The PKCS#11 URI Scheme
draft-pechanec-pkcs11uri-00

Abstract

This memo specifies a PKCS#11 Uniform Resource Identifier (URI) Scheme for identifying PKCS#11 objects stored in PKCS#11 tokens, or for identifying PKCS#11 tokens themselves. The URI is based on how PKCS#11 objects are identified in the PKCS #11 Cryptographic Token Interface Standard.

Status of this Memo

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

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work in progress.”

The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html.

This Internet-Draft will expire on September 2, 2010.

Copyright Notice

Copyright (c) 2010 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 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License.

Table of Contents

1.  Introduction
2.  PKCS#11 URI Scheme Definition
    2.1.  PKCS#11 URI Scheme Name
    2.2.  PKCS#11 URI Scheme Status
    2.3.  PKCS#11 URI Scheme Syntax
3.  Examples of PKCS#11 URI Schemes
4.  IANA Considerations
5.  Security Considerations
6.  Normative References
§  Authors' Addresses

1.  Introduction

The PKCS #11: Cryptographic Token Interface Standard [pkcs11_spec] (RSA Laboratories, “PKCS #11: Cryptographic Token Interface Standard v2.20,” June 2004.) specifies an API, called Cryptoki, for devices which hold cryptographic information and perform cryptographic functions. Cryptoki, pronounced crypto-key and short for cryptographic token interface, follows a simple object-based approach, addressing the goals of technology independence (any kind of device may be used?) and resource sharing (multiple applications may access multiple devices), presenting applications with a common, logical view of the device - a cryptographic token.

It is desirable for applications or libraries that work with PKCS#11 tokens to accept a common identifier that consumers could use to identify an existing PKCS#11 object in a PKCS#11 token, or an existing token itself. The set of object types that can be stored in a PKCS#11 token includes a public key, a private key, a certificate, a secret key, and a data object. These objects can be uniquely identifiable via the PKCS#11 URI scheme defined in this document. The set of attributes that identifies a PKCS#11 token can contain a token label, a manufacturer name, a serial number, and a token model.

Note that the PKCS#11 URI is not intended to be used to create new PKCS#11 objects in tokens, or to create PKCS#11 tokens. It is solely to be used to identify existing objects or existing tokens.

2.  PKCS#11 URI Scheme Definition

In accordance with [RFC4395] (Hansen, T., Hardie, T., and L. Masinter, “Guidelines and Registration Procedures for New URI Schemes,” February 2006.), this section provides the information required to register the PKCS#11 URI scheme.

2.1.  PKCS#11 URI Scheme Name

pkcs11

2.2.  PKCS#11 URI Scheme Status

Permanent.

2.3.  PKCS#11 URI Scheme Syntax

The PKCS#11 URI scheme is a sequence of attribute value pairs. Given that the PKCS#11 specification allows for any byte value to be used in the PKCS#11 attributes used, any byte sequence must also be allowed in the URI. Semicolons may be escaped with a backslash.

A PKCS#11 URL takes the form (for explanation of Augmented BNF, see [RFC5234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” January 2008.)):

  pk11-URI		= pk11-scheme ":" pk11-identifier
  pk11-scheme		= "pkcs11"
  pk11-identifier	= *1(pk11-attr *(%x3B pk11-attr))
  pk11-attr		= pk11-token / pk11-manufacturer /
 			  pk11-serial / pk11-model / pk11-object /
  			  pk11-objecttype / pk11-passphrasedialog
  pk11-semicolon	= "\" %x3B
  pk11-label		= *(%x00-3A / %x3C-FF / pk11-semicolon)
  pk11-token		= "token" "=" pk11-label
  pk11-manufacturer	= "manufacturer" "=" pk11-label
  pk11-serial		= "serial" "=" pk11-label
  pk11-model		= "model" "=" pk11-label
  pk11-object		= "object" "=" pk11-label
  pk11-objecttype	= "objecttype" "=" ("public" / "private" /
  			  "cert" / "secretkey" / "data")
  pk11-passphrasedialog	= "passphrasedialog" "=" "builtin" / exec
  exec			= "exec" ":" filename
  filename		= 1*(%x00-3A / %x3C-FF / pk11-semicolon)

While the PKCS#11 specification limits the length of some fields, eg. the manufacturer label can be up to thirty-two characters long, the PKCS#11 URI does not impose such limitations. It is up to the consumer of the PKCS#11 URI to perform any necessary sanity checks.

The attribute "token" represents a token label, the attribute "manufacturer" represents a manufacturer ID, the attribute "serial" represents a token serial number, the attribute "model" represents a token model, the attribute "object" represents a PKCS#11 object label, the attribute "objecttype" represents the type of the object, and the attribute "passphrasedialog" specifies how the application or library should ask for the token PIN, if needed. The "builtin" value suggests that the application or the library should use whatever means of reading the PIN it can provide, and the "exec:<filename>" value specifies an external application whose standard output should be used as the token PIN.

3.  Examples of PKCS#11 URI Schemes

This section contains some examples of how PKCS#11 tokens or PKCS#11 token objects can be identified using the PKCS#11 URI scheme.

An empty PKCS#11 URI might be useful to PKCS#11 consumers:

  pkcs11:

One of the simplest and most useful forms might be a PKCS#11 URI that specifies only an object label and its type. The default token is used so the URI does not specify it. Note that when specifying public objects, a token PIN might not be required.

  pkcs11:object=my-pubkey;objecttype=public

Specifying a private key will usually need to use the "passphrasedialog" attribute:

  pkcs11:object=my-key;objecttype=private;passphrasedialog=builtin

The following example identifies a certificate in the software token. Note that all attributes aside from "passphrasedialog" and "objecttype" may have an empty value. In our case, "serial" is empty. It's up to the consumer of the URI to perform necessary checks if that is not allowed. Also note that in all three of the following examples, newlines and spaces were inserted for better readability. Usage of newlines or spaces after semicolons is illegal in the PKCS#11 URI scheme defined above.

  pkcs11:token=Software PKCS#11 softtoken;
         manufacturer=Snake Oil, Inc.;
         serial=;
         model=1.0;
         object=my-certificate;
         objecttype=cert;
         passphrasedialog=exec:/bin/askpass.sh

The token alone can be identified without specifying any PKCS#11 objects. A PIN may still be needed to list all objects, for example.

  pkcs11:token=Sun Software PKCS#11 softtoken;
         manufacturer=Sun Microsystems, Inc.;
         passphrasedialog=exec:/bin/askpass.sh

The following example shows that the attribute value can contain a semicolon. In this case, it must be escaped.

  pkcs11:token=The token\; created by Joe;
         object=my-certificate;
         objecttype=cert;
         passphrasedialog=exec:/bin/askpass.sh

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 many security considerations for URI schemes discussed in [RFC3986] (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.).

Given that the PKCS#11 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 PKCS#11 token PIN as a URI attribute.

6. Normative References

Authors' Addresses