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Internet Engineering Task Force S. Walter, Ed.
Internet-Draft GNOME
Intended status: BCP September 2010
Expires: March 5, 2011
Storing Trust Assertions in PKCS#11 Modules
draft-walter-pkcs11-trust
Abstract
PKCS#11 is a standard that defines ways to store certificates, keys
and perform crypto operations. It does not specify a way to store
trust assertions.
Trust assertions are used to assign an explicit level of trust to a
certificate. Examples of trust assertions are certificate authority
root certificates, certificate revocation lists, and certificate
trust exceptions.
This document outlines a way to store trust assertions with PKCS#11.
This is not a new design, but documentation of the method already in
use by libraries such as NSS.
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on March 5, 2011.
Walter Expires March 5, 2011 [Page 1]
Internet-Draft PKCS#11 Trust Assertions September 2010
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. PKCS#11 Primer . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Trust Assertions . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Level of Trust . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Usage or Purpose . . . . . . . . . . . . . . . . . . . . . 4
2.3. Certificate Reference . . . . . . . . . . . . . . . . . . 4
3. PKCS#11 Trust Assertion Objects . . . . . . . . . . . . . . . 4
4. Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Checking Trust Assertions . . . . . . . . . . . . . . . . 7
4.1.1. Checking a Root Certificate Authority . . . . . . . . 7
4.1.2. Checking a Self-Signed Certificate . . . . . . . . . . 8
4.1.3. Checking an otherwise Trusted Certificate . . . . . . 8
4.2. Storing Trust Assertions . . . . . . . . . . . . . . . . . 8
4.3. Reading Trust Assertions . . . . . . . . . . . . . . . . . 8
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
6. Further Considerations . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Additional Stuff . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 10
Walter Expires March 5, 2011 [Page 2]
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1. Introduction
PKCS#11 is a useful and widely supported standard for storage and use
of keys and certificates. It is often used with smart cards.
1.1. PKCS#11 Primer
Xxxx
1.2. Terminology
Xxxxx
Xxxx 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.
2. Trust Assertions
A trust assertion describes a level of trust in an object for a given
usage or purpose. Conceptually each trust assertion is a triple
containing:
o Certificate Reference
o Usage or Purpose
o Level of Trust
We examine each of these parts of the triple in further detail below.
2.1. Level of Trust
A trust assertion ultimately denotes a level of trust. These are:
o Untrusted: The certificate is explicitly untrusted.
o Unknown: The trust is not known and should be determined
elsewhere.
o Trusted: The certificate itself is explicitly trusted.
o Trusted Delegator: The certificate is trusted as a certificate
authority trust root. Trust is confers to certificates that this
certificate has signed, or signed certificates have signed, and so
on.
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2.2. Usage or Purpose
A trust assertion always refers to a specific purpose or usage. A
certificate may be trusted for purposes like: email, code signing,
authenticating a server.
2.3. Certificate Reference
Each trust assertion contains a reference to a certificate.
There are two ways to refer to a certificate depending on whether
that certificate is self-signed (like a certificate authority) or
signed by another trusted certificate.
Self-signed certificates are referred to by their complete hash of
the DER value of the certificate.
Certificates signed by another certificate are referred to by the DER
value of the issuer field, and the serial number.
Referring to a self-signed certificate by its issuer and serial
number is meaningless.
Referring to a signed certificate by its hash, would preclude uses
such as certificate relocation lists, which do not contain
certificates or enough information to generate a hash.
Therefore different methods MUST be used to refer to self-signed and
issuer-signed certificates.
3. PKCS#11 Trust Assertion Objects
Trust assertions are stored as objects on a PKCS#11 token. Although
these are specific to a certificate, they do not need to be stored on
the same token as the certificate. Trust assertions objects are of
the class CKO_NETSCAPE_TRUST and have the following attributes.
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Trust object attributes.
+----------------------------+-----------------+--------------------+
| Attribute | Type | Description |
+----------------------------+-----------------+--------------------+
| CKA_CLASS | CK_OBJECT_CLASS | CKO_NETSCAPE_TRUST |
+----------------------------+-----------------+--------------------+
| CKA_ISSUER | Byte array | DER-encoding of |
| | | the certificate |
| | | issuer name |
+----------------------------+-----------------+--------------------+
| CKA_SUBJECT | Byte array | DER-encoding of |
| | | the certificate |
| | | subject name. |
| | | Optional, default |
| | | empty |
+----------------------------+-----------------+--------------------+
| CKA_SERIAL_NUMBER | Byte array | DER-encoding of |
| | | the certificate |
| | | serial number |
+----------------------------+-----------------+--------------------+
| CKA_CERT_SHA1_HASH | Byte array | SHA1 hash of the |
| | | the DER-encoding |
| | | of certificate. |
| | | Required for |
| | | self-signed |
| | | certificates. |
+----------------------------+-----------------+--------------------+
| CKA_CERT_MD5_HASH | Byte array | MD5 hash of the |
| | | the DER-encoding |
| | | of certificate. |
| | | Required for |
| | | self-signed |
| | | certificates. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_SERVER_AUTH | CK_TRUST | Level of trust for |
| | | server |
| | | authentication |
| | | extended usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_CLIENT_AUTH | CK_TRUST | Level of trust for |
| | | client |
| | | authentication |
| | | extended usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_CODE_SIGNING | CK_TRUST | Level of trust for |
| | | code signing |
| | | extended usage. |
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| CKA_TRUST_EMAIL_PROTECTION | CK_TRUST | Level of trust for |
| | | email protection |
| | | extended usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_IPSEC_END_SYSTEM | CK_TRUST | Level of trust for |
| | | IPSEC end system |
| | | extended usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_IPSEC_TUNNEL | CK_TRUST | Level of trust for |
| | | IPSEC tunnel |
| | | extended usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_IPSEC_USER | CK_TRUST | Level of trust for |
| | | IPSEC user |
| | | extended usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_TIME_STAMPING | CK_TRUST | Level of trust for |
| | | IPSEC time |
| | | stamping extended |
| | | usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_DIGITAL_SIGNATUR | CK_TRUST | Level of trust for |
| E | | digital signature |
| | | key usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_NON_REPUDIATION | CK_TRUST | Level of trust for |
| | | non-repudiation |
| | | key usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_KEY_ENCIPHERMENT | CK_TRUST | Level of trust for |
| | | key-encipherment |
| | | key usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_DATA_ENCIPHERMEN | CK_TRUST | Level of trust for |
| T | | data-encipherment |
| | | key usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_KEY_AGREEMENT | CK_TRUST | Level of trust for |
| | | key-agreement key |
| | | usage. |
+----------------------------+-----------------+--------------------+
| CKA_TRUST_KEY_CERT_SIGN | CK_TRUST | Level of trust for |
| | | certificate |
| | | signing key usage. |
+----------------------------+-----------------+--------------------+
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+----------------------------+-----------------+--------------------+
| CKA_TRUST_KEY_CRL_SIGN | CK_TRUST | Level of trust for |
| | | crl signing key |
| | | usage. |
+----------------------------+-----------------+--------------------+
Xxxx: Possible additional attributes: CKA_TRUST_TYPE
(CKT_CERTIFICATE_SELF_SIGNED, CKT_CERTIFICATE_SIGNED),
CKA_CERT_SHA256_HASH
Table 1: Trust Object Attributes
CK_TRUST represenst a level of trust.
+-----------------------+-------------------------------------------+
| Value | Description |
+-----------------------+-------------------------------------------+
| CKT_UNTRUSTED | Explicitly untrusted. |
| CKT_UNKNOWN | Trust is unknown and should be determined |
| | elsewhere. |
| CKT_TRUSTED | Explicitly trusts the certificate in the |
| | assertion. |
| CKT_TRUSTED_DELEGATOR | Trusts the certificate as a certificate |
| | authority. |
+-----------------------+-------------------------------------------+
Table 2: CK_TRUST values
4. Operations
4.1. Checking Trust Assertions
Trust assertions are checked using a PKCS#11 C_FindObjects operation.
Because trust is involved and presence/lack of results is important,
this operation MUST be done with a specific set of lookup attributes.
The attributes used differ depending on whether the certificate is
self-signed or is signed by an issuer.
Checking of trust assertions is always done for a specific purpose.
4.1.1. Checking a Root Certificate Authority
A C_FindObjects operation is done using the following attributes.
Walter Expires March 5, 2011 [Page 7]
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+--------------------+---------------------------------------+
| Attribute | Value |
+--------------------+---------------------------------------+
| CKA_CLASS | CKO_NETSCAPE_TRUST |
| CKA_CERT_SHA1_HASH | 20 byte value of hash of certificate. |
| Purpose attribute | CKT_TRUSTED_DELEGATOR |
+--------------------+---------------------------------------+
4.1.2. Checking a Self-Signed Certificate
A C_FindObjects operation is done using the following attributes.
+--------------------+---------------------------------------+
| Attribute | Value |
+--------------------+---------------------------------------+
| CKA_CLASS | CKO_NETSCAPE_TRUST |
| CKA_CERT_SHA1_HASH | 20 byte value of hash of certificate. |
| Purpose attribute | CKT_TRUSTED |
+--------------------+---------------------------------------+
4.1.3. Checking an otherwise Trusted Certificate
A C_FindObjects operation is done using the following attributes.
+-------------------+--------------------------------------------+
| Attribute | Value |
+-------------------+--------------------------------------------+
| CKA_CLASS | CKO_NETSCAPE_TRUST |
| CKA_ISSUER | DER encoding of certificate issuer. |
| CKA_SERIAL_NUMBER | DER encoding of certificate serial number. |
| Purpose attribute | CKT_UNTRUSTED |
+-------------------+--------------------------------------------+
4.2. Storing Trust Assertions
Xxxx
4.3. Reading Trust Assertions
Xxxx
5. Acknowledgements
NSS: Who?
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6. Further Considerations
xxxx
7. Security Considerations
Xxxx: Use of multiple PKCS#11 modules
Not using just any module.
8. References
8.1. Normative References
[min_ref] authSurName, authInitials., "Minimal Reference", 2006.
8.2. Informative References
[DOMINATION]
Mad Dominators, Inc., "Ultimate Plan for Taking Over the
World", 1984, <http://www.example.com/dominator.html>.
Appendix A. Additional Stuff
This becomes an Appendix.
Author's Address
Stef Walter (editor)
GNOME
Phone: +1 505 926 1827
Email: stefw@gnome.org
Walter Expires March 5, 2011 [Page 9]
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Full Copyright Statement
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contained in BCP 78, and except as set forth therein, the authors
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Walter Expires March 5, 2011 [Page 10]
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