BACKGROUND
[0001] Computers and other electronic devices are pervasive in the
professional and personal lives of people. In professional settings, people exchange
and share confidential information during project collaborations. In personal settings,
people engage in electronic commerce and the transmission of private information. In
these and many other instances, electronic security is deemed to be important.
[0002] Electronic security paradigms can keep professional information
confidential and personal information private. Electronic security paradigms may
involve some level of encryption and/or protection against malware, such as viruses,
worms, and spyware. Both encryption of information and protection from malware
have historically received significant attention, especially in the last few years.
[0003] However, controlling access to information is an equally important
aspect of securing the safety of electronic information. This is particularly true for scenarios in which benefits are derived irom the sharing and/or transferring of electronic information. In such scenarios, certain people are to be granted access while others are to be excluded.
2
|0004] Access control has been a common feature of shared computers and
application servers since the early time-shared systems. There are a number of different approaches that have been used to control access to information. They share a common foundation in combining authentication of the entity requesting access to some resource with a mechanism of authorizing the allowed access. Authentication mechanisms include passwords, Kerberos, and x.509 certificates. Their purpose is to allow a resource-controlling entity to positively identify the requesting entity or information about the entity that it requires.
[0005] Authorization examples include access control lists (ACLs) and policy-
based mechanisms such as the extensible Access Control Markup Language (XACML) or the PrivilEge and Role Management Infi-astruclure (PERMIS). These mechanisms define what entities may access a given resource, such as files in a file system, hardware devices, database information, and so forth. They perform this authorization by providing a mapping between authenticated information about a requestor and the allowed access to a resource,
[0006] As computer systems have become more universally connected over
large networks such as the Internet, these mechanisms have proven to be somewhat limited and inflexible in dealing with evolving access control requirements. Systems

of geographically dispersed users and computer resources, including those that span multiple administrative domains, in particular present a number of challenges that are poorly addressed by currently-deployed technology. SUMMARY
|0007| The delegation of rights may be controlled in a number of manners. In
an example implementation, a delegation authority assertion is formulated with a delegator principal, a delegatee principal, a verb phrase, a resource, and a delegation-directive verb. In another example implementation, a delegation mechanism involving an assertor, a first principal, and a second principal enables a delegation to be specifically controlled. In yet another example implementation, a chained delegation mechanism enables explicit control of a permitted transitive chaining depth.
[0008] This Summary is provided to introduce a selection of concepts in a
simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. Moreover, other method, system, scheme, apparatus, device, media, procedure, API, arrangement, protocol, etc. implementations are described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The same numbers are used throughout the drawings to reference like
and/or corresponding aspects, features, and components.
[0010] FIG. I is a block diagram illustrating an example general environment
in which an example security scheme may be implemented.
[0011] FIG. 2 is a block diagram illustrating an example security environment
having two devices and a number of example security-related components.
[0012] FIG. 3 is a block diagram illustrating the example security
environment of FIG. 2 in which example security-related data is exchanged among the security-related components.
[0013| FIG. 4 is a block diagram of an example device that may be used for
security-related implementations as described herein.
J0014J FIG. 5 is a block diagram illustrating an example assertion format for a
general security scheme.

|0015] FIG. 6 is a block diagram illustrating an example delegation
mechanism from a functional perspective along with an example delegation scenario
and including a delegation authority assertion.
(00161 FIG. 7 is a block diagram illustrating an example delegation
mechanism from a logical perspective along with example delegation types.
[00171 FIG- 8 is a block diagram illustrating an example assertion format for a
delegation authority assertion of a delegation mechanism.
[00181 FlG. 9 is a block diagram illustrating an example chained delegation
mechanism from a functional perspective along with an example chained delegation
scenario.
[0019] FIG. 10 is a block diagram illustrating two example format approaches
for a chained delegation mechanism.
(0020) FIG. 11 is a flow diagram illustrating an example of a method for
creating a delegation authority assertion.
DETAILED DESCRIPTION
EXAMPLE SECURITY ENVIRONMENTS
[00211 FIG. 1 is a block diagram illustrating an example general environment
in which an example security scheme 100 may be implemented. Security scheme 100
represents an integrated approach to security. As illustrated, security scheme 100
includes a number of security concepts: security tokens 100(A), security policies
100(B), and an evaluation engine 100(C). Generally, security tokens 100(A) and
security policies 100(B) jointly provide inputs to evaluation engine 100(C).
Evaluation engine ] 00(C) accepts the inputs and produces an authorization output that
indicates if access to some resource should be permitted or denied.
|0022| In a described implementation, security scheme 100 can be overlaid
and/or integrated with one or more devices 102, which can be comprised of hardware, software, firmware, some combination thereof, and so forth. As illustrated, "d" devices, with "d" being some integer, are intercormected over one or more networks 104. More specifically, device 102(1), device i02(2), device 102(3) ... device 102(d) are capable of communicating over network 104.
[0023] Each device 102 may be any device that is capable of implementing at
least a part of security scheme 100, Examples of such devices include, but are not

limited to, computers (e.g., a client computer, a server computer, a personal computer, a workstation, a desktop, a laptop, a palm-top, etc.), game machines (e.g., a console, a portable game device, etc.), set-top boxes, televisions, consumer electronics (e.g., DVD player/recorders, camcorders, digital video recorders (DVRs), etc.), personal digital assistants (PDAs), mobile phones, portable media players, some combination thereof, and so forth. An example electronic device is described herein below with particular reference to FIG. 4.
[0024| Network 104 may be formed from any one or more networks that are
linked together and/or overlaid on lop of each other. Examples of networks 104 include, but are not limited to, an internet, a telephone network, an Ethernet, a local area network (LAN), a wide area network (WAN), a cable network, a fibre network, a digital subscriber line (DSL) network, a cellular network, a Wi-Fi® network, a WiMAX® network, a virtual private network (VPN), some combination thereof, and so forth. Network 104 may include multiple domains, one or more grid networks, and so forth. Each of these networks or combination of networks may be operating in accordance with any networking standard.
|0025| As illustrated, device 102(1) corresponds to a user 106 that is
interacting with it. Device 102(2) corresponds to a service 108 that is executing on it. Device 102(3) is associated with a resource 110. Resource 110 may be part of device 102(3) or separate from device 102(3).
[0026] User 106, service 108, and a machine such as any given device 102
form a non-exhaustive list of example entities. Entities, from time to time, may wish to access resource IIO. Security scheme 100 ensures that entities that are properly authenticated and authorized are permitted to access resource 110 while other entities are prevented from accessing resource 110.
[0027] FIG. 2 is a block diagram illustrating an example security environment
200 having two devices 102(A) and 102(B) and a number of example security-related
components. Security environment 200 also includes an authority 202, such as a
security token service (STS) authority. Device 102(A) corresponds to an entity 208.
Device 102(B) is associated with resource IIO. Although a security scheme 100may
be implemented in more complex environments, this relatively-simple two-device
security environment 200 is used to describe example security-related components.
[00281 As illustrated, device 102(A) includes two security-related
components: a security token 204 and an application 210. Security token 204

includes one or more assertions 206, Device 102(B) includes five security-related components: an authorization context 212, a resource guard 214, an audit log 216. an authorization engine 218, and a security policy 220. Security policy 220 includes a trust and authorization policy 222, an authorization query table 224, and an audit policy 226.
[0029] Each device 102 may be configured differently and still be capable of
implementing all or a part of security scheme 100. For example, device 102(A) may have multiple security tokens 204 and/or applications 210. As another example, device 102(B) may not include an audit log 216 or an audit policy 226. Other configurations are also possible.
(0030| In a described implementation, authority 202 issues security token 204
having assertions 206 to entity 208. Assertions 206 are described herein below, including in the section entitled "Security Policy Assertion Language Example Characteristics". Entity 208 is therefore associated with security token 204. In operation, entity 208 wishes to use application 210 to access resource 110 by virtue of security token 204.
|0031I Resource guard 214 receives requests to access resource HO and
effectively manages the authentication and authorization process with the other
security-related components of device 102(B). Trust and authorization policy 222, as
its name implies, includes policies directed to trusting entities and authorizing actions
within security environment 200. Trust and authorization policy 222 may include, for
example, security policy assertions (not explicitly shown in FIG. 2). Authorization
query table 224 maps requested actions, such as access requests, to an appropriate
authorization query. Audit policy 226 delineates audit responsibilities and audit tasks
related to implementing security scheme 100 in security environment 200.
|0032] Authorization context 212 collects assertions 206 from security token
204, which is/are used to authenticate the requesting entity, and security policy
assertions from trust and authorization policy 222. These collected assertions in
authorization context 212 form an assertion context. Hence, authorization context
212 may include other information in addition to the various assertions,
|0033] The assertion context from authorization context 212 and an
authorization query from authorization query table 224 are provided to authorization engine 218. Using the assertion context and the authorization query, authorization engine 218 makes an authorization decision. Resource guard 214 responds to the

access request based on the authorization decision. Audit log 216 contains audit
information such as, for example, identification of the requested resource 110 and/or
the algorithmic evaluation logic performed by authorization engine 218.
[0034| FIG. 3 is a block diagram illustrating example security environment
200 in which example security-related data is exchanged among the security-related components. The security-related data is exchanged in support of an example access request operation. In this example access request operation, entity 208 wishes to access resource 110 using application 210 and indicates its authorization to do so with security token 204. Hence, application 210 sends an access request* to resource guard 214. In this description of FIG. 3, an asterisk (i.e., "*") indicates that the stated security-related data is explicitly indicated in FIG. 3.
[0035] In a described implementation, entity 208 authenticates* itself to
resource guard 214 with a token*, security token 204. Resource guard 214 forwards the token assertions* to authorization context 212. These token assertions are assertions 206 (of FIG. 2) of security token 204. Security policy 220 provides the authorization query table* to resource guard 214. The authorization query table derives from authorization query table module 224. The authorization query table sent to resource guard 214 may be confined to the portion or portions directly related to the current access request.
[0036] Policy assertions are extracted from trust and authorization policy 222
by security policy 220. The policy assertions may include both trust-related assertions and authorization-related assertions. Security policy 220 forwards the policy assertions* to authorization context 212. Authorization context 212 combines the token assertions and the policy assertions into an assertion context. The assertion context* is provided from authorization context 212 to authorization engine 218 as indicated by the encircled "A".
[0037] An authorization query is ascertained from the authorization query
table. Resource guard 214 provides the authorization query (auth. query*) to authorization engine 218. Authorization engine 218 uses the authorization query and the assertion context in an evaluation algorithm to produce an authorization decision. The authorization decision (auth. den.*) is returned to resource guard 214. Whether entity 208 is granted access* to resource 110 by resource guard 214 is dependent on the authorization decision. If the authorization decision is affirmative, then access is granted. If, on the other hand, the authorization decision issued by authorization

engine 218 is negative, then resource guard 214 does not grant entity 208 access to resource 110.
[0038] The authorization process can also be audited using semantics that are
complementary to the authorization process. The auditing may entail monitoring of
the authorization process and/or the storage of any intermediate and/or final products
of, e.g., the evaluation algorithm logically performed by authorization engine 218. To
that end, security policy 220 provides to authorization engine 218 an audit policy*
from audit policy 226. At least when auditing is requested, an audit record* having
audit information may be forwarded from authorization engine 218 to audit log 216.
Alternatively, audit information may be routed to audit log 216 via resource guard
214, for example, as part of the authorization decision or separately.
|0039| FIG, 4 is a block diagram of an example device 102 that may be used
for security-related implementations as described herein. Multiple devices 102 are
capable of communicating across one or more networks 104. As illustrated, two
devices 102(A/B) and 102(d) are capable of engaging in communication exchanges
via network 104. Although two devices 102 are specifically shov™, one or more than
two devices 102 may be employed, depending on the implementation.
|0040) Generally, a device 102 may represent any computer or processing-
capable device, such as a client or server device; a workstation or other general computer device; a PDA; a mobile phone; a gaming platform; an entertainment device; one of the devices listed above with reference to FIG. 1; some combination thereof; and so forth. As illustrated, device 102 includes one or more input/output (I/O) interfaces 404, at least one processor 406, and one or more media 408. Media 408 include processor-executable instructions 410.
[0041] In a described implementation of device 102, I/O interfaces 404 may
include (i) a network interface for communicating across network 104, (ii) a display device interface for displaying information on a display screen, (iii) one or more man-machine interfaces, and so forth. Examples of (i) network interfaces include a nelwork card, a modem, one or more ports, and so forth. Examples of (ii) display device interfaces include a graphics driver, a graphics card, a hardware or software driver for a screen or monitor, and so forth. Printing device interfaces may similarly be included as part of I/O interfaces 404. Examples of (iii) man-machine interfaces include those that communicate by wire or wirelessly to man-machine interface

devices 402 (e.g., a keyboard, a remote, a mouse or other graphical pointing device, etc.).
(0042] Generally, processor 406 is capable of executing, performing, and/or
otherwise effectuating processor-executable instructions, such as processor-executable instructions 410, Media 408 is comprised of one or more processor-accessible media. In other words, media 408 may include processor-executable instructions 410 that are executable by processor 406 to effectuate the performance of functions by device 102.
[0043] Thus, realizations for security-related implementations may be
described in the general context of processor-executable instructions. Generally, processor-executable instructions include routines, programs, applications, coding, modules, protocols, objects, components, metadata and definitions thereof, data structures, application programming interfaces (APIs), schema, etc. that perform and/or enable particular tasks and/or implement particular abstract data types. Processor-executable instructions may be located in separate storage media, executed by different processors, and/or propagated over or extant on various transmission media.
[0044] Processor(s) 406 may be implemented using any applicable
processing-capable technology. Media 408 may be any available media that is included as part of and/or accessible by device 102. It includes volatile and non¬volatile media, removable and non-removable media, and storage and transmission media (e.g., wireless or wired communication channels). For example, media 408 may include an array of disks/flash memory/optical media for longer-term mass storage of processor-executabic instructions 410, random access memory (RAM) for shorter-term storing of instructions that are currently being executed, link(s) on network 104 for transmitting communications (e.g., security-related data), and so forth.
(0045) As specifically illustrated, media 408 comprises at least processor-
executable instructions 410. Generally, processor-executable instructions 410, when executed by processor 406, enable device 102 to perform the various functions described herein, including those actions that are illustrated in the various flow diagrams. By way of example only, processor-executable instructions 410 may include a security token 204, at least one of its assertions 206, an authorization context module 212, a resource guard 214, an audit log 216, an authorization engine

218, a security policy 220 (e.g., a trust and authorization policy 222, an authorization query table 224, and/or an audit policy 226, etc.), some combination thereof, and so forth. Although not explicitly shown in FIG. 4, processor-executable instructions 410 may also include an application 210 and/or a resource 110.
SECURITY POLICY ASSERTION LANGUAGE
EXAMPLE CHARACTERISTICS
[0046] This section describes example characteristics of an implementation of
a security policy assertion language (SecPAL). The SecPAL implementation of this
section is described in a relatively informal manner and by way of example only. It
has an ability to address a wide spectrum of security policy and security token
obligations involved in creating an end-to-end solution. These security policy and
security token obligations include, by way of example but not limitation: describing
expHcit trust relationships; expressing security token issuance policies; providing
security tokens containing identities, attributes, capabilities, and/or delegation
policies; expressing resource authorization and delegation policies; and so forth.
10047J In a described implementation, SecPAL is a declarative, logic-based
language for expressing security in a flexible and tractable manner. It can be
comprehensive, and it can provide a uniform mechanism for expressing trust
relationships, authorization policies, delegation policies, identity and attribute
assertions, capability assertions, revocations, audit requirements, and so forth. This
uniformity provides tangible benefits in terms of making the security scheme
understandable and analyzable. The uniform mechanism also improves security
assurance by allowing one to avoid, or at least significantly curtail, the need for
semantic translation and reconciliafion between disparate security technologies.
[0048] A SecPAL implementation may include any of the following example
features: [I] SecPAL can be relatively easy to understand. It may use a definitional
syntax that allows its assertions to be read as English-language sentences. Also, its
grammar may be restrictive such that it requires users to understand only a few
subject-verb-object {e.g., subject-verb phrase) constructs with cleanly defined
semantics. Finally, the algorithm for evaluating the deducible facts based on a
collection of assertions may rely on a small number of relatively simple rules.
[0049] [2] SecPAL can leverage industry standard infi-astructure in its
implementation to ease its adoption and integration into existing systems. For

example, an extensible markup language (XML) syntax may be used that is a
straightforward mapping from the formal model. This enables use of standard parsers
and syntactic correctness validation tools. It also allows use of the W3C XML Digital
Signature and Encryption standards for integrity, proof of origin, and confidentiality.
[0050] [3] SecPAL may enable distributed policy management by supporting
distributed policy authoring and composition. This allows flexible adaptation to
different operational models governing where policies, or portions of policies, are
authored based on assigned administrative duties. Use of standard approaches to
digitally signing and encrypting policy objects allow for their secure distribution. [4]
SecPAL enables an efficient and safe evaluation. Simple syntactic checks on the
inputs are sufficient to ensure evaluations will terminate and produce correct answers.
10051] [5] SecPAL can provide a complete solution for access control
requirements supporting required policies, authorization decisions, auditing, and a public-key infrastructure (PKI) for identity management. In contrast, most other approaches only manage to focus on and address one subset of the spectrum of security issues. [6] SecPAL may be sufficiently expressive for a number of purposes, including, but not limited to, handling the security issues for Grid enviroiunenls and other types of distributed systems. Extensibility is enabled in ways that maintain the language semantics and evaluation properties while allowing adaptation to the needs of specific systems.
(0052] FIG. 5 is a block diagram illustrating an example assertion format 500
for a general security scheme. Security scheme assertions that are used in the
implemeniations described otherwise herein may differ from example assertion
format 500. However, assertion format 500 is a basic illustration of one example
format for security scheme assertions, and il provides a basis for undersianding
example described implementation of various aspects of a general security scheme.
(00531 -s illustrated at the top row of assertion format 500, an example
assertion at a broad level includes: a principal portion 502, a says portion 504, and a claim portion 506. Textually, the broad level of assertion format 500 may be represented hy. principal says claim.
[0054] At the next row of assertion format 500, claim portion 506 is separated
into example constituent parts. Hence, an example claim portion 506 includes: a fact portion 508, an if portion 510, "n" conditional facti n portions 508(1...n), and a c portion 512. The subscript "n" represents some integer value. As indicated by legend

524, c portion 512 represents a constraint portion. Although only a single constraint
is illustrated, c portion 512 may actually represent multiple constraints (e.g., C], ..,,
Cm). The set of conditional fact portions 508(1...n) and constraints 512(1...m) on the
right-hand side of if portion 5]0may be termed the antecedent.
[0055] Textually, claim portion 506 may be represented by: fact if fad], ... ,
factn, c. Hence, the overall assertion format 500 may be represented textually as follows: principal says fad if fact], ... yfaci„, c. However, an assertion may be as simple as: principal says fad. In this abbreviated, three-part version of an assertion, the conditional portion that starts with if portion 510 and extends to c portion 512 is omitted.
[0056] Each fact portion 508 may also be further subdivided into its
constituent parts. Example constituent parts are: an e portion 514 and a verb phrase
portion 516. As indicated by legend 524. e portion 514 represents an expression
portion. Textually. a fact portion 508 may be represented by: e verbphrase.
(0057] Each e or expression portion 514 may take on one of two example
options. These two example expression options are: a constant 514(c) and a variable
514(v). Principals may fall under constants 514(c) and/or variables 514(v).
[0058] Each verb phrase portion 516 may also take on one of three example
options. These three example verb phrase options are: a predicate portion 518 followed by one or more ei,,,n portions 514(1...n), a can assert portion 520 followed by a fact portion 508. and an alias portion 522 followed by an expression portion 514. Textually, these three verb phrase options may be represented by: predicate e\ ... e„, can asscn fact, and alias e, respectively. The integer "n" may take different values for facts 508(1...n) and expressions 514(t...n).
[0059] Generally, SecPAL statements are in the form of assertions made by a
security principal. Security principals are typically identified by cryptographic keys so that they can be authenticated across system boundaries. In their simplest form, an assertion states that the principal believes a fact is valid (e.g., as represented by a claim 506 that includes a fact portion 508). They may also state a fact is valid if one or more other facts are valid and some set of conditions are satisfied (e.g., as represented by a claim 506 that extends from a fact portion 508 to an if portion 510 to conditional fact portions 508(1,,.n) to a c portion 512). There may also be conditional facts 508(1...n) without any constraints 512 and/or constraints 512 without any conditional facts 508(1.. .n).

(0060| In a described implementation, facts are statements about a principal.
Four example types of fact statements are described here in this section. First, a fact
can state that a principal has the right to exercise an action(s) on a resource with an
"action verb". Example action verbs include, but are not limited to, call, send, read,
list, execute, write, modify, append, delete, install, own, and so forth. Resources may
be identified by universal resource indicators (URIs) or any other approach.
[0061| Second, a fact can express the binding between a principal identifier
and one or more attribute(s) using the "possess" verb. Example attributes include, but
are not limited to, email name, common name, group name, role title, account name,
domain name server/service (DNS) name, intemet protocol (IP) address, device name,
application name, organization name, service name, account identification/identifier
(ID), and so forth. An example third type of fact is that two principal identifiers can
be defined to represent the same principal using the "alias" verb.
[0062| "Qualifiers" or fact qualifiers may be included as part of any of the
above three fact types. Qualifiers enable an assertor to indicate environmental
parameters (e.g., time, principal locafion, etc) that it believes should hold if the fact is
to be considered valid. Such statements may be cleanly separated between the
assertor and a relying party's validity checks based on these qualifier values.
100631 An example fourth type of fact is defined by the "can assert" verb.
This "can assert" verb provides a flexible and powerful mechanism for expressing trust relafionships and delegafions. For example, it allows one principal (A) to state its willingness to believe certain types of facts asserted by a second principal (B). For instance, given the assertions ''A says B can assert/ac/O" and "S says faciO'", it can be concluded that A believes factO to be valid and therefore it can be deduced that " says/ac/0".
[00641 Such trust and delegation assertions may be (i) unbounded and
transitive to permit downstream delegation or (ii) bounded to preclude downstream
delegation. Although qualifiers can be applied to "can assert" type facts, omitting
support for qualifiers to these "can assert" type facts can significantly simpliiy the
semantics and evaluation safety properties of a given security scheme.
(00651 'o described implementation, concrete facts can be stated, or policy
expressions may be written using variables. The variables are typed and may either be unrestricted (e.g., allowed to match any concrete value of the correct type) or

restricted (e.g., required lo match a subset of concrete values based on a specified pattern).
[0066] Security authorization decisions are based on an evaluation algorithm
(e.g., that may be conducted at authorization engine 218) of an authorization query against a collection of assertions (e.g., an assertion context) from applicable security policies (e.g., a security policy 220) and security tokens (e.g.. one or more security tokens 204). Authorization queries are logical expressions, which may become quite complex, that combine facts and/or conditions. These logical expressions may include, for example, AND, OR, and/or NOT logica) operations on facts, either with or without attendant conditions and/or constraints.
[0067] This approach to authorization queries provides a flexible mechanism
for defining what must be known and valid before a given action is authorized. Query templates (e.g., from authorization query table 224) form a part of the overall security scheme and allow the appropriate authorization query to be declaratively stated for different types of access requests and other operations/actions.
EXAMPLE IMPLEMENTATIONS FOR
CONTROLLING THE DELEGATION OF RIGHTS
(0068] Modem systems, especially distributed systems, often function more
effectively when rights may be delegated between entities. This is manifested in a wide variety of functional situations. Ex.Tmple situations include, but are not limited to:
• The ability for a user to delegate some portion of their resource access rights to an application executing on their behalf;
• The ability for a manager to delegate some portion of its resource access rights to a subordinate or peer; and
• The ability for an executing application to delegate its resource access rights to another application.
[0069] These types of delegations should typically be controlled in one or
more of many various ways. For example, they may be allowed for only restricted periods of time, and they may need to be limited to the particular resources a delegatee needs to perform the intended function. Effective control over the ability to allow downstream delegation of rights can also be beneficial. In other words, it may

be beneficial for a delegatee to further delegate downstream some or all of the access rights it has been granted.
(0070) Existing systems provide a limited ability to support controlled
delegation. In most systems, it is limited to allowing a running program to
impersonate a user. Impersonation represents the ability for the delegatee to exercise
the full access rights of the delegator. At most, there is some time restriction on this
impersonation, but it is typically a default system value, which is measured in hours,
and can not be controlled on a per-interaclion basis. The Microsoft Windows®
Kerberos implementation further supports the ability for a service to have delegation
rights when processing requests on behalf of a user. This allows a service to pass
along the right to impersonate the user to another service, but it provides no effective
controls for constraining use of this capability. As a result, users of these existing
systems must fully trust the delegatee to not abuse its impersonation rights.
[0071] The Grid community has developed a delegation approach based on
X.509 proxy certificates. These also provide a very limited ability to control a
delegation. Although they do allow the setting of a time limit on a particular
deJegation, they also still allow the delegatee to use the identity and attributes of the
delegator when making access requests. The developers of the standard that defines
proxy certificates did recognize a need for controlled delegation, and they provided a
placeholder where a controlled delegation policy could be inserted into a certificate.
However, they did not define any mechanism to express or enforce such controls.
[0072] FIG. 6 is a block diagram illustrating an example delegation
mechanism 600 from a functional perspective along with an example delegation scenario. As illustrated, the example delegation scenario includes an assertor 602, a principal #1 604, and a principal #2 606. There is also a right-granting ability 608, a right 610, and two transfers 612(1) and 612(2). Example delegation mechanism 600 includes delegation authority assertion 614 and, in certain implementations, delegation granting assertion 616,
10073] In a described implementation for the example delegation scenario of
FIG. 6, assertor 602 corresponds to an authority, principal #1 604 corresponds to a delegator, and principal #2 606 corresponds to a delegatee. Assertor 602 has a right-granting ability 608. Via transfer 612(1) of delegation authority assertion 614, right-granting ability 608 is delegated from assertor 602 to principal #1 604.

10074) Hence, principal #1 604 gains right-granting ability 608 as a resuh of
delegation authority assertion 614. Principal #1 604 has a right 610. Because of delegation authority assertion 614, principal #1 604 may grant right 610 to one or more other principals, such as principal #2 606. The delegalee principal{s), the nature of the granted right, and/or how the granted right may be exercised is controllable by delegation authority assertion 614. Via transfer 612(2) of delegation granting assertion 616, right 610 is granted from principal #1 604 to principal #2 606. It should be understood that transfer 612(1) may be implicit and that delegation authority assertion 614 may be made known via a security policy ID resource guard 214 (of FIG. 2), It is resource guard 214 that enforces resource access based on right 610 and delegation granting assertion 616.
[0075] Thus, delegation mechanism 600 includes at least delegation authority
assertion 614 and may include delegation granting assertion 616 to complete a full
delegation process. Example implementations of delegation authority assertion 614
and delegation granting assertion 616 are described further herein below.
10076) FIG. 7 is a block diagram illustrating an example delegation
mechanism 600 from a logical perspective along with example delegation types 714.
As illustrated, example delegation mechanism 600 includes a number of example
factors 702-712 that may be used to control the delegation of rights. These example
factors include, by way of example but not limitation, principal 702, verb phrase 704,
resource 706, fact qualifiers 708, attributes 710, transitive chaining 712, and so forth.
(0077] Delegation mechanism 600 is capable of implementing a number of
different types of delegation control. As illustrated, these example delegation control types include, but are not limited to, attributed-based delegation 714(1), constrained delegation 714(2), depth-bound delegation 714(3), and width-bound delegation 714(4). These four specific example types of controlled delegafion are described below in greater detail after additional description of general controlled-delegafion concepts and implementations. As representing by other delegation types 714(T), delegation mechanism 600 may be capable of implementing many other types of controlled delegation.
J0078] In a described implementation, each of blocks 702-710 logically
represents a capability of delegafion mechanism 600 to control delegation with respect to the indicated (actor. Accordingly, delegation mechanism 600 may control a delegation by way of an identified principal or principals 702, a certain verb phrase

704, a particular resource 706, one or more indicated fact qualifiers 708, at least one given attribute 710, and/or a permitted transitive chaining (depth) 712. By way of example only, delegation mechanism 600 may be realized as an application programming interface (API) that can be used to control delegations using at least the factors of 702-712.
[0079] As described herein above, fact qualifiers include environmental
restrictions such as time periods / time spans, location, network cormectivity
mechanism, revocation check frequency, and so forth. Attributes refer to attribute
name-attribute value pairs in which a principal may possess one or more or attributes.
[0080] Any of these factors may be related to principal #1 604 and/or
principa] #2 606. In other words, and by way of example only, delegation mechanism 600 may control what accesses {e.g., by way of verb phrases 704) on which resources 706 may be delegated by principal #1 604 to principal #2 606. Delegation mechanism 600 may control which principals qualify as a principal #2 606, Furthermore, delegation mechanism 600 may require that a would-be principal #2 606 possess a given attribute 710. Additionally, restrictive environmental controls on delegation may be enforced through fact qualifiers 708 (e.g., in conjunction with conditional constraints). These and other possibilities are further illuminated by the description herein below.
10081] Delegation mechanism 600 may also control whether transitive
chaining delegation is enabled and, if so, to what degree or depth transhive chaining delegation is permilled by transitive chaining factor 7J2. Transitive chaining refers to whether principal #1 604 is permitted to further transfer or delegate right-granting ability 608 to principai #2 606. !f this is permitted, then principal #1 604 is enabled to issue a delegation authority assertion 614 to principal #2 606. Principal #2 606, in turn, is then enabled to issue a delegation granting assertion 616 to some third principal. This transitive chaining delegation is described further herein below with particular reference to FIGS. 9 and 10.
[0082| FIG. 8 is a block diagram illustrating an example assertion format 800
for a delegation authority assertion of a delegation mechanism. The concept of a delegation authority assertion 614 is introduced and described above (with reference to FIG. 6) as being part of a delegation mechanism 600. A delegation authority assertion 614 initiates a delegation by transferring a right-granting ability 608 from one to another, such as from an assertor to a first principal.

[0083] A portion of the example assertion format 500 of FIG. 5 is reproduced
in FIG. 8. However, principal portion 502 is replaced by an assertor portion 802, and the capacity for multiple or "m" constraints 512 is explicitly shown. It should be noted that the nomenclature "assertor", "principal #1", and ''principal #2" is utilized herein to facilitate differentiation of respective parties in a delegation scenario. However, each party may be considered to be essentially and effectively a principal in the overall scheme of a described security language.
(0084] Thus, in a described implementation, example assertion format 800
includes an assertor portion 802, a says portion 504, a fact portion 508, an if portion 510, "n" conditional facti „ portions 508(1...n), and "m" constrainti ,„, portions 512(1. ..m). Fact 508 is realized as a delegation fact by including a delegation-directive verb 520. Examples included, by way of example but not limitation, "can assert", "can say", ''can profess", "may contend", and so forth. Some delegation-related assertion examples set forth herein below use the specific example of "can assert" without loss of generality.
(00851 Delegation fact 508 includes a principal #1 portion 502(1), delegation-
directive verb 520, and a delegated fact portion 508(D). Delegated fact 508(D) includes a principal #2 portion 502(2), a verb phrase portion 516, a resource portion 804, and a fact qualifieri /portion 806(1...f). Hence, an example assertion format 800 may comport with a form of:
assertor says principall delegation-directive-verb "principal! verb-
phrase resource fac(-quatifier\ ./' if fad\, facl2, .-., fact„,
constrainti „ .
[0086| Thus, in a described implementation, a program may include an
application programming interface (API) for a delegation mechanism. The delegation mechanism is initiated by an assertor and enables a first principal to delegate a right to a second principal for the second principal to make at least one assertion. The delegation mechanism enables the delegation to be specifically controlled. For example, the delegation mechanism may enable a delegation to be controNed using any of factors 702-712.
10087] For example, delegation mechanism 600 may enable an assertor to
specify at least one attribute that a first principal is to possess for the first principal to be capable of delegating a right to make an assertion and/or to specify at least one attribute that a second principal is to possess for the second principal to be permitted

to make an assertion. For instance, delegation authority assertion 614 may include a conditional fact 508(1) such as: principal} possesses (attribute name, attribute value) OT principal2 possesses (attribute name, attribute value).
[0088] As another example, delegation mechanism 600 may enable an assertor
to specify that a first principal can only delegate a right to make an assertion if the first principal has a certain capability with respect to a particular resource and/or that a second principal is only permitted to make an assertion if the second principal has a certain capability with respect to a particular resource. For instance, delegation authority assertion 614 may include a conditional fact 508(1) such as: principal} read resource_a cyx principal! verb Foo.
|0089] As yet another example, delegation mechanism 600 may enable an
assertor to specify at least one fact qualifier that restricts a manner in which the delegation or the right may be exercised. For instance, delegation authority assertion 614 may include a delegated fact 508(D) such as: '"principa[2 write resource_b [connectivity mechanism]'", with a constraint 512 such as: connect! vity_mechanism=L AN.
(00901 Thus, in a described implementation, a general mechanism enables
fine-grained controls to be expressed on delegated access rights. By way of example but not limitation, fine-grained control over delegated access rights can be expressed with respect to the following:
• The resource(s) to which access is being delegated;
• The right(s) that can be exercised on those resources; The principal(s) to whom those rights are being delegated;
• The ability of a delegatee to further delegate those, or a subset of those, access rights (e.g., via transitive chaining); and
• Environmental restrictions (e.g., timespan, location, etc.) on the exercise of the delegated access rights (e.g., via fact qualifiers).
(0091) A delegation mechanism as described herein is capable of expressing
these delegation control factors using a uniform declarative representation that allows specification of both delegation policy and delegate rights. As illustrated in FIGS. 5 and 8 and as described above, the genera) form of security assertions is leveraged to create an example form for delegation authority assertions 614 that enables the expression of controlled delegation policies. The example format is repeated here for convenient reference:

asserlor says principal] delegation-directive-verb 'principal! verb-
phrase resource fact-qualifier\, ,f \i fact\, faclj, ..., faci„,
constrainti . „ .
In this form, the asserior is the authority who authorizes the delegation to be made;
principal! is the potential delegator who may make the delegation; and principall is
the delegatee.
[0092] Some example delegation policies include:
(1) The right for B to delegate read access to the file Foo for 8 hours to any
principal may be expressed as:
A says B can assert ";t read Foo [t}j2\' if (t2-tl) < 8Hrs . By controlling the values that the variable 'x' may bind to, the set of principals who may be delegatees may be restricted. For example, equality and inequality constraints may be applied to the variable 'x(2) The right for a principal p to delegate rights it holds to a resource Foo
to other principals may be expressed as:
A says p can assert "x v Foo" if/) v Foo . If B read|write Foo is true, then the above delegation policy implies A says B can assert '''x read]write Foo".
[0093J Delegation policies, such as the examples above, are combined with
asserted capabilities to create a full delegation. In the example scenario of FIG. 6, delegation granting assertion 616 is an asserted capability. Given the policy (1) above, if B also asserts "fi says C read Foo [0800,1200]", then would believe that C is allowed to read Foo during the indicated lime span. SimilarJy, given policy (2) above and the two assertions, ''A says B read Foo" and "S says C read Foo", A would believe that C is alJowed to read Foo.
(0094) With regard to the transitive chaining of delegation rights, a
mechanism is also described for controlling the ability for a delegatee to further delegate the access rights it has been granted. The following example set of assertions is presented to expand upon this concept:
(3) A says B can assert "x read Foo" ;
(4) B says C can assert ""x read Foo" ; and
(5) C says D read Foo ,
J0095] The question is whether or not A believes that D is authorized to read
Foo based on assertion (3), which only states that B has the right to delegate read

access to Foo. But, in this example, B has in turn asserted (4) that C has the right to delegate read access to Foo.
[0096] If one allows imcontrolled chaining, then thru logical deductions based
on these statements, the answer to the question is yes. This affirmative answer is because one can conclude "B says D read Foo" is valid by deduction using assertions (4) and (5). Based on that deduction and assertion (3), one can conclude that " say D read Foo" is valid. If, on the other hand, one disallows logical chaining thru deduced facts, then the answer to the question is no. When chaining is not allowed, one could only reach conclusions thru direct combination of assertion (3) with either assertion (4) or assertion (5), but not thru Vjoth (4) and (5).
(0097] In a described implementation, an example chaining delegation
mechanism enables precise control over this type of logical chaining by introducing a 'depth" indicator or parameter that modifies the delegation-directive verb (e.g., can assert). If one wishes to disallow logical chaining, then the depth indicator has a value of zero, and assertion (3) is rewritten as:
(3.1) A says B can asserto "x read Foo".
[00981 Ahematively, if one wanted to explicitly allow B to pass along the
delegation to exactly one more principal, then assertions (3), (4), and (5) are rewritten with the depth indicator having a value of one as:
(3.2) A says B can assert] "x read Foo" ;
(4.2) B says C can asserto " read Foo" ; and
(5.2) C says £) read Foo .
The depth indicator is set to a value of zero in assertion (4.2) to enforce that C is not
allowed to pass along the access rights it has been delegated, [fit were permitted to
do so, the chain of logical deductions needed to establish an assertion that is valid
with respect to assertion (3.2) would exceed the indicated allowed depth of 1. With
this approach, to enable an unbounded ability to pass along delegated access rights to
other principals, a depth indicator value of infinity may be used.
[0099| Thus, in an example implementation, the depth indicator may be set to
zero, infinity, or any positive integer. An example corresponding syntax is, respectively: can asserto, can assert, and can assert. This enables unbounded delegation (e.g., with the infinity) or bounded delegation with a precise setting to any desired transitive chaining depth (e.g., 0, 1.2, ...).

[0100] However, in another example implementation, the depth indicator may
only be set to zero or infinity. This enables (i) the prevention of any delegation
chaining (e.g., with the zero value) or (ii) unbounded delegation. In this alternative
example implementation, bounded but non-zero chaining may be enabled with nested
delegation-directive verbs, which is described in the following paragraph,
(OIOIj More specifically, using a "can assert" implementation, chained
delegation may be implemented with nesting using an assertion comporting with a form of: A says B can asserto x can asserto y can asserto z possesses group name=g. The preceding example is an explicit 3-level delegation. The number of delegation-directed verbs or level of nesting establishes the chaining depth. To reduce the use of depth indicators, either no chaining or unbounded chaining may be considered the default transitive chaining rule when there is not explicit indication. Nesting may also be used with depth indicators of positive integer values. Other combinations or derivations may be implemented.
[0102] FIG. 9 is a block diagram illustrating an example chained delegation
mechanism 600C from a functional perspective along with an example chained
delegation scenario. As illustrated, example chained delegation scenario includes
assertor 602, principal #1 604(1), principal #2 604(2), ..., principal #d 604(d). The
variable "d" is an integer corresponding to the chaining depth. The delegation
scenario also includes principal 606. right-granting ability 608, and right 610.
J0103] In a described implementation, assertor 602 delegates right-granting
ability 608 to principal #1 604(1). Principal #1 604(1) delegates right-granting ability 608 to principal #2 604(2). Principal #2 604(2) delegates right-granting ability 608 to principal #d 604(d), perhaps through other intermediate principals 604, as indicated by the ellipses. Principal #d 604(d) then grants right 610 to principal 606. Example general approaches to a security language implementation that enables chained delegation mechanism 600C are described herein above (e.g., the transitive chaining descriptions and examples above, as well as the general delegation authority assertion format 800). Example format approaches that are specific to a chained delegation mechanism are described below with reference to FIG. 10.
[0104| FIG- 10 is a block diagram illustrating two example format approaches
1000 for a chained delegation mechanism. Formal 1000(1) illustrates a delegation format having a depth indicator, and format 1000(2) illustrates a delegation format

utilizing nesting. By way of example only, the delegation-directive verb is realized
using a "can assert" impJemenlation in example format approaches 1000.
[0105] More specifically, format 1000(1) includes a principal #1 portion
502(1), a can assert portion 520, and a delegated fact portion 508(D). Fomiat 1000(1) also includes a chaining depth indicator 1002. Chaining depth indicator 1002 is associated with can assert portion 520. Chaining depth indicator 1002 may take on any value to establish the allowed transitive chaining depth. Examples from above include zero, infinity, and positive integers.
[0106] Formal 1000(2) includes a principal #1 portion 502(1), a can assen
portion 520, a principal #2 portion 502(2), a can assert portion 520, a principal #3 portion 502(3), a can assert portion 520, and a delegated fact portion 508(D). Although not shown, each can assert portion 520 of format 1000(2) may also be associated with a chaining depth indicator 1002. For example, such a chaining depth indicator 1002 may be set to zero to indicate that each individual can assert portion 520 of format 1000(2) does not allow transitive chaining (e.g., beyond that permitted by the nesting).
(0107] FIG. 11 is a flow diagram 1100 illustrating an example of a method for
creating a delegation authority assertion. Flow diagram 1100 includes seven (7) blocks 1102-1114. Although the actions of flow diagram 1100 may be performed in other environments and with a variety of hardware/software/firmware combinations, some of the features, components, and aspects of FIGS. 1-10 are used to illustrate an example of the method.
[0108) In a described implementation, at block 1102, a delegator principal and
a delegatee principal are specified. For example, a principal #1 604 and a principal #2
606 ma)' be identified with a principal factor 702 of a delegation mechanism 600.
10109] At block 1104, a verb phrase is specified. For example, a certain verb
phrase may be specified with a verb phrase factor 704. At block 1106, a resource is specified. For example, a particular resource 110 may be specified with resource factor 706. The verb phrase and resource may be combined to represent a right that may be granted from principal #1 604 to principal #2 606.
(0110! At block 1108, a chaining depth is specified. For example, in
accordance with transitive chaining factor 712, a chaining depth may be specified by way of a chaining depth indicator 1002 (to comport with assertion format approach

1000(1)) and/or a nested expression of multiple delegation-directive verbs (to comport with assertion formal approach 1000(2)).
[0111] At block 1110, a fact qualifier is specified. For example, at least one
environmental restriction or other fact qualifier factor 708 may be indicated to be
applied to any right with regard to the resource. Although not shown in FIG. H, a
given attribute with respect to one or both principals may also be specified (and
incorporated into the delegation authority assertion of block 1112). For example, it
may be specified that principal #1 604 and/or principal #2 606 must possess a given
attribute for a delegation to be permitted with attributes factor 710.
[0112] At block 1112, a delegation authority assertion with the specified
factors is formulated with a delegation-directive verb. For example, a delegation authority assertion 614 comporting with assertion format 800 and including a delegation-directive verb portion 520 may be formulated using any of the specified factors 702-712. For instance, a principal #1 portion 502(1), a principal #2 portion 502(2), a verb phrase portion 516, a resource portion 804, and fact qualifier] / portion(s) 806(1...f) may each be included as part of delegation authority assertion 614. Given attributes may be specified as needing to be possessed by an identified principal using one or more conditional factsj,. „ 508(1...n).
10113] At block 1114, the delegation authority assertion is added to a trust and
authorization policy. For example, delegation authority assertion 614 may be added to a trust and authorization policy 222. Thereafter, a delegation granting assertion 616 and/or any other relevant assertions may be combined into an assertion context within authorization context 212.
[0114] In a described implementation, delegation granting assertion 616, for
the delegation to be properly effected, also includes at least the particular resource,
the certain verb phrase, and the delegatee principal specified in the corresponding
delegated fact 508(D) (of FIG. 8) in delegation granting assertion 616. An
authorization query from authorization query table 224 is then evaluated in
conjunction with the assertion context in authorization engine 218 to determine an
authorization decision with respect to the particular resource 110.
[01I5] Four example delegation-related policy idioms are presented below.
Each corresponds to an example delegation type 714 (of FIG. 7). Specifically, attribute-based delegation 714(1), constrained delegafion 714(2), depth-bound delegafion 714(3), and width-bound delegation 714(4) examples are presented.

[0116] Attribute-Based Delegation Type 714(1): Attribute-based (as opposed
to identity-based) authorization enables collaboration between parties whose identities are initially unknown to each other. The authority to assert that a subject holds an attribute (such as being a student) may then be delegated to other parties, who in turn may be characterized by attributes rather than identity.
[0117] In the example below, students are entitled to a discount. The
expiration date of the student attribute can be checked with a constraint. The authority over the student attribute is delegated to holders of the university attribute, and authority over the university attribute is delegated to a known principal, the Board of Education.
Admin says x is entitled to discount if
X is a student till date,
currentTimeO date
Admin says wnfv can assertj, x is a student till (/o/e if
univ is a university
Admin says BoardOfEducation can assert, univ is a university
[0118] Constrained Delegation Type 714(2): Delegators may wish to restrict
the parameters of the delegated fact. This can be done with constraints. In the example below, an STS is given the right to issue tickets for accessing some resource for a specified validity period of no longer than eight hours.
Admin says STS can asserts- x has access from tl till t2 if [2 ■ ll < 8
hours
[0119] The delegation depth specified in the assertion above is unlimited, so
STS can in turn delegate the same right to some STS2. With STS's assertion below, Admin accepts tickets issued by STS2 with a validity period of at most eight hours, where the start date is not before 01/01/2007.
STS says STS2 can asserto x has access from // till i2 if tl > 01/01/2007

[0120] Depth-Bounded Delegation Type 714(3); In a described
implementation, the delegation-depth subscript of the can assert keyword can only be 0 (no re-delegation) or oo (unlimited re-delegation). Nevertheless, such an example security language can express any fixed integer delegation depth by nesting can assert. In the following example, Alice delegates the authority over is a friend facts to Bob and allows Bob to re-delegate one level further.
Alice says Bob can asserto x is a friend
Alice says Bob can asserto x can asserto y is a friend
[0121] Suppose Bob re-delegates to Charlie with the assertion "Bob says
Charlie can assert x is a friend". Now, "Alice says Eve is a friend" follows from "Charlie says Eve is a friend". Since Alice does not accept any longer delegation chains, Alice (in contrast to Bob) does not allow Charlie to re-delegate with
Charlie says Doris can asserto x is a friend
[0122] Furthermore, Charlie cannot circumvent the delegation depth restriction
with the following trick either, because the restriction also applies to conditional facts.
Charlie says x is a friend if x is Doris' friend
Charlie says Doris can assert0x is Doris' friend
[0123] Accordingly, if it is assumed that the only assertions by Alice and Bob
that mention the verbphrase x is a friend are those listed above, it can be shown that the resuh of the query Alice says x is a friend depends only of Charlie's assertions—not those of Doris for instance.
[0124] Width-Bounded Delegation Type 714(4): Suppose Alice wants to
delegate authority over is a friend facts to Bob. She does not care about the length of the delegation chain, but she requires every delegator in the chain to satisfy some property, e.g. to possess an email address from fabrikam.com. The following assertions implement this policy by encoding controlled transitive delegation using the can assert keyword with a 0 subscript. Principals with the is a delegator attribute are authorized by Alice to assert is a friend facts, and to transitively re-delegate this attribute, but only amongst principals with a matching email address,
Alice says x can asserto y is a friend if
X is a delegator

Alice says Bob is a delegator
Alice says x can asserto y is a delegator if
X: is a delegator,
y possesses Email email,
email matches *@fabrikam.com
[0125] The devices, actions, aspects, features, functions, procedures, modules,
data structures, protocols, components, etc. of FIGS. 1-11 are illustrated in diagrams
that are divided into multiple blocks. However, the order, interconnections,
interrelationships, layout, etc. in which FIGS. I-l 1 are described and/or shown are not
intended to be construed as a limitation, and any number of the blocks can be
modified, combined, rearranged, augmented, omitted, etc. in any manner to
implement one or more systems, methods, devices, procedures, media, apparatuses,
APIs, protocols, arrangements, etc, for controlling the delegation of rights.
[0126] Although systems, media, devices, methods, procedures, apparatuses,
mechanisms, schemes, approaches, processes, arrangements, and other implementations have been described in language specific to structural, logical, algorithmic, and functional features and/or diagrams, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.