                Etc.
                 o
                / \
               /   \
              /     \
             /       \
            /         \
           /           \
          /_____________\
           o    o     o
          /            \
         o              o
       Shadowed Information

                 ADDITIONS TO FIGURE 3, SECTION 7.2, X.525

   IV) Add supporting text to section 7.2 in the paragraph after Figure
   3. Insert after the sentence "Subordinate knowledge may also be
   replicated" the following sentences "Implicit in the Add supporting
   text to section 7.2 in the paragraph after Figure 3.  Insert after
   the sentence subordinate knowledge is the access control information
   which governs access to the RDN of the subordinate knowledge. When
   the subordinate entry is an administrative point in another DSA, then
   part of this access control information may be held in
   prescriptiveACI subentries beneath the subordinate knowledge."

   v) Add a new point d) to 9.2.4.1: "if subordinate knowledge (not
   extended knowledge) is shadowed then any prescriptiveACI in
   subordinate subentries shall also be copied."




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Annex 3 Defect Report on 1997 X.500 Standard Proposing an Enhancement to
the Shadowing Agreement in order to support 1 Level Searches in Shadow
DSAs.

   Nature of Defect:

   The 1997 edition of the X.500 Standard has allowed, for reasons of
   operational efficiency, one level Searches to be carried out in the
   superior DSA, when the actual entries are context prefixes in
   subordinate DSAs. The HOBs have been extended to allow this entry
   information to be carried up to the superior DSA. Unfortunately, we
   forgot to add the corresponding text to Part 9, so that shadow DSAs
   are able to copy this additional information from the supplier DSA.
   This defect report proposes the additional text for Part 9.

   Solution Proposed by the Source:

   All the following changes are to X.525|ISO 9594-9.

   I) Section 9.2, add a new subordinates parameter to
   UnitOfReplication, viz:

   UnitOfReplication   ::= SEQUENCE{
   area                AreaSpecification,
   attributes          AttributeSelection,
   knowledge           Knowledge OPTIONAL,
   subordinates        BOOLEAN DEFAULT FALSE }

   subordinates is used to indicate that subordinate entries, rather
   than simply subordinate references, are to be copied to the
   consumer DSA. subordinates may only be TRUE if knowledge is
   requested and extendedKnowledge is FALSE.

   II) Insert a new fourth paragraph (assuming previous defect for
   List was accepted) into 7.2.2.3:

   "If subordinates is specified, then the supplier shall send
   subordinate entries rather than subordinate references, and the
   SDSEs will be of type subr, entry and cp. The subordinate entries
   will contain attributes according to the attribute selection.

   In addition, if the supplying DSE is of type admPoint, then the
   SDSE shall additionally be of type admPoint and the
   administrativeRole attribute shall be supplied. All appropriate
   subentries below the admPoint DSE shall also be supplied as SDSEs
   in the shadowed information."





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