Network Working Group N. Williams
Internet-Draft Cryptonector
Updates: 2743, 2744 (if approved) August 12, 2013
Intended status: Standards Track
Expires: February 13, 2014
Generic Naming Attributes for the Generic Security Services Application
Programming Interface (GSS-API)
draft-williams-kitten-generic-naming-attributes-01
Abstract
This document specifies several useful generic naming attributes for
use with the Generic Security Services Application Programming
Interface (GSS-API) Naming Extensions specified in RFC6680.
These attributes allow applications to extract discrete components of
a GSS-API "mechanism name" (MN) object: issuer (e.g., realm name,
domain name, certification authority name), service and host names
(for host-based service names), user names, and others.
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 February 13, 2014.
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Table of Contents
1. Introduction and Motivation . . . . . . . . . . . . . . . 3
1.1. Naming Constraints . . . . . . . . . . . . . . . . . . . . 3
1.2. Conventions used in this document . . . . . . . . . . . . 4
2. Generic Attributes . . . . . . . . . . . . . . . . . . . . 5
2.1. Concrete Attributes . . . . . . . . . . . . . . . . . . . 5
2.1.1. Issuer Name . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2. User Name . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.3. Service Name . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.4. Host Name . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.5. Domain Name . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Prefix Attributes . . . . . . . . . . . . . . . . . . . . 6
2.2.1. GSS_C_ATTR_GENERIC_UNCONSTRAINED . . . . . . . . . . . . . 7
2.2.2. GSS_C_ATTR_GENERIC_UNCONSTRAINED_OK . . . . . . . . . . . 7
2.2.3. GSS_C_ATTR_GENERIC_FAST . . . . . . . . . . . . . . . . . 7
3. Local Name Attributes . . . . . . . . . . . . . . . . . . 8
3.1. GSS_C_ATTR_LOCAL_LOGIN_USER . . . . . . . . . . . . . . . 8
4. Suggested Mechanism-Specific Name Attributes
(INFORMATIONAL) . . . . . . . . . . . . . . . . . . . . . 9
4.1. Suggested Kerberos-Specific Name Attributes . . . . . . . 9
4.2. Suggested PKU2U-Specific Name Attributes . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction and Motivation
The Generic Security Services Application Programming Interface (GSS-
API) [RFC2743] allows applications -and application protocol
specifications- to use various security mechanisms in a generic way.
There are some shortcomings of this API that preclude a fully-generic
treatment of security mechanisms. This document builds on the naming
extensions to the GSS-API [RFC6680] to correct some of those
shortcomings.
In RFC6680 we introduced an interface by which to access "attributes"
of names, but we did not specify any attributes. This document
specifies some such attributes. Some of the new attributes are
specifically intended to make it possible to use the GSS-API in a
mechanism-generic way in common use cases where it is otherwise not
possible to do so.
For example, some applications need to be able to observe the
discrete elements of a peer principal's host-based service name, but
they generally could only do so by parsing mechanism-specific display
syntaxes or exported name token formats. Such applications are
inherently not generic: they can only function correctly when used
with security mechanism whose principal naming conventions/formats
the applications understand.
More generally, we use the the extended naming interface to introduce
an attribute model of principal naming.
1.1. Naming Constraints
This document also introduces a notion of naming constraints, not
unlike PKIX's [RFC5280]. Naming constraints apply to "issuers" of
principal names and/or their attributes. For example, to Kerberos
[RFC4120] realms, to PKIX certification authorities, to identity
providers (IdPs), and so on. The goal is allow specification of
policies which constrain the set of principal names that a given
issuer can issue credentials for.
For example, the Kerberos realm FOO.EXAMPLE would generally not be
expected to issue credentials to host-based principals in domains
other than "foo.example".
For each concrete attribute specified below there are several ways to
inquire a NAME's value for that attribute:
1. with naming constraint checking, providing no output if naming
constraints are violated;
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2. with naming constraint checking, providing an output indicator of
naming constraint violations;
3. without naming constraint checking;
4. any of the above with "fast" (no slow I/O involved) naming
constraint checking.
(1) is the default behavior. The others are obtained by adding an
appropriate prefix to the attribute name.
Existing security mechanisms may not have any formal notion of naming
constraints, but it is common to have some naming constraint
conventions nonetheless. For example, Kerberos realm naming
conventions are that realm names should mirror Domain Name System
(DNS) [RFC1035] domain names, and that hostnames embedded in Kerberos
principal names should a) be fully-qualified, b) within the domain
corresponding to the DNS domain name derived from the realm's name.
Or a Kerberos implementation might lookup a host's realm and check
that it matches the principal's realm. Naming constraints should be
formalized for all GSS-API security mechanisms.
1.2. Conventions used in this document
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 [RFC2119].
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2. Generic Attributes
We add a number of generic name attributes, to be used via the GSS-
API extended naming facility [RFC6680]. Some of these attributes can
be used as prefixes of other attributes, that is, they can be used to
modify the semantics of other attributes (see section 6 of RFC6680).
Note: in all cases the display form of each attribute SHALL consist
of text using the character set, codeset, and encoding from the
caller's locale.
2.1. Concrete Attributes
These attributes generally have a single value each. Only one of
these attributes can also be used a prefix: the issuer name
attribute.
2.1.1. Issuer Name
We add an attribute by which to obtain a name of an issuer of a
mechanism name (MN) or of an attribute of an MN. The API name for
this attribute is GSS_C_ATTR_GENERIC_ISSUERNAME, and it's actual
attribute name is "urn:ietf:id:ietf-kitten-name-attrs-00-issuername".
The display form of issuer names is mechanism-specific.
The non-display form of issuer names SHALL be the exported name token
form of the issuer's name. Not all mechanisms will support issuer
names as MNs, therefore implementations MAY output a null non-display
value.
For example, for the Kerberos mechanism [RFC4121] an issuer name
would generally (but not always!) be a Kerberos realm name, probably
displayed as just the realm name. (But note that there is not yet a
Kerberos realm name as MN specification. We will specify one
separately.)
This attribute can be used as prefix of other attributes. When used
as a prefix, this attribute indicates that the application wishes to
know the name of the issuer of the prefixed attribute of the given
MN.
2.1.2. User Name
We add an attribute by which to obtain the component of an MN naming
a user. The API name for this attribute is
GSS_C_ATTR_GENERIC_USERNAME, and it's actual attribute name is
"urn:ietf:id:ietf-kitten-name-attrs-00-username".
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The display form of user names is mechanism-specific.
The non-display form of user names is mechanism-specific.
2.1.3. Service Name
We add an attribute by which to obtain the component of an MN naming
a service as part of a host- or domain-based service name. The API
name for this attribute is GSS_C_ATTR_GENERIC_SERVICENAME, and it's
actual attribute name is
"urn:ietf:id:ietf-kitten-name-attrs-00-servicename".
The non-display form of the service name SHALL be the UTF-8 encoding
of the service name.
2.1.4. Host Name
We add an attribute by which to obtain the component of an MN naming
a host as part of a host- or domain-based service name. The API name
for this attribute is GSS_C_ATTR_GENERIC_HOSTNAME, and it's actual
attribute name is "urn:ietf:id:ietf-kitten-name-attrs-00-hostname".
The display form of a host name MAY be stylized and SHOULD NOT be
A-labels. [RFC5890].
The non-display form of host names SHOULD be a character string as
described in [RFC1123], and SHOULD NOT be U-labels [RFC5890].
2.1.5. Domain Name
We add an attribute by which to obtain the component of an MN naming
a domain as part of a domain-based service name. The API name for
this attribute is GSS_C_ATTR_GENERIC_DOMAINNAME, and it's actual
attribute name is "urn:ietf:id:ietf-kitten-name-attrs-00-domainname".
The display form of a domain name MAY be stylized and SHOULD NOT be
A-labels. [RFC5890].
The non-display form of domain names SHOULD be a character string as
described in [RFC1123], and SHOULD NOT be U-labels [RFC5890].
2.2. Prefix Attributes
GSS_Get_name_attribute() using attributes described in the preceding
section SHALL fail if there are any name constraints that can be
applied to the issuers of those names and, in applying those
constraints, it is discovered that the issuer was not permitted to
issue credentials for the MN.
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For example, a Kerberos realm named "FOO.EXAMPLE" might not be
expected to issue credentials (tickets, keys) to host-based service
names for hosts not ending in ".foo.example" or which are not
"foo.example".
Several generic attribute prefixes are described below for overriding
this behavior.
2.2.1. GSS_C_ATTR_GENERIC_UNCONSTRAINED
This attribute prefix, named GSS_C_ATTR_GENERIC_UNCONSTRAINED in the
API, and with an actual name of
"urn:ietf:id:ietf-kitten-name-attrs-00-gen-unconstrained", indicates
that the application wants the value of the prefixed attribute
without any name constraint checking.
2.2.2. GSS_C_ATTR_GENERIC_UNCONSTRAINED_OK
This attribute prefix, named GSS_C_ATTR_GENERIC_UNCONSTRAINED_OK in
the API, and with an actual name of
"urn:ietf:id:ietf-kitten-name-attrs-00-gen-unconstrained-ok",
indicates that the application wants the value of the prefixed
attribute regardless of any applicable naming constraints, but to
indicate the name constraint status via the 'authenticated' output
parameter of the GSS_Get_name_attribute() interface.
2.2.3. GSS_C_ATTR_GENERIC_FAST
This attribute prefix, named GSS_C_ATTR_GENERIC_FAST in the API, and
with an actual name of
"urn:ietf:id:ietf-kitten-name-attrs-00-gen-fast", indicates that the
application requires that the mechanism not perform any slow
operations (e.g., connecting to a directory for the purposes of name
constraint validation) in obtaining the prefixed attribute of the
given MN.
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3. Local Name Attributes
Normally an Internet specification would not be expected to specify
any local name attributes of GSS names. However, there is one common
and very useful local name attribute, which we specify below.
Implementations are free to use different names for this attribute or
exclude it altogether -- it is a local name attribute, after all.
3.1. GSS_C_ATTR_LOCAL_LOGIN_USER
This attribute, with suggested API symbolic name
GSS_C_ATTR_LOCAL_LOGIN_USER, and suggested actual name "local-login-
user", requests a local user name corresponding to the given MN, if
any.
Obtaining the local user name corresponding to an MN may require
complex name mapping or lookup operations that are completely
implementation-defined.
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4. Suggested Mechanism-Specific Name Attributes (INFORMATIONAL)
[[anchor1: This section should really be split out into separate
Internet-Drafts. It is here only because the author lacks the time
at the moment of writing to create such separate I-Ds.]]
4.1. Suggested Kerberos-Specific Name Attributes
o realm (corresponding to issuer name)
o component 0 (first component of a principal name)
o component 1 (second component of a principal name)
o ..
o component 9 (10th component of a principal name)
o components (ordered set of components of a principal name)
o transit path (ordered set of realm and CA names)
o specific authorization data elements
o PKINIT client certificate
o session key enctype
o enctypes involved in transit path (this would only be available to
initiators)
4.2. Suggested PKU2U-Specific Name Attributes
[[anchor2: Add reference to PKU2U.]]
o issuer CA name
o trust path to a trust anchor
o certificate
o certificate subject public key
o certificate subject name
o certificate subject alternate names
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o specific certificate extensions
o certificate algorithm names
o session key enctype
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5. Security Considerations
[Add text regarding name constraint checking and explaining the
default-to-safe design of the generic name attributes defined in
section 2.]
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6. IANA Considerations
[Add text regarding the registration and assignment of the name
attributes described in the preceding sections. In particular we
should want these attributes' names to not reflect an Internet-Draft
name, but an RFC number.]
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC2744] Wray, J., "Generic Security Service API Version 2 :
C-bindings", RFC 2744, January 2000.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC6680] Williams, N., Johansson, L., Hartman, S., and S.
Josefsson, "Generic Security Service Application
Programming Interface (GSS-API) Naming Extensions",
RFC 6680, August 2012.
7.2. Informative References
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
Version 5 Generic Security Service Application Program
Interface (GSS-API) Mechanism: Version 2", RFC 4121,
July 2005.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
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Author's Address
Nicolas Williams
Cryptonector, LLC
Email: nico@cryptonector.com
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