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LTANS                                                   A. Jerman Blazic
Internet-Draft                                                    SETCCE
Intended status: Experimental                               P. Sylvester
Expires: August 28, 2008                                         EdelWeb
                                                              C. Wallace
                                                      Cygnacom Solutions
                                                       February 25, 2008


                   Long-term Archive Protocol (LTAP)
                        draft-ietf-ltans-ltap-06

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on August 28, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This document describes a service operated as a trusted third party
   to securely archive electronic documents called a long-term archive
   service (LTA).  We describe an architecture framework and a protocol
   allowing clients to interact with such a service.  Bindings to
   concrete transport and security protocol layers are given.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements notation  . . . . . . . . . . . . . . . . . .  5
   2.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Framework  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Functional Overview  . . . . . . . . . . . . . . . . . . .  7
     3.2.  Service functions of an LTA  . . . . . . . . . . . . . . .  8
     3.3.  Transactions . . . . . . . . . . . . . . . . . . . . . . .  9
     3.4.  Life cycles of objects . . . . . . . . . . . . . . . . . . 10
     3.5.  Roles, Service Types, Policies and Configurations  . . . . 12
     3.6.  Identification . . . . . . . . . . . . . . . . . . . . . . 14
     3.7.  External definitions . . . . . . . . . . . . . . . . . . . 15
     3.8.  Entities . . . . . . . . . . . . . . . . . . . . . . . . . 18
     3.9.  Data Model . . . . . . . . . . . . . . . . . . . . . . . . 19
   4.  Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     4.1.  Artifacts  . . . . . . . . . . . . . . . . . . . . . . . . 22
     4.2.  MessageDigest  . . . . . . . . . . . . . . . . . . . . . . 22
     4.3.  MetaData . . . . . . . . . . . . . . . . . . . . . . . . . 23
     4.4.  Nonce  . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     4.5.  RawData  . . . . . . . . . . . . . . . . . . . . . . . . . 26
     4.6.  DataOrTransaction  . . . . . . . . . . . . . . . . . . . . 27
     4.7.  Data . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     4.8.  SerialNumber . . . . . . . . . . . . . . . . . . . . . . . 28
     4.9.  LtapTime . . . . . . . . . . . . . . . . . . . . . . . . . 28
     4.10. Version  . . . . . . . . . . . . . . . . . . . . . . . . . 28
     4.11. EntityIdentifier . . . . . . . . . . . . . . . . . . . . . 29
     4.12. ServiceType  . . . . . . . . . . . . . . . . . . . . . . . 30
     4.13. StatusInformation  . . . . . . . . . . . . . . . . . . . . 31
     4.14. RequestInformation . . . . . . . . . . . . . . . . . . . . 32
   5.  Top level protocol elements  . . . . . . . . . . . . . . . . . 34
     5.1.  Request  . . . . . . . . . . . . . . . . . . . . . . . . . 34
     5.2.  StatusNotice . . . . . . . . . . . . . . . . . . . . . . . 35
     5.3.  OperationResponse  . . . . . . . . . . . . . . . . . . . . 35
     5.4.  Response . . . . . . . . . . . . . . . . . . . . . . . . . 36
   6.  Service Operations . . . . . . . . . . . . . . . . . . . . . . 36
     6.1.  ARCHIVE operation  . . . . . . . . . . . . . . . . . . . . 37
     6.2.  EXPORT operation . . . . . . . . . . . . . . . . . . . . . 38
     6.3.  DELETE operation . . . . . . . . . . . . . . . . . . . . . 38
     6.4.  VERIFY operation . . . . . . . . . . . . . . . . . . . . . 39
     6.5.  STATUS operation . . . . . . . . . . . . . . . . . . . . . 39
     6.6.  LISTIDS operation  . . . . . . . . . . . . . . . . . . . . 39
   7.  Presentation and Bindings  . . . . . . . . . . . . . . . . . . 40
     7.1.  Common parameters and encoding requirements  . . . . . . . 41
     7.2.  e-mail bindings  . . . . . . . . . . . . . . . . . . . . . 43
     7.3.  HTTP Bindings  . . . . . . . . . . . . . . . . . . . . . . 43
     7.4.  Security . . . . . . . . . . . . . . . . . . . . . . . . . 44
   8.  Credits  . . . . . . . . . . . . . . . . . . . . . . . . . . . 45



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   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 45
   10. IPR Patent Information . . . . . . . . . . . . . . . . . . . . 46
   11. IANA considerations  . . . . . . . . . . . . . . . . . . . . . 47
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48
     12.1. Normative references . . . . . . . . . . . . . . . . . . . 48
     12.2. Informative references . . . . . . . . . . . . . . . . . . 48
   Appendix A.  ASN.1 module in current syntax  . . . . . . . . . . . 49
   Appendix B.  ASN.1 module in 1988 syntax . . . . . . . . . . . . . 52
   Appendix C.  XML schema for LTAP . . . . . . . . . . . . . . . . . 55
   Appendix D.  Additional XML definitions  . . . . . . . . . . . . . 62
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 65
   Intellectual Property and Copyright Statements . . . . . . . . . . 66







































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1.  Introduction

   Conservation of documents is important, one can even say that
   appropriate conservation rules are a prerequisite for data to become
   a document.  Conservation has several aspects, e.g., duration or
   accessibility, which vary based on the nature of the document.  For
   example, a document may be conserved for a certain period and may be
   destroyed after that, or its lifetime may be extended when the
   document becomes part of a conflict.  Also, documents may become part
   of historical archives.  A document may be accessible on a public or
   restricted basis to a set of potentially interested or authorized
   entities.

   The protocol described in this document enables the use of a
   specialized service for conservation of electronic documents.  The
   service creates and makes available enough information to demonstrate
   the existence, integrity and authenticity of electronic data over any
   period of time.  In other words, the service assumes the
   responsibility to retrieve and, optionally, store data for
   conservation, create and store evidence to guarantee data integrity
   and completeness, and to maintain accessibility of data and evidence
   created.

   This document describes a protocol for interacting with a long-term
   archive service (LTA).  The document contains only description of a
   general request and response structure, and a detailed protocol
   description concerning access to an LTA.  Other specifications and
   descriptions, e.g. a framework protocol containing mappings to
   transport and security services, are addressed elsewhere.  The
   protocol is intended to be used in client-server architecture, where
   client is simply an end user (a physical user or another service) and
   the server as an LTA.

   The process of replacing paper based workflow and document handling
   which is also known as 'dematerialization' ignores to a certain
   degree the requirements for long-term stability of documents.
   Document conservation is generally performed by specialized services.
   For electronic formats it is proposed to use similar approaches,
   while maintaining the distance of technical characteristics (paper
   versus electronic).  Conservation might be taken out from other
   workflow activities, while the same procedures (evidence creation)
   might be used for any milestone in an electronic document lifecycle
   (e.g. version marking).

   Since conservation of documents created by one entity is only
   necessary if there is a potential entity to which the document may be
   presented at some time, the conservation service (LTA) acts as a
   trusted third party for those two entities.  The main role of an LTA



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   is to generate and provide enough information for archived data
   existence in time, integrity and authenticity demonstration over long
   periods of time.  Provision of data storage services is optional and
   may be assured by supportive infrastructure (e.g. database or
   document storage/management system).

   Conservation is more that just storing a document.  Not only, but in
   particular when the life time is very long, appropriate measures to
   ensure the integrity of the document must be used.  This aspect is
   handled by this specification.  Sometimes, complete transfer of the
   document information to a new physical support has to be done like
   transformations from marble to paper or paper to microfilm.  The need
   for such transformation makes the definition of what constitutes the
   actual document somewhat difficult, in particular it should be done
   independantly of the support, and even independantly of a current
   format of the document information.  Transformation of documents are
   largely the scope of this specification besides the obvious
   possibility of storing all formats of a document and assertions about
   the transformations.

   Defined data structures are presented in XSD and ASN1 forms.  The XSD
   form has been automatically generated from the ASN.1.  When the ASN.1
   defined data structured are encoded using XER encoding rules, they
   are compatible with data structures encoded according to the XSD.

1.1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2.  Background

   A conservation service or long-term archive (LTA) consists of several
   functional blocks.  Some of these blocks are not considered as they
   present the basic infrastructure, such as the communication network,
   storage device, data management, etc.  Instead, an LTA implements the
   archive interaction protocol as defined by this specification (LTAP)
   and manages archive objects (logically interpreted as packages of
   archive data and conservation attributes) and evidence records
   [RFC4998].  An LTA is a part of a general archive service that
   provides evidence used to demonstrate the existence of an archived
   data object at a given time and the integrity of the archived data
   object since that time.  The LTA is the primary part tasked with
   creating and delivering conservation attributes for archived data.

   [RFC4810] defines the services that must be provided by an LTA.  A



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   pricipal function of the LTA is to generate or obtain evidence
   information for (archive) data submited.  An LTA may accept and store
   data for which it generates (or acquires from another service) and
   maintains evidence inforamtion.  Alternatively, it may simply act as
   an evidence and demonstration information servce without data storage
   capabilities (it relies upon other services for storage of the
   archived data).  Evidence generated and maintained by an LTA
   addresses the problems of long-term integrity and temporal existence.

   Archive objects are the central logical structures defined by the LTA
   and maintained on a long-term basis.  They are atomic elements of an
   LTA service consisting of three logical elements.  The logical
   structure of an archive object consists of:

   o  Archive data (including metadata or other related data) entering
      the LTA using the interaction protocol,

   o  Archive process-related meta or binding information and

   o  Evidence information

   The archive data may contain any data type, e.g., raw data, signed
   data, encrypted data or time stamped data as defined by [RFC4810].
   Archive data may be associated with additional data or attributes,
   e.g. meta information or digital signatures.

   Data generated or collected by the LTA are archive process-related
   meta or binding information including demonstration information and
   evidence information.  Archive metadata is needed to provide enough
   information for e.g. special (i.e., legal) purposes or validity
   demonstration purposes (e.g. complementary information to digital
   signatures).  The LTA collects meta or binding information directly
   from a user or some other entity (e.g.  Certificate Authority).  Such
   information may contain the data owner name, organization, location,
   etc.  Meta or binding information may be submitted using the LTAP.

   Demonstration information is collected to demonstrate facts on the
   archive data.  Such information may be digital signature reference
   information.  The LTA may use external resources to collect such
   information, usually without user intervention.  Evidence data is
   generated by the LTA or collected from an external resource, e.g. a
   time stamping authority.  Evidence information is provided for all
   data: archive data submitted by a client and archive process-related
   data (including binding and demonstration information) collected by
   the LTA from the client or alternative resource.

   The LTA performs perpetual maintenance of archive objects and
   associated metadata for the main purpose of demonstrating archive



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   data existence in time and providing integrity information for the
   complete archiving time.  Archive objects are periodically processed
   to provide long-term stability (e.g. by proof-reading, copying to new
   material, or performing time stamp renewal).

   The LTAP protocol interprets the logical data structure to hold all
   needed information (including references) to build an archive object
   including archive data itself (or reference to archive data).  The
   logical structure of the LTAP messages includes archive data,
   archiving process-related information and references together with
   request and processing information.  Using LTAP, the LTA should have
   enough information to build and perform operations on an archive
   object or group of archive objects.


3.  Framework

   This chapter describes a general framework for secure exchange of
   request and response messages between an archive client and archive
   server, e.g. an LTA.  It provides a high level outline and identifies
   common and external aspects from the concrete protocol data units.

3.1.  Functional Overview

   An LTA, as defined by [RFC4810], is a service that is responsible for
   preserving evidence data and/or data for long periods of time.  The
   service is accessible using the protocol defined in this document.

   The protocol is intended to be used as well as basic functionality
   available to customers of a service provider, as well as an internal
   protocol inside the LTA to access basic building blocks as a black
   box in a standardised way.  The latter usage is intended to permit
   the creating of security zones and auditable implementations.
   Therefore, some functions defined in the protocol may not be
   available to all external customers of an LTA.

   The protocol consists of two layers, the higher layer defines the
   available service functions and their mapping to encodings, the lower
   layer defines the rules for the exchange of protocol messages common
   for all all functions.

   It is assumed that an LTA ensures the long-term availability of
   stored data and created evidence information, as necessary, and uses
   appropriate means to manage data and access rights.  The details of
   these important features of an LTA are outside the scope of this
   specification.

   The common high-level architecture consists of a protocol used to



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   exchange requests and responses securely, potentially over different
   types of transport connections, to ensure the long-term validity of
   responses.

   Clients and servers use one of several object types to build requests
   and responses.  Data objects include raw (archive) data, request
   information, meta information, identification information and
   attestations.

   Requests and responses are exchanged in a secure way responding to
   different security requirements, which may concern the security of
   the transport as well as the long-term validity of the data being
   exchanged.

   The LTA is not a method for implementing something like a secure file
   system.  In general, archived data are rarely accessed, restored or
   transferred.  Thus, the archive operation is the most important one
   and performance is an important concern.  In this case that client
   applications need frequent access to the data, they generally keep a
   copy of the data including evidence information, whose integrity can
   be compared from time to time or when requested.

3.2.  Service functions of an LTA

   The primary aim of this protocol is to enable a formal interaction
   between a client and an LTA.  The result of the interaction is a
   verifiable attestation of procedures performed by an LTA (e.g.
   archive data plus evidence record).  The format for data structures
   used to demonstrate integrity, i.e. to demonstrate that data has not
   undergone any transformations while in the care of the archive, is
   partially defined in other documents, namely in [RFC4998].  This
   specification does not place any requirements on the structure of
   archived data objects.  However, it operates on elements that are
   derived from archive data objects (e.g. message imprints).

   The LTA interface enables clients to perform at least the following
   operations in cooperation with an LTA:

   ARCHIVE:  Submit data to an LTA and request creation of evidence
      information for data

   EXPORT:  Retrieve data (including archive data, meta information and
      evidence information) from an LTA

   DELETE:  Remove data and/or evidence information from an LTA.






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   VERIFY:  Determine the integrity and validity of LTA archived data.

   STATUS:  Inform about the status of data.

   LISTIDS:  Return a list of references to archived objects.

   These operations form the minimal set that MUST be implemented by an
   LTA service although they may not be available to all clients.
   Furthermore, there is a minimal profile for the parameter structures
   for transactions with a single server that does act as a final
   repository.  Parameters and functions MAY be extended in order to
   allow services to propose more complex operations like data splitting
   or relaying.

   The operations are intended for different types of clients, including
   archive data owners but also entities that want to audit the service
   or are authorised to access to data.  Thus, clients do not need to
   implement all functions, e.g., a client may only implement the
   ARCHIVE operation.

   An LTA may propose additional services either by extending the
   operations by the means of additional parameters or by defining new
   operations.

   For example, often an extension of the initial lifetime of an object
   must be possible.  To extend the lifetime of an object, an EXPORT
   operation followed by an ARCHIVE operation has be used to transfer or
   copy the object to an LTA service having the required lifetime
   policy/configuration.  At last, the initial object may be deleted or
   not.  The combination of such a sequence of operations into single
   one is an example of an extended service provided to clients.

   The LISTIDS operation was originally part of the STATUS function
   where no reference to data is given.  It has been separated for the
   following reasons.  The result of the two modes of the function is
   very different.  A small programming error, i.e., omission of the
   reference to data has dramatic consequences.  This probably means
   that implementation will provide an appropriate API separating the
   two functionalities.  It seems useful to map this directly to the
   protocol layer.  The LTA MUST maintain a chronological order for
   references to archived data.

3.3.  Transactions

   The model for the exchange of LTAP requests and responses is borrowed
   from other environments and technologies like EDI, X.400 or ebXML.
   It's main characteristic is that exchanges for LTAP are conceptually
   asynchronous.  As a consequence, it is necessary to provide a



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   mechanism to allow a client to determime that the LTA has received
   and processed a request.  An LTAP exchange consists of sending a
   request and retrieving at least one of two different types of
   responses.  A client initiates an archive service by submiting a
   request.  This LTAP request consists of data to be archived and
   information related to the archive process.  The process information
   may include client authorization, archive policy, service parameters,
   etc.  The first type of response is a technical acknowledgement from
   the LTA that the request has been received and the process
   information has been accepted (or rejected).  The second type of
   response is a statement from an LTA containing an indication of the
   outcome of the requested operation.  This result (called an
   attestation) is, in general, a document with long-term validity
   allowing the client to reference the operation, and, in particular,
   to reference the data that has been preserved by the LTA.

   The asynchronous nature of the LTAP protocol is required by LTA
   operations, which may require a specific amount of time to perform,
   e.g. the archive operation needs to safely store the data and to
   produce evidence information.

   The possibility to deliver the result attestation in a asynchronous
   way permits cost effective implementations of the LTA.

   An LTA may deliver immediately a second type response.  This occurs
   for example for a STATUS or LISTIDS function or when an operation is
   retried and the final result is available.

   A client can repeat an operation, since the request or the response
   might have been lost.

   For an ARCHIVE operation, the client MAY provide a unique
   identification for the request that to be used by the LTA to ensure
   idempotence of the operation.  When retrying an ARCHIVE operation, a
   client MAY replace the raw data to be archived by a MessageDigest
   representing the data in order to reduce the payload size.

   For the ARCHIVE, DELETE, VERIFY operations, after receipt of the
   technical acknowledgement (first type response), the client can also
   use a STATUS operation for the object in order to indirectly
   determine the outcome of a transaction.  Depending on the lower layer
   bindings, sending a STATUS request or retrying another operation may
   be the only way to determine the outcome of an archive operation.

3.4.  Life cycles of objects

   Using the defined transactions and the operations on objects, two
   levels of life cycles are defined.  One is directly derived from the



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   operation of a single transaction.  The other is related to the long-
   term situation of an object.

3.4.1.  Transaction Level Life Cycle

   When a client initiates an archive operation, client and server have
   some knowledge of the progress of the operation.  The following list
   explains the different states of a transaction seen by both the
   client and the service, and decribes actions and events changing the
   state of the transaction.

   T0:  The client has not initiated an archive operation.  The LTA does
      not know anything about an object.

   T1:  The client has initiated an archive operation.  The LTA may have
      received the object or not; the client cannot assume that the LTA
      has received the request.  Client may retry the operation after a
      timeout.

   T2:  The LTA has received the request and has generated a first type
      response.  The server ensures idempotence of at least the ARCHIVE
      operation, i.e. on multiple occurrences of an identical request,
      the LTA sends the same response and transaction identification.
      The LTA may still lose the state, e.g., in case of a power
      failure.

   T3:  The client has received the initial response.  The client can
      retry the initial operation using the transaction identification
      at the place of the data in order to receive a final answer.  In
      case of negative response, i.e.  LTA in state T0, client can fall
      back to T1.

   T4:  The LTA has send a definitive answer for an operation and has
      assumed the responsibility of operation.

   T5:  The client has received a definitive answer and can consider the
      operation as terminated.

   In case of negative reponses to a transaction, the LTA keeps the
   result for a certain time in order to provide a reasonable answer to
   a client that retries an operation.

3.4.2.  Long term life cycle.

   We can distinguish the following phases in the lifetimes of an
   archived object:





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   L0:  The LTA has no knowledge about an object.

   L1:  An LTA has received an archive object and is proceeding the
      request.  The LTA may accept or reject the request, or may lose
      knowledge about it.

   L2:  An LTA has archived an object.  An LTA can accept other
      operations, i.e., EXPORT, DELETE or VERIFY operations.  When
      receiving an EXPORT or VERIFY operation, some metadata may be
      updated, e.g., last time of access, last verification operation
      etc.

   L3:  After a DELETE operation prior to the initially defined lifetime
      of the operation, the LTA MAY keep an information about the actual
      status of the object (e.g. deleted) until the end of the lifetime.
      If available, the LTA MAY returns other remaining metadata
      containing for example a new location of the data.

   L4:  After the lifetime of an object, an object or the reference to
      is being deleted.  At the end of this internal operation, the LTA
      is in state L0.

   When an LTA has archived an object, it keeps a certain number of
   metadata, which gives information about the current status of the
   object.  Some metadata MAY remain available even after deleting the
   object.  Among the remaining metadata there may be the date of
   deletion or a reference to where the information can actually be
   received.

   With the basic operations it is not possible to extend directly the
   lifetime of an object.  In order to do so, a client has to read the
   object and store it under a different service (not necssarily with
   the same provider).

   A change from state L2 can also occur when an LTA determines loss of
   integrity or loss of data.

3.5.  Roles, Service Types, Policies and Configurations

   The protocol assumes a number of different actors playing different
   roles.  The basic roles are a client and a server.  These roles are
   simply defined by the types of protocol data units, i.e., requests
   and responses.  Several other roles may exist, which are currently
   not in the scope of the protocol specification.  An example of an
   additional role is a relay or a proxy using both the basic roles of
   client and server.  In general two entities are distinguished, based
   on different characteristics: an entity that requests its data to be
   archived or to be acted upon, and an entity that accepts data and



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   assures responsibility of archived data, or acts on the data.  Other
   entities serving as a lower layer transport services, data storage
   services or security services are out of the scope of protocol
   definition.

   Clients may occur in different roles.  Besides users that archive
   data, there may be relying or controlling entities like a judge who
   must be able to get access to it.  Or, there are entities like
   auditors that may access to some data.  The protocol distinguishs
   such roles by the definition of the following service types and
   service policy information.

   The LTA interface implementation MUST enable clients to perform all
   the service operations.

   A client implementation MAY only support a subset of the service
   types in order to have a small footprint.  This is motivated by the
   fact that different operations are generally invoked by different
   entities in totally different environments, e.g., a client may only
   submit data and never verify an evidence record.

   The way a particular operation is performed is only defined at the
   LTA server side implementation and can be influenced by policy
   information parameters.  A client MAY indicate one or more service
   policy identifiers associated to a service type in order to select
   different features to be performed by the LTA.  The goal of policy
   identifiers is to keep client configurations simple.

   An LTA service may provide additional features, which may be
   identified by clients, that govern how services are performed.  An
   LTA might offer a series of features based on quality
   characteristics, e.g. number of timestamps used, refresh period, etc.
   The protocol specification builds on the assumption that features are
   clearly identifiable and are included in the protocol elements.
   Features enable clients to request specific handling by the LTA, such
   as requesting a premium service that assures prompt and immediate
   archiving vs. a standard service that handles queues and generates
   evidence data periodically based on data collections, i.e., one
   timestamp per a document bundle.  Also, services may differ according
   to data storage characteristics (e.g. client may request full
   evidence and storage capacity or only evidence creation service),
   redundancy characteristics (single timestamp versus multiple time
   stamping), etc.  Service characteristics are defined by archive or
   operation policies.

   An LTA may use external services, like validation and evidence
   creation services.  Another service is provision of physical
   infrastructure or data storage and management systems.  Such entities



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   can also be referenced by service policy identifiers.

   In general, for each client, in particular those that are archiving,
   a default or single possible configuration is defined at the server
   in order to group features and policies into defined sets.  A server
   may operate different configurations and from the protocol
   standpoint, general configuration is selected by the policy
   identificator.

   As a last mechanism to provide parameters to the archive server, LTA
   clients MAY use specific configuration parameters in their requests.
   The definition of such parameters is not in the scope of this
   protocol.  Configuration parameters allow clients to transfer
   arbitary key/value pairs from the client to the server.

   In principle, a single sequence of policy information is sufficient
   to indicate both the service type and the configuration parameters.
   A multi-dimensional approach with configuration and service types
   rounds up the requirements for LTA and scenarios of archiving
   processes.

   This specification defines no particular policy or configuration.

3.6.  Identification

   This text defines two ASN.1 modules.  One module uses current ASN.1
   syntax, the other provides limited support in 88 syntax both
   providing the same BER/DER encodings.  The modules export all their
   definitions.  Depending on the ASN.1 syntax version, identifiers are
   imported from different other ASN.1 modules.  A version number is
   added as the last component of the module object identifier.  A
   version of 0 indicates modules of any draft of this memo.

   Definitions of data are made as well in XML schema notation XSD as
   well as in ASN.1.  The XSD schema has been generated automatically
   using the asn1xsd tool from OSS Nokalva.  The ASN.1 has been
   validated using the asn1c compiler from OSS Nokalva.

   The module with current (2005) syntax is defined with the following
   syntax:

   Current ASN.1 Module start

   LTAP {iso(1) identified-organization(3) dod(6)
         internet(1) security(5) mechanisms(5)
         ltans(11) id-mod(0) id-mod-ltap(4) 0}
   DEFINITIONS IMPLICIT TAGS ::=
   BEGIN



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   The module in 88 ASN.1 syntax is identified by the following
   definitions

   ASN.1 Module in 88 syntax start

   LTAP {iso(1) identified-organization(3) dod(6)
         internet(1) security(5) mechanisms(5)
         ltans(11) id-mod(0) id-mod-ltap88(3) 0}
   DEFINITIONS IMPLICIT TAGS ::=
   BEGIN

   The following XSD schema is generated:

   XML Schema Identification

   <schema xmlns="http://www.w3.org/2001/XMLSchema"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     xmlns:enc="http://www.w3.org/2001/04/xmlenc#"
     targetNamespace="http://www.setcce.org/schemas/ltap"
     elementFormDefault="qualified"
     attributeFormDefault="unqualified">
   <annotation><documentation xml:lang="en">
      XML Schema for LTAP
   </documentation></annotation>


3.7.  External definitions

   The modules export all their definitions, and import several
   definitions from other modules.  The modules differ depending of the
   ASN.1 syntax but generate identical encodings.




















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   Current ASN.1 Module external definition

   -- EXPORTS ALL
   IMPORTS

      certificateExtensions
   FROM UsefulDefinitions {joint-iso-itu-t ds(5) module(1)
         usefulDefinitions(0) 5}

      PolicyInformation, GeneralNames
   FROM CertificateExtensions certificateExtensions

      PKCS7-CONTENT-TYPE
   FROM PKCS7
      {iso(1) member-body(2) us(840) rsadsi(113549)
     pkcs(1) pkcs-7(7) modules(0) pkcs-7(1)}
   ;

   The module in 88 syntax form imports from modules which are also in
   88 syntax.  If the type UTF8String is supported by a particular
   compiler, the definitions in PKIX1Explicit88 must be commented out
   and the type not imported.

   ASN.1 Module in 88 syntax start

   -- EXPORTS ALL --

   IMPORTS UTF8String, PolicyInformation,
        GeneralNames
   FROM PKIX1Explicit88
        { iso(1) identified-organization(3) dod(6) internet(1)
          security(5) mechanisms(5) pkix(7)
          id-mod(0) id-pkix1-explicit(18) }
   ;

   The id-ct object identifier arc is redefined locally.

   SMIME ContentType arc root

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

   These are corresponding XML definitions for the imported structures.

   XML Schema for imported data structures

   <xsd:complexType name="Name">



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    <xsd:choice>
      <xsd:element name="rdnSequence" type="RDNSequence"/>
    </xsd:choice>
   </xsd:complexType>

   <xsd:complexType name="RDNSequence">
    <xsd:sequence minOccurs="0" maxOccurs="unbounded">
     <xsd:element name="RelativeDistinguishedName"
                  type="RelativeDistinguishedName"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="RelativeDistinguishedName">
    <xsd:sequence minOccurs="0" maxOccurs="unbounded">
     <xsd:element name="AttributeTypeAndDistinguishedValue"
                  type="AttributeTypeAndDistinguishedValue"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="AttributeTypeAndDistinguishedValue">
    <xsd:sequence>
     <xsd:element name="type">
      <xsd:simpleType>
       <xsd:restriction base="OBJECT_IDENTIFIER"/>
      </xsd:simpleType>
     </xsd:element>
     <xsd:element name="value">
      <xsd:complexType mixed="true">
       <xsd:choice>
        <xsd:any processContents="lax"/>
       </xsd:choice>
      </xsd:complexType>
     </xsd:element>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="PolicyInformation">
    <xsd:sequence>
     <xsd:element name="policyIdentifier"
                  type="CertPolicyId"/>
     <xsd:element name="policyQualifiers" minOccurs="0">
      <xsd:complexType>
       <xsd:sequence minOccurs="0" maxOccurs="unbounded">
        <xsd:element name="PolicyQualifierInfo"
                     type="PolicyQualifierInfo"/>
       </xsd:sequence>
      </xsd:complexType>
     </xsd:element>



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    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="PolicyQualifierInfo">
    <xsd:sequence>
     <xsd:element name="policyQualifierId">
      <xsd:simpleType>
       <xsd:restriction base="OBJECT_IDENTIFIER"/>
      </xsd:simpleType>
     </xsd:element>
     <xsd:element name="qualifier" minOccurs="0">
      <xsd:complexType mixed="true">
       <xsd:choice>
        <xsd:any processContents="lax"/>
       </xsd:choice>
      </xsd:complexType>
     </xsd:element>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:simpleType name="CertPolicyId">
    <xsd:restriction base="OBJECT_IDENTIFIER"/>
   </xsd:simpleType>


3.8.  Entities

   Entities that participate in protocol exchanges are represented by
   identifiers and may possess attributes.  It is outside the scope of
   this definition to define an organisation of identifiers and
   attributes, in particular the way how entity identifiers are related
   to identifiers used for authentication, or what attributes are
   associated to data.

   As the current LTAP specification assumes end-to-end communication
   only, there is no distinction between technical roles like 'client,
   'server', 'relay', 'proxy' or 'authorized agent'.  For LTAP, only
   client and server roles are defined.

   The explicit usage of identifiers and attributes enables decisions to
   be traceable, i.e., the participating entities can indicate to a
   certain degree why they want a service or why it has been provided.

   Furthermore, entity identifiers and attributes MAY be provided by the
   transport or security layer information.  These information can be
   added to protocol elements as trace attributes.





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3.8.1.  Entity Identifiers

   Entity identifiers are used in the protocol to indicate the
   participating entities.  A client can indicate one or more
   identifiers indicating who is making the request or participating in
   its creation and one or more identifiers indicating who should
   perform the service.  A server can indidate who has provided the
   service and who is the indented client.

   It MUST be ensured in some way that in an actual context of a client/
   server network names are scalable and global both in terms of actual
   community space and time to live of the treated data objects.

   Identifiers are labeled in some way, i.e. string representations are
   typed and can be derived from various external layers.  Identifiers
   SHOULD use an appropriate structure such as ASN.1 definition of
   GeneralName.

3.8.2.  Attributes

   Entities may possess additional attributes like roles, scopes or
   capabilities.  Entities MAY indicate attribute values in protocol
   exchanges so that they can be used for authentication purposes or
   billing.

   Attributes may be related to attributes of data, for example, an
   entity may acts as a judge or arbitrator for a particular
   jurisdiction.  The attribute jurisdiction is associated to the entity
   and to data treated by the service, and thus, can be used for
   authorisation control.

3.9.  Data Model

   The data fields of a LTAP request are as follows:

   o  request information or status information

   o  raw data to archive, or references to data or to transactions.

   o  metadata providing additional information about the data to
      archive

   o  authorisation and authentication information of the entities
      paticipating in the procedure

   o  other information, required for supporting functions like billing





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3.9.1.  Data objects

   The data to be archived are arbitrary binary data and, minimally, an
   associated type that MUST be either available as part of a server
   configuration policy or explicitly indicated by the client.

   Data can be referenced by identifiers.  Data identifiers are used to
   uniquely identify data objects.  Data identifiers SHOULD have an
   additional local structure (e.g., contain a checksum), in order to
   avoid or detect client copying errors.  An additional measure to
   enhance the redundancy of identifiers is the usage of time values
   which can be used in combination with data identifiers.

   Servers MUST create a server-wide unique identifier for each data
   object managed by the LTA.  The identifier MUST be global during the
   intended lifetime of an object.

   Clients may provide their own data identifiers in requests.  Whether
   the client provided identifiers are unique is outside the scope of
   the protocol.  LTAs treat these identifiers as opaque information.

   In order to identify data for the short lifespan of a transaction,
   artifacts can be used to reference data or transactions.

3.9.2.  Collection objects

   Data grouping can occur for various reasons, i.e. logical,
   contextual, semantic, operational, etc.  It is out of the scope of
   the LTA to perform grouping for other reasons than operational, e.g.
   reducing costs or improving performance or scalability.  Grouping is
   performed on the level of evidence creation by building hash trees as
   defined in [RFC4998].  Grouping characteristics are defined by
   service policies, e.g. per user or on a daily or volume basis.  The
   global parameters for selecting appropriate collection strategies are
   entity and policy identfiers.

   Collections of data can be defined explicitly or implicitly.  A
   document is added to a collection using policy and entity identifiers
   to request a specific collection strategy (e.g. a collection of data
   that is processed on a daily basis for a specific user).  A
   collection identifier may be presented as an extension to an object
   identifier and is intially local to one object.  Adding another
   object to a collection requires the identification of the initial
   object and the identification of one object in the collection.

   An LTA may implement indexes of metadata accessible by extended
   operations.




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3.9.3.  MetaData

   Meta information is associated with archive data and can be included
   implicitly, i.e. be a part of a document, or explicitly, i.e. as a
   document attachment.  An LTA does not interprete metadata that may
   express logical relations among documents in the archive that is
   submitted selectively using several requests.  For LTAs, the client
   is only in control of selecting and enclosing meta information, which
   is logically, contextually or for any other reason related to a
   document.

   Meta information may occur in various forms and may be an integral
   part of archive data, e.g. security attributes in form of digital
   signatures.  To process such information, the LTA MUST retrieve
   enough information on the type and purpose of information enclosed,
   which may simply be defined with the use of an apropriate archive
   service policy, e.g. archive service for digitally signed documents.

   An LTA may perform specific actions related to meta information
   processing (and preservation, such as complementary data collection
   in form of digital certificates).  This can also be done by an
   external service, e.g.  [RFC3029] or SVCP.

   In some scenarios, a specific set of meta information must be
   preserved together with archive data, e.g. information identifying
   the document owner/author, location or time.  The LTAP protocol does
   not define constraints on information type and structure.  The LTAP
   request structure is defined to accept any type of data.

3.9.4.  Binding Information

   Clients and servers MAY include additional information in their
   requests and responses concerning the lower layer binding to a
   transport like SOAP, HTTP or S/MIME, e.g. end-point addresses.  This
   category may also include things like billing/accounting information,
   i.e. whatever a business transaction needs but which is not part of
   metadata, i.e. outside the scope of the archived data.

3.9.5.  Evidence Data

   Evidence information demonstrates the integrity and existence of
   archived data.  The LTA accepts data for the single purpose of
   generating or obtaining evidence information for data submitted by a
   client.  The evidence information structure is defined in [RFC4998].

   In the case where LTA accepts data only for the purpose of generating
   evidence information (without storage capabilites to avoid, e.g.
   confidentiality issues), the archivation process is limited in time.



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   When an LTA performs a renewal of evidence, archived data may be
   required to be available, e.g. when renewing a hash tree.  In such
   scenarios, the LTA requires availability of archived data for hash
   re-computation.  The LTAP protocol does not support function for data
   re-submission.


4.  Data Types

   A number of data types are common to both requests and responses.

4.1.  Artifacts

   Artifacts are identifiers used to reference a transaction, or a
   result of a transaction.  They can be returned as a protocol answer
   in an initial response, to allow retrieval of a response or progress
   of a transaction later by the initial client or another authorised
   entity.

   ASN.1 definition

   Artifact ::= PrintableString

   The corresponding XML type is:

   XML Schema element

      <xsd:simpleType name="Artifact">
    <xsd:restriction base="PrintableString"/>
       </xsd:simpleType>

4.2.  MessageDigest

   A MessageDigest is a short representation of data which can be used
   in evidences to link to some data.  This is just another way of
   saying that they are the result of a one way hash function applied to
   some data.

   It is not assumed that a MessageDigest will always identify some data
   in a unique way (which is not the case by definition of a hash
   function), neither it is assumed that collisions may not exist now or
   in the future.  It is only assumed that within a bounded collection
   of data objects (in time and number), which are stored phyically
   safe, a MessageDigest uniquely designate other data.

   Nevertheless, it is assumed that for the lifetime of protocol
   exchanges, a hash function used to create a MessageDigest is
   crytographically safe.



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   The structure of a MessageDigest is a sequence of an globally defined
   identification of a hash function and an representation of an octet
   string encoding a value of the hash function.

   XML Schema element

   <xsd:complexType name="MessageDigest">
    <xsd:sequence>
     <xsd:element name="digestAlgorithm"
                  type="DigestMethodType"/>
     <xsd:element name="digestValue"
                  type="DigestValueType"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:simpleType name="DigestValueType">
    <xsd:restriction base="OCTET_STRING"/>
   </xsd:simpleType>

   <xsd:simpleType name="DigestMethodType">
    <xsd:restriction base="OBJECT_IDENTIFIER"/>
   </xsd:simpleType>

   ASN.1 Definition

   MessageDigest ::= SEQUENCE {
       digestAlgorithm DigestMethodType,
       digestValue     DigestValueType
   }

   DigestMethodType ::= OBJECT IDENTIFIER
   DigestValueType ::= OCTET STRING


4.3.  MetaData

   Metadata are a list of open types which can be regarded as key/value
   pairs giving addtional information about entities or data or which
   are related to the preservation process.

   The following ASN.1 definition allows to have hierarchical metadata
   structures that can be decoded and encoded without the need to modify
   the ASN.1 definition.  It is left to the application layers or other
   metadata defnitions to define restrictions and semantics.

   The 'type' identfies in a globally unique way the semantics of the
   value.  The 'oid' choice can be used in a similar way as withe MIBs
   in SNMP.  The 'uri' choce allows to reference metadata defined by



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   URIs.  The semantics 'attribute' choice normally depends on the
   semantics of a surrounding definition.  Global values for 'attribute'
   may exist, i.e. the choice can be used in the outermost MetaData
   sequence.

   This specification defines one global 'attribute' "datatype".  The
   'values' item MUST contain one occurence of either a 'stringValue'
   which indicates a mime-type, or an 'oidValue' or 'uriValue'
   indicating an FTAM document type.

   Some global metadata are essential for the LTA service and require a
   standardised interpretation.  An LTA MUST provide a complete
   description of all metadata it associates to an archived data object.
   A client is not required to implement any particular treatment of
   such metadata.

   Although it is possible to recur to some other existing metedata
   specification, e.g., the Dublin Core, we do not want to depend on
   external semantics here.  An LTA is free to map metadata.

   ASN.1 Definition

   MetaData ::= SEQUENCE OF MetaItem

   MetaItem ::= SEQUENCE {
     type CHOICE {oid OBJECT IDENTIFIER,
                  attribute UTF8String,
                  uri  IA5String } ,
     values SEQUENCE OF
        value CHOICE {
           oidValue  OBJECT IDENTIFIER,
           stringValue UTF8String,
           uriValue IA5String,
           integerValue INTEGER,
           opaqueValue OCTET STRING,
           composedValue MetaItem
        }
   }













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   XML Schema element

   <xsd:complexType name="MetaData">
    <xsd:sequence minOccurs="0"
                  maxOccurs="unbounded">
     <xsd:element name="MetaItem"
                  type="MetaItem"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="MetaItem">
    <xsd:sequence>
     <xsd:element name="type">
      <xsd:complexType>
       <xsd:choice>
        <xsd:element name="oid"
                     type="OBJECT_IDENTIFIER"/>
        <xsd:element name="attribute"
                     type="UTF8String"/>
        <xsd:element name="uri"
                     type="IA5String"/>
       </xsd:choice>
      </xsd:complexType>
     </xsd:element>
     <xsd:element name="values">
      <xsd:complexType>
       <xsd:sequence minOccurs="0"
                     maxOccurs="unbounded">
        <xsd:choice>
         <xsd:element name="oidValue"
                      type="OBJECT_IDENTIFIER"/>
         <xsd:element name="stringValue"
                      type="UTF8String"/>
         <xsd:element name="uriValue"
                      type="IA5String"/>
         <xsd:element name="integerValue"
                      type="INTEGER"/>
         <xsd:element name="opaqueValue"
                      type="OCTET_STRING"/>
         <xsd:element name="composedValue"
                      type="MetaItem"/>
        </xsd:choice>
       </xsd:sequence>
      </xsd:complexType>
     </xsd:element>
    </xsd:sequence>
   </xsd:complexType>




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4.4.  Nonce

   A Nonce is an octetstring usable to prevent replays of responses for
   the STATUS operation.  If present in a request, a server MUST respond
   with a response containing the Nonce value.  It does not indicate
   that the server must determine in a back-end operation the actual
   status.

   XML Schema element

   <xsd:simpleType name="Nonce">
    <xsd:restriction base="OCTET_STRING"/>
   </xsd:simpleType>

   ASN.1 Definition

   Nonce ::= OCTET STRING

4.5.  RawData

   This type carries data to be verified, archived or returned.  A
   client MUST select a metadata type to indicate the type of the data
   or the type of the data MUST be defined as part of the service
   policy.

   For preservation purposes, an LTA must have information on archive
   data type (e.g., signed or unsigned).  If type is not included, it is
   assumed that data retrieved must be processed as binary string (e.g
   signatures are not verifed.).

   XML Schema element

   <xsd:complexType name="RawData">
    <xsd:choice>
     <xsd:element name="opaque" type="OCTET_STRING"/>
     <xsd:element name="string" type="UTF8String"/>
     <xsd:element name="structured" type="MetaData"/>
     </xsd:choice>
   </xsd:complexType>

   ASN.1 Definition

   RawData ::= CHOICE {
   opaque     OCTET STRING,
   string     UTF8String,
   structured MetaData
   }




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4.6.  DataOrTransaction

   This choice type is used to identify data by:

   o  themselves

   o  an artifact identifying a transaction

   o  a data identifier

   XML Schema element

   <xsd:complexType name="DataOrTransaction">
    <xsd:choice>
     <xsd:element name="data" type="RawData"/>
     <xsd:element name="artifact" type="Artifact"/>
     <xsd:element name="reference" type="IA5String"/>
    </xsd:choice>
   </xsd:complexType>

   ASN.1 Definition

   DataOrTransaction ::= CHOICE {
   data      RawData,
   artifact  Artifact,
   reference IA5String
       }

4.7.  Data

   This type is used to describe data together with metadata.

   XML Schema element

   <xsd:complexType name="Data">
    <xsd:sequence>
     <xsd:element name="dataReference" type="DataOrTransaction"/>
     <xsd:element name="metaData" type="MetaData"/>
     <xsd:element name="messageImprint" type="MessageDigest"/>
    </xsd:sequence>
   </xsd:complexType>










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   ASN.1 Definition

   Data ::= SEQUENCE {
       dataReference  DataOrTransaction,
       metaData       MetaData,
       messageImprint MessageDigest
   }

4.8.  SerialNumber

   A SerialNumber is an integer value used to identify a request and its
   response.  Servers MAY add an additional verifyable structure to such
   a number, e.g. checksum digits, in order to avoid copying errors in
   long-term applications with potential media break.

   XML Schema element

   <xsd:simpleType name="SerialNumber">
    <xsd:restriction base="INTEGER"/>
   </xsd:simpleType>

   ASN.1 Definition

   SerialNumber ::= INTEGER

4.9.  LtapTime

   Clients and servers can add an indication of (its idea of) the time
   when a request or response was created, search intervals etc.  The
   LtapTime type is used.  The encoding of the string content MUST be
   according to the distinguished encoding rules (DER).

   XML Schema element

   <xsd:simpleType name="LtapTime">
    <xsd:restriction base="GeneralizedTime"/>
   </xsd:simpleType>

   ASN.1 Definition

   LtapTime ::= GeneralizedTime

4.10.  Version

   Version is used in requests and responses to indicate the protocol
   version used.  This specification is provided for two values:





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   o  v0 - This version should be used by implementation that want to
      experiment with draft version of this specification.

   o  v1 - this version is used to indicate that the request and
      response corresponds to this specification.

   This memo does not define an extension mechanism.

   XML Schema element

   <xsd:complexType name="Version">
    <xsd:choice>
     <xsd:element name="v0" type="NULL"/>
     <xsd:element name="v1" type="NULL"/>
    </xsd:choice>
   </xsd:complexType>

   ASN.1 Definition

   Version ::= ENUMERATED {
       v0,
       v1
   }

4.11.  EntityIdentifier

   Entity identifiers are used in the protocol to indicate the
   participating entities.  A client can indicate one or more
   identifiers indicating who is making the request or participating in
   its creation and one or more identifiers indicating who should
   perform the service.  A server can indidate who has provided the
   service and who is the indented client.

   A client MAY also indicate an address to who a response is to be
   return in case of an asynchronous reponse, e.g. an e-mail address.

   It MUST be ensured in some way that in an actual context of a client/
   server network names are scalable and global both in terms of actual
   community space and time to live of the treated data objects.

   Identifiers are defined as GeneralNames imported from
   InformationFramework.









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   XML Schema element

   <xsd:complexType name="EntityIdentifier">
    <xsd:sequence minOccurs="0" maxOccurs="unbounded">
     <xsd:choice>
      <xsd:element name="rfc822Name" type="IA5String"/>
      <xsd:element name="dNSName" type="IA5String"/>
      <xsd:element name="directoryName" type="Name"/>
      <xsd:element name="uniformResourceIdentifier"
                   type="IA5String"/>
      <xsd:element name="iPAddress" type="OCTET_STRING"/>
      <xsd:element name="registeredID"
                   type="OBJECT_IDENTIFIER"/>
      </xsd:choice>
    </xsd:sequence>
   </xsd:complexType>

   ASN.1 Definition

   EntityIdentifier ::= GeneralNames

4.12.  ServiceType

   This type is either enumeration of basic services defined in this
   memo of an object identifier defined by a service provider.  It
   indicates operations accessible by the protocol.

   XML Schema element

   <xsd:complexType name="ServiceType">
    <xsd:choice>
     <xsd:element name="ltapbasicservice">
      <xsd:complexType>
       <xsd:choice>
        <xsd:element name="archive" type="NULL"/>
        <xsd:element name="delete" type="NULL"/>
        <xsd:element name="export" type="NULL"/>
        <xsd:element name="status" type="NULL"/>
        <xsd:element name="verify" type="NULL"/>
        <xsd:element name="listids" type="NULL"/>
       </xsd:choice>
      </xsd:complexType>
     </xsd:element>
     <xsd:element name="ltapextendedservice"
                  type="OBJECT_IDENTIFIER"/>
    </xsd:choice>
   </xsd:complexType>




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   ASN.1 Definition

   ServiceType ::= CHOICE {
      ltapbasicservice ENUMERATED {
         archive,
         delete,
         export,
         status,
         verify,
         listids
      },
      ltapextendedservice OBJECT IDENTIFIER
   }

4.13.  StatusInformation

   The LTA indicates the global status of a transaction using this
   enumeration type.  The semantics of the values is as follows:

      The response is an initial first type reponse.  The request has
      been technically accepted by the LTA.

      The response is an second type final response from the LTA.

      The response is an second type final response from the LTA.  The
      operation performed by the LTA but only with some modifications.

      The operation has not been accepted.

   In case of modifications or error, the LTA MUST also return details
   using the following GeneralErrorNotice

   XML Schema element

   <xsd:complexType name="StatusInformation">
    <xsd:choice>
     <xsd:element name="granted" type="NULL"/>
      <xsd:element name="grantedWithMods" type="NULL"/>
      <xsd:element name="rejection" type="NULL"/>
      <xsd:element name="waiting" type="NULL"/>
      <xsd:element name="more" type="NULL"/>
    </xsd:choice>
   </xsd:complexType>








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   ASN.1 Definition

   StatusInformation ::= ENUMERATED {
       granted,
       grantedWithMods,
       rejection,
       waiting,
       more
   }

4.14.  RequestInformation

   This data structure comprises information about the request others
   that the raw data and metadata.  The structure is filled in partially
   by a requestor and augmented or modified by the responder.  It
   resumes the operation that has been performed.

   ASN.1 Definition


   RequestInformation ::= SEQUENCE {
       version           Version DEFAULT v1,
       servicePolicyInfo PolicyInformation,
       serviceType       ServiceType,

       requestorID       EntityIdentifier,
       serviceID         EntityIdentifier,
       returnID          EntityIdentifier OPTIONAL,
       serial            SerialNumber OPTIONAL,
       nonce             Nonce OPTIONAL,
       requestTime       LtapTime OPTIONAL,
       startTime         [0] LtapTime OPTIONAL,
       nextTime          [1] LtapTime OPTIONAL,
       bindingInfo       [2] MetaData OPTIONAL
   }
















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   XML Schema element

   <xsd:complexType name="RequestInformation">
    <xsd:sequence>
     <xsd:element name="version"
                  type="Version" minOccurs="0"/>
     <xsd:element name="servicePolicyInfo"
                  type="PolicyInformation"/>
     <xsd:element name="serviceType"
                  type="ServiceType"/>
     <xsd:element name="requestorID"
                  type="EntityIdentifier"/>
     <xsd:element name="serviceID"
                  type="EntityIdentifier"/>
     <xsd:element name="returnID"
                  type="EntityIdentifier" minOccurs="0"/>
     <xsd:element name="serial"
                  type="SerialNumber" minOccurs="0"/>
     <xsd:element name="nonce"
                  type="Nonce" minOccurs="0"/>
     <xsd:element name="requestTime"
                  type="LtapTime" minOccurs="0"/>
     <xsd:element name="startTime"
                  type="LtapTime" minOccurs="0"/>
     <xsd:element name="nextTime"
                  type="LtapTime" minOccurs="0"/>
     <xsd:element name="bindingInfo"
                  type="MetaData" minOccurs="0"/>
    </xsd:sequence>
   </xsd:complexType>

   The version item indicates the version of the protocol to be used.

   The item serviceType indicate the operation to be performed.  The
   value can be one of the enumeration values defined in this memo or an
   object identifier defining another operation.  Additional operation
   MUST NOT modify the ASN.1 but use metadata for additional parameters.

   The serviceID item identifies the LTA service provider(s)

   The servicePolicyInfo item defines the service policy.

   If a client specifies a nonce item, the server MUST return either the
   same value, or a value that has the client value as a prefix.

   The meaning of the startTime and nextTime items depend on the value
   of the serviceType item and is described later.




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   The serial item indicates a serial number of a request has been
   received, the field MUST NOT be set by the requestor and MUST be set
   by the responder in order to uniquely identify the request.

   The requestTime item indicates the time when the request has been
   received, the field MAY be set by the requestor in case of a proxy
   and it SHOULD be set in any response.

   The bindingInfo item contains additional information required by the
   LTA or returned to the client.  These metadata are associated with
   the request and not with the archived data.

   The semantics of the items startTime and nextTime depend on the
   serviceType.


5.  Top level protocol elements

   On the top level, there are three protocol elements, one is used in
   requests, and the two other are either describing the successful
   outcome of an operation or an error notice.

5.1.  Request

   This data structure describes a request made by a client.  It
   contains a RequestInformation data structure, as well as data or data
   references.  At least one of the Data and MessageDigest elements must
   be provided.

   XML Schema element

   <xsd:complexType name="Request">
    <xsd:sequence>
     <xsd:element name="information" type="RequestInformation"/>
     <xsd:element name="data" type="Data"/>
     <xsd:element name="transactionIdentifier"
                  type="IA5String" minOccurs="0"/>
    </xsd:sequence>
   </xsd:complexType>

   ASN.1 Definition

   Request ::= SEQUENCE {
      information           RequestInformation,
      data                  Data,
      transactionIdentifier IA5String OPTIONAL
   }




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5.2.  StatusNotice

   A server may return a general error notice indicating an important
   failure with referencing the request.  The element can be created
   either by the service, e.g., when a request cannot be decoded, but
   also by a client lower layer, e.g. when a connection cannot be
   established.

   XML Schema element

   <xsd:complexType name="StatusNotice">
    <xsd:sequence>
     <xsd:element name="status"
                  type="StatusInformation"/>
     <xsd:element name="errorInformation">
      <xsd:complexType mixed="true">
       <xsd:complexContent mixed="true">
        <xsd:extension base="UTF8String"/>
       </xsd:complexContent>
      </xsd:complexType>
     </xsd:element>
     <xsd:element name="lastValid"
                  type="LtapTime" minOccurs="0"/>
     <xsd:element name="transactionIdentifier"
                  type="IA5String" minOccurs="0"/>
    </xsd:sequence>
   </xsd:complexType>

   ASN.1 Definition

   StatusNotice ::= SEQUENCE {
       status           StatusInformation,
       errorInformation UTF8String (SIZE(0..8192)),
       lastValid        LtapTime OPTIONAL,
       transactionIdentifier IA5String OPTIONAL
   }

5.3.  OperationResponse

   This structure is returned on a successful or unsuccessful operation
   of the service.  It references the initial request as well as the
   data that had been submitted.









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   XML Schema element

   <xsd:complexType name="OperationResponse">
    <xsd:sequence>
     <xsd:element name="information"
                  type="RequestInformation"/>
     <xsd:element name="status" type="StatusNotice"/>
     <xsd:element name="data" type="Data"/>
    </xsd:sequence>
   </xsd:complexType>

   ASN.1 Definition

   OperationResponse ::= SEQUENCE {
       information RequestInformation,
       status             StatusNotice,
       data               Data
   }

5.4.  Response

   This structure is returned on a successful or unsuccessful operation
   of the service.

   XML Schema element

   <xsd:complexType name="Response">
    <xsd:choice>
     <xsd:element name="operationResponse"
                  type="OperationResponse"/>
     <xsd:element name="errorNotice"
                  type="StatusNotice"/>
    </xsd:choice>
   </xsd:complexType>

   ASN.1 Definition

   Response ::= CHOICE {
       operationResponse OperationResponse,
       errorNotice   [0] StatusNotice
   }


6.  Service Operations

   This section describes in detail the different operations that a
   client can initiate with a request and their outcomes.  All
   operations share the same data types for the input and output but the



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   choices are filled in differently.

   For all operations, the archive service may react in the following
   ways:

      The request is not understood or cannot be transmitted, an
      ErrorNotice is returned.

      The request is accepted, an OperationResponse indicating that the
      transaction is 'waiting'.  The item nextTime in the
      requestInformation SHOULD be set by the responder in case when the
      client needs to poll for the final response to indicate to the
      client not poll before that date.

      The request is rejected. an OperationResponse describing the error
      is returned.

      This a final response, an OperationResponse containing the result
      of the transaction is returned.

   When the transport layer is asynchronous, the protocol is the
   following: The client MUST fill the item 'returnID' in the
   requestInformation.  A server MAY respond either with the final
   result or with two messages indicating acceptance and result.  The
   client MAY retry the operation (slightly modified) after that date.
   Since any operation can be lost, a client has to set an appropriate
   value for initial retry timeout.

   When the transport layer is synchronous, e.g. if HTTP is used, the
   server immediately returns either an error or acceptance, and the
   client MUST retry the operation (slightly modified) in order to get
   the final result.

   A server may offer a mixed environment where the initial response is
   obtained in a synchronous way, and the final response can be
   transferred in an asynchronous way.  In this case, the client MAY be
   required to set a returnID.

6.1.  ARCHIVE operation

   The major operation of the archive service is the ARCHIVE operation.
   A client prepares the data and associated metadata, and transfers the
   request to the archive service.  The client builds a Request with an
   information item including service policy interpreting service
   characteristics and service configuration parameters.  Data to be
   archived and metadata are enclosed.





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   o  the service type is set to "archive"

   o  If this is an initial request, the data are filled in with a
      rawData and a messageDigest.

   o  If this a retry of a previous operation, the client MAY choose
      either to simply repeat an identical operation, or remove the
      rawData and send the messageDigest and, if provided, an artifact.

   The server SHOULD use an artifact when the StatusInformation is
   'waiting', in order to simplify its processing when the client
   retries the operation.  When an operation is retried, the client
   SHOULD use the returned artifact instead of the data.

   The final response contains a data reference to be usable in other
   operations concerning the same data object.

   When a client archives may objects in parallel operations, it may be
   unreasonable to poll for each outstanding result individually.  An
   LTA MAY support a LISTIDS function returning artifacts for finished
   archive operations.

6.2.  EXPORT operation

   This operation allows a client to retrieve data.

   o  Data identification must be a data reference and/or a message
      imprint.

   o  The service type is set to "export".

   In the final result, the LTA returns data and metadata of the object.

6.3.  DELETE operation

   This operation allows a client to delete data or request data
   shredding.  After a successful operation, the the server does not
   maintain any status information about the object.

   o  Data identification must include data itself or data reference or
      message imprint.

   o  The metadata MAY be set to replace the existing metadata of the
      object.

   o  The service type is set to "delete".

   The LTA MAY either return a result with updated metadata or nothing.



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   If the client retries a delete operation, it may happen that the LTA
   has already deleted all traces of the operation.  In this case, the
   server always pretends having deleted the referenced data.  The
   client cannot distinguish whether the data have ever existed.

6.4.  VERIFY operation

   This operation allows a client to verify the authenticity of
   information stored in the archive.  Depending on the actual status of
   the object and on the policy of the LTA, the LTA initiates an
   internal procedure to determine the validity of the data.  An LTA may
   perform the similar steps as for the initial archiving operation.
   The LTA MAY choose not to perform the operation if the actual status
   is sufficiently recent.  In this case, the operation is identical to
   STATUS operation.

   o  Data identification must be a data reference and/or a message
      imprint.

   o  The service type is set to "verify".

   The LTA returns updated metadata of the object.

6.5.  STATUS operation

   A client can request the status of a data object.

   Client builds a Request with request information including service
   policy interpreting service characteristics and service configuration
   parameters.

   o  The service type is set to "status".

   o  Data identification must be a data reference and/or a message
      imprint.

   In the final response, the LTA returns the current status and the
   metadata for the object.

6.6.  LISTIDS operation

   A client can request a list of reference of objects archived.  The
   client builds a Request with request information including service
   policy interpreting service characteristics and service configuration
   parameters.






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   o  The service type is set to "LISTIDS".

   o  Data identification MUST be a data reference, an artifact and/or a
      message imprint.  If present, the LTA returns references to
      objects starting with this reference in the chronological order
      defined by the LTA.  The reference or artifact MUST be known to
      the LTA.

   o  The startDate and endDate MAY be set to indidate a range.  The
      exact definition of when an object belongs to that range is
      defined by the LTA.

   The LTA returns a list of references as a sequence of
   DataOrTransaction items.  The artifact and dataReference choices are
   allowed.  If the request contains an artifact, the LTA MUST return
   the artifacts that correspond to terminated transactions.

   The number of references returned is defined by the LTA and may not
   be the complete set.  If the LTA has more data to provide, it sets
   the StatusInformation to 'more'.  The client has to repeat the
   operation using the last returned reference as data identification.
   A client can distinguish this case from the initial acknowledge which
   has the same value for StatusInformation.  For the Acceptance
   response no references are returned.  There may be a final response
   with no references incase when no data exist for the specified
   criteria.


7.  Presentation and Bindings

   In the previous chapters we have presented all basic data types as
   well as XSD schema as in with ASN.1.  This is done in order to allow
   implentations work on both data syntaxes and to be able to present
   and transform messages in a defined way.

   There is no mandatory transport mechanism in this document.  All
   mechanisms are optional.  Two examples of transport protocols are
   given that allow online exchange of request and a response, and
   asynchronous communication between a client and an LTA.  An LTA MAY
   use a combination of protocols, for example in order to return
   additional responses.

   This memo defines bindings for the transfer of requests and/or
   responses, one using HTTP and another using e-mail.







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7.1.  Common parameters and encoding requirements

   This memo defines are two basic ways how requests and responses are
   encoded, either using a restricted BER encoding or XML.  An LTA MUST
   provide at least one of them.  Furthermore, we define optional
   enveloping protection mechanisms which depend on the encoding.  CMS
   protection of signedData and envelopedData can be used independantly
   of the encoding of the request or response.  XML-DSIG and XML-ENC can
   only be used for XML encoded requesta nd responses.

   For requests encoded in XML either based on XER or on XSD, the
   associated MIME type is application/ltap-request+xml.  For request
   not encoded in XML, the associated MIME type is application/
   ltap-request.

   Similarly, for responses have an associated MIME types application/
   ltap-response and application/ltap-response+xml.

   When request and responses are exchanged using an XML encoding, the
   XSD top level elements LTAPRequest or LTAPResponse are used, an not
   an XER version of ContentInfo.

   When a XML Signature is used, an enveloping signature for a Request
   or Response or enc:EncryptedData MUST be used

   EncryptedData MUST decrypt to a Request or Response or ds:Signature

   When the request is presented with the application/ltap-request type,
   the client MAY encode it using BER with strings nested at most one
   level.  Similarily, a response presented with the application/
   ltap-response type may have BER with strings nested at most one
   level.

   The Request and Response items can be encapsulated inside CMS
   signedData and/or CMS envelopedData, or, If not protected, the
   Request is encapsulated in a ContentInfo using id-ct-LTAPRequest as
   identification, and the Response is encapsulated in a ContentInfo
   structure using id-ct-LTAPResponse for identification.

   If the Request and Response which are not encoded in XML are
   encapsulated inside SignedData and/or EnvelopedData, the contenttype
   of the innermost encapsulatedContent is set to using id-ct-
   LTAPRequest or id-ct-LTAPResponse respectively.

   Any of the four MIME parts can be encapsulated inside CMS using an
   id-data content-type.





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   CMS ContentTypes identifiers

   id-ct-LTAPRequest  OBJECT IDENTIFIER ::=
            { id-ct 4711 }
   id-ct-LTAPResponse  OBJECT IDENTIFIER ::=
            { id-ct 4711 }

   In current ASN.1 we have the following ContentType definitions.

   CMS ContentTypes

   ltap-Request  PKCS7-CONTENT-TYPE ::= {Request
        IDENTIFIED BY  id-ct-LTAPRequest }
   ltap-Response PKCS7-CONTENT-TYPE ::= {Request
        IDENTIFIED BY  id-ct-LTAPResponse }

   LTAPRequest ::= ContentInfo
   LTAPResponse ::= ContentInfo



   XML top level definitions

   <xsd:element name="Request" type="Request"/>
   <xsd:element name="Response" type="Response"/>
   <xsd:element name="LTAPRequest" type="LTAPRequest"/>
   <xsd:element name="LTAPResponse" type="LTAPResponse"/>

   <xsd:complexType name="LTAPResponse">
    <xsd:choice>
     <xsd:element name="response" type="Request"/>
     <xsd:element name="signedResponse" type="ds:Signature"/>
     <xsd:element name="encryptedResponse" type="enc:EncryptedData"/>
    </xsd:choice>
   </xsd:complexType>

   <xsd:complexType name="LTAPRequest">
    <xsd:choice>
     <xsd:element name="request" type="Request"/>
      <xsd:element name="signedRequest" type="xd:Signature"/>
      <xsd:element name="encryptedRequest" type="enc:EncryptedData"/>
    </xsd:choice>
   </xsd:complexType>








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7.2.  e-mail bindings

   In a request, the last element of item requestorID corresponds to the
   From header, the last element of the item serviceID to the To header
   and the last element of the returnID to reply-to header.  The e-mail
   header is not used by the LTA, but rather the items in the
   requestInformation.  When a server acts as a relay, it MAY add
   appropriate values to these items.

   For the response, an LTA normally sets the From and To header fields
   to either the last items of serviceID and returnID (or requestorID).
   In case of a relaying LTA, when the LTA receives a response from
   another LTA, it first determines its own identity in
   requestInformation, sets the From: header to its own identity and the
   To: header to the identity of its client.

7.3.  HTTP Bindings

   Servers MUST understand HTTP 1.1 requests at least for the ARCHIVE,
   EXPORT and LISTIDS functions allowing chunked input of a POST request
   and 'Continue' responses.  A server SHOULD understand a Content-
   Encoding value of gzip.  In case of a HTTP 1.0 request and response,
   a positive value Content-Length indicating the total size of the data
   MUST be used.  A client MUST send a Host header in the request.

   The Request URI may be used to indicate a particular service
   endpoint.  When using HTTPS, TLS MUST be supported by clients and
   servers.  Clients SHOULD send a TLS servername extension in the
   ClientHello.

   The Content-Type header MUST be set to "application/ltap-request" or
   "application/ltap-request+xml".  The LTAPrequest message MUST be sent
   in the body of the HTTP Request.

   The Content-Type header MUST be set to "application/ltap-response" or
   "application/ltap-response+xml".  The LTAP response message MUST be
   sent in the body of the HTTP Response.

   The HTTP status code MUST be set to 200 if a LTAP response message is
   returned.  Otherwise, the status code can be set to 3xx to indicate a
   redirection, 4xx to indicate a low-level client error (such as a
   malformed request), or 5xx to indicate a low-level server error.
   Clients SHOULD react automatically to redirections.

   When using HTTPS, TLS 1.0 MUST be supported.  SSL 3.0 MAY be
   supported by servers.  Future versions of TLS MAY be supported.
   Clients SHOULD send a TLS servername extension in the ClientHello.




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   RSA ciphersuites MUST be supported.  Diffie-Hellman and DSS
   ciphersuites MAY be supported.  TripleDES ciphersuites MUST be
   supported.  AES ciphersuites SHOULD be supported.

7.4.  Security

   A request and a response MAY be encapsulated in an [RFC3852]
   signedData or envelopedData where the content type indicated in the
   eContentType of the encapContentInfo is one of the LTAP content types
   and the eContent of the encapContentInfo, carried as an octet string
   containing an encoded request or response structure.

   When using a SignedData structure for authentication, LTAP requests
   and responses MAY contain one or more SignerInfo structures, each of
   which may contain countersignature attributes depending on
   operational environments.  When an end user client creates a request,
   there are only one signerInfo.  A relaying LTA MAY add an additional
   signature or a countersignature attribute or remove the encapsulation
   and create a new one depending on the requirements of the next LTA.

   For the XML encoded structures, alternatively, security mechanisme
   from [W3C.xmldsig-core] and [W3C.xmlenc-core] may be used.  An LTA
   MAY impose restrictions on the usage of these features.

   Clients and relays MUST ensure authenticity of a server when
   submitting data.  In order to do so, they MAY add another
   encapsulation from [RFC3852] that provides for confidentiality,
   and/or MAY use a secure transport layer, e.g., TLS to perform server
   authentication and to ensure confidentiality of the transport.

   Responses are generally protected in similar way by using a
   SignedData encapsulation with one or more SignerInfos, and
   CounterSignatures, depending on the number of participating servers.
   The number of signatures is not related to the number of
   participating servers but rather to the number of entities that may
   be used to authenticate a response or part of it.

   In some circumstances, a client/server communication may be secured
   only by lower layer transport mechanism, e.g.  SSL/TLS.

   A client MUST NOT trust a response that cannot be authenticated.

   Archive clients and servers MUST always create requests and responses
   that can be authenticated with the explicit exception of a global
   error status, which may be returned as a non-signed response.

   In order to be able to associate a possible error response with a
   request, the requester SHOULD use the field 'transactionIdentifier'.



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   The requester SHOULD not make any assumption about the usage of
   message header fields by the responding service, in particular the
   usage of fields like Subject, Message-ID or References.


8.  Credits

   This document has been created using XML2RFC ([RFC2629]).

   The XSD schema has been generated automatically using the asn1xsd
   tool from OSS Nokalva.

   The ASN.1 has been validated using the asn1c compiler from OSS
   Nokalva.


9.  Security Considerations

   This section discusses addition security considerations of the
   framework.

   When designing an LTA service, the following considerations have been
   identified that have an impact upon the validity or "trust" in the
   ltans server responses.

   An LTA is assumed to operate with best effort.  Nevertheless, an
   operation can fail or get totally lost.  A client SHOULD be able to
   recover from lost requests, i.e., avoid deleting data until an
   attestation has been received.

   It is possible for an LTA to report loss of integrity for archived
   data, or simply non-existence of data which is equivalent to loss of
   data.  Depending on the value of the data, appropriate measures to
   address these catastrophic scenarios need to be provided outside the
   basic service, e.g., by using redundant copies managed either by a
   client of internally of a broker type service.

   The validity of data should be checked by periodic execution of
   VERIFY operations intended to ensure data with demonstratable
   integrity is available throughout the lifetime of an archived data
   object.  The rate of refresh will be driven by a number of factors,
   some of which have a direct impact of demonstration of integrity.
   For example, the confidence in the strength of cryptographic
   algorithms or the quality of storage devices are factors determining
   the verification intervals.

   Depending on the lifetime and the quality of data, relying on
   cryptographic protection of data object may not be a sufficient means



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   to determine authenticity in time, other means may be required, e.g.
   physical protection of data storage material.

   It is imperative that keys used to sign responses are guarded with
   proper security and controls in order to minimize the possibility of
   compromise.  Nevertheless, in case the private key does become
   compromised, an audit trail of all the response generated by the
   service SHOULD be kept as a means to help discriminate between
   genuine and false responses.  Aa LTA MAY provide for a service to
   validate responses created by this service or another one solely
   based on the audit trail.

   As already indicated, when confidentiality and server authentication
   is required, requests and responses MAY be protected using
   appropriate mechanisms (e.g., CMS encapsulation [RFC3852] or TLS
   [RFC4366]).

   Server authentication is highly recommended for all service which
   transfer data to a server.

   Client identification and authentication MAY use services defined by
   TLS ([RFC4366]) instead of, or in addition to, using a document or
   message protection format, e.g.  CMS.

   It is possible for an LTA to report loss of integrity for archived
   data, or simply non-existence of data which is equivalent to loss of
   data.  Depending on the value of the data, appropriate measures to
   address these catastrophic scenarios need to be provided outside the
   basic service, e.g., by using redundant copies managed either by a
   client of internally of a broker type service.


10.  IPR Patent Information

   The material presented in this document was initially drafted in
   2005.

   The following United States Patents related to data validation and
   certification services, listed in chronological order, are known by
   the authors to exist at this time.  This may not be an exhaustive
   list.  Other patents may exist or be issued at any time.
   Implementers of this protocol and applications using the protocol
   SHOULD perform their own patent search and determine whether or not
   any encumberences exist on their implementation.  The list is
   intitially taken from [RFC3029].

   # 4,309,569 Method of Providing Digital Signatures
   (issued) January 5, 1982



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   (inventor) Ralph C. Merkle
   (assignee) The Board of Trustees of the Leland Stanford Junior
   University

   # 5,001,752 Public/Key Date-Time Notary Facility
   (issued) March 19, 1991
   (inventor) Addison M. Fischer

   # 5,022,080 Electronic Notary
   (issued) June 4, 1991
   (inventors) Robert T. Durst, Kevin D. Hunter

   # 5,136,643 Public/Key Date-Time Notary Facility
   (issued) August 4, 1992
   (inventor) Addison M. Fischer

   (Note: This is a continuation of patent # 5,001,752.)
   # 5,136,646 Digital Document Time-Stamping with Catenate Certificate
   (issued) August 4, 1992
   (inventors) Stuart A. Haber, Wakefield S. Stornetta Jr.
   (assignee) Bell Communications Research, Inc.

   # 5,136,647 Method for Secure Time-Stamping of Digital Documents
   (issued) August 4, 1992
   (inventors) Stuart A. Haber, Wakefield S. Stornetta Jr.
   (assignee) Bell Communications Research, Inc.

   # 5,373,561 Method of Extending the Validity of a Cryptographic
   Certificate
   (issued) December 13, 1994
   (inventors) Stuart A. Haber, Wakefield S. Stornetta Jr.
   (assignee) Bell Communications Research, Inc.,

   # 5,422,95 Personal Date/Time Notary Device
   (issued) June 6, 1995
   (inventor) Addison M. Fischer

   # 5,781,629 Digital Document Authentication System
   (issued) July 14, 1998
   (inventor) Stuart A. Haber, Wakefield S. Stornetta Jr.
   (assignee) Surety Technologies, Inc.



11.  IANA considerations

   LTAP request and response messages are identified using Object
   Identifiers (OIDs), which are defined in an arc delegated by IANA to



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   the LTANS Working Group.  This document also includes four MIME type
   registrations in Section 7.3.  No further action by IANA is necessary
   for this document.


12.  References

12.1.  Normative references

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3852]  Housley, R., "Cryptographic Message Syntax (CMS)",
              RFC 3852, July 2004.

   [RFC4366]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 4366, April 2006.

   [RFC4998]  Gondrom, T., Brandner, R., and U. Pordesch, "Evidence
              Record Syntax (ERS)", RFC 4998, August 2007.

12.2.  Informative references

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC3029]  Adams, C., Sylvester, P., Zolotarev, M., and R.
              Zuccherato, "Internet X.509 Public Key Infrastructure Data
              Validation and Certification Server Protocols", RFC 3029,
              February 2001.

   [RFC4810]  Wallace, C., Pordesch, U., and R. Brandner, "Long-Term
              Archive Service Requirements", RFC 4810, March 2007.

   [W3C.xmldsig-core]
              Eastlake, D., Reagle , J., and D. Solo, "XML-Signature
              Syntax and Processing", W3C Recommendation xmldsig-core,
              October 2000, <http://www.w3.org/TR/xmldsig-core/>.

   [W3C.xmlenc-core]
              Eastlake, D. and J. Reagle , "XML Encryption Syntax and
              Processing", W3C Candidate Recommendation xmlenc-core,
              August 2002, <http://www.w3.org/TR/xmlenc-core/>.







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Appendix A.  ASN.1 module in current syntax

   The following ASN.1 module has been checked using the asn1c tool.

   LTAP {iso(1) identified-organization(3) dod(6)
         internet(1) security(5) mechanisms(5)
         ltans(11) id-mod(0) id-mod-ltap(4) 0}
   DEFINITIONS IMPLICIT TAGS ::=
   BEGIN


   -- EXPORTS ALL
   IMPORTS

      certificateExtensions
   FROM UsefulDefinitions {joint-iso-itu-t ds(5) module(1)
         usefulDefinitions(0) 5}

      PolicyInformation, GeneralNames
   FROM CertificateExtensions certificateExtensions

      PKCS7-CONTENT-TYPE
   FROM PKCS7
      {iso(1) member-body(2) us(840) rsadsi(113549)
     pkcs(1) pkcs-7(7) modules(0) pkcs-7(1)}
   ;

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

   Artifact ::= PrintableString

   MessageDigest ::= SEQUENCE {
       digestAlgorithm DigestMethodType,
       digestValue     DigestValueType
   }

   DigestMethodType ::= OBJECT IDENTIFIER
   DigestValueType ::= OCTET STRING


   MetaData ::= SEQUENCE OF MetaItem

   MetaItem ::= SEQUENCE {
     type CHOICE {oid OBJECT IDENTIFIER,
                  attribute UTF8String,
                  uri  IA5String } ,



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     values SEQUENCE OF
        value CHOICE {
           oidValue  OBJECT IDENTIFIER,
           stringValue UTF8String,
           uriValue IA5String,
           integerValue INTEGER,
           opaqueValue OCTET STRING,
           composedValue MetaItem
        }
   }

   Nonce ::= OCTET STRING

   RawData ::= CHOICE {
   opaque     OCTET STRING,
   string     UTF8String,
   structured MetaData
   }

   DataOrTransaction ::= CHOICE {
   data      RawData,
   artifact  Artifact,
   reference IA5String
       }

   Data ::= SEQUENCE {
       dataReference  DataOrTransaction,
       metaData       MetaData,
       messageImprint MessageDigest
   }

   SerialNumber ::= INTEGER

   LtapTime ::= GeneralizedTime

   Version ::= ENUMERATED {
       v0,
       v1
   }

   EntityIdentifier ::= GeneralNames

   ServiceType ::= CHOICE {
      ltapbasicservice ENUMERATED {
         archive,
         delete,
         export,
         status,



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         verify,
         listids
      },
      ltapextendedservice OBJECT IDENTIFIER
   }

   StatusInformation ::= ENUMERATED {
       granted,
       grantedWithMods,
       rejection,
       waiting,
       more
   }


   RequestInformation ::= SEQUENCE {
       version           Version DEFAULT v1,
       servicePolicyInfo PolicyInformation,
       serviceType       ServiceType,

       requestorID       EntityIdentifier,
       serviceID         EntityIdentifier,
       returnID          EntityIdentifier OPTIONAL,
       serial            SerialNumber OPTIONAL,
       nonce             Nonce OPTIONAL,
       requestTime       LtapTime OPTIONAL,
       startTime         [0] LtapTime OPTIONAL,
       nextTime          [1] LtapTime OPTIONAL,
       bindingInfo       [2] MetaData OPTIONAL
   }

   Request ::= SEQUENCE {
      information           RequestInformation,
      data                  Data,
      transactionIdentifier IA5String OPTIONAL
   }


   StatusNotice ::= SEQUENCE {
       status           StatusInformation,
       errorInformation UTF8String (SIZE(0..8192)),
       lastValid        LtapTime OPTIONAL,
       transactionIdentifier IA5String OPTIONAL
   }

   OperationResponse ::= SEQUENCE {
       information RequestInformation,
       status             StatusNotice,



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       data               Data
   }

   Response ::= CHOICE {
       operationResponse OperationResponse,
       errorNotice   [0] StatusNotice
   }

   id-ct-LTAPRequest  OBJECT IDENTIFIER ::=
            { id-ct 4711 }
   id-ct-LTAPResponse  OBJECT IDENTIFIER ::=
            { id-ct 4711 }

   ltap-Request  PKCS7-CONTENT-TYPE ::= {Request
        IDENTIFIED BY  id-ct-LTAPRequest }
   ltap-Response PKCS7-CONTENT-TYPE ::= {Request
        IDENTIFIED BY  id-ct-LTAPResponse }

   LTAPRequest ::= ContentInfo
   LTAPResponse ::= ContentInfo



   END


Appendix B.  ASN.1 module in 1988 syntax

   The following ASN.1 module has been checked using the asn1c tool.

   LTAP {iso(1) identified-organization(3) dod(6)
         internet(1) security(5) mechanisms(5)
         ltans(11) id-mod(0) id-mod-ltap88(3) 0}
   DEFINITIONS IMPLICIT TAGS ::=
   BEGIN

   -- EXPORTS ALL --

   IMPORTS UTF8String, PolicyInformation,
        GeneralNames
   FROM PKIX1Explicit88
        { iso(1) identified-organization(3) dod(6) internet(1)
          security(5) mechanisms(5) pkix(7)
          id-mod(0) id-pkix1-explicit(18) }
   ;

   id-ct OBJECT IDENTIFIER ::= { iso(1) member-body(2)
                us(840) rsadsi(113549) pkcs(1) pkcs9(9)



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                id-smime(16) 1 }

   Artifact ::= PrintableString

   MessageDigest ::= SEQUENCE {
       digestAlgorithm DigestMethodType,
       digestValue     DigestValueType
   }

   DigestMethodType ::= OBJECT IDENTIFIER
   DigestValueType ::= OCTET STRING


   MetaData ::= SEQUENCE OF MetaItem

   MetaItem ::= SEQUENCE {
     type CHOICE {oid OBJECT IDENTIFIER,
                  attribute UTF8String,
                  uri  IA5String } ,
     values SEQUENCE OF
        value CHOICE {
           oidValue  OBJECT IDENTIFIER,
           stringValue UTF8String,
           uriValue IA5String,
           integerValue INTEGER,
           opaqueValue OCTET STRING,
           composedValue MetaItem
        }
   }

   Nonce ::= OCTET STRING

   RawData ::= CHOICE {
   opaque     OCTET STRING,
   string     UTF8String,
   structured MetaData
   }

   DataOrTransaction ::= CHOICE {
   data      RawData,
   artifact  Artifact,
   reference IA5String
       }

   Data ::= SEQUENCE {
       dataReference  DataOrTransaction,
       metaData       MetaData,
       messageImprint MessageDigest



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   }

   SerialNumber ::= INTEGER

   LtapTime ::= GeneralizedTime

   Version ::= ENUMERATED {
       v0,
       v1
   }

   EntityIdentifier ::= GeneralNames

   ServiceType ::= CHOICE {
      ltapbasicservice ENUMERATED {
         archive,
         delete,
         export,
         status,
         verify,
         listids
      },
      ltapextendedservice OBJECT IDENTIFIER
   }

   StatusInformation ::= ENUMERATED {
       granted,
       grantedWithMods,
       rejection,
       waiting,
       more
   }


   RequestInformation ::= SEQUENCE {
       version           Version DEFAULT v1,
       servicePolicyInfo PolicyInformation,
       serviceType       ServiceType,

       requestorID       EntityIdentifier,
       serviceID         EntityIdentifier,
       returnID          EntityIdentifier OPTIONAL,
       serial            SerialNumber OPTIONAL,
       nonce             Nonce OPTIONAL,
       requestTime       LtapTime OPTIONAL,
       startTime         [0] LtapTime OPTIONAL,
       nextTime          [1] LtapTime OPTIONAL,
       bindingInfo       [2] MetaData OPTIONAL



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   }

   Request ::= SEQUENCE {
      information           RequestInformation,
      data                  Data,
      transactionIdentifier IA5String OPTIONAL
   }


   StatusNotice ::= SEQUENCE {
       status           StatusInformation,
       errorInformation UTF8String (SIZE(0..8192)),
       lastValid        LtapTime OPTIONAL,
       transactionIdentifier IA5String OPTIONAL
   }

   OperationResponse ::= SEQUENCE {
       information RequestInformation,
       status             StatusNotice,
       data               Data
   }

   Response ::= CHOICE {
       operationResponse OperationResponse,
       errorNotice   [0] StatusNotice
   }

   id-ct-LTAPRequest  OBJECT IDENTIFIER ::=
            { id-ct 4711 }
   id-ct-LTAPResponse  OBJECT IDENTIFIER ::=
            { id-ct 4711 }

   END


Appendix C.  XML schema for LTAP

   <schema xmlns="http://www.w3.org/2001/XMLSchema"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     xmlns:enc="http://www.w3.org/2001/04/xmlenc#"
     targetNamespace="http://www.setcce.org/schemas/ltap"
     elementFormDefault="qualified"
     attributeFormDefault="unqualified">
   <annotation><documentation xml:lang="en">
      XML Schema for LTAP
   </documentation></annotation>





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   <xsd:complexType name="Name">
    <xsd:choice>
      <xsd:element name="rdnSequence" type="RDNSequence"/>
    </xsd:choice>
   </xsd:complexType>

   <xsd:complexType name="RDNSequence">
    <xsd:sequence minOccurs="0" maxOccurs="unbounded">
     <xsd:element name="RelativeDistinguishedName"
                  type="RelativeDistinguishedName"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="RelativeDistinguishedName">
    <xsd:sequence minOccurs="0" maxOccurs="unbounded">
     <xsd:element name="AttributeTypeAndDistinguishedValue"
                  type="AttributeTypeAndDistinguishedValue"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="AttributeTypeAndDistinguishedValue">
    <xsd:sequence>
     <xsd:element name="type">
      <xsd:simpleType>
       <xsd:restriction base="OBJECT_IDENTIFIER"/>
      </xsd:simpleType>
     </xsd:element>
     <xsd:element name="value">
      <xsd:complexType mixed="true">
       <xsd:choice>
        <xsd:any processContents="lax"/>
       </xsd:choice>
      </xsd:complexType>
     </xsd:element>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="PolicyInformation">
    <xsd:sequence>
     <xsd:element name="policyIdentifier"
                  type="CertPolicyId"/>
     <xsd:element name="policyQualifiers" minOccurs="0">
      <xsd:complexType>
       <xsd:sequence minOccurs="0" maxOccurs="unbounded">
        <xsd:element name="PolicyQualifierInfo"
                     type="PolicyQualifierInfo"/>
       </xsd:sequence>
      </xsd:complexType>



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     </xsd:element>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="PolicyQualifierInfo">
    <xsd:sequence>
     <xsd:element name="policyQualifierId">
      <xsd:simpleType>
       <xsd:restriction base="OBJECT_IDENTIFIER"/>
      </xsd:simpleType>
     </xsd:element>
     <xsd:element name="qualifier" minOccurs="0">
      <xsd:complexType mixed="true">
       <xsd:choice>
        <xsd:any processContents="lax"/>
       </xsd:choice>
      </xsd:complexType>
     </xsd:element>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:simpleType name="CertPolicyId">
    <xsd:restriction base="OBJECT_IDENTIFIER"/>
   </xsd:simpleType>


      <xsd:simpleType name="Artifact">
    <xsd:restriction base="PrintableString"/>
       </xsd:simpleType>

   <xsd:complexType name="MessageDigest">
    <xsd:sequence>
     <xsd:element name="digestAlgorithm"
                  type="DigestMethodType"/>
     <xsd:element name="digestValue"
                  type="DigestValueType"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:simpleType name="DigestValueType">
    <xsd:restriction base="OCTET_STRING"/>
   </xsd:simpleType>

   <xsd:simpleType name="DigestMethodType">
    <xsd:restriction base="OBJECT_IDENTIFIER"/>
   </xsd:simpleType>

   <xsd:complexType name="MetaData">



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    <xsd:sequence minOccurs="0"
                  maxOccurs="unbounded">
     <xsd:element name="MetaItem"
                  type="MetaItem"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="MetaItem">
    <xsd:sequence>
     <xsd:element name="type">
      <xsd:complexType>
       <xsd:choice>
        <xsd:element name="oid"
                     type="OBJECT_IDENTIFIER"/>
        <xsd:element name="attribute"
                     type="UTF8String"/>
        <xsd:element name="uri"
                     type="IA5String"/>
       </xsd:choice>
      </xsd:complexType>
     </xsd:element>
     <xsd:element name="values">
      <xsd:complexType>
       <xsd:sequence minOccurs="0"
                     maxOccurs="unbounded">
        <xsd:choice>
         <xsd:element name="oidValue"
                      type="OBJECT_IDENTIFIER"/>
         <xsd:element name="stringValue"
                      type="UTF8String"/>
         <xsd:element name="uriValue"
                      type="IA5String"/>
         <xsd:element name="integerValue"
                      type="INTEGER"/>
         <xsd:element name="opaqueValue"
                      type="OCTET_STRING"/>
         <xsd:element name="composedValue"
                      type="MetaItem"/>
        </xsd:choice>
       </xsd:sequence>
      </xsd:complexType>
     </xsd:element>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:simpleType name="Nonce">
    <xsd:restriction base="OCTET_STRING"/>
   </xsd:simpleType>



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   <xsd:complexType name="RawData">
    <xsd:choice>
     <xsd:element name="opaque" type="OCTET_STRING"/>
     <xsd:element name="string" type="UTF8String"/>
     <xsd:element name="structured" type="MetaData"/>
     </xsd:choice>
   </xsd:complexType>

   <xsd:complexType name="DataOrTransaction">
    <xsd:choice>
     <xsd:element name="data" type="RawData"/>
     <xsd:element name="artifact" type="Artifact"/>
     <xsd:element name="reference" type="IA5String"/>
    </xsd:choice>
   </xsd:complexType>

   <xsd:complexType name="Data">
    <xsd:sequence>
     <xsd:element name="dataReference" type="DataOrTransaction"/>
     <xsd:element name="metaData" type="MetaData"/>
     <xsd:element name="messageImprint" type="MessageDigest"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:simpleType name="SerialNumber">
    <xsd:restriction base="INTEGER"/>
   </xsd:simpleType>

   <xsd:simpleType name="LtapTime">
    <xsd:restriction base="GeneralizedTime"/>
   </xsd:simpleType>

   <xsd:complexType name="Version">
    <xsd:choice>
     <xsd:element name="v0" type="NULL"/>
     <xsd:element name="v1" type="NULL"/>
    </xsd:choice>
   </xsd:complexType>

   <xsd:complexType name="EntityIdentifier">
    <xsd:sequence minOccurs="0" maxOccurs="unbounded">
     <xsd:choice>
      <xsd:element name="rfc822Name" type="IA5String"/>
      <xsd:element name="dNSName" type="IA5String"/>
      <xsd:element name="directoryName" type="Name"/>
      <xsd:element name="uniformResourceIdentifier"
                   type="IA5String"/>
      <xsd:element name="iPAddress" type="OCTET_STRING"/>



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      <xsd:element name="registeredID"
                   type="OBJECT_IDENTIFIER"/>
      </xsd:choice>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="ServiceType">
    <xsd:choice>
     <xsd:element name="ltapbasicservice">
      <xsd:complexType>
       <xsd:choice>
        <xsd:element name="archive" type="NULL"/>
        <xsd:element name="delete" type="NULL"/>
        <xsd:element name="export" type="NULL"/>
        <xsd:element name="status" type="NULL"/>
        <xsd:element name="verify" type="NULL"/>
        <xsd:element name="listids" type="NULL"/>
       </xsd:choice>
      </xsd:complexType>
     </xsd:element>
     <xsd:element name="ltapextendedservice"
                  type="OBJECT_IDENTIFIER"/>
    </xsd:choice>
   </xsd:complexType>

   <xsd:complexType name="StatusInformation">
    <xsd:choice>
     <xsd:element name="granted" type="NULL"/>
      <xsd:element name="grantedWithMods" type="NULL"/>
      <xsd:element name="rejection" type="NULL"/>
      <xsd:element name="waiting" type="NULL"/>
      <xsd:element name="more" type="NULL"/>
    </xsd:choice>
   </xsd:complexType>

   <xsd:complexType name="RequestInformation">
    <xsd:sequence>
     <xsd:element name="version"
                  type="Version" minOccurs="0"/>
     <xsd:element name="servicePolicyInfo"
                  type="PolicyInformation"/>
     <xsd:element name="serviceType"
                  type="ServiceType"/>
     <xsd:element name="requestorID"
                  type="EntityIdentifier"/>
     <xsd:element name="serviceID"
                  type="EntityIdentifier"/>
     <xsd:element name="returnID"



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                  type="EntityIdentifier" minOccurs="0"/>
     <xsd:element name="serial"
                  type="SerialNumber" minOccurs="0"/>
     <xsd:element name="nonce"
                  type="Nonce" minOccurs="0"/>
     <xsd:element name="requestTime"
                  type="LtapTime" minOccurs="0"/>
     <xsd:element name="startTime"
                  type="LtapTime" minOccurs="0"/>
     <xsd:element name="nextTime"
                  type="LtapTime" minOccurs="0"/>
     <xsd:element name="bindingInfo"
                  type="MetaData" minOccurs="0"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="Request">
    <xsd:sequence>
     <xsd:element name="information" type="RequestInformation"/>
     <xsd:element name="data" type="Data"/>
     <xsd:element name="transactionIdentifier"
                  type="IA5String" minOccurs="0"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="StatusNotice">
    <xsd:sequence>
     <xsd:element name="status"
                  type="StatusInformation"/>
     <xsd:element name="errorInformation">
      <xsd:complexType mixed="true">
       <xsd:complexContent mixed="true">
        <xsd:extension base="UTF8String"/>
       </xsd:complexContent>
      </xsd:complexType>
     </xsd:element>
     <xsd:element name="lastValid"
                  type="LtapTime" minOccurs="0"/>
     <xsd:element name="transactionIdentifier"
                  type="IA5String" minOccurs="0"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="OperationResponse">
    <xsd:sequence>
     <xsd:element name="information"
                  type="RequestInformation"/>
     <xsd:element name="status" type="StatusNotice"/>



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     <xsd:element name="data" type="Data"/>
    </xsd:sequence>
   </xsd:complexType>

   <xsd:complexType name="Response">
    <xsd:choice>
     <xsd:element name="operationResponse"
                  type="OperationResponse"/>
     <xsd:element name="errorNotice"
                  type="StatusNotice"/>
    </xsd:choice>
   </xsd:complexType>

   <xsd:element name="Request" type="Request"/>
   <xsd:element name="Response" type="Response"/>
   <xsd:element name="LTAPRequest" type="LTAPRequest"/>
   <xsd:element name="LTAPResponse" type="LTAPResponse"/>

   <xsd:complexType name="LTAPResponse">
    <xsd:choice>
     <xsd:element name="response" type="Request"/>
     <xsd:element name="signedResponse" type="ds:Signature"/>
     <xsd:element name="encryptedResponse" type="enc:EncryptedData"/>
    </xsd:choice>
   </xsd:complexType>

   <xsd:complexType name="LTAPRequest">
    <xsd:choice>
     <xsd:element name="request" type="Request"/>
      <xsd:element name="signedRequest" type="xd:Signature"/>
      <xsd:element name="encryptedRequest" type="enc:EncryptedData"/>
    </xsd:choice>
   </xsd:complexType>

   </schema>


Appendix D.  Additional XML definitions

   A number of additional XML definitions are necessary.  They
   correspond to universal ASN.1 types.

      <xsd:simpleType name="INTEGER">
    <xsd:restriction base="xsd:integer"/>
       </xsd:simpleType>

       <xsd:complexType name="BOOLEAN">
    <xsd:choice>



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        <xsd:element name="true" type="NULL"/>
        <xsd:element name="false" type="NULL"/>
    </xsd:choice>
       </xsd:complexType>

       <xsd:simpleType name="NULL">
    <xsd:restriction base="xsd:string">
        <xsd:length value="0"/>
    </xsd:restriction>
       </xsd:simpleType>

       <xsd:complexType name="IA5String" mixed="true">
    <xsd:sequence minOccurs="0" maxOccurs="unbounded">
        <xsd:choice>
     <xsd:element name="nul" type="NULL"/>
     <xsd:element name="soh" type="NULL"/>
     <xsd:element name="stx" type="NULL"/>
     <xsd:element name="etx" type="NULL"/>
     <xsd:element name="eot" type="NULL"/>
     <xsd:element name="enq" type="NULL"/>
     <xsd:element name="ack" type="NULL"/>
     <xsd:element name="bel" type="NULL"/>
     <xsd:element name="bs" type="NULL"/>
     <xsd:element name="vt" type="NULL"/>
     <xsd:element name="ff" type="NULL"/>
     <xsd:element name="so" type="NULL"/>
     <xsd:element name="si" type="NULL"/>
     <xsd:element name="dle" type="NULL"/>
     <xsd:element name="dc1" type="NULL"/>
     <xsd:element name="dc2" type="NULL"/>
     <xsd:element name="dc3" type="NULL"/>
     <xsd:element name="dc4" type="NULL"/>
     <xsd:element name="nak" type="NULL"/>
     <xsd:element name="syn" type="NULL"/>
     <xsd:element name="etb" type="NULL"/>
     <xsd:element name="can" type="NULL"/>
     <xsd:element name="em" type="NULL"/>
     <xsd:element name="sub" type="NULL"/>
     <xsd:element name="esc" type="NULL"/>
     <xsd:element name="is4" type="NULL"/>
     <xsd:element name="is3" type="NULL"/>
     <xsd:element name="is2" type="NULL"/>
     <xsd:element name="is1" type="NULL"/>
        </xsd:choice>
    </xsd:sequence>
       </xsd:complexType>

       <xsd:simpleType name="OCTET_STRING">



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    <xsd:restriction base="xsd:string">
        <xsd:whiteSpace value="collapse"/>
        <xsd:pattern value="( *([0-9]|[A-F]|[a-f]) *)*"/>
    </xsd:restriction>
       </xsd:simpleType>

       <xsd:simpleType name="OBJECT_IDENTIFIER">
    <xsd:restriction base="xsd:string">
        <xsd:pattern value="( *([a-z]|[0-9]|\{|\}|\.)* *)"/>
    </xsd:restriction>
       </xsd:simpleType>

       <xsd:complexType name="UTF8String" mixed="true">
    <xsd:sequence minOccurs="0" maxOccurs="unbounded">
        <xsd:choice>
     <xsd:element name="nul" type="NULL"/>
     <xsd:element name="soh" type="NULL"/>
     <xsd:element name="stx" type="NULL"/>
     <xsd:element name="etx" type="NULL"/>
     <xsd:element name="eot" type="NULL"/>
     <xsd:element name="enq" type="NULL"/>
     <xsd:element name="ack" type="NULL"/>
     <xsd:element name="bel" type="NULL"/>
     <xsd:element name="bs" type="NULL"/>
     <xsd:element name="vt" type="NULL"/>
     <xsd:element name="ff" type="NULL"/>
     <xsd:element name="so" type="NULL"/>
     <xsd:element name="si" type="NULL"/>
     <xsd:element name="dle" type="NULL"/>
     <xsd:element name="dc1" type="NULL"/>
     <xsd:element name="dc2" type="NULL"/>
     <xsd:element name="dc3" type="NULL"/>
     <xsd:element name="dc4" type="NULL"/>
     <xsd:element name="nak" type="NULL"/>
     <xsd:element name="syn" type="NULL"/>
     <xsd:element name="etb" type="NULL"/>
     <xsd:element name="can" type="NULL"/>
     <xsd:element name="em" type="NULL"/>
     <xsd:element name="sub" type="NULL"/>
     <xsd:element name="esc" type="NULL"/>
     <xsd:element name="is4" type="NULL"/>
     <xsd:element name="is3" type="NULL"/>
     <xsd:element name="is2" type="NULL"/>
     <xsd:element name="is1" type="NULL"/>
        </xsd:choice>
    </xsd:sequence>
       </xsd:complexType>




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       <xsd:simpleType name="PrintableString">
    <xsd:restriction base="xsd:string">
        <xsd:pattern value="[ &apos;\(\)\+-:=\?A-Za-z]*"/>
    </xsd:restriction>
       </xsd:simpleType>

       <xsd:simpleType name="GeneralizedTime">
    <xsd:restriction base="xsd:string">
        <xsd:whiteSpace value="collapse"/>
        <xsd:pattern
    value="( *([0-9]{8}([0-9]{2})?([0-9]{2})?([0-9]{2})?
          (\.[0-9]+)?((Z)|([\+\-][0-9]{4}))?) *)"/>
    </xsd:restriction>
       </xsd:simpleType>


Authors' Addresses

   Aleksej Jerman Blazic
   SETCCE
   Jamova 39
   Ljubljana  SI-1000
   SLOVENIA

   Fax:   +386 1 4773861
   Email: aljosa@setcce.org


   Peter Sylvester
   EdelWeb
   15 quai de Dion-Bouton
   Puteaux  F-92816
   FRANCE

   Fax:   +33 1 40 99 14 14
   Email: Peter.Sylvester@edelweb.fr


   Carl Wallace
   Cygnacom Solutions
   Suite 5200
   7925 Jones Branch Drive
   McLean, VA  22102

   Email: cwallace@cygnacom.com






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