Internet DRAFT - draft-mccallum-jose-pkcs11-jwk
draft-mccallum-jose-pkcs11-jwk
Internet Engineering Task Force N. McCallum
Internet-Draft Red Hat, Inc.
Updates: 7517 (if approved) June 30, 2017
Intended status: Standards Track
Expires: January 1, 2018
PKCS #11 for JSON Web Keys
draft-mccallum-jose-pkcs11-jwk-00
Abstract
This document updates RFC 7517 in order to specify an extension to
the JSON Web Key (JWK) format so that private key material may be
stored in cryptographic hardware using PKCS #11. It defines a new
property for JWKs which contains the PKCS #11 URI identifying the
location of the private key material. Implementations can use this
URI to offload the cryptographic operations to the identified
hardware.
Status of This Memo
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This Internet-Draft will expire on January 1, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Document Conventions . . . . . . . . . . . . . . . . . . . . 2
3. JWK PKCS #11 URI Property . . . . . . . . . . . . . . . . . . 2
4. Implementation Considerations . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 3
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
JSON Web Key (JWK) [RFC7517] defines a format for keys which can be
used to perform cryptographic operations. When these JWKs contain
private key material, illegitimate access to this material creates
the possibility for wide-scale security compromise.
As a defensive strategy, other key types will offload their private
key material to cryptographic hardware or other secure storage using
PKCS #11. The locations of these keys are communicated using PKCS
#11 URIs [RFC7512]. Therefore, this document defines a method to
replace the private key material of a JWK with a PKCS #11 URI.
2. Document Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. JWK PKCS #11 URI Property
JWKs that wish to offload their private key material using PKCS #11
will provide a JSON property named "p11" instead of the private key
material. The "p11" property MUST contain a valid PKCS #11 URI
[RFC7517] that points to a private key object (that is,
type=private).
Private key material is defined by the Parameter Information Class of
Section 8.1.1 of RFC 7517 [RFC7517]. JWKs MUST NOT provide both the
"p11" property and other private key material. However,
implementations SHOULD provide full public key material appropriate
to the key type. This enables implementations to perform public key
cryptographic operations without consulting PKCS #11.
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4. Implementation Considerations
The PKCS #11 URI standard provides mappings to URI format for most
metadata attributes available over PKCS #11. Some of these
attributes may differ based on operating system, driver or even
hardware implementations. The generation of URIs which can only be
used in a specific context should be avoided for the sake of clarity.
The following path attributes are RECOMMENDED for general use:
o model
o manufacturer
o serial
o token
o id
o object
o type
The following query attributes are RECOMMENDED for general use:
o pin-value
Tools which generate PKCS #11 URIs for use in JWKs SHOULD NOT
generate path or query attributes that are not recommended above. On
the other hand, tools which process JWKs containing the "p11"
property MAY process path or query attributes that are not
recommended above.
Using PKCS #11 for cryptographic operations is usually associated
with a performance penalty. Implementations SHOULD perform public
key operations, such as asymmetric signature verification or
asymmetric encryption, without using PKCS #11 in order to increase
speed and should fall back to PKCS #11 where access to the private
key material is required.
5. Security Considerations
Accessing a JWK containing the "p11" property in place of the private
key material may still allow an attacker to perform operations using
the private key while not obtaining the private key itself. This is
particularly true when the "pin-value" query attribute is used.
Nevertheless, because the attacker does not learn the private key
itself, the attacker's access to use of the key can be limited to a
particular context; for example, only the host with direct access to
the hardware. Because of this, the ability to remove the attacker's
access to this context provides the option for significant damage
mitigation strategies. Therefore, offloading the private key
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material should not be misunderstood to be a cryptographic panacea
but rather a way to reduce the cost of a compromise.
Exposing the "p11" property can leak institutional or configuration
information to an attacker that could be used as part of a
multifaceted attack. This is particularly true when the PKCS #11 URI
contains the "pin-value" or "pin-source" query attributes since this
PIN is used to protect access to the private key material. For this
reason, the "p11" property MUST be treated as a private key material
in its own right and care should be taken not to expose it.
It may be desirable to avoid the use of the "pin-value" query
attribute altogether by passing in this value out of band. This
strategy implies that the attacker will need to target the out of
band delivery mechanism in addition to the JWK in order to use the
private key material.
6. IANA Considerations
The following has been added to the "JSON Web Key Parameters"
registry:
o Parameter Name: "p11"
o Parameter Description: The PKCS #11 URI
o Parameter Information Class: Private
o Used with "kty" Value(s): *
o Change Controller: IESG
o Specification Document(s): Section 3 of THIS DOCUMENT
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC7512] Pechanec, J. and D. Moffat, "The PKCS #11 URI Scheme",
RFC 7512, DOI 10.17487/RFC7512, April 2015,
<http://www.rfc-editor.org/info/rfc7512>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<http://www.rfc-editor.org/info/rfc7517>.
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Author's Address
Nathaniel McCallum
Red Hat, Inc.
100 East Davie Street
Raleigh, NC 27601
USA
EMail: npmccallum@redhat.com
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