RFC2704 - The KeyNote Trust-Management System Version 2

Network Working Group M. Blaze

Request for Comments: 2704 J. Feigenbaum

Category: Informational J. Ioannidis

AT&T Labs - Research

A. Keromytis

U. of Pennsylvania

September 1999

The KeyNote Trust-Management System Version 2

Status of this Memo

This memo provides information for the Internet community. It does

not specify an Internet standard of any kind. Distribution of this

memo is unlimited.

Abstract

This memo describes version 2 of the KeyNote trust-management system.

It specifies the syntax and semantics of KeyNote `assertions',

describes `action attribute' processing, and outlines the application

architecture into which a KeyNote implementation can be fit. The

KeyNote architecture and language are useful as building blocks for

the trust management ASPects of a variety of Internet protocols and

services.

1. IntrodUCtion

Trust management, introduced in the PolicyMaker system [BFL96], 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.

A trust-management system has five basic components:

* 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.

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.

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.

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.

For a general discussion of the use of trust management in

distributed system security, see [Bla99].

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.

In KeyNote:

* 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.

This document describes the KeyNote policy and credential assertion

language, the structure of KeyNote action descriptions, and the

KeyNote model of computation.

We assume that applications communicate with a locally trusted

KeyNote compliance checker via a `function call' style interface,

sending a collection of KeyNote policy and credential assertions plus

an action description as input and accepting the resulting policy

compliance value as output. However, the requirements of different

applications, hosts, and environments may give rise to a variety of

different interfaces to KeyNote compliance checkers; this document

does not aim to specify a complete compliance checker API.

2. KeyNote Concepts

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.

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.

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 in Section 3 of this

document.

KeyNote provides advice to applications about 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.

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.

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 in Section

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.

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.

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.

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 [Cro82]. A KeyNote

assertion contains a sequence of sections, called `fields', each of

which specifies 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:

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"

The meanings of the various sections are described in Sections 4 and

5 of this document.

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 in Section

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. A detailed discussion of

monotonicity and safety in trust management can be found in [BFL96]

and [BFS98].

3. Action Attributes

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.

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.

Action attribute names and values are represented by arbitrary-length

strings. KeyNote guarantees support of attribute names and values up

to 2048 characters long. The handling of longer attribute names or

values is not specified and is KeyNote-implementation-dependent.

Applications and assertions should therefore avoid depending on the

the use of attributes with names or values longer than 2048

characters. The length of an attribute value is represented by an

implementation-specific mechanism (e.g., NUL-terminated strings, an

explicit length field, etc.).

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".

Attribute names are of the form:

<AttributeID>:: {Any string starting with a-z, A-Z, or the

underscore character, followed by any number of

a-z, A-Z, 0-9, or underscore characters} ;

That is, 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.

The exact mechanism for passing the action attribute set to the

compliance checker is determined by the KeyNote implementation.

Depending on specific requirements, an implementation may provide a

mechanism for including the entire attribute set as an explicit

parameter of the query, or it may provide some form of callback

mechanism invoked as each attribute is dereferenced, e.g., for access

to kernel variables.

If an action attribute is not defined its value is considered to be

the empty string.

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:

Name Purpose

------------------------ ------------------------------------

_MIN_TRUST Lowest-order (minimum) compliance

value in query; see Section 5.1.

_MAX_TRUST Highest-order (maximum) compliance

value in query; see Section 5.1.

_VALUES Linearly ordered set of compliance

values in query; see Section 5.1.

Comma separated.

_ACTION_AUTHORIZERS Names of principals directly

authorizing action in query.

Comma separated.

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 Section 5.

The assignment and semantics of any other attribute names beginning

with "_" is unspecified and implementation-dependent.

The names of other attributes in the action attribute set are not

specified by KeyNote but must be agreed upon by the writers of any

policies and credentials that are to inter-operate in a specific

KeyNote query evaluation.

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.

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.

For example, an email application might reserve the app_domain

"RFC822-EMAIL" and might use the attributes named "address" (the

email 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.

Note that "RFC822-EMAIL" is a hypothetical example; such a name may

or may not appear in the actual registry with these or different

attributes. (Indeed, we recognize that the reality of email security

is considerably more complex than this example might suggest.)

4. KeyNote Assertion Syntax

In the following sections, the notation [X]* means zero or more

repetitions of character string X. The notation [X]+ means one or

more repetitions of X. The notation <X>* means zero or more

repetitions of non-terminal <X>. The notation <X>+ means one or more

repetitions of X, whereas <X>? means zero or one repetitions of X.

Nonterminal grammar symbols are enclosed in angle brackets. Quoted

strings in grammar productions represent terminals.

4.1 Basic Structure

<Assertion>:: <VersionField>? <AuthField> <LicenseesField>?

<LocalConstantsField>? <ConditionsField>?

<CommentField>? <SignatureField>? ;

All KeyNote assertions are encoded in ASCII.

KeyNote assertions are divided into sections, called `fields', that

serve various semantic functions. Each field starts with an

identifying label at the beginning of a line, followed by the ":"

character and the field's contents. There can be at most one field

per line.

A field may be continued over more than one line by indenting

subsequent lines with at least one ASCII SPACE or TAB character.

Whitespace (a SPACE, TAB, or NEWLINE character) separates tokens but

is otherwise ignored outside of quoted strings. Comments with a

leading octothorp character (see Section 4.2) may begin in any

column.

One mandatory field is required in all assertions:

Authorizer

Six optional fields may also appear:

Comment

Conditions

KeyNote-Version

Licensees

Local-Constants

Signature

All field names are case-insensitive. The "KeyNote-Version" field,

if present, appears first. The "Signature" field, if present,

appears last. Otherwise, fields may appear in any order. Each field

may appear at most once in any assertion.

Blank lines are not permitted in assertions. Multiple assertions

stored in a file (e.g., in application policy configurations),

therefore, can be separated from one another unambiguously by the use

of blank lines between them.

4.2 Comments

<Comment>:: "#" {ASCII characters} ;

The octothorp character ("#", ASCII 35 decimal) can be used to

introduce comments. Outside of quoted strings (see Section 4.3), all

characters from the "#" character through the end of the current line

are ignored. However, commented text is included in the computation

of assertion signatures (see Section 4.6.7).

4.3 Strings

A `string' is a lexical object containing a sequence of characters.

Strings may contain any non-NUL characters, including newlines and

nonprintable characters. Strings may be given as literals, computed

from complex expressions, or dereferenced from attribute names.

4.3.1 String Literals

<StringLiteral>:: "\"" {see description below} "\"" ;

A string literal directly represents the value of a string. String

literals must be quoted by preceding and following them with the

double-quote character (ASCII 34 decimal).

A printable character may be `escaped' inside a quoted string literal

by preceding it with the backslash character (ASCII 92 decimal)

(e.g., "like \"this\"."). This permits the inclusion of the double-

quote and backslash characters inside string literals.

A similar escape mechanism is also used to represent non-printable

characters. "\n" represents the newline character (ASCII character

10 decimal), "\r" represents the carriage-return character (ASCII

character 13 decimal), "\t" represents the tab character (ASCII

character 9 decimal), and "\f" represents the form-feed character

(ASCII character 12 decimal). A backslash character followed by a

newline suppresses all subsequent whitespace (including the newline)

up to the next non-whitespace character (this allows the continuation

of long string constants across lines). Un-escaped newline and

return characters are illegal inside string literals.

The constructs "\0o", "\0oo", and "\ooo" (where o represents any

octal digit) may be used to represent any non-NUL ASCII characters

with their corresponding octal values (thus, "\012" is the same as

"\n", "\101" is "A", and "\377" is the ASCII character 255 decimal).

However, the NUL character cannot be encoded in this manner; "\0",

"\00", and "\000" are converted to the strings "0", "00", and "000"

respectively. Similarly, all other escaped characters have the

leading backslash removed (e.g., "\a" becomes "a", and "\\" becomes

"\"). The following four strings are equivalent:

"this string contains a newline\n followed by one space."

"this str ing contains a newline\n followed by one space."

"this string contains a newline\012\040followed by one space."

4.3.2 String Expressions

In general, anywhere a quoted string literal is allowed, a `string

expression' can be used. A string expression constructs a string

from string constants, dereferenced attributes (described in Section

4.4), and a string concatenation operator. String expressions may be

parenthesized.

<StrEx>:: <StrEx> "." <StrEx> /* String concatenation */

<StringLiteral> /* Quoted string */

"(" <StrEx> ")"

<DerefAttribute> /* See Section 4.4 */

"$" <StrEx> ; /* See Section 4.4 */

The "$" operator has higher precedence than the "." operator.

4.4 Dereferenced Attributes

Action attributes provide the primary mechanism for applications to

pass information to assertions. Attribute names are strings from a

limited character set (<AttributeID> as defined in Section 3), and

attribute values are represented internally as strings. An attribute

is dereferenced simply by using its name. In general, KeyNote allows

the use of an attribute anywhere a string literal is permitted.

Attributes are dereferenced as strings by default. When required,

dereferenced attributes can be converted to integers or floating

point numbers with the type conversion operators "@" and "&". Thus,

an attribute named "foo" having the value "1.2" may be interpreted as

the string "1.2" (foo), the integer value 1 (@foo), or the floating

point value 1.2 (&foo).

Attributes converted to integer and floating point numbers are

represented according to the ANSI C `long' and `float' types,

respectively. In particular, integers range from -2147483648 to

2147483647, whilst floats range from 1.17549435E-38F to

3.40282347E+38F.

Any uninitialized attribute has the empty-string value when

dereferenced as a string and the value zero when dereferenced as an

integer or float.

Attribute names may be given literally or calculated from string

expressions and may be recursively dereferenced. In the simplest

case, an attribute is dereferenced simply by using its name outside

of quotes; e.g., the string value of the attribute named "foo" is by

reference to `foo' (outside of quotes). The "$<StrEx>" construct

dereferences the attribute named in the string expression <StrEx>.

For example, if the attribute named "foo" contains the string "bar",

the attribute named "bar" contains the string "xyz", and the

attribute "xyz" contains the string "qua", the following string

comparisons are all true:

foo == "bar"

$("foo") == "bar"

$foo == "xyz"

$(foo) == "xyz"

$$foo == "qua"

If <StrEx> evaluates to an invalid or uninitialized attribute name,

its value is considered to be the empty string (or zero if used as a

numeric).

The <DerefAttribute> token is defined as:

<DerefAttribute>:: <AttributeID> ;

4.5 Principal Identifiers

Principals are represented as ASCII strings called `Principal

Identifiers'. Principal Identifiers may be arbitrary labels whose

structure is not interpreted by the KeyNote system or they may encode

cryptographic keys that are used by KeyNote for credential signature

verification.

<KeyID> ;

4.5.1 Opaque Principal Identifiers

Principal Identifiers that are used by KeyNote only as labels are

said to be `opaque'. Opaque identifiers are encoded in assertions as

strings (see Section 4.3):

<OpaqueID>:: <StrEx> ;

Opaque identifier strings should not contain the ":" character.

4.5.2 Cryptographic Principal Identifiers

Principal Identifiers that are used by KeyNote as keys, e.g., to

verify credential signatures, are said to be `cryptographic'.

Cryptographic identifiers are also lexically encoded as strings:

<KeyID>:: <StrEx> ;

Unlike Opaque Identifiers, however, Cryptographic Identifier strings

have a special form. To be interpreted by KeyNote (for signature

verification), an identifier string should be of the form:

<IDString>:: <ALGORITHM>":"<ENCODEDBITS> ;

"ALGORITHM" is an ASCII substring that describes the algorithms to be

used in interpreting the key's bits. The ALGORITHM identifies the

major cryptographic algorithm (e.g., RSA [RSA78], DSA [DSA94], etc.),

structured format (e.g., PKCS1 [PKCS1]), and key bit encoding (e.g.,

HEX or BASE64). By convention, the ALGORITHM substring starts with

an alphabetic character and can contain letters, digits, underscores,

or dashes (i.e., it should match the regular expression "[a-zA-Z][a-

zA-Z0-9_-]*"). The IANA (or some other appropriate authority) will

provide a registry of reserved algorithm identifiers.

"ENCODEDBITS" is a substring of characters representing the key's

bits, the encoding and format of which depends on the ALGORITHM. By

convention, hexadecimal encoded keys use lower-case ASCII characters.

Cryptographic Principal Identifiers are converted to a normalized

canonical form for the purposes of any internal comparisons between

them; see Section 5.2.

Note that the keys used in examples throughout this document are

fictitious and generally much shorter than would be required for

security in practice.

4.6 KeyNote Fields

4.6.1 The KeyNote-Version Field

The KeyNote-Version field identifies the version of the KeyNote

assertion language under which the assertion was written. The

KeyNote-Version field is of the form

<VersionField>:: "KeyNote-Version:" <VersionString> ;

<IntegerLiteral> ;

where <VersionString> is an ASCII-encoded string. Assertions in

production versions of KeyNote use decimal digits in the version

representing the version number of the KeyNote language under which

they are to be interpreted. Assertions written to conform with this

document should be identified with the version string "2" (or the

integer 2). The KeyNote-Version field, if included, should appear

first.

4.6.2 The Local-Constants Field

This field adds or overrides action attributes in the current

assertion only. This mechanism allows the use of short names for

(frequently lengthy) cryptographic principal identifiers, especially

to make the Licensees field more readable. The Local-Constants field

is of the form:

<LocalConstantsField>:: "Local-Constants:" <Assignments> ;

<Assignments>:: /* can be empty */

<AttributeID> "=" <StringLiteral> <Assignments> ;

<AttributeID> is an attribute name from the action attribute

namespace as defined in Section 3. The name is available for use as

an attribute in any subsequent field. If the Local-Constants field

defines more than one identifier, it can occupy more than one line

and be indented. <StringLiteral> is a string literal as described in

Section 4.3. Attributes defined in the Local-Constants field

override any attributes with the same name passed in with the action

attribute set.

An attribute may be initialized at most once in the Local-Constants

field. If an attribute is initialized more than once in an

assertion, the entire assertion is considered invalid and is not

considered by the KeyNote compliance checker in evaluating queries.

4.6.3 The Authorizer Field

The Authorizer identifies the Principal issuing the assertion. This

field is of the form

<AuthField>:: "Authorizer:" <AuthID> ;

<DerefAttribute> ;

The Principal Identifier may be given directly or by reference to the

attribute namespace (as defined in Section 4.4).

4.6.4 The Licensees Field

The Licensees field identifies the principals authorized by the

assertion. More than one principal can be authorized, and

authorization can be distributed across several principals through

the use of `and' and threshold constructs. This field is of the form

<LicenseesField>:: "Licensees:" <LicenseesExpr> ;

<LicenseesExpr>:: /* can be empty */

<PrincExpr> ;

<PrincExpr>:: "(" <PrincExpr> ")"

<K>"-of(" <PrincList> ")" /* Threshold */

<DerefAttribute> ;

<PrincList> "," <PrincList> ;

<K>:: {Decimal number starting with a digit from 1 to 9} ;

The "&&" operator has higher precedence than the "" operator. <K>

is an ASCII-encoded positive decimal integer. If a <PrincList>

contains fewer than <K> principals, the entire assertion is omitted

from processing.

4.6.5 The Conditions Field

This field gives the `conditions' under which the Authorizer trusts

the Licensees to perform an action. `Conditions' are predicates that

operate on the action attribute set. The Conditions field is of the

form:

<ConditionsField>:: "Conditions:" <ConditionsProgram> ;

<ConditionsProgram>:: /* Can be empty */

<Clause> ";" <ConditionsProgram> ;

<Clause>:: <Test> "->" "{" <ConditionsProgram> "}"

<Test> ;

<Value>:: <StrEx> ;

<Test>:: <RelExpr> ;

<RelExpr>:: "(" <RelExpr> ")" /* Parentheses */

<RelExpr> "&&" <RelExpr> /* Logical AND */

<RelExpr> "" <RelExpr> /* Logical OR */

"!" <RelExpr> /* Logical NOT */

"true" /* case insensitive */

"false" ; /* case insensitive */

<IntEx> ">=" <IntEx> ;

<FloatEx> ">=" <FloatEx> ;

<StringRelExpr>:: <StrEx> "==" <StrEx> /* String equality */

<StrEx> "!=" <StrEx> /* String inequality */

<StrEx> "<" <StrEx> /* Alphanum. comparisons */

<StrEx> "~=" <RegExpr> ; /* Reg. expr. matching */

<IntEx>:: <IntEx> "+" <IntEx> /* Integer */

<IntEx> "^" <IntEx> /* Exponentiation */

"-" <IntEx>

"(" <IntEx> ")"

"@" <StrEx> ;

<FloatEx>:: <FloatEx> "+" <FloatEx> /* Floating point */

<FloatEx> "^" <FloatEx> /* Exponentiation */

"-" <FloatEx>

"(" <FloatEx> ")"

"&" <StrEx> ;

<IntegerLiteral>:: {Decimal number of at least one digit} ;

<FloatLiteral>:: <IntegerLiteral>"."<IntegerLiteral> ;

<StringLiteral> is a quoted string as defined in Section 4.3

<AttributeID> is defined in Section 3.

The operation precedence classes are (from highest to lowest):

{ (, ) }

{unary -, @, &, $}

{^}

{*, /, %}

{+, -, .}

Operators in the same precedence class are evaluated left-to-right.

Note the inability to test for floating point equality, as most

floating point implementations (hardware or otherwise) do not

guarantee accurate equality testing.

Also note that integer and floating point expressions can only be

used within clauses of condition fields, but in no other KeyNote

field.

The keyWords "true" and "false" are not reserved; they can be used as

attribute or principal identifier names (although this practice makes

assertions difficult to understand and is discouraged).

<RegExpr> is a standard regular expression, conforming to the POSIX

1003.2 regular expression syntax and semantics.

Any string expression (or attribute) containing the ASCII

representation of a numeric value can be converted to an integer or

float with the use of the "@" and "&" operators, respectively. Any

fractional component of an attribute value dereferenced as an integer

is rounded down. If an attribute dereferenced as a number cannot be

properly converted (e.g., it contains invalid characters or is empty)

its value is considered to be zero.

4.6.6 The Comment Field

The Comment field allows assertions to be annotated with information

describing their purpose. It is of the form

<CommentField>:: "Comment:" <text> ;

No interpretation of the contents of this field is performed by

KeyNote. Note that this is one of two mechanisms for including

comments in KeyNote assertions; comments can also be inserted

anywhere in an assertion's body by preceding them with the "#"

character (except inside string literals).

4.6.7 The Signature Field

The Signature field identifies a signed assertion and gives the

encoded digital signature of the principal identified in the

Authorizer field. The Signature field is of the form:

<SignatureField>:: "Signature:" <Signature> ;

<Signature>:: <StrEx> ;

The <Signature> string should be of the form:

<IDString>:: <ALGORITHM>":"<ENCODEDBITS> ;

The formats of the "ALGORITHM" and "ENCODEDBITS" substrings are as

described for Cryptographic Principal Identifiers in Section 4.4.2

The algorithm name should be the same as that of the principal

appearing in the Authorizer field. The IANA (or some other suitable

authority) will provide a registry of reserved names. It is not

necessary that the encodings of the signature and the authorizer key

be the same.

If the signature field is included, the principal named in the

Authorizer field must be a Cryptographic Principal Identifier, the

algorithm must be known to the KeyNote implementation, and the

signature must be correct for the assertion body and authorizer key.

The signature is computed over the assertion text, beginning with the

first field (including the field identifier string), up to (but not

including) the Signature field identifier. The newline preceding the

signature field identifier is the last character included in

signature calculation. The signature is always the last field in a

KeyNote assertion. Text following this field is not considered part

of the assertion.

The algorithms for computing and verifying signatures must be

configured into each KeyNote implementation and are defined and

documented separately.

Note that all signatures used in examples in this document are

fictitious and generally much shorter than would be required for

security in practice.

5. Query Evaluation Semantics

The KeyNote compliance checker finds and returns the Policy

Compliance Value of queries, as defined in Section 5.3, below.

5.1 Query Parameters

A KeyNote query has four parameters:

* 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.

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).

5.1.1 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.

5.1.2 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.

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.

5.2 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.

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.

Opaque identifiers are compared as case-sensitive strings.

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).

5.3 Policy Compliance Value Calculation

The Policy Compliance Value of a query is the Principal Compliance

Value of the principal named "POLICY". This value is defined as

follows:

5.3.1 Principal Compliance Value

The Compliance Value of a principal <X> is the highest order

(maximum) of:

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

- the Assertion Compliance Values of all assertions identifying

<X> in the Authorizer field.

5.3.2 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.

5.3.3 Assertion Compliance 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.

5.3.4 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.

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 defined Section 5.1.

If an assertion's Conditions field is missing entirely, its

Conditions Compliance Value is considered to be the _MAX_TRUST value,

as defined in Section 5.1.

The set of successful test clause values is calculated as follows:

Recall from the grammar of section 4.6.5 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

foo=="bar";

is equivalent to

foo=="bar" -> _MAX_TRUST;

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:

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)

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).

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.

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,

a=="b" -> { b=="c" -> "value1";

d=="e" -> "value2";

true -> "value3"; } ;

is equivalent to

(a=="b") && (b=="c") -> "value1";

(a=="b") && (d=="e") -> "value2";

(a=="b") -> "value3";

String comparisons are case-sensitive.

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.

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:

foo == "bar" -> {

@a == 1/0 -> "oneval"; # subclause 1

@a == 2 -> "anotherval"; # subclause 2

};

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.

An invalid <RegExpr> is considered a runtime error and causes the

test in which it occurs to be considered false.

5.3.5 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.

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.

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.

The licensees expression (as defined in Section 4.6.4) is evaluated

as follows:

* 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.

For example, consider the following Licensees field:

Licensees: ("alice" && "bob") "eve"

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".

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.

5.4 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).

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.

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.

5.5 Implementation Issues

Informally, the semantics of KeyNote evaluation can be thought of as

involving the construction a directed graph of KeyNote assertions

rooted at a POLICY assertion that connects with at least one of the

principals that requested the action.

Delegation of some authorization from principal <A> to a set of

principals <B> is expressed as an assertion with principal <A> given

in the Authorizer field, principal set <B> given in the Licensees

field, and the authorization to be delegated encoded in the

Conditions field. How the expression digraph is constructed is

implementation-dependent and implementations may use different

algorithms for optimizing the graph's construction. Some

implementations might use a `bottom up' traversal starting at the

principals that requested the action, others might follow a `top

down' approach starting at the POLICY assertions, and still others

might employ other heuristics entirely.

Implementations are encouraged to employ mechanisms for recording

exceptions (such as division by zero or syntax error), and reporting

them to the invoking application if requested. Such mechanisms are

outside the scope of this document.

6. Examples

In this section, we give examples of KeyNote assertions that might be

used in hypothetical applications. These examples are intended

primarily to illustrate features of KeyNote assertion syntax and

semantics, and do not necessarily represent the best way to integrate

KeyNote into applications.

In the interest of readability, we use much shorter keys than would

ordinarily be used in practice. Note that the Signature fields in

these examples do not represent the result of any real signature

calculation.

1. TRADITIONAL CA / EMAIL

A. A policy unconditionally authorizing RSA key abc123 for all

actions. This essentially defers the ability to specify

policy to the holder of the secret key corresponding to

abc123:

Authorizer: "POLICY"

Licensees: "RSA:abc123"

B. A credential assertion in which RSA Key abc123 trusts either

RSA key 4401ff92 (called `Alice') or DSA key d1234f (called

`Bob') to perform actions in which the "app_domain" is

"RFC822-EMAIL", where the "address" matches the regular

expression "^.*@keynote\.research\.att\.com$". In other

words, abc123 trusts Alice and Bob as certification

authorities for the keynote.research.att.com domain.

KeyNote-Version: 2

Local-Constants: Alice="DSA:4401ff92" # Alice's key

Bob="RSA:d1234f" # Bob's key

Authorizer: "RSA:abc123"

Licensees: Alice Bob

Conditions: (app_domain == "RFC822-EMAIL") &&

(address ~= # only applies to one domain

"^.*@keynote\\.research\\.att\\.com$");

Signature: "RSA-SHA1:213354f9"

C. A certificate credential for a specific user whose email

address is mab@keynote.research.att.com and whose name, if

present, must be "M. Blaze". The credential was issued by the

`Alice' authority (whose key is certified in Example B

above):

KeyNote-Version: 2

Authorizer: "DSA:4401ff92" # the Alice CA

Licensees: "DSA:12340987" # mab's key

Conditions: ((app_domain == "RFC822-EMAIL") &&

(name == "M. Blaze" name == "") &&

(address == "mab@keynote.research.att.com"));

Signature: "DSA-SHA1:ab23487"

D. Another certificate credential for a specific user, also

issued by the `Alice' authority. This example allows three

different keys to sign as jf@keynote.research.att.com (each

for a different cryptographic algorithm). This is, in

effect, three credentials in one:

KeyNote-Version: "2"

Authorizer: "DSA:4401ff92" # the Alice CA

Licensees: "DSA:abc991" # jf's DSA key

"RSA:cde773" # jf's RSA key

"BFIK:fd091a" # jf's BFIK key

Conditions: ((app_domain == "RFC822-EMAIL") &&

(name == "J. Feigenbaum" name == "") &&

(address == "jf@keynote.research.att.com"));

Signature: "DSA-SHA1:8912aa"

Observe that under policy A and credentials B, C and D, the

following action attribute sets are accepted (they return

_MAX_TRUST):

_ACTION_AUTHORIZERS = "dsa:12340987"

app_domain = "RFC822-EMAIL"

address = "mab@keynote.research.att.com"

and

_ACTION_AUTHORIZERS = "dsa:12340987"

app_domain = "RFC822-EMAIL"

address = "mab@keynote.research.att.com"

name = "M. Blaze"

while the following are not accepted (they return

_MIN_TRUST):

_ACTION_AUTHORIZERS = "dsa:12340987"

app_domain = "RFC822-EMAIL"

address = "angelos@dsl.cis.upenn.edu"

and

_ACTION_AUTHORIZERS = "dsa:abc991"

app_domain = "RFC822-EMAIL"

address = "mab@keynote.research.att.com"

name = "M. Blaze"

and

_ACTION_AUTHORIZERS = "dsa:12340987"

app_domain = "RFC822-EMAIL"

address = "mab@keynote.research.att.com"

name = "J. Feigenbaum"

2. WORKFLOW/ELECTRONIC COMMERCE

E. 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.

Authorizer: "POLICY"

Licensees: "RSA:dab212" # the CFO's key

Conditions: (app_domain=="SPEND") && (@dollars < 10000);

F. 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.

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"

G. According to this policy, any two signers from the list of

managers will do if @(dollars) < 1000:

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);

H. 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.

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"

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:

_ACTION_AUTHORIZERS = "DSA:978add"

app_domain = "SPEND"

dollars = "45"

unmentioned_attribute = "whatever"

and

_ACTION_AUTHORIZERS = "RSA:abc123,DSA:cde333"

app_domain = "SPEND"

dollars = "550"

The following return "ApproveAndLog":

_ACTION_AUTHORIZERS = "DSA:feed1234,DSA:cde333"

app_domain = "SPEND"

dollars = "5500"

and

_ACTION_AUTHORIZERS = "DSA:cde333"

app_domain = "SPEND"

dollars = "150"

However, the following return "Reject" (_MIN_TRUST):

_ACTION_AUTHORIZERS = "DSA:def975"

app_domain = "SPEND"

dollars = "550"

and

_ACTION_AUTHORIZERS = "DSA:cde333,DSA:978add"

app_domain = "SPEND"

dollars = "5500"

7. Trust-Management Architecture

KeyNote provides a simple mechanism for describing security policy

and representing credentials. It differs from traditional

certification systems in that the security model is based on binding

keys to predicates that describe what the key is authorized by policy

to do, rather than on resolving names. The infrastructure and

architecture to support a KeyNote system is therefore rather

different from that required for a name-based certification scheme.

The KeyNote trust-management architecture is based on that of

PolicyMaker [BFL96,BFS98].

It is important to understand the separation between the

responsibilities of the KeyNote system and those of the application

and other support infrastructure. A KeyNote compliance checker will

determine, based on policy and credential assertions, whether a

proposed action is permitted according to policy. The usefulness of

KeyNote output as a policy enforcement mechanism depends on a number

of factors:

* The action attributes and the assignment of their values must

reflect accurately the security requirements of the application.

Identifying the attributes to include in the action attribute set

is perhaps the most important task in integrating KeyNote into new

applications.

* The policy of the application must be correct and well-formed. In

particular, trust must be deferred only to principals that should,

in fact, be trusted by the application.

* The application itself must be trustworthy. KeyNote does not

directly enforce policy; it only provides advice to the

applications that call it. In other words, KeyNote assumes that

the application itself is trusted and that the policy assertions

it specifies are correct. Nothing prevents an application from

submitting misleading or incorrect assertions to KeyNote or from

ignoring KeyNote altogether.

It is also up to the application (or some service outside KeyNote) to

select the appropriate credentials and policy assertions with which

to run a particular query. Note, however, that even if inappropriate

credentials are provided to KeyNote, this cannot result in the

approval of an illegal action (as long as the policy assertions are

correct and the the action attribute set itself is correctly passed

to KeyNote).

KeyNote is monotonic; adding an assertion to a query can never result

in a query's having a lower compliance value that it would have had

without the assertion. Omitting credentials may, of course, result

in legal actions being disallowed. Selecting appropriate credentials

(e.g., from a distributed database or `key server') is outside the

scope of the KeyNote language and may properly be handled by a remote

client making a request, by the local application receiving the

request, or by a network-based service, depending on the application.

In addition, KeyNote does not itself provide credential revocation

services, although credentials can be written to expire after some

date by including a date test in the predicate. Applications that

require credential revocation can use KeyNote to help specify and

implement revocation policies. A future document will address

expiration and revocation services in KeyNote.

Because KeyNote is designed to support a variety of applications,

several different application interfaces to a KeyNote implementation

are possible. In its simplest form, a KeyNote compliance checker

would exist as a stand-alone application, with other applications

calling it as needed. KeyNote might also be implemented as a library

to which applications are linked. Finally, a KeyNote implementation

might run as a local trusted service, with local applications

communicating their queries via some interprocess communication

mechanism.

8. Security Considerations

Trust management is itself a security service. Bugs in or incorrect

use of a KeyNote compliance checker implementation could have

security implications for any applications in which it is used.

9. IANA Considerations

This document contains three identifiers to be maintained by the

IANA. This section explains the criteria to be used by the IANA to

assign additional identifiers in each of these lists.

9.1 app_domain Identifiers

The only thing required of IANA on allocation of these identifiers is

that they be unique strings. These strings are case-sensitive for

KeyNote purposes, however it is strongly recommended that IANA assign

different capitalizations of the same string only to the same

organization.

9.2 Public Key Format Identifiers

These strings uniquely identify a public key algorithm as used in the

KeyNote system for representing keys. Requests for assignment of new

identifiers must be accompanied by an RFC-style document that

describes the details of this encoding. Example strings are "rsa-

hex:" and "dsa-base64:". These strings are case-insensitive.

9.3 Signature Algorithm Identifiers

These strings uniquely identify a public key algorithm as used in the

KeyNote system for representing public key signatures. Requests for

assignment of new identifiers must be accompanied by an RFC-style

document that describes the details of this encoding. Example strings

are "sig-rsa-md5-hex:" and "sig-dsa-sha1-base64:". Note that all

such strings must begin with the prefix "sig-". These strings are

case-insensitive.

A. Acknowledgments

We thank Lorrie Faith Cranor (AT&T Labs - Research) and Jonathan M.

Smith (University of Pennsylvania) for their suggestions and comments

on earlier versions of this document.

B. Full BNF (alphabetical order)

<ALGORITHM>:: {see section 4.4.2} ;

<Assertion>:: <VersionField>? <AuthField> <LicenseesField>?

<LocalConstantsField>? <ConditionsField>?

<CommentField>? <SignatureField>? ;

;

<AttributeID>:: {Any string starting with a-z, A-Z, or the

underscore character, followed by any number of

a-z, A-Z, 0-9, or underscore characters} ;

<AuthField>:: "Authorizer:" <AuthID> ;

<AuthID>:: <PrincipalIdentifier> <DerefAttribute> ;

<Clause>:: <Test> "->" "{" <ConditionsProgram> "}"

<Test> "->" <Value> <Test> ;

<Comment>:: "#" {ASCII characters} ;

<CommentField>:: "Comment:" {Free-form text} ;

<ConditionsField>:: "Conditions:" <ConditionsProgram> ;

<ConditionsProgram>:: "" <Clause> ";" <ConditionsProgram> ;

<DerefAttribute>:: <AttributeID> ;

<ENCODEDBITS>:: {see section 4.4.2} ;

"(" <FloatEx> ")" <FloatLiteral> "&" <StrEx> ;

<FloatEx> ">=" <FloatEx> ;

<FloatLiteral>:: <IntegerLiteral>"."<IntegerLiteral> ;

<IDString>:: <ALGORITHM>":"<ENCODEDBITS> ;

<IntegerLiteral>:: {Decimal number of at least one digit} ;

"-" <IntEx> "(" <IntEx> ")" <IntegerLiteral>

"@" <StrEx> ;

<IntEx> "<=" <IntEx> <IntEx> ">=" <IntEx> ;

<K>:: {Decimal number starting with a digit from 1 to 9} ;

<KeyID>:: <StrEx> ;

<LicenseesExpr>:: "" <PrincExpr> ;

<LicenseesField>:: "Licensees:" <LicenseesExpr> ;

<LocalConstantsField>:: "Local-Constants:" <Assignments> ;

<OpaqueID>:: <StrEx> ;

<DerefAttribute> ;

<PrincipalIdentifier>:: <OpaqueID> <KeyID> ;

<PrincList> "," <PrincList> ;

<RegExpr>:: {POSIX 1003.2 Regular Expression}

"true" "false" ;

<Signature>:: <StrEx> ;

<SignatureField>:: "Signature:" <Signature> ;

<StrEx>:: <StrEx> "." <StrEx> <StringLiteral> "(" <StrEx> ")"

<DerefAttribute> "$" <StrEx> ;

<StringLiteral>:: {see section 4.3.1} ;

<StrEx> "~=" <RegExpr> ;

<Test>:: <RelExpr> ;

<Value>:: <StrEx> ;

<VersionField>:: "KeyNote-Version:" <VersionString> ;

<VersionString>:: <StringLiteral> <IntegerLiteral> ;

References

[BFL96] M. Blaze, J. Feigenbaum, J. Lacy. Decentralized Trust

Management. Proceedings of the 17th IEEE Symp. on Security

and Privacy. pp 164-173. IEEE Computer Society, 1996.

Available at

<FTP://ftp.research.att.com/dist/mab/policymaker.ps>

[BFS98] M. Blaze, J. Feigenbaum, M. Strauss. Compliance-Checking in

the PolicyMaker Trust-Management System. Proc. 2nd Financial

Crypto Conference. Anguilla 1998. LNCS #1465, pp 251-265,

Springer-Verlag, 1998. Available at

<ftp://ftp.research.att.com/dist/mab/pmcomply.ps>

[Bla99] M. Blaze, J. Feigenbaum, J. Ioannidis, A. Keromytis. The

Role of Trust Management in Distributed System Security.

Chapter in Secure Internet Programming: Security Issues for

Mobile and Distributed Objects (Vitek and Jensen, eds.).

Springer-Verlag, 1999. Available at

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[Cro82] Crocker, D., "Standard for the Format of ARPA Internet Text

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Authors' Addresses

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authors at:

Matt Blaze

AT&T Labs - Research

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EMail: mab@research.att.com

Joan Feigenbaum

AT&T Labs - Research

180 Park Avenue

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EMail: jf@research.att.com

John Ioannidis

AT&T Labs - Research

180 Park Avenue

Florham Park, New Jersey 07932-0971

EMail: ji@research.att.com

Angelos D. Keromytis

Distributed Systems Lab

CIS Department, University of Pennsylvania

200 S. 33rd Street

PhilaDelphia, Pennsylvania 19104-6389

EMail: angelos@dsl.cis.upenn.edu

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