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Versions: 00 01

Network Working Group                                           C. Latze
Internet-Draft                                                  Swisscom
Intended status: Standards Track                    N. Mavrogiannopoulos
Expires: July 29, 2013                                         KU Leuven
                                                        January 25, 2013


                         The TPMKEY URI Scheme
                   draft-mavrogiannopoulos-tpmuri-01

Abstract

   This memo specifies a TPMKEY Uniform Resource Identifier (URI) Scheme
   for identifying cryptographic keys stored in TPM chips and accessed
   using the TCG Software Stack (TSS).  The URI is based on how TPM keys
   are identified in the TSS specification.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 29, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  TPMKEY URI Scheme Definition  . . . . . . . . . . . . . . . . . 3
     2.1.  TPMKEY URI Scheme Name  . . . . . . . . . . . . . . . . . . 3
     2.2.  TPMKEY URI Scheme Status  . . . . . . . . . . . . . . . . . 3
     2.3.  TPMKEY URI Scheme Syntax  . . . . . . . . . . . . . . . . . 3
     2.4.  TPMKEY URI scheme semantics . . . . . . . . . . . . . . . . 4
     2.5.  Applicability of the TPMKEY URI scheme  . . . . . . . . . . 4
   3.  Examples of TPMKEY URI Schemes  . . . . . . . . . . . . . . . . 4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 6



































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1.  Introduction

   The Trusted Platform Module (TPM) is a trusted piece of hardware
   built into many current devices that has been specified by the
   Trusted Computing Group (TCG) [TPMMAIN].  In addition to the chip
   itself, the TCG defined one standard way to interface with a TPM,
   called the TCG Software Stack (TSS) [TSS].

   The TSS defines several layers.  The most important ones in the
   context of this document are the TCG Service Provider (TSP) and the
   TCG Core Services (TCS).  The TSP provides the TCG services to
   applications, which in turn provide access to the TPM.  Each
   application accesses a single TSP and there is only one TCS for
   several TSPs.  The task of the TCS is to provide a common set of
   services per platform for all TSPs.

   TPM keys can be stored either in the TSP (called "user space") or in
   the TCS (called "system space").  Furthermore, the TSS assigns a UUID
   to each key.  That UUID is unique for a specific key hierarchy on a
   specific platform.  Last, keys can also be stored in so called key
   blobs, which are basically files.

   The URI scheme defined in this document is designed with a mapping to
   TPM keys that are accessed via the TSS in mind.  The URI uses only
   the scheme and the path components which are required by the Uniform
   Resource Identifier generic syntax [RFC3986].  The URI scheme does
   not use the hierarchical element for a naming authority in the path
   since the authority part could not be mapped to TPM key elements.
   The URI scheme does not use the optional query and fragment elements.

2.  TPMKEY URI Scheme Definition

   In accordance with [RFC4395], this section provides the information
   required to register the TPMKEY URI scheme.

2.1.  TPMKEY URI Scheme Name

   tpmkey

2.2.  TPMKEY URI Scheme Status

   Provisional.

2.3.  TPMKEY URI Scheme Syntax

   The TPMKEY URI scheme is a sequence of attribute value pairs
   separated by a semicolon.  In accordance with [RFC3986], the data
   should first be encoded as octets according to the UTF-8 character



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   encoding [RFC3629]; then only those octets that do not correspond to
   characters in the unreserved set or to permitted characters from the
   reserved set should be percent-encoded.  Rules "unreserved" and "pct-
   encoded" in the TPMKEY specification below were imported from
   [RFC3986].  As a special case, note that according to [RFC3986], a
   space must be percent-encoded.

   A TPMKEY URI takes the form (for explanation of Augmented BNF, see
   [RFC5234]):


      tpmkey-URI            = "tpmkey" ":" tpmkey-identifier
      tpmkey-identifier     = *1(tpmkey-attr *(";" tpmkey-attr))
      tpmkey-attr           = tpmkey-uuid / tpmkey-file / pk11-storage
      tpmkey-reserved-avail = ":" / "[" / "]" / "@" / "!" / "$" /
                              "&" / "'" / "(" / ")" / "*" / "+" /
                              "," / "="
      tpmkey-char           = unreserved / tpmkey-reserved-avail /
                              pct-encoded
      tpmkey-file          = "file" "=" *tpmkey-char
      tpmkey-uuid          = "uuid" "=" UUID
      tpmkey-storage       = "storage" "=" *1("user" / "system")

   More specifically, the attribute "uuid" represents a unique
   identifier of a TPM key and its structure is defined in [RFC4122].
   The attribute "storage" corresponds to the storage subsystem used
   (user or system).  The attribute "file" represents a filename and
   corresponds to a file that contains a BER-encoded blob in accordance
   with the ASN.1 data definitions in the Portable Data section of the
   Trusted Computing Group Software Stack Specification Version 1.2.

2.4.  TPMKEY URI scheme semantics

   The TPMKEY URI scheme is used to reference TPM keys through the TSS.
   The allowed operations on the URI are defined by the TSS
   specification.

2.5.  Applicability of the TPMKEY URI scheme

   The TPMKEY URI scheme is relevant to applications and protocols that
   need to identify TPM keys that are accessed through TSS.

3.  Examples of TPMKEY URI Schemes

   One of the simplest forms is from a key stored in the TSP.

        tpmkey:uuid=7f468c16-cb7f-11e1-824d-b3a4f4b20343;storage=user




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   A TPM key that is stored in a system's file.

        tpmkey:file=/path/to/file

4.  IANA Considerations

   This document registers a URI scheme.  The registration template can
   be found in Section 2 of this document.

5.  Security Considerations

   There are security considerations for URI schemes discussed in
   [RFC3986].

   Given that the TPMKEY URI is also supposed to be used in command line
   arguments to running programs, and those arguments can be world
   readable on some systems, the URI intentionaly does not allow for
   specifying the TPM key password as a URI attribute.

6.  Acknowledgements

   This document derives from [I-D.pechanec-pkcs11uri].  Furthermore the
   authors want to thank Greg Kazmierczak for early feedback.

7.  References

7.1.  Normative References

   [RFC3986]                 Berners-Lee, T., Fielding, R., and L.
                             Masinter, "Uniform Resource Identifier
                             (URI): Generic Syntax", STD 66, RFC 3986,
                             January 2005.

   [RFC4395]                 Hansen, T., Hardie, T., and L. Masinter,
                             "Guidelines and Registration Procedures for
                             New URI Schemes", BCP 35, RFC 4395,
                             February 2006.

   [RFC3629]                 Yergeau, F., "UTF-8, a transformation
                             format of ISO 10646", STD 63, RFC 3629,
                             November 2003.

   [RFC4122]                 Leach, P., Mealling, M., and R. Salz, "A
                             Universally Unique IDentifier (UUID) URN
                             Namespace", RFC 4122, July 2005.

   [TPMMAIN]                 TCG, "TPM Main Specification Version 1.2",
                             March 2011.



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   [TSS]                     TCG, "TCG Software Stack (TSS)
                             Specification Version 1.2", March 2007.

7.2.  Informative References

   [RFC5234]                 Crocker, D. and P. Overell, "Augmented BNF
                             for Syntax Specifications: ABNF", STD 68,
                             RFC 5234, January 2008.

   [I-D.pechanec-pkcs11uri]  Pechanec, J. and D. Moffat, "The PKCS#11
                             URI Scheme", draft-pechanec-pkcs11uri-07
                             (work in progress), December 2012.

Authors' Addresses

   Carolin Latze
   Swisscom Switzerland Ltd
   Ostermundigenstrasse 93
   Bern,   3008
   Switzerland

   EMail: carolin.latze@swisscom.com


   Nikos Mavrogiannopoulos
   ESAT/SCD/COSIC KU Leuven - IBBT
   Kasteelpark Arenberg 10, bus 2446
   Leuven-Heverlee,   B-3001
   Belgium

   EMail: nikos.mavrogiannopoulos@esat.kuleuven.be




















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