Network Working Group J. Pechanec
Internet-Draft D. Moffat
Intended status: Standards Track Oracle Corporation
Expires: April 03, 2014 September 30, 2013
The PKCS#11 URI Scheme
draft-pechanec-pkcs11uri-13
Abstract
This memo specifies a PKCS#11 Uniform Resource Identifier (URI)
Scheme for identifying PKCS#11 objects stored in PKCS#11 tokens, for
identifying PKCS#11 tokens themselves, or for identifying PKCS#11
libraries. The URI is based on how PKCS#11 objects, tokens, and
libraries are identified in the PKCS#11 Cryptographic Token Interface
Standard.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 03, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 3
3. PKCS#11 URI Scheme Definition . . . . . . . . . . . . . . . . 3
3.1. PKCS#11 URI Scheme Name . . . . . . . . . . . . . . . . . 4
3.2. PKCS#11 URI Scheme Status . . . . . . . . . . . . . . . . 4
3.3. PKCS#11 URI Scheme Syntax . . . . . . . . . . . . . . . . 4
3.4. PKCS#11 URI Matching Guidelines . . . . . . . . . . . . . 7
3.5. PKCS#11 URI Comparison . . . . . . . . . . . . . . . . . 8
4. Examples of PKCS#11 URIs . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
The PKCS #11: Cryptographic Token Interface Standard [pkcs11_spec]
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 storage object in a PKCS#11 token, an
existing token itself, or an existing Cryptoki library (also called a
producer, module, or provider). The set of storage object types that
can be stored in a PKCS#11 token includes a certificate, a public,
private or secret key, and a data object. These objects can be
uniquely identifiable via the PKCS#11 URI scheme defined in this
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document. The set of attributes describing a storage object can
contain an object label, its type, and its ID. 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. Attributes
that can identify a Cryptoki library are a library manufacturer, a
library description, and a library version. Library attributes may
be necessary to use if more than one Cryptoki library provides a
token and/or PKCS#11 objects of the same name(s).
The PKCS#11 URI cannot identify other objects aside from storage
objects, for example a hardware feature or mechanism. Note that a
Cryptoki library does not have to provide for storage objects at all.
The URI can still be used to identify a specific PKCS#11 token or an
API producer in such a case.
A subset of existing PKCS#11 structure members and object attributes
was chosen believed to be sufficient in uniquely identifying a
PKCS#11 token, storage object, or library in a configuration file, on
a command line, or in a configuration property of something else.
Should there be a need for a more complex information exchange on
PKCS#11 entities a different means of data marshalling should be
chosen accordingly.
A 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 and work with existing storage objects and tokens
through the PKCS#11 API, or identify Cryptoki libraries themselves.
The URI scheme defined in this document is designed specifically with
a mapping to the PKCS#11 API in mind. The URI uses the scheme, path
and query components defined in the Uniform Resource Identifier
(URI): Generic Syntax [RFC3986] document. The URI does not use the
hierarchical element for a naming authority in the path since the
authority part could not be mapped to PKCS#11 API elements. The URI
does not use the fragment component.
If an application has no access to a producer or producers of the
PKCS#11 API it is left to its implementation to provide adequate user
interface to locate and load such producer(s).
2. Contributors
Stef Walter, Nikos Mavrogiannopoulos, Nico Williams, Dan Winship, and
Jaroslav Imrich contributed to the development of this document.
3. PKCS#11 URI Scheme Definition
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In accordance with [RFC4395], this section provides the information
required to register the PKCS#11 URI scheme.
3.1. PKCS#11 URI Scheme Name
pkcs11
3.2. PKCS#11 URI Scheme Status
Permanent.
3.3. PKCS#11 URI Scheme Syntax
The PKCS#11 URI is a sequence of attribute value pairs separated by a
semicolon that form a one level path component, optionally followed
by a query. In accordance with Section 2.5 of [RFC3986], the data
should first be encoded as octets according to the UTF-8 character
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. This specification suggests
one allowable exception to that rule for the "id" attribute, as
stated later in this section. Grammar rules "unreserved" and "pct-
encoded" in the PKCS#11 URI specification below are imported from
[RFC3986]. As a special case, note that according to Appendix A of
[RFC3986], a space must be percent-encoded.
PKCS#11 specification imposes various limitations on the value of
attributes, be it a more restrictive character set for the "serial"
attribute or fixed sized buffers for almost all the others, including
"token", "manufacturer", and "model" attributes. However, the
PKCS#11 URI notation does not impose such limitations aside from
removing generic and PKCS#11 URI delimiters from a permitted
character set. We believe that being too restrictive on the
attribute values could limit the PKCS#11 URI's usefulness. What is
more, possible future changes to the PKCS#11 specification should not
affect existing attributes.
A PKCS#11 URI takes the form (for explanation of Augmented BNF, see
[RFC5234]):
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pk11-URI = "pkcs11" ":" pk11-path *1("?" pk11-query)
; Path component and its attributes. Path may be empty.
pk11-path = *1(pk11-pattr *(";" pk11-pattr))
pk11-pattr = pk11-token / pk11-manuf / pk11-serial /
pk11-model / pk11-lib-manuf /
pk11-lib-ver / pk11-lib-desc /
pk11-object / pk11-type / pk11-id /
pk11-x-pattr
; Query component and its attributes. Query may be empty.
pk11-qattr = pk11-pin-source / pk11-x-qattr
pk11-query = *1(pk11-qattr *("&" pk11-qattr))
; RFC 3986 section 2.2 mandates all potentially reserved characters
; that do not conflict with actual delimiters of the URI do not have
; to be percent-encoded.
pk11-res-avail = ":" / "[" / "]" / "@" / "!" / "$" /
"'" / "(" / ")" / "*" / "+" / "," / "="
pk11-path-res-avail = pk11-res-avail / "&"
; We allow "/" and "?" in the query to be unencoded but "&" must
; be encoded since it may be used as a delimiter in the component.
pk11-query-res-avail = pk11-res-avail / "/" / "?"
pk11-pchar = unreserved / pk11-path-res-avail / pct-encoded
pk11-qchar = unreserved / pk11-query-res-avail / pct-encoded
pk11-token = "token" "=" *pk11-pchar
pk11-manuf = "manufacturer" "=" *pk11-pchar
pk11-serial = "serial" "=" *pk11-pchar
pk11-model = "model" "=" *pk11-pchar
pk11-lib-manuf = "library-manufacturer" "=" *pk11-pchar
pk11-lib-desc = "library-description" "=" *pk11-pchar
pk11-lib-ver = "library-version" "=" 1*DIGIT *1("." 1*DIGIT)
pk11-object = "object" "=" *pk11-pchar
pk11-type = "type" "=" *1("public" / "private" / "cert" /
"secret-key" / "data")
pk11-id = "id" "=" *pk11-pchar
pk11-pin-source = "pin-source" "=" *pk11-qchar
pk11-x-attr-nm-char = ALPHA / DIGIT / "-" / "_"
; Permitted value of a vendor specific attribute is based on
; whether the attribute is used in the path or in the query.
pk11-x-pattr = "x-" 1*pk11-x-attr-nm-char "=" *pk11-pchar
pk11-x-qattr = "x-" 1*pk11-x-attr-nm-char "=" *pk11-qchar
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The URI path component contains attributes that identify a resource
in a one level hierarchy provided by Cryptoki producers. The query
component may contain a PIN source attribute that may be needed to
retrieve the resource identified by the URI path. Both path and
query components may contain vendor specific attributes. Such
attribute names must start with an "x-" prefix. Attributes in the
path component are delimited by ';' character, attributes in the
query component use '&' as a delimiter.
The general '/' delimiter was removed from available characters that
do not have to be percent-encoded in the path component so that
generic URI parsers never split the path component into multiple
segments. The '/' delimiter can be used unencoded in the query
component. Delimiter '?' was removed since the PKCS#11 URI uses a
query component. Delimiter '#' was removed so that generic URI
parsers are not confused by unencoded hash characters. All other
generic delimiters are allowed to be used unencoded (':', '[', ']',
and '@') in the PKCS#11 URI.
The attribute "token" represents a token label and corresponds to the
"label" member of the CK_TOKEN_INFO structure, the attribute
"manufacturer" corresponds to the "manufacturerID" member of
CK_TOKEN_INFO, the attribute "serial" corresponds to the
"serialNumber" member of CK_TOKEN_INFO, the attribute "model"
corresponds to the "model" member of CK_TOKEN_INFO, the attribute
"library-manufacturer" represents the Cryptoki library manufacturer
and corresponds to the "manufacturerID" member of the CK_INFO
structure, the attribute "library-description" corresponds to the
"libraryDescription" member of CK_INFO, the attribute "library-
version" corresponds to the "libraryVersion" member of CK_INFO, the
attribute "object" represents a PKCS#11 object label and corresponds
to the "CKA_LABEL" object attribute, the attribute "type" represents
the type of the object and corresponds to the "CKA_CLASS" object
attribute, the attribute "id" represents the object ID and
corresponds to the "CKA_ID" object attribute, and the attribute "pin-
source" specifies where the application or library should find the
token PIN, if needed.
The PKCS#11 URI must not contain duplicate attributes of the same
name in the URI path component. It means that each attribute may be
present at most once in the PKCS#11 URI path. Aside from the "pin-
source" attribute, duplicate attributes may be present in the URI
query component and it is up to the URI consumer to decide on how to
deal with such duplicates.
The "pin-source" attribute may represent a filename that contains a
token PIN but an application may overload this attribute. For
example, "pin-source=%7Cprog-name" could mean to read a PIN from an
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external application (%7C denotes a pipe '|' character). Note that
an application may always ask for a PIN and/or interpret the "pin-
source" attribute by any means it decides to. However, as discussed
in Section 6, the attribute should never contain the PIN itself.
It is recommended to percent-encode the whole value of the "id"
attribute which is supposed to be handled as arbitrary binary data.
Value "M" of the "library-version" attribute should be interpreted as
"M" for the major and "0" for the minor version of the library. Note
that if the "library-version" attribute is present, the major version
number is mandatory.
An empty PKCS#11 URI path attribute that does allow for an empty
value matches a corresponding structure member or an object attribute
with an empty value. Note that according to the PKCS#11
specification [pkcs11_spec], empty character values in a PKCS#11 API
producer must be padded with spaces and should not be NULL
terminated.
3.4. PKCS#11 URI Matching Guidelines
The PKCS#11 URI can identify PKCS#11 storage objects, tokens, or
Cryptoki libraries. The following guidelines should help a PKCS#11
URI consumer (eg. an application accepting PKCS#11 URIs) to match the
URI with the desired resource.
o the consumer must know whether the URI is to identify PKCS#11
storage object(s), token(s), or Cryptoki producer(s).
o an unrecognized attribute in the URI path component, including a
vendor specific attribute, should result in an empty set of
matched resources. The consumer should consider whether an error
message presented to the user is appropriate in such a case.
o an unrecognized attribute in the URI query should be ignored. The
consumer should consider whether a warning message presented to
the user is appropriate in such a case.
o an attribute not present in the URI path but known to a consumer
matches everything. Each additional attribute present in the URI
path further restricts the selection.
o a logical extension of the above is that an empty URI path matches
everything. For example, if used to identify storage objects, it
matches all accessible objects in all tokens provided by all
PKCS#11 API producers found in the system.
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o use of the PIN attribute may change the set of storage objects
visible to the consumer.
o in addition to the PIN attribute, query string attributes may
contain further information about how to perform the selection or
other related information.
3.5. PKCS#11 URI Comparison
Comparison of two URIs is a way of determining whether the URIs are
equivalent without comparing the actual resource the URIs point to.
The comparison of URIs aims to minimize false negatives while
strictly avoiding false positives.
Two PKCS#11 URIs are said to be equal if URIs as character strings
are identical as specified in Section 6.2.1 of [RFC3986], or if both
following rules are fulfilled:
o set of attributes present in the URI is equal. Note that the
ordering of attributes in the URI string is not significant for
the mechanism of comparison.
o values of respective attributes are equal based on rules specified
below
The rules for comparing values of respective attributes are:
o values of attributes "library-description", "library-
manufacturer", "manufacturer", "model", "object", "serial",
"token", and "type" must be compared using a simple string
comparison as specified in Section 6.2.1 of [RFC3986] after the
case and the percent-encoding normalization are both applied as
specified in Section 6.2.2 of [RFC3986]
o value of attribute "id" must be compared using the simple string
comparison after all bytes are percent-encoded using uppercase
letters for digits A-F
o value for attribute "pin-source", if deemed containing the
filename with the PIN value, must be compared using the simple
string comparison after the full syntax based normalization as
specified in Section 6.2.2 of [RFC3986] is applied. If value of
the "pin-source" attribute is believed to be overloaded it is
recommended to perform case and percent-encoding normalization
before the values are compared but the exact mechanism of
comparison is left to the application.
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o value of attribute "library-version" must be processed as a
specific scheme-based normalization permitted by Section 6.2.3 of
[RFC3986]. The value must be split into a major and minor version
with character '.' (dot) serving as a delimiter. Library version
"M" must be treated as "M" for the major version and "0" for the
minor version. Resulting minor and major version numbers must be
then separately compared numerically.
o when comparing vendor specific attributes it is recommended to
perform case and percent-encoding normalization before the values
are compared but the exact mechanism of comparison is left to the
application.
4. Examples of PKCS#11 URIs
This section contains some examples of how PKCS#11 token objects,
PKCS#11 tokens, and PKCS#11 libraries can be identified using the
PKCS#11 URI scheme. Note that in some of the following examples,
newlines and spaces were inserted for better readability. As
specified in Appendix C of [RFC3986], whitespace should be ignored
when extracting the URI. Also note that all spaces as part of the
URI are percent-encoded, as specified in Appendix A of [RFC3986].
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;type=public
When a private key is specified either the "pin-source" attribute or
an application specific method would be usually used. Note that '/'
is not percent-encoded in the "pin-source" attribute value since this
attribute is part of the query component, not the path, and thus is
separated by '?' from the rest of the URI.
pkcs11:object=my-key;type=private?pin-source=/etc/token
The following example identifies a certificate in the software token.
Note an empty value for the attribute "serial". Also note that the
"id" attribute value is entirely percent-encoded, as recommended.
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While ',' is in the reserved set it does not have to be percent-
encoded since it does not conflict with any sub-delimiters used. The
'#' character as in "The Software PKCS#11 Softtoken" must be percent-
encoded.
pkcs11:token=The%20Software%20PKCS%2311%20Softtoken;
manufacturer=Snake%20Oil,%20Inc.;
model=1.0;
object=my-certificate;
type=cert;
id=%69%95%3E%5C%F4%BD%EC%91;
serial=
?pin-source=/etc/token_pin
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=Software%20PKCS%2311%20softtoken;
manufacturer=Snake%20Oil,%20Inc.
?pin-source=/etc/token_pin
The Cryptoki library alone can be also identified without specifying
a PKCS#11 token or object.
pkcs11:library-manufacturer=Snake%20Oil,%20Inc.;
library-description=Soft%20Token%20Library;
library-version=1.23
The following example shows that the attribute value can contain a
semicolon. In such case, it is percent-encoded. The token attribute
value must be read as "My token; created by Joe". Lower case letters
can also be used in percent-encoding as shown below in the "id"
attribute value but note that Sections 2.1 and 6.2.2.1 of [RFC3986]
read that all percent-encoded characters should use the uppercase
hexadecimal digits. More specifically, if the URI string was to be
compared, the algorithm defined in Section 3.5 explicitly requires
percent-encoding to use the uppercase digits A-F in the "id"
attribute values. And as explained in Section 3.3, library version
"3" should be interpreted as "3" for the major and "0" for the minor
version of the library.
pkcs11:token=My%20token%25%20created%20by%20Joe;
library-version=3;
id=%01%02%03%Ba%dd%Ca%fe%04%05%06
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If there is any need to include literal "%;" substring, for example,
both characters must be escaped. The token value must be read as "A
name with a substring %;".
pkcs11:token=A%20name%20with%20a%20substring%20%25%3B;
object=my-certificate;
type=cert
?pin-source=/etc/token_pin
The next example includes a small A with acute in the token name. It
must be encoded in octets according to the UTF-8 character encoding
and then percent-encoded. Given that a small A with acute is U+225
unicode code point, the UTF-8 encoding is 195 161 in decimal, and
that is "%C3%A1" in percent-encoding.
pkcs11:token=Name%20with%20a%20small%20A%20with%20acute:%20%C3%A1;
object=my-certificate;
type=cert
Both the path and query components may contain vendor specific
attributes. Attributes in the query component may be delimited by
either ';' or '&'. We use '&' in the example that follows.
pkcs11:token=my-token;
object=my-certificate;
type=cert;
x-vend-aaa=value-a
?pin-source=/etc/token_pin&
x-vend-bbb=value-b
5. IANA Considerations
This document moves the "pkcs11" URI scheme from the provisional to
the permanent URI scheme registry. The registration template for the
URI scheme is accessible on http://www.iana.org/assignments/uri-
schemes.
6. Security Considerations
There are general security considerations for URI schemes discussed
in Section 7 of [RFC3986].
From those security considerations, Section 7.1 of [RFC3986] applies
since there is no guarantee that the same PKCS#11 URI will always
identify the same object, token, or a library in the future.
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Section 7.5 of [RFC3986] applies since the PKCS#11 URI may be used in
command line arguments to run applications, and those arguments can
be world readable on some systems. For that reasons, the URI
intentionally does not allow for specifying the PKCS#11 token PIN as
a URI attribute.
7. References
7.1. Normative References
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 3629, STD 63, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", RFC 3986, STD
66, January 2005.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 5234, STD 68, January 2008.
7.2. Informative References
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", RFC 4395,
February 2006.
[pkcs11_spec]
RSA Laboratories, "PKCS #11: Cryptographic Token Interface
Standard v2.20", June 2004.
Authors' Addresses
Jan Pechanec
Oracle Corporation
4180 Network Circle
Santa Clara CA 95054
USA
Email: Jan.Pechanec@Oracle.COM
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Darren J. Moffat
Oracle Corporation
Oracle Parkway
Thames Valley Park
Reading RG6 1RA
UK
Email: Darren.Moffat@Oracle.COM
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