path: root/lib/libkeynote/keynote.4

.\" $OpenBSD: keynote.4,v 1.15 2000/04/12 21:48:03 aaron Exp $
.\"
.\" The author of this code is Angelos D. Keromytis (angelos@dsl.cis.upenn.edu)
.\"
.\" This code was written by Angelos D. Keromytis in Philadelphia, PA, USA,
.\" in April-May 1998
.\"
.\" Copyright (C) 1998, 1999 by Angelos D. Keromytis.
.\"
.\" Permission to use, copy, and modify this software without fee
.\" is hereby granted, provided that this entire notice is included in
.\" all copies of any software which is or includes a copy or
.\" modification of this software.
.\" You may use this code under the GNU public license if you so wish. Please
.\" contribute changes back to the author.
.\"
.\" THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR
.\" IMPLIED WARRANTY. IN PARTICULAR, THE AUTHORS MAKES NO
.\" REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE
.\" MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR
.\" PURPOSE.
.\"
.Dd May 22, 1999
.Dt keynote 4
.\" .TH KeyNote 4 local
.Os
.Sh NAME
.Nm keynote
.Nd a trust-management system
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <regex.h>
.Fd #include <keynote.h>
.Fd Link options: -lkeynote -lm -lcrypto
.Sh DESCRIPTION
For more details on
.Nm KeyNote ,
see RFC 2704.
.Pp
Details on the API, assertion syntax, and command-line tool are given in
the man pages listed at the end of this manual.
.Pp
Trust management, introduced in the PolicyMaker system, is a unified
approach to specifying and interpreting security policies,
credentials, and relationships; it allows direct authorization of
security-critical actions. A trust-management system provides
standard, general-purpose mechanisms for specifying application
security policies and credentials. Trust-management credentials
describe a specific delegation of trust and subsume the role of public
key certificates; unlike traditional certificates, which bind keys to
names, credentials can bind keys directly to the authorization to
perform specific tasks.
.Pp
A trust-management system has five basic components:

.nf
* A language for describing `actions,' which are operations with
  security consequences that are to be controlled by the system.

* A mechanism for identifying `principals,' which are entities that
  can be authorized to perform actions.

* A language for specifying application `policies,' which govern the
  actions that principals are authorized to perform.

* A language for specifying `credentials,' which allow principals
  to delegate authorization to other principals.

* A `compliance checker,' which provides a service to applications
  for determining how an action requested by principals should be
  handled, given a policy and a set of credentials.
.fi

The trust-management approach has a number of advantages over other
mechanisms for specifying and controlling authorization, especially
when security policy is distributed over a network or is otherwise
decentralized.
.Pp
Trust management unifies the notions of security policy, credentials,
access control, and authorization. An application that uses a
trust-management system can simply ask the compliance checker whether
a requested action should be allowed. Furthermore, policies and
credentials are written in standard languages that are shared by all
trust-managed applications; the security configuration mechanism for
one application carries exactly the same syntactic and semantic
structure as that of another, even when the semantics of the
applications themselves are quite different.
.Pp
Trust-management policies are easy to distribute across networks,
helping to avoid the need for application-specific distributed policy
configuration mechanisms, access control lists, and certificate
parsers and interpreters.
.Pp
For a general discussion of the use of trust management in distributed
system security, see the papers listed at the end of this manual.
.Pp
KeyNote is a simple and flexible trust-management system designed to
work well for a variety of large- and small- scale Internet-based
applications. It provides a single, unified language for both local
policies and credentials. KeyNote policies and credentials, called
`assertions,' contain predicates that describe the trusted actions
permitted by the holders of specific public keys. KeyNote assertions
are essentially small, highly-structured programs. A signed assertion,
which can be sent over an untrusted network, is also called a
`credential assertion.' Credential assertions, which also serve the
role of certificates, have the same syntax as policy assertions but
are also signed by the principal delegating the trust.
.Pp
In KeyNote:

.nf
* Actions are specified as a collection of name-value pairs.

* Principal names can be any convenient string and can directly
  represent cryptographic public keys.

* The same language is used for both policies and credentials.

* The policy and credential language is concise, highly expressive,
  human readable and writable, and compatible with a variety of
  storage and transmission media, including electronic mail.

* The compliance checker returns an application-configured `policy
  compliance value' that describes how a request should be handled
  by the application.  Policy compliance values are always
  positively derived from policy and credentials, facilitating
  analysis of KeyNote-based systems.

* Compliance checking is efficient enough for high-performance and
  real-time applications.
.fi

In KeyNote, the authority to perform trusted actions is associated
with one or more `principals.' A principal may be a physical entity, a
process in an operating system, a public key, or any other convenient
abstraction. KeyNote principals are identified by a string called a
`Principal Identifier.' In some cases, a Principal Identifier will
contain a cryptographic key interpreted by the KeyNote system (e.g.,
for credential signature verification). In other cases, Principal
Identifiers may have a structure that is opaque to KeyNote.
.Pp
Principals perform two functions of concern to KeyNote: They request
`actions' and they issue `assertions.' Actions are any trusted
operations that an application places under KeyNote control.
Assertions delegate the authorization to perform actions to other
principals.
.Pp
Actions are described to the KeyNote compliance checker in terms of a
collection of name-value pairs called an `action attribute set.' The
action attribute set is created by the invoking application. Its
structure and format are described in detail elsewhere of this
document.
.Pp
KeyNote provides advice to applications on the interpretation of
policy with regard to specific requested actions. Applications invoke
the KeyNote compliance checker by issuing a `query' containing a
proposed action attribute set and identifying the principal(s)
requesting it. The KeyNote system determines and returns an
appropriate `policy compliance value' from an ordered set of possible
responses.
.Pp
The policy compliance value returned from a KeyNote query advises the
application how to process the requested action. In the simplest case,
the compliance value is Boolean (e.g., "reject" or "approve").
Assertions can also be written to select from a range of possible
compliance values, when appropriate for the application (e.g., "no
access", "restricted access", "full access"). Applications can
configure the relative ordering (from `weakest' to `strongest') of
compliance values at query time.
.Pp
Assertions are the basic programming unit for specifying policy and
delegating authority. Assertions describe the conditions under which a
principal authorizes actions requested by other principals. An
assertion identifies the principal that made it, which other
principals are being authorized, and the conditions under which the
authorization applies. The syntax of assertions is given
.Xr keynote 5 .
.Pp
A special principal, whose identifier is "POLICY", provides the root
of trust in KeyNote. "POLICY" is therefore considered to be authorized
to perform any action.
.Pp
Assertions issued by the "POLICY" principal are called `policy
assertions' and are used to delegate authority to otherwise untrusted
principals. The KeyNote security policy of an application consists of
a collection of policy assertions.
.Pp
When a principal is identified by a public key, it can digitally sign
assertions and distribute them over untrusted networks for use by
other KeyNote compliance checkers. These signed assertions are also
called `credentials,' and serve a role similar to that of traditional
public key certificates. Policies and credentials share the same
syntax and are evaluated according to the same semantics. A principal
can therefore convert its policy assertions into credentials simply by
digitally signing them.
.Pp
KeyNote is designed to encourage the creation of human-readable
policies and credentials that are amenable to transmission and storage
over a variety of media. Its assertion syntax is inspired by the
format of RFC822-style message headers. A KeyNote assertion contains a
sequence of sections, called `fields,' each of which specifying one
aspect of the assertion's semantics. Fields start with an identifier
at the beginning of a line and continue until the next field is
encountered. For example:

.nf
  KeyNote-Version: 2
  Comment: A simple, if contrived, email certificate for user mab
  Local-Constants:  ATT_CA_key = "RSA:acdfa1df1011bbac"
                    mab_key = "DSA:deadbeefcafe001a"
  Authorizer: ATT_CA_key
  Licensees: mab_key
  Conditions: ((app_domain == "email")  # valid for email only
            && (address == "mab@research.att.com"));
  Signature: "RSA-SHA1:f00f2244"
.fi

For the exact meanings of all the fields, see the RFC reference at the
end of this manual, and/or
.Xr keynote 5 .
.Pp
KeyNote semantics resolve the relationship between an application's
policy and actions requested by other principals, as supported by
credentials. The KeyNote compliance checker processes the assertions
against the action attribute set to determine the policy compliance
value of a requested action. These semantics are defined later in this
document.
.Pp
An important principle in KeyNote's design is `assertion
monotonicity'; the policy compliance value of an action is always
positively derived from assertions made by trusted principals.
Removing an assertion never results in increasing the compliance value
returned by KeyNote for a given query. The monotonicity property can
simplify the design and analysis of complex network-based security
protocols; network failures that prevent the transmission of
credentials can never result in spurious authorization of dangerous
actions.
.Pp
Trusted actions to be evaluated by KeyNote are described by a
collection of name-value pairs called the `action attribute set'.
Action attributes are the mechanism by which applications communicate
requests to KeyNote and are the primary objects on which KeyNote
assertions operate. An action attribute set is passed to the KeyNote
compliance checker with each query.
.Pp
Each action attribute consists of a name and a value. The semantics of
the names and values are not interpreted by KeyNote itself; they vary
from application to application and must be agreed upon by the writers
of applications and the writers of the policies and credentials that
will be used by them.
.Pp
Action attribute names and values are represented by arbitrary-length
strings. KeyNote guarantees support of attribute names and values up
to 2048 characters long. Applications and assertions should therefore
avoid depending on the use of attributes with names or values
longer than 2048 characters.
.Pp
Attribute values are inherently untyped and are represented as
character strings by default. Attribute values may contain any non-
NUL ASCII character. Numeric attribute values should first be
converted to an ASCII text representation by the invoking application,
e.g., the value 1234.5 would be represented by the string "1234.5".
.Pp
An <AttributeID> begins with an alphabetic or underscore character and
can be followed by any number of alphanumerics and underscores.
Attribute names are case-sensitive.
.Pp
If an action attribute is not defined its value is considered to be
the empty string.
.Pp
Attribute names beginning with the "_" character are reserved for use
by the KeyNote runtime environment and cannot be passed from
applications as part of queries. The following special attribute names
are used:

.Bl -tag -width indent
.It _MIN_TRUST
Lowest-order (minimum) compliance value in query.
.It _MAX_TRUST
Highest-order (maximum) compliance value in query.
.It _VALUES
Linearly ordered set of compliance value in query.
.It _ACTION_AUTHORIZERS
Names of principals directly authorizing action in query. Comma
separated.
.El
.Pp
In addition, attributes with names of the form "_<N>", where <N> is an
ASCII-encoded integer, are used by the regular expression matching
mechanism described in
.Xr keynote 5 .
.Pp
By convention, the name of the application domain over which action
attributes should be interpreted is given in the attribute named
"app_domain". The IANA (or some other suitable authority) will provide
a registry of reserved app_domain names. The registry will list the
names and meanings of each application's attributes.
.Pp
The app_domain convention helps to ensure that credentials are
interpreted as they were intended. An attribute with any given name
may be used in many different application domains but might have
different meanings in each of them. However, the use of a global
registry is not always required for small-scale, closed applications;
the only requirement is that the policies and credentials made
available to the KeyNote compliance checker interpret attributes
according to the same semantics assumed by the application that
created them.
.Pp
For example, an email application might reserve the app_domain
"RFC822-EMAIL" and might use the attributes named "address" (the mail
address of a message's sender), "name" (the human name of the message
sender), and any "organization" headers present (the organization
name). The values of these attributes would be derived in the obvious
way from the email message headers. The public key of the message's
signer would be given in the "_ACTION_AUTHORIZERS" attribute.
.Pp
.Sh QUERY SEMANTICS
The discussion in the following sections assume some familiarity with
assertion syntax. Please refer to
.Xr keynote 5
for more details on the syntax.
.Pp
.Sh QUERY PARAMETERS
A KeyNote query has four parameters:

.nf
* The identifier of the principal(s) requesting the action.

* The action attribute set describing the action.

* The set of compliance values of interest to the application,
  ordered from _MIN_TRUST to _MAX_TRUST

* The policy and credential assertions that should be included in
  the evaluation.
.fi

The mechanism for passing these parameters to the KeyNote evaluator is
application dependent. In particular, an evaluator might provide for
some parameters to be passed explicitly, while others are looked up
externally (e.g., credentials might be looked up in a network- based
distribution system), while still others might be requested from the
application as needed by the evaluator, through a `callback' mechanism
(e.g., for attribute values that represent values from among a very
large namespace).
.Pp
.Sh ACTION REQUESTER
At least one Principal must be identified in each query as the
`requester' of the action. Actions may be requested by several
principals, each considered to have individually requested it. This
allows policies that require multiple authorizations, e.g., `two
person control'. The set of authorizing principals is made available
in the special attribute "_ACTION_AUTHORIZERS"; if several principals
are authorizers, their identifiers are separated with commas.
.Pp
.Sh ORDERED COMPLIANCE VALUE SET
The set of compliance values of interest to an application (and their
relative ranking to one another) is determined by the invoking
application and passed to the KeyNote evaluator as a parameter of the
query. In many applications, this will be Boolean, e.g., the ordered
sets {FALSE, TRUE} or {REJECT, APPROVE}. Other applications may
require a range of possible values, e.g., {No_Access, Limited_Access,
Full_Access}. Note that applications should include in this set only
compliance value names that are actually returned by the assertions.
.Pp
The lowest-order and highest-order compliance value strings given in
the query are available in the special attributes named "_MIN_TRUST"
and "_MAX_TRUST", respectively. The complete set of query compliance
values is made available in ascending order (from _MIN_TRUST to
_MAX_TRUST) in the special attribute named "_VALUES". Values are
separated with commas; applications that use assertions that make use
of the _VALUES attribute should therefore avoid the use of compliance
value strings that themselves contain commas.
.Pp
.Sh PRINCIPAL IDENTIFIER NORMALIZATION
Principal identifier comparisons among Cryptographic Principal
Identifiers (that represent keys) in the Authorizer and Licensees
fields or in an action's direct authorizers are performed after
normalizing them by conversion to a canonical form.
.Pp
Every cryptographic algorithm used in KeyNote defines a method for
converting keys to their canonical form and that specifies how the
comparison for equality of two keys is performed. If the algorithm
named in the identifier is unknown to KeyNote, the identifier is
treated as opaque.
.Pp
Opaque identifiers are compared as case-sensitive strings.
.Pp
Notice that use of opaque identifiers in the Authorizer field requires
that the assertion's integrity be locally trusted (since it cannot be
cryptographically verified by the compliance checker).
.Pp

.Sh POLICY COMPLIANCE VALUE CALCULATION
The Policy Compliance Value of a query is the Principal Compliance
Value of the principal named "POLICY".
.Pp
.Sh PRINCIPAL COMPLIANCE VALUE
The Compliance Value of a principal <X> is the highest order (maximum)
of:

.nf
- the Direct Authorization Value of principal <X>; and

- the Assertion Compliance Values of all assertions identifying
  <X> in the Authorizer field.
.fi
.Sh DIRECT AUTHORIZATION VALUE
The Direct Authorization Value of a principal <X> is _MAX_TRUST if <X>
is listed in the query as an authorizer of the action. Otherwise, the
Direct Authorization Value of <X> is _MIN_TRUST.
.Pp
.Sh ASSERTION COMPLIANC VALUE
The Assertion Compliance Value of an assertion is the lowest order
(minimum) of the assertion's Conditions Compliance Value and its
Licensee Compliance Value.
.Pp
.Sh CONDITIONS COMPLIANCE VALUE
The Conditions Compliance Value of an assertion is the highest-order
(maximum) value among all successful clauses listed in the conditions
section.
.Pp
If no clause's test succeeds or the Conditions field is empty, an
assertion's Conditions Compliance Value is considered to be the
_MIN_TRUST value, as described previously.
.Pp
If an assertion's Conditions field is missing entirely, its Conditions
Compliance Value is considered to be the _MAX_TRUST value, as defined
previously.
.Pp
The set of successful test clause values is calculated as follows:
.Pp
Recall from the grammar of the Conditions field (see
.Xr keynote 5
for more details) that each clause in the conditions section has two
logical parts: a `test' and an optional `value', which, if present, is
separated from the test with the "->" token. The test subclause is a
predicate that either succeeds (evaluates to logical `true') or fails
(evaluates to logical `false'). The value subclause is a string
expression that evaluates to one value from the ordered set of
compliance values given with the query. If the value subclause is
missing, it is considered to be _MAX_TRUST. That is, the clause
.Bd -literal
       foo=="bar";
.Ed

is equivalent to
.Bd literal
       foo=="bar" -> _MAX_TRUST;
.Ed

If the value component of a clause is present, in the simplest case it
contains a string expression representing a possible compliance value.
For example, consider an assertion with the following Conditions
field:
.Bd -literal
       Conditions:
          @user_id == 0 -> "full_access";             # clause (1)
          @user_id < 1000 -> "user_access";           # clause (2)
          @user_id < 10000 -> "guest_access";         # clause (3)
          user_name == "root" -> "full_access";       # clause (4)
.Ed

Here, if the value of the "user_id" attribute is "1073" and the
"user_name" attribute is "root", the possible compliance value set
would contain the values "guest_access" (by clause (3)) and
"full_access" (by clause (4)). If the ordered set of compliance values
given in the query (in ascending order) is {"no_access",
"guest_access", "user_access", "full_access"}, the Conditions
Compliance Value of the assertion would be "full_access" (because
"full_access" has a higher-order value than "guest_access"). If the
"user_id" attribute had the value "19283" and the "user_name"
attribute had the value "nobody", no clause would succeed and the
Conditions Compliance Value would be "no_access", which is the
lowest-order possible value (_MIN_TRUST).
.Pp
If a clause lists an explicit value, its value string must be named in
the query ordered compliance value set. Values not named in the query
compliance value set are considered equivalent to _MIN_TRUST.
.Pp
The value component of a clause can also contain recursively-nested
clauses. Recursively-nested clauses are evaluated only if their parent
test is true. That is,
.Bd -literal
       a=="b" ->  { b=="c" -> "value1";
                    d=="e"  -> "value2";
                    true -> "value3"; } ;
.Ed

is equivalent to
.Bd -literal
       (a=="b") && (b=="c") -> "value1";
       (a=="b") && (d=="e") -> "value2";
       (a=="b") -> "value3";
.Ed

Notice that string comparisons are case-sensitive.
.Pp
A regular expression comparison ("~=") is considered true if the
left-hand-side string expression matches the right-hand-side regular
expression. If the POSIX regular expression group matching scheme is
used, the number of groups matched is placed in the temporary meta-
attribute "_0" (dereferenced as _0), and each match is placed in
sequence in the temporary attributes (_1, _2, ..., _N). These
match-attributes' values are valid only within subsequent references
made within the same clause. Regular expression evaluation is case-
sensitive.
.Pp
A runtime error occurring in the evaluation of a test, such as
division by zero or an invalid regular expression, causes the test to
be considered false. For example:
.Bd -literal
      foo == "bar" -> {
                        @a == 1/0 -> "oneval";    # subclause 1
                        @a == 2 -> "anotherval";  # subclause 2
                      };
.Ed

Here, subclause 1 triggers a runtime error. Subclause 1 is therefore
false (and has the value _MIN_TRUST). Subclause 2, however, would be
evaluated normally.
.Pp
An invalid <RegExpr> is considered a runtime error and causes the test
in which it occurs to be considered false.
.Pp
.Sh LICENSEE COMPLIANCE VALUE
The Licensee Compliance Value of an assertion is calculated by
evaluating the expression in the Licensees field, based on the
Principal Compliance Value of the principals named there.
.Pp
If an assertion's Licensees field is empty, its Licensee Compliance
Value is considered to be _MIN_TRUST. If an assertion's Licensees
field is missing altogether, its Licensee Compliance Value is
considered to be _MAX_TRUST.
.Pp
For each principal named in the Licensees field, its Principal
Compliance Value is substituted for its name. If no Principal
Compliance Value can be found for some named principal, its name is
substituted with the _MIN_TRUST value.
.Pp
The licensees expression (see
.Xr keynote 5 )
is evaluated as follows:

.nf
* A "(...)" expression has the value of the enclosed subexpression.

* A "&&" expression has the lower-order (minimum) of its two
  subexpression values.

* A "||" expression has the higher-order (maximum) of its two
  subexpression values.

* A "<K>-of(<List>)" expression has the K-th highest order
  compliance value listed in <list>.  Values that appear multiple
  times are counted with multiplicity.  For example, if K = 3 and
  the orders of the listed compliance values are (0, 1, 2, 2, 3),
  the value of the expression is the compliance value of order 2.
.fi

For example, consider the following Licensees field:
.Bd -literal
        Licensees: ("alice" && "bob") || "eve"
.Ed

If the Principal Compliance Value is "yes" for principal "alice", "no"
for principal "bob", and "no" for principal "eve", and "yes" is higher
order than "no" in the query's Compliance Value Set, then the
resulting Licensee Compliance Value is "no".
.Pp
Observe that if there are exactly two possible compliance values
(e.g., "false" and "true"), the rules of Licensee Compliance Value
resolution reduce exactly to standard Boolean logic.
.Pp
.Sh ASSERTION MANAGEMENT
Assertions may be either signed or unsigned. Only signed assertions
should be used as credentials or transmitted or stored on untrusted
media. Unsigned assertions should be used only to specify policy and
for assertions whose integrity has already been verified as conforming
to local policy by some mechanism external to the KeyNote system
itself (e.g., X.509 certificates converted to KeyNote assertions by a
trusted conversion program).
.Pp
Implementations that permit signed credentials to be verified by the
KeyNote compliance checker generally provide two `channels' through
which applications can make assertions available. Unsigned,
locally-trusted assertions are provided over a `trusted' interface,
while signed credentials are provided over an `untrusted' interface.
The KeyNote compliance checker verifies correct signatures for all
assertions submitted over the untrusted interface. The integrity of
KeyNote evaluation requires that only assertions trusted as reflecting
local policy are submitted to KeyNote via the trusted interface.
.Pp
Note that applications that use KeyNote exclusively as a local policy
specification mechanism need use only trusted assertions. Other
applications might need only a small number of infrequently changed
trusted assertions to `bootstrap' a policy whose details are specified
in signed credentials issued by others and submitted over the
untrusted interface.
.Pp
.Sh EXAMPLES
A policy that delegates authority for the "SPEND" application domain
to RSA key dab212 when the amount given in the "dollars" attribute is
less than 10000.
.Bd -literal
        Authorizer: "POLICY"
        Licensees: "RSA:dab212"  # the CFO's key
        Conditions: (app_domain=="SPEND") && (@dollars < 10000);
.Ed

RSA key dab212 delegates authorization to any two signers, from a
list, one of which must be DSA key feed1234 in the "SPEND" application
when @dollars < 7500. If the amount in @dollars is 2500 or greater,
the request is approved but logged.
.Bd -literal
        KeyNote-Version: 2
        Comment: This credential specifies a spending policy
        Authorizer: "RSA:dab212"        # the CFO
        Licensees: "DSA:feed1234" &&    # The vice president
                       ("RSA:abc123" || # middle manager #1
                        "DSA:bcd987" || # middle manager #2
                        "DSA:cde333" || # middle manager #3
                        "DSA:def975" || # middle manager #4
                        "DSA:978add")   # middle manager #5
        Conditions: (app_domain=="SPEND")  # note nested clauses
                      -> { (@(dollars) < 2500)
                             -> _MAX_TRUST;
                           (@(dollars) < 7500)
                             -> "ApproveAndLog";
                         };
        Signature: "RSA-SHA1:9867a1"
.Ed

According to this policy, any two signers from the list of managers
will do if @(dollars) < 1000:
.Bd -literal
        KeyNote-Version: 2
        Authorizer: "POLICY"
        Licensees: 2-of("DSA:feed1234", # The VP
                        "RSA:abc123",   # Middle management clones
                        "DSA:bcd987",
                        "DSA:cde333",
                        "DSA:def975",
                        "DSA:978add")
        Conditions: (app_domain=="SPEND") &&
                    (@(dollars) < 1000);
.Ed

A credential from dab212 with a similar policy, but only one signer is
required if @(dollars) < 500. A log entry is made if the amount is at
least 100.
.Bd -literal
        KeyNote-Version: 2
        Comment: This one credential is equivalent to six separate
                 credentials, one for each VP and middle manager.
                 Individually, they can spend up to $500, but if
                 it's $100 or more, we log it.
        Authorizer: "RSA:dab212"      # From the CFO
        Licensees: "DSA:feed1234" ||  # The VP
                   "RSA:abc123" ||    # The middle management clones
                   "DSA:bcd987" ||
                   "DSA:cde333" ||
                   "DSA:def975" ||
                   "DSA:978add"
        Conditions: (app_domain="SPEND")  # nested clauses
                      -> { (@(dollars) < 100) -> _MAX_TRUST;
                           (@(dollars) < 500) -> "ApproveAndLog";
                         };
        Signature: "RSA-SHA1:186123"
.Ed

Assume a query in which the ordered set of Compliance Values is
{"Reject", "ApproveAndLog", "Approve"}. Under policies E and G, and
credentials F and H, the Policy Compliance Value is "Approve"
(_MAX_TRUST) when:
.Bd -literal
        _ACTION_AUTHORIZERS = "DSA:978add"
        app_domain = "SPEND"
        dollars = "45"
        unmentioned_attribute = "whatever"
    and
        _ACTION_AUTHORIZERS = "RSA:abc123,DSA:cde333"
        app_domain = "SPEND"
        dollars = "550"
.Ed

The following return "ApproveAndLog":
.Bd -literal
        _ACTION_AUTHORIZERS = "DSA:feed1234,DSA:cde333"
        app_domain = "SPEND"
        dollars = "5500"
    and
        _ACTION_AUTHORIZERS = "DSA:cde333"
        app_domain = "SPEND"
        dollars = "150"
.Ed

However, the following return "Reject" (_MIN_TRUST):
.Bd -literal
        _ACTION_AUTHORIZERS = "DSA:def975"
        app_domain = "SPEND"
        dollars = "550"
    and
        _ACTION_AUTHORIZERS = "DSA:cde333,DSA:978add"
        app_domain = "SPEND"
        dollars = "5500"
.Ed
.Pp
.Sh FILES
.Fd keynote.h
.Fd libkeynote.a
.Sh SEE ALSO
.Xr keynote 1 ,
.Xr keynote 3 ,
.Xr keynote 5
.Bl -tag -width "AAAAAAA"
.It ``The KeyNote Trust-Management System, Version 2''
M. Blaze, J. Feigenbaum, A. D. Keromytis,
Internet Drafts, RFC 2704.
.It ``Decentralized Trust Management''
M. Blaze, J. Feigenbaum, J. Lacy,
1996 IEEE Conference on Privacy and Security
.It ``Compliance-Checking in the PolicyMaker Trust Management System''
M. Blaze, J. Feigenbaum, M. Strauss,
1998 Financial Crypto Conference
.El
.Sh AUTHOR
Angelos D. Keromytis (angelos@dsl.cis.upenn.edu)
.Sh WEB PAGE
http://www.cis.upenn.edu/~keynote
.Sh BUGS
None that we know of.
If you find any, please report them at
.Bd -literal -offset indent -compact
keynote@research.att.com
.Ed