Network Working Group C. Latze
Internet-Draft Swisscom
Intended status: Standards Track N. Mavrogiannopoulos
Expires: July 22, 2013 KU Leuven
January 18, 2013
The TPMKEY URI Scheme
draft-mavrogiannopoulos-tpmuri-00
Abstract
This memo specifies a TPMKEY Uniform Resource Identifier (URI) Scheme
for identifying cryptographic keys stored in TPM chips and access
using the TCG Software Stack (TSS). The URI is based on how TPM keys
are identified in the TSS specification.
Status of This Memo
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This Internet-Draft will expire on July 22, 2013.
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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. TPMKEY encoding considerations . . . . . . . . . . . . . . 4
2.6. applications/ protocols that use the TPMKEY URI scheme . . 4
3. Examples of TPMKEY URI Schemes . . . . . . . . . . . . . . . . 5
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
tsskey
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]):
tsskey-URI = "tsskey" ":" tsskey-identifier
tsskey-identifier = *1(tsskey-attr *(";" tsskey-attr))
tsskey-attr = tsskey-uuid / tsskey-file / pk11-storage
tsskey-reserved-avail = ":" / "[" / "]" / "@" / "!" / "$" /
"&" / "'" / "(" / ")" / "*" / "+" /
"," / "="
tsskey-char = unreserved / tsskey-reserved-avail /
pct-encoded
tsskey-file = "file" "=" *tsskey-char
tsskey-uuid = "uuid" "=" *tsskey-char
tsskey-storage = "storage" "=" *1("user" / "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. The attribute "uuid"
represents a unique identifier of a TPM key and the attribute
"storage" corresponds to the storage subsystem used (user or system).
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. TPMKEY encoding considerations
Not sure what to write here
2.6. applications/ protocols that use the TPMKEY URI scheme
The TPMKEY URI scheme SHOULD be used by all application and protocols
that use the TPM through the TSS.
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3. Examples of TPMKEY URI Schemes
One of the simplest forms is from a key stored in the TSP.
tsskey:uuid=7f468c16-cb7f-11e1-824d-b3a4f4b20343;storage=user
A TPM key that is stored in a system's file.
tsskey:file=/path/to/file
4. IANA Considerations
This document registers a URI scheme. The registration template can
be found in Section 3 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 [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.
[TPMMAIN] "TPM Main Specification".
[TSS] "TCG Software Stack (TSS) Specification".
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7.2. Informative References
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[PKCS11URI] "The PKCS#11 URI Scheme", Internet Draft , Feb 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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