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Network Working Group                                       A. ArsenaultRequest for Comments: 3157                                    DiversinetCategory: Informational                                       S. Farrell                                                  Baltimore Technologies                                                             August 2001Securely Available Credentials - RequirementsStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2001).  All Rights Reserved.Abstract   This document describes requirements to be placed on Securely   Available Credentials (SACRED) protocols.Table Of Contents1. Introduction.................................................12. Framework Requirements.......................................43. Protocol Requirements........................................74. Security Considerations.....................................10   References.....................................................12   Acknowledgements...............................................12   Authors' Addresses.............................................13Appendix A: A note on SACRED vs. hardware support..............14Appendix B: Additional Use Cases...............................14   Full Copyright Statement.......................................201. Introduction   "Credentials" are information that can be used to establish the   identity of an entity, or help that entity communicate securely.   Credentials include such things as private keys, trusted roots,   tickets, or the private part of a Personal Security Environment (PSE)   [RFC2510] - that is, information used in secure communication on the   Internet.  Credentials are used to support various Internet   protocols, e.g., S/MIME, IPSec and TLS.Arsenault & Farrell          Informational                      [Page 1]

RFC 3157                 SACRED - Requirements               August 2001   In simple models, users and other entities (e.g., computers like   routers) are provided with credentials, and these credentials stay in   one place.  However, the number, and more importantly the number of   different types, of devices that can be used to access the Internet   is increasing.  It is now possible to access Internet services and   accounts using desktop computers, laptop computers, wireless phones,   pagers, personal digital assistants (PDAs) and other types of   devices.  Further, many users want to access private information and   secure services from a number of different devices, and want access   to the same information from any device.  Similarly credentials may   have to be moved between routers when they are upgraded.   This document identifies a set of requirements for credential   mobility.  The Working Group will also produce companion documents,   which describe a framework for secure credential mobility, and a set   of protocols for accomplishing this goal.   The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"   in this document are to be interpreted as described in [RFC2119].1.1 Background and Motivation   In simple models of Internet use, users and other entities are   provided with credentials, and these credentials stay in one place.   For example, Mimi generates a public and private key on her desktop   computer, provides the public key to a Certification Authority (CA)   to be included in a certificate, and keeps the private key on her   computer.  It never has to be moved.   However, Mimi may want to able to send signed e-mail messages from   her desktop computer when she is in the office, and from her laptop   computer when she is on the road, and she does not want message   recipients to know the difference.  In order to do this, she must   somehow make her private key available on both devices - that is,   that credential must be moved.   Similarly, Will may want to retrieve and read encrypted e-mail from   either his wireless phone or from his two-way pager.  He wants to use   whichever device he has with him at the moment, and does not want to   be denied access to his mail or to be unable to decrypt important   messages simply because he has the wrong device.  Thus, he must be   able to have the same private key available on both devices.   The following scenario relating to routers has also been offered:   "Once upon a time, a router generated a keypair.  The administrators   transferred the public key of that router to a lot of other (peer)   routers and used that router to encrypt traffic to the other routers.   And this was good for many years.  Then one day, the networkArsenault & Farrell          Informational                      [Page 2]

RFC 3157                 SACRED - Requirements               August 2001   administrators found that this particular little router couldn't   handle an OC-192.  So they trashed it and replaced it with a really   big router.  While they were there, the craft workers inserted a   smart card into the router and logged into the router.  They gave the   appropriate commands and entered the correct answers and so the   credentials (keypair) were transferred to the new, big router.   Alternatively, the craft people could have logged into the router,   given it a minimal configuration and transferred the credentials from   a credential server to the router.  They had to perform the correct   incantations and authentications for the transfer to be successful.   In this way, the identity of the router was moved from an old router   to a new one.  The administrators were glad that they didn't have to   edit the configurations of all of the peer routers as well."   It is generally accepted that the private key in these examples must   be transferred securely.  In the first example, the private key   should not be exposed to anyone other than Mimi herself (and ideally,   it would not be directly exposed to her).  Furthermore, it must be   transferred correctly.  It must be transferred to the proper device,   and it must not be corrupted - improperly modified - during transfer.   Making credentials securely available (in an interoperable fashion)   will provide substantial value to network owners, administrators, and   end users.  The intent is that this value be provided largely   independent of the hardware device used to access the secure   credential and the type of storage medium to which the secure   credential is written.  Different credential storage devices, (e.g.,   desktop or laptop PC computer memory, a 3.5 inch flexible diskette, a   hard disk file, a cell phone, a smart card, etc.) will have very   different security characteristics and, often very different protocol   handling capabilities.  Using SACRED protocols, users will be able to   securely move their credentials between different locations,   different Internet devices, and different storage media as needed.   In the remainder of this document we present a set of requirements   for the secure transfer of software-based credentials.1.2 Working Group Organization and Documents   The SACRED Working Group is working on the standardization of a set   of protocols for securely transferring credentials among devices.  A   general framework is being developed that will give an abstract   definition of protocols which can meet the credential-transfer   requirements.  This framework will allow for the development of a set   of protocols, which may vary from one another in some respects.   Specific protocols that conform to the framework can then be   developed.Arsenault & Farrell          Informational                      [Page 3]

RFC 3157                 SACRED - Requirements               August 2001   Work is being done on a number of documents.  This document   identifies the requirements for the general framework, as well as the   requirements for specific protocols.  Another document will describe   the protocol framework.  Still others will define the protocols   themselves.1.3 Structure of This DocumentSection 1 of this document provides an introduction to the problem   being solved by this working group.Section 2 describes requirements   on the framework.Section 3 identifies the overall requirements for   secure credential-transfer protocols, and separate requirements for   two different classes of solutions.Section 4 identifies Security   Considerations.Appendix A describes the relationship of the SACRED   solutions and credential-mobility solutions involving hardware   components such as smart cards.Appendix B contains some additional   scenarios which were considered when developing the requirements.2. Framework Requirements   This section describes requirements that the SACRED framework has to   meet, as opposed to requirements that are to be met by a specific   protocol that uses the framework.2.1 Credential Server and Direct solutions   There are at least two different ways to solve the problem of secure   credential transfer between devices.  One class of solutions uses a   "credential server" as an intermediate node, and the other class   provides direct transfer between devices.   A "credential server" can be likened to a server that sits in front   of a repository where credentials can be securely stored for later   retrieval.  The credential server is active in the protocol, that is,   it implements security enforcing functionality.   To transfer credentials securely from one end device to another is a   straightforward two-step process.  Users can have their credentials   securely "uploaded" from one device, e.g., a wireless phone, to the   credential server.  They can be stored on the credential server, and   "downloaded" when needed using another device; e.g., a two-way pager.   Some advantages of a credential server approach compared to   credential transfer are:Arsenault & Farrell          Informational                      [Page 4]

RFC 3157                 SACRED - Requirements               August 2001   1. It provides a conceptually clean and straightforward approach.      For all end devices, there is one protocol, with a set of actions      defined to transfer credentials from the device to the server, and      another set of actions defined to transfer credentials from the      server to the device.  Furthermore, this protocol involves clients      (the devices) and a server (the credential server), like many      other Internet protocols; thus, the design of this protocol is      likely to be familiar to most people familiar with most other      Internet protocols.   2. It provides for a place where credentials can be securely stored      for arbitrary lengths of time.  Given a reasonable-quality server      operating under generally accepted practices, it is unlikely the      credentials will be permanently lost due to a hardware failure.      This contrasts with systems where credentials are only stored on      end devices, in which a failure of or the loss of the device could      mean that the credentials are lost forever.   3. The credential server may be able to enforce a uniform security      policy regarding credential handling.  This is particularly the      case where credentials are issued by an organization for its own      purposes, and are not "created" by the end user, and so must be      governed by the policies of the issuer, not the user.   However, the credential server approach has some potential   disadvantages, too:   1. It might be somewhat expensive to maintain and run the credential      server, particularly if there are stringent requirements on      availability and reliability of the server.  This is particularly      true for servers which are used for a large community of users.      When the credential server is intended for a small community, the      complexity and cost would be much less.   2. The credential server may have to be "trusted" in some sense and      also introduces a point of potential vulnerability.  (See the      Security Considerations section for some of the issues.)  Good      protocol and system design will limit the vulnerability that      exists at the credential server, but at a minimum, someone with      access to the credential server will be able to delete credentials      and thus deny the SACRED service to system users.   Thus, some users may prefer a different class of solution, in which   credentials are transferred directly from one device to another   (i.e., having no intermediary element that processes or has any   understanding of the credentials).Arsenault & Farrell          Informational                      [Page 5]

RFC 3157                 SACRED - Requirements               August 2001   For example, consider the case where Mimi sends a message from her   wireless phone containing the credentials in question, and retrieves   it using her two-way pager.  In getting from one place to another,   the bits of the message cross the wireless phone network to a base   station.  These bits are likely transferred over the wired phone   network to a message server run by the wireless phone operator, and   are transferred from there over the Internet to a message server run   by the paging operator.  From the paging operator they are   transferred to a base station and then finally to Mimi's pager.   Certainly, there are devices other than the original wireless phone   and ultimate pager that are involved in the credential transfer, in   the sense that they transmit bits from one place to another.   However, to all devices except the pager and the wireless phone, what   is being transferred is an un-interpreted and unprocessed set of   bits.  No security-related decisions are made, and no actions are   taken based on the fact that this message contains credentials, at   any of the intermediate nodes.  They exist simply to forward bits.   Thus, we consider this to be a "direct" transfer of credentials.   Solutions involving the direct transfer of credentials from one   device to another are potentially somewhat more complex than the   credential-server approach, owing to the large number of different   devices and formats that may have to be supported.  Complexity is   also added due to the fact that each device may in turn have to   exhibit the behavior of both a client and a server.   We believe that both classes of solutions are useful in certain   environments, and thus that the SACRED framework will have to define   solutions for both.  The extent to which elements of the above   solutions overlap remains to be determined.   This all leads to our first set of requirements:   F1.   The framework MUST support both "credential server" and         "direct" solutions.   F2.   The "credential server" and "direct" solutions SHOULD use the         same technology as far as possible.2.2 User authentication   There is a wide range of deployment options for credential mobility   solutions.  In many of these cases, it is useful to be able to re-use   an existing user authentication scheme, for example where passwords   have previously been established, it may be more secure to re-use   these than try to manage a whole new set of passwords.  Different   devices may also limit the types of user authentication scheme that   are possible, e.g., not all mobile devices are practically capable of   carrying out asymmetric cryptography.Arsenault & Farrell          Informational                      [Page 6]

RFC 3157                 SACRED - Requirements               August 2001   F3.   The framework MUST allow for protocols which support different         user authentication schemes2.3 Credential Formats         Today there is no single standard format for credentials and         this is not likely to change in the near future.  There are a         number of fairly widely deployed formats, e.g., [PGP],         [PKCS#12] that have to be supported.  This means that the         framework has to allow for protocols supporting any credential         format.   F4.   The details of the actual credential type or format MUST be         opaque to the protocol, though not to processing within the         protocol's peers.  The protocol MUST NOT depend on the internal         structure of any credential type or format.2.4 Transport Issues   Different devices allow for different transport layer possibilities,   e.g., current WAP 1.x devices do not support TCP.  For this reason   the framework has to be transport "agnostic".   F5.   The framework MUST allow use of different transports.3. Protocol Requirements   In this section, we identify the requirements for secure credential-   transfer solutions.  We will begin by listing a set of relevant   vulnerabilities and the requirements that must be met by all   solutions.  Then we identify additional requirements that must be met   by solutions involving a credential server, followed by additional   requirements that must be met by solutions involving direct transfer   of credentials.3.1 Vulnerabilities   This section lists the vulnerabilities against which a SACRED   protocol SHOULD offer protection.  Any protocol claiming to meet the   requirements listed in this document MUST explicitly indicate how (or   whether) it offers protection for each of these vulnerabilities.   V1.      A passive attacker can watch all packets on the network and            later carry out a dictionary attack.   V2.      An attacker can attempt to masquerade as a credential server            in an attempt to get a client to reveal information on line            that allows for a later dictionary attack.Arsenault & Farrell          Informational                      [Page 7]

RFC 3157                 SACRED - Requirements               August 2001   V3.      An attacker can attempt to get a client to decrypt a chosen            "ciphertext" and get the client to make use of the resulting            plaintext - the attacker may then be able to carry out a            dictionary attack (e.g., if the plaintext resulting from            "decryption" of a random string is used as a DSA private            key).   V4.      An attacker could overwrite a repository entry so that when            a user subsequently uses what they think is a good            credential, they expose information about their password            (and hence the "real" credential).   V5.      An attacker can copy a credential server's repository and            carry out a dictionary attack.   V6.      An attacker can attempt to masquerade as a client in an            attempt to get a server to reveal information that allows            for a later dictionary attack.   V7.      An attacker can persuade a server that a successful login            has occurred, even if it hasn't.   V8.      (Upload) An attacker can overwrite someone else's            credentials on the server.   V9.      (When using password-based authentication) An attacker can            force a password change to a known (or "weak") password.   V10.     An attacker can attempt a man-in-the-middle attack for lots   V11.     User enters password instead of name.   V12.     An attacker could attempt various denial-of-service attacks.3.2 General Protocol Requirements   Looking again at the examples described inSection 1.1, we can   readily see that there are a number of requirements that must apply   to the transfer of credentials if the ultimate goal of supporting the   Internet security protocols (e.g., TLS, IPSec, S/MIME) is to be met.   For example, the credentials must remain confidential at all times;   it is unacceptable for nodes other than the end-user's device(s) to   see the credentials in any readable, cleartext form.   These, then, are the requirements that apply to all secure   credential-transfer solutions:   G1.      Credential transfer both to and from a device MUST be            supported.   G2.      Credentials MUST NOT be forced by the protocol to be present            in cleartext at any device other than the end user's.   G3.      The protocol SHOULD ensure that all transferred credentials            be authenticated in some way (e.g., digitally signed or            MAC-ed).   G4.      The protocol MUST support a range of cryptographic            algorithms, including symmetric and asymmetric algorithms,            hash algorithms, and MAC algorithms.Arsenault & Farrell          Informational                      [Page 8]

RFC 3157                 SACRED - Requirements               August 2001   G5.      The protocol MUST allow the use of various credential types            and formats (e.g., X.509, PGP, PKCS12, ...).   G6.      One mandatory to support credential format MUST be defined.   G7.      One mandatory to support user authentication scheme MUST be            defined.   G8.      The protocol MAY allow credentials to be labeled with a text            handle, (outside the credential), to allow the end user to            select amongst a set of credentials or to name a particular            credential.   G9.      Full I18N support is REQUIRED (via UTF8 support) [RFC2277].   G10.     It is desirable that the protocol be able to support            privacy, that is, anonymity for the client.   G11.     Transferred credentials MAY incorporate timing information,            for example a "time to live" value determining the maximum            time for which the credential is to be usable following            transfer/download.3.3 Requirements for Credential Server-based solutions   The following requirements assume that there is a credential server   from which credentials are downloaded to the end user device, and to   which credentials are uploaded from an end user device.   S1.      Credential downloads (to an end user) and upload (to the            credential server) MUST be supported.   S2.      Credentials MUST only be downloadable following user            authentication or else only downloaded in a format that            requires completion of user authentication for deciphering.   S3.      It MUST be possible to ensure the authenticity of a            credential during upload.   S4.      Different end user devices MAY be used to            download/upload/manage the same set of credentials.   S5.      Credential servers SHOULD be authenticated to the user for            all operations except download.  Note: This requirement can            be ignored if the credential format itself is strongly            protected, as there is no risk (other than user confusion)            from an unauthenticated credential server.   S6.      It SHOULD be possible to authenticate the credential server            to the user as part of a download operation.   S7.      The user SHOULD only have to enter a single secret value in            order to download and use a credential.   S8.      Sharing of secrets across multiple servers MAY be possible,            so that penetration of some servers does not expose the            private parts of a credential ("m-from-n" operation).   S9.      The protocol MAY support "away-from-home" operation, where            the user enters both a name and a domain (e.g.            RoamingStephen@baltimore.ie) and the domain can be used in            order to locate the user's credential server.Arsenault & Farrell          Informational                      [Page 9]

RFC 3157                 SACRED - Requirements               August 2001   S10.     The protocol MUST provide operations allowing users to            manage their credentials stored on the credential server,            e.g., to retrieve a list of their credentials stored on a            server; add credentials to the server; delete credentials            from the server.   S11.     Client-initiated authentication information (e.g., password)            change MUST be supported.   S12.     The user SHOULD be able to retrieve a list of            accesses/changes to their credentials.   S13.     The protocol MUST support user self-enrollment.  One            scenario calling for this is where a previously unknown user            uploads his credential without requiring manual operator            intervention.   S14.     The protocol MUST NOT prevent bulk initializing of a            credential server's repository.   S15.     The protocol SHOULD require minimal client configuration.3.4 Requirements for Direct-Transfer Solutions   The full set of requirements for this case has not been elucidated,   and this list is therefore provisional.  An additional requirements   document (or a modification of this one) will be required prior to   progression of a direct-transfer protocol.   The following requirements apply to solutions supporting the "direct"   transfer of credentials from one device to another.  (SeeSection 2   for the note on the meaning of "direct" in this case.)   D1.   It SHOULD be possible for the receiving device to authenticate         that the credential package indeed came from the purported         sending device.   D2.   In order for a sender to know that a credential has been         received by a recipient, it SHOULD be possible for the         receiving device to send an acknowledgment of credential         receipt back to the sending device, and for the sending device         to authenticate this acknowledgment.4. Security Considerations4.1 Hardware vs. Software   Mobile credentials will never be as secure as a "pure" hardware-based   solution, because of potential attacks through the operating system   of the end-user device.  However, an acceptable level of security may   be accomplished through some simple means.  In fact the level of   security may be improved (compared to password encrypted files)   through the use of SACRED protocols.Arsenault & Farrell          Informational                     [Page 10]

RFC 3157                 SACRED - Requirements               August 2001   The platforms to which credentials are downloaded usually cannot be   regarded as tamper-resistant, and it therefore is not too hard to   analyze contents of their memories.  Further, storage of private   keys, even if they are encrypted, on a credential server, will be   unacceptable in some environments.  Lastly, replacement of installed   or downloaded SACRED client software with a Trojan horse program will   always be possible, such a program could email the username and   password to the program's author.4.2 Auditing   Although out of scope of the SACRED protocol development work,   implementations should carefully audit events that may be security   relevant.  In particular credential server implementations should   audit all operations and should include information about the time   and source (e.g., IP address) of the operation, the claimed identity   of the client (possibly masked - see below), the type and result of   the operation and possibly other operation specific information.   Implementations should also take care not to include security   sensitive information in the audit trail, especially not sensitive   authentication information.   It may be sensible to mask the claimed identity in some way in order   to ensure that even if a user enters her password in a "username"   field, that that information is not in clear in the audit trail,   regardless of whether or not it was received in clear.   Similar mechanisms which should be supported, but which are out of   scope of protocol development include alerts and account locking, in   particular following repeated authentication failures.4.3 Defense against attacks   Credential servers are major targets.  Someone who can successfully   attack a credential server might be able to gain access to the   credentials of a number of users, unless those credentials are   sufficiently protected (e.g., encrypted sufficiently that they cannot   be read or used by someone who gains access to them).  Attackers   might also be able to substitute credentials of users, to carry out   other system attacks (e.g., an attacker could provide a user with a   "trusted root" credential that the attacker controls, which would   later allow the attacker to have some other certificate accepted by   the user counter to policy).   In addition, a credential server is a major target for denial of   service attacks.  Ensuring that a credential server is unavailable to   legitimate users can be of great assistance to attackers.  Users who   were not able to retrieve needed credentials might be forced toArsenault & Farrell          Informational                     [Page 11]

RFC 3157                 SACRED - Requirements               August 2001   operate insecurely, or not operate at all.  Credential servers are   especially vulnerable to denial of service attacks if they do lots of   expensive cryptographic operations - it might not take very many   operations for the attacker to bring service to an unacceptable   level.   Thus, great care should be taken in designing systems that use   credential servers to protect against these attacks.References   [PGP]       Callas, J., Donnerhacke, L., Finney, H. and R. Thayer,               "OpenPGP Message Format",RFC 2440, November 1998.   [PKCS12]    "PKCS #12 v1.0: Personal Information Exchange Syntax               Standard", RSA Laboratories, June 24, 1999.   [CMS]       Housley, R., "Cryptographic Message Syntax",RFC 2630,               June 1999.   [PKCS15]    "PKCS #15 v1.1: Cryptographic Token Information Syntax               Standard," RSA Laboratories, June 2000.   [RFC2026]   Bradner, S., "The Internet Standards Process -- Revision               3",BCP 9,RFC 2026, October 1996.   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2277]   Alvestrand, H., " IETF Policy on Character Sets and               Languages",BCP 18,RFC 2277, January 1998.   [RFC2510]   Adams, C. and S. Farrell, "Internet X.509 Public Key               Infrastructure Certificate Management Protocols",RFC2510, March 1999.   [RFC2616]   Fielding, R., Gettys, J., Mogul, J., Frysyk, H.,               Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext               Transfer Protocol - HTTP/1.1",RFC 2616, June 1999.Acknowledgements   The authors gratefully acknowledge the text containing additional use   cases inAppendix B that was supplied by Neal Mc Burnett   (nealmcb@avaya.com).Arsenault & Farrell          Informational                     [Page 12]

RFC 3157                 SACRED - Requirements               August 2001Authors' Addresses   Alfred Arsenault   Diversinet Corp.   P.O. Box 6530   Ellicott City, MD 21042   USA   Phone: +1 410-480-2052   EMail: aarsenault@dvnet.com   Stephen Farrell,   Baltimore Technologies,   39 Parkgate Street,   Dublin 8,   IRELAND   Phone: +353-1-881-6000   EMail: stephen.farrell@baltimore.ieArsenault & Farrell          Informational                     [Page 13]

RFC 3157                 SACRED - Requirements               August 2001Appendix A: A note on SACRED vs. hardware support.   One way of accomplishing many of the goals of the SACRED WG is to put   the credentials on hardware tokens - e.g., smart cards, PCMCIA cards,   or other devices.  There are a number of types of hardware tokens   today that provide secure storage for sensitive information, some   degree of authentication, and interfaces to a number of types of   wireless and other devices.  Thus, in the second example fromsection1.1, Will could simply put his private key on a smart card, always   take the smart card with him, and be assured that whichever device he   uses to retrieve his e-mail, he will have all of the information   necessary to decrypt and read messages.   However, hardware tokens are not appropriate for every environment.   They cost more than software-only solutions, and the additional   security they provide may or may not be worth the incremental cost.   Not all devices have interfaces for the same hardware tokens.  And   hardware tokens are subject to different failure modes than typical   computers - it is not at all unusual for a smart card to be lost or   stolen; or for a PCMCIA card to physically break.   Thus, it is appropriate to develop complementary software-based   solution that allows credentials to be moved from one device to   another, and provides a level of security sufficient for its   environments.  While we recognize that the level of security provided   by a software solution may not be as high as that provided by the   hardware solutions discussed above, and some organizations may not   consider it sufficient at all, we believe that a worthwhile solution   can be developed.   Finally, SACRED protocols can also complement hardware credential   solutions by providing standard mechanisms for the update of   credentials which are stored on the hardware device.  Today, this   often requires returning (with) the device to an administrative   centre, which is often inconvenient and may be costly.  SACRED   protocols provide a way to update and manage credentials stored on   hardware devices without requiring such physical presence.Appendix B: Additional Use Cases   This appendix describes some additional use cases for SACRED   protocols.  SACRED protocols are NOT REQUIRED to support all these   use cases, that is, this text is purely informative.Arsenault & Farrell          Informational                     [Page 14]

RFC 3157                 SACRED - Requirements               August 2001B.1 Home/Work Desktop Computer   Scenario Overview   A university utilizing a PKI for various applications and services   on-campus is likely to find that many of its users would like to make   use of the same PKI-enabled services and applications on computers   located in their residence.  These home computers may be owned either   by the university or by the individual but are permanently located at   the residence as opposed to laptop systems that may be taken home.   The usage depicted in this scenario may be motivated by formal   telecommuting arrangements or simply by the need to catch up on work   from home in the evenings.  The basic scenario should apply equally   well to the commercial, health care, and higher education   environments.   Assumptions   This scenario assumes that the institution has not implemented a   hardware token-based PKI mobility solution   The home computer has a dial-up as opposed to a permanent network   connection.   The PKI applications, whenever practical, should be functional in   both on-line and off-line modes.  For example, the home user signing   an email message to be queued for later bulk sending and the reading   of a received encrypted message may be supported off-line while   composing and queuing of an encrypted message might not be supported   in off-line mode.   Applications using digital signatures may require "non-repudiation".   The institution prefers that the user be identified via a single   certificate / key-pair from all computers used by the individual.   The home computer system can not be directly supported by the   institution's IT staff.  Hardware, operating system versions, and   operating system configurations will vary widely.  Significant   software installation or specialized configurations will be difficult   to implement.   Uniqueness of Scenario   vThe PKI mobility support needed for this scenario is, in general,   similar to the other mobility scenarios.  However, it does have   several unique aspects:Arsenault & Farrell          Informational                     [Page 15]

RFC 3157                 SACRED - Requirements               August 2001   1. The home-user scenario differs from the general public workstation      case in that it provides the opportunity to permanently store the      user's certificate and key-pair on the workstation.   2. Likewise the appropriate CA certificates and even certificates for      other users can be permanently stored or cached on the home      workstation.   3. Another key difference is the need to support off-line use of the      PKI credentials given the assumed dial-up network connection.   4. The level of hardware and software platform consistency (operating      system versions and configurations) will vary widely.   5. Finally, the level of available technical support is significantly      less for home systems than for equivalent systems managed by the      IT staff at the office location.B.2 Public Lab / On-campus Shared Workstation   Scenario Overview   Many colleges and universities operate labs full of computer systems   that are available for use by the general student population.  These   computers are typically configured with identical hardware and an   operating system build that is replicated to all of the systems in   the lab.  Many typical configurations provide no permanent storage of   any type while others may offer individual disk space for personal   files on a central server.  Some scheme is generally used to ensure   that the configuration of the operating system is preserved across   users and that temporary files created by one user are removed before   the next user logs in.  Students generally sit down at the next   available workstation without any clear pattern of usage.   The same basic technical solutions used to operate public labs are   often also used in general environments where several people share a   single workstation.  This is often found in locations with shift work   such as medical facilities and service bureaus that provide services   to multiple time zones.   Assumptions   1. This scenario assumes that the institution has not implemented a      hardware token-based PKI mobility solution.   2. The computer systems are permanently networked with LAN      connections.Arsenault & Farrell          Informational                     [Page 16]

RFC 3157                 SACRED - Requirements               August 2001   3. The configuration of the computer system is centrally maintained      and customizations are relatively easy to implement.  For example      it would be easy to load enterprise root certificates, LDAP server      configurations, specialized software, and any other needed      components of the PKI on to the workstations.   4. Applications using digital signatures may require "non-      repudiation" in some of the anticipated environments.  Examples of      this might include homework submission in a public lab environment      or medical records in a health care environment.   5. The institution prefers that the user be identified via a single      certificate / key-pair from all computers used by the individual.   6. Many anticipated implementations of this scenario will not      implement any user authentication at the desktop operating system      level.  Instead, user authentication will occur at during the      startup of networked applications such as email, web-based      services, etc.  Login at the desktop level may be with generic      user names that are more targeted at matching printouts to      machines than identifying users.   7. Users, with almost ridiculous frequency, will walk away from a      system forgetting to first logout from running authenticated      applications.   Uniqueness of Scenario   The PKI mobility support needed for this scenario is, in general,   similar to the other mobility scenarios.  However, it does have   several unique aspects:   1. Unlike situations with personal workstations, there is no      permanent storage available to hold user key pairs and      certificates.   2. Appropriate CA certificates and custom software are easily added      and maintained for these types of shared systems.   3. The workstations are installed in public locations and users will      frequently forget to close applications before permanently walking      away from the workstation.Arsenault & Farrell          Informational                     [Page 17]

RFC 3157                 SACRED - Requirements               August 2001B.3 Public Kiosk Mobility   Overview   This scenario describes the needs of the traveler or the shopper.   This person is traveling light (no computer) or is burdened with   everything but a computer.  It recognizes the increasing availability   of Internet access points in public spaces, such as libraries,   airports, shopping malls, and "cyber cafes".   The Need   In our increasingly mobile society, the chances of needing   information when away from the normal computing place are great.  One   may need to look up a telephone number.  Have you tried to find a   phone book at a public phone lately?  It may become necessary to use   a data device to find the next place to rush to.  With the   proliferation of wireless devices (electronic leashes), others have   the ability to create a need for quick access to electronic   information.  A pager can generate a need to check the email inbox or   address book.  A cell phone can drive you to your database to answer   a pressing question.   The ability to quickly access sensitive or protected information or   services from publicly available devices will only become more   necessary as we become more and more "connected".   The Device   The access device is more a function of the best discount or   marketing effort than of design.  Any number of hardware platforms   will be encountered.   Since these devices are open to the public I/O ports are not likely   to be.  In order to protect the device and its immediate network   environment, most devices will be in some sort of protective   container.  Access to serial, parallel, USB, firewire, SCSI, or   PCMCIA connections will not be possible.  Likewise floppy, zip, or CD   drives.  Therefore, any software "token" must be obtained from the   network itself.   The Concerns   1. Getting the "token".  Since it will be necessary to obtain the      token (key, certificate, credential) from across the network.  How      can it be protected during transit?Arsenault & Farrell          Informational                     [Page 18]

RFC 3157                 SACRED - Requirements               August 2001   2. Where did you get it?  One of the primary controls in PKI is      protection of the private key.  Placing the key on a host that is      accessible from a public network means that there is an inherent      exposure from that network.  The access controls and other      security measures on the host machine are an area of concern.   3. How did you get it?  When you obtained the token from the server,      how did it know that you are you?  Authentication becomes      critical.   4. What happens to the token when you leave?  You've checked your      mail, downloaded a recipe from that super-secure recipe server,      found out how to get to the adult beverage store for the... uh...      accessories... for the meal, and you're off!  Is your token?  Or      is it still sitting there on the public kiosk waiting for those      youngsters coming out of the music store to notice and cruise the      information highway on your ticket?Arsenault & Farrell          Informational                     [Page 19]

RFC 3157                 SACRED - Requirements               August 2001Full Copyright Statement   Copyright (C) The Internet Society (2001).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Arsenault & Farrell          Informational                     [Page 20]