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CVS gss/doc/specification
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gss-commit |
Subject: |
CVS gss/doc/specification |
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Thu, 24 Feb 2005 00:07:52 +0100 |
Update of /home/cvs/gss/doc/specification
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draft-ietf-kitten-gss-naming-01.txt
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Network Working Group S. Hartman
Internet-Draft MIT
Expires: August 21, 2005 February 20, 2005
Desired Enhancements to GSSAPI Naming
draft-ietf-kitten-gss-naming-01.txt
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. 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 become aware will be disclosed, in accordance with
RFC 3668.
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 August 21, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The Generic Security Services API (GSS-API) provides a naming
architecture that supports name-based authorization. GSS-API
authenticates two named parties to each other. Names can be stored
on access control lists to make authorization decisions. Advances in
security mechanisms and the way implementers wish to use GSS-API
require this model to be extended. As people move within an
organization or change their names, the name authenticated by GSS-API
may change. Using some sort of constant identifier would make ACLs
Hartman Expires August 21, 2005 [Page 1]
Internet-Draft GSS Names February 2005
more stable. Some mechanisms such as public-key mechanisms do not
have a single name to be used across all environments. Other
mechanisms such as Kerberos include may include group membership or
role information as part of authentication. This document motivates
extensions to GSS-API naming and describes the extensions under
discussion.
Hartman Expires August 21, 2005 [Page 2]
Internet-Draft GSS Names February 2005
1. Introduction
The Generic Security Services API [2] authenticates two named parties
to each other. GSS names can be imported in a variety of formats
through the gss_import_name call. Several mechanism-independent name
formats are provided including GSS_C_NT_HOSTBASED_SERVICE for
services running on an Internet host and GSS_C_NT_USER_NAME for the
names of users. Other mechanism-specific name types are also
provided. By the time a name is used in acquiring a
mechanism-specific credential or establishing a security context, it
has been transformed into one of these mechanism-specific name types.
In addition, the GSS-API provides a function called gss_export_name
that will flatten a GSS-API name into a binary blob suitable for
comparisons. This binary blob can be stored on ACLs and then
authorization decisions can be made simply by comparing the name
exported from a newly accepted context to the name on the ACL.
Storing names on ACLs can be problematic because names tend to change
over time . If the name contains organizational information such as
a domain part or an indication of what department someone works for,
this changes as the person moves around the organization. Even if no
organizational information is included in the name, the name will
change as people change their names. Updating ACLs to reflect name
changes is difficult.
Inherent in the GSS naming model is the idea that mechanism names
need to be able to be represented in a single canonical form. Anyone
importing that name needs to be able to retrieve the canonical form
of that name.
Several security mechanisms have been proposed for which this naming
architecture is too restrictive. In some cases it is not always
possible to canonicalize any name that is imported. In other cases
there is no single canonical name.
Also, as GSS-API is used in more complex environments, there is a
desire to use attribute certificates [6], Kerberos authorization data
[3], or other non-name-based authorization models. GSS-API needs to
be enhanced in order to support these uses in a mechanism-independent
manner.
This document discusses the particular naming problems with two
important classes of GSS-API mechanisms. It also discusses the set
of proposed solutions and open issues with these solutions. This
draft limits discussion to these solutions and provides a description
of the problem against which the solutions can be judged.
Hartman Expires August 21, 2005 [Page 3]
Internet-Draft GSS Names February 2005
2. Kerberos Naming
The Kerberos mechanism demonstrates both the naming stability problem
and the authorization extension problem.
The Kerberos Referrals draft [4] proposes a new type of Kerberos name
called an enterprise name. The intent is that the enterprise name is
an alias that the user knows for themselves and can use to login.
The Kerberos KDC translates this name into a normal Kerberos
principal and gives the user tickets for this principal. This normal
principal is used for authorization. The intent is that the
enterprise name tracks the user as they move throughout the
organization, even if they move to parts of the organization that
have different naming policies. The name they type at login remains
constant, but the Kerberos principal used to authenticate them to
services changes.
Performing a mapping from enterprise name to principal name is not
generally possible for unauthenticated services. Even authenticated
services may not be authorized to perform this mapping except for
their own name. Also, Kerberos does not (and does not plan to)
provide a mechanism for mapping enterprise names to principals
besides authentication as the enterprise name. Thus, any such
mapping would be vendor-specific. With this feature in Kerberos, it
is not possible to implement gss_canonicalize_name for enterprise
name types.
Another issue arises with enterprise names. IN some cases it would
be desirable to put the enterprise name on the ACL instead of a
principal name for greater ACL stability. At first glance this could
be accomplished by including the enterprise name in the name exported
by gss_export_name. Unfortunately, if this were done, the exported
name would change whenever the mapping changed, invalidating any ACL
entries based off the old exported name and defeating the purpose of
including the enterprise name in the exported name. In some cases it
would be desirable to have the exported name be based on the
enterprise name and in others based on the principal name, but this
is not permitted by the current GSS-API.
Another development also complicates GSS-API naming for Kerberos.
Several vendors have been looking at mechanisms to include group
membership information in Kerberos authorization data. It is
desirable to put these group names on ACLs. Again, GSS-API currently
has no mechanism to use this information.
Hartman Expires August 21, 2005 [Page 4]
Internet-Draft GSS Names February 2005
3. X.509 Names
X.509 names are more complicated than Kerberos names. In the
Kerberos case there is a single principal carried in all Kerberos
messages. X.509 certificates have multiple options. It seems the
subject name might be the appropriate name to use as the name to be
exported in a GSS-API mechanism. However RFC 3280 [5] does not even
require the subject name to be a non-empty sequence. Instead there
are cases where the subjectAltName extension is the only thing to
identify the subject of the certificate. As in the case of Kerberos
group memberships, there may be many subjectAltName extensions
available in a certificate. Different applications will care about
different extensions. Thus there is no single value that can be
defined as the exported GSS-API name that will be useful in all
environments.
A profile of a particular X.509 GSS-API mechanism could require a
specific name be used. However this would limit that mechanism to
require a particular type of certificate. There is interest in being
able to use arbitrary X.509 certificates with GSS-API for some
applications.
Experience so far has not lead to sufficient interoperability with
GSS-API X.509 mechanisms. Even if the subject name is used, there is
ambiguity in how to handle sorting of name components. Martin Rex
said that he was aware of several SPKM [1] implementations but no two
were fully interoperable on names.
Also, as discussed in the introduction, it is desirable to support
X.509 attribute certificates.
Hartman Expires August 21, 2005 [Page 5]
Internet-Draft GSS Names February 2005
4. Composite Names
One proposal to solve these problems is to extend the concept of a
GSS-API name to include a set of name attributes. Each attribute
would be an octet-string labeled by an OID. Examples of attributes
would include Kerberos enterprise names, group memberships in an
authorization infrastructure, Kerberos authorization data attributes
and subjectAltName attributes in a certificate. Several new
operations would be needed:
1. Add an attribute to name.
2. Query attributes of name.
3. Query values of an attribute.
4. Delete an attribute from a name.
5. Export a complete composite name and all its attributes for
transport between processes.
Note that an exported composite name would not be suitable for binary
comparison. Avoiding confusion between this operation and the
existing gss_export_name operation will require careful work.
4.1 Usage of Name Attributes
Since attributes are part of GSS-API names, the acceptor can retrieve
the attributes of the initiator's and acceptor's name from the
context. These attributes can then be used for authorization.
Most name attributes will probably not come from explicit operations
to add attributes to a name. Instead, name attributes will probably
come from mechanism specific credentials. Components of these
mechanism specific credentials may come from platform or
environment-specific names. Mechanism specific naming and group
membership can be mapped into name attributes by the mechanism
implementation. The specific form of this mapping will generally
require protocol specification for each mechanism.
The value of many name attributes may be suitable for use in binary
comparison. This should enable applications to use these name
attributes on ACLs the same way exported names are now used on ACLs.
For example if a particular Subjectaltname extension contains the
appropriate identity for an application, then the name attribute
for this Subjectaltname can be placed on the ACL. This is only true
if the name attribute is stored in some canonical form.
4.2 Open issues
This section describes parts of the proposal to add attributes to
names that will need to be explored before the proposal can become a
protocol specification.
Hartman Expires August 21, 2005 [Page 6]
Internet-Draft GSS Names February 2005
Are mechanisms expected to be able to carry arbitrary name attributes
as part of a context establishment? At first it seems like this
would be desirable. However the purpose of GSS-API is to establish
an authenticated context between two peers. In particular, a context
authenticates two named entities to each other. The names of these
entities and attributes associated with these names will be used for
authorization decisions. If an initiator or acceptor is allowed to
assert name attributes and the authenticity of these assertions is
not validated by the mechanisms, then security problems will result.
On the other hand, requiring that name attributes be mechanism
specific and only be carried by mechanisms that understand the name
attributes and can validate them compromises GSS-API's place as a
generic API. Application authors would be forced to understand
mechanism-specific attributes to make authorization decisions. In
addition if mechanisms are not required to transport arbitrary
attributes, then application authors will need to deal with different
implementations of the same mechanism that support different sets of
name attributes. One possible solution is to carry a source along
with each name attribute; this source could indicate whether the
attribute comes from a mechanism data structure or from the other
party in the authentication.
Another related question is how will name attributes be mapped into
their mechanism-specific forms. For example it would be desirable to
map many Kerberos authorization data elements into name attributes.
In the case of the Microsoft PAC, it would be desirable for some
applications to get the entire PAC. However in many cases, the
specific lists of security IDs contained in the PAC would be more
directly useful to an application. So there may not be a good
one-to-one mapping between the mechanism-specific elements and the
representation desirable at the GSS-API layer.
Specific name matching rules need to be developed. How do names with
attributes compare? What is the effect of a name attribute on a
target name in gss_accept_sec_context?
4.3 Handling gss_export_name
For many mechanisms, there will be an obvious choice to use for the
name exported by gss_export_name. For example in the case of
Kerberos, the principal name can continue to be used as the exported
name. This will allow applications depending on existing GSS-API
name-based authorization to continue to work. However it is probably
desirable to allow GSS-API mechanisms for which gss_export_name
cannot meaningfully be defined. The behavior of gss_export_name in
such cases should probably be to return some error. Such mechanisms
may not work with existing applications and cannot conform to the
current version of the GSS-API.
Hartman Expires August 21, 2005 [Page 7]
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5. Credential Extensions
An alternative to the name attributes proposal is to extend GSS-API
credentials with extensions labeled by OIDs. Interfaces would be
needed to manipulate these credential extensions and to retrieve the
credential extensions for credentials used to establish a context.
Even if name attributes are used, credential extensions may be useful
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- CVS gss/doc/specification, gss-commit, 2005/02/02
- CVS gss/doc/specification, gss-commit, 2005/02/15
- CVS gss/doc/specification, gss-commit, 2005/02/15
- CVS gss/doc/specification, gss-commit, 2005/02/15
- CVS gss/doc/specification, gss-commit, 2005/02/16
- CVS gss/doc/specification, gss-commit, 2005/02/16
- CVS gss/doc/specification,
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