Towards More Controllable and Practical Delegation - Computer Network Security - page 251

Table 1. Core Syntax of REAL05

(1) Predicate Name 〈pn〉 ::= canRequest | canHold | canActivate | hasActivated |canAdmin | canUse |
〈user-defined-predicate〉
(2) Predicate 〈p〉 ::= 〈entity〉.〈pn〉(〈list of v〉)
(3) Rule 〈rule〉 ::= 〈p〉. | 〈p〉 ← 〈c〉. | 〈p〉 ← 〈list of p〉. | 〈p〉 ← 〈list of p〉, 〈c〉.
(4) Query 〈Query〉 ::= ? ← 〈p〉.
(5) Permission 〈pm〉 ::= pm(〈name〉, 〈list of var〉)
(6) Role 〈role〉 ::= dR(〈rv〉) | aR(〈rv〉) | sR(〈rv〉)
(7) Role Variable 〈rv〉 ::= 〈entity〉, 〈name〉
(8) Parameter Vector 〈v〉 ::= 〈constant〉 | 〈var〉 | 〈entity〉 | 〈permission〉 | 〈role〉 | 〈dc〉
(9) List (macro) 〈list of X〉 ::= 〈X〉 | 〈list of X〉, 〈list of X〉
(10) Delegation Constraint 〈dc〉 ::= sc(〈scope〉, 〈depth〉, 〈scope〉) | ∅ | *
(11) Trust Scope 〈scope〉 ::= 〈role〉 | 〈scope〉 ∩ 〈scope〉 | {list of 〈entity〉} | {} | *
(12) Delegation Depth 〈depth〉 ::= 〈natural-number〉 | 0 | *
(14) Constraint 〈c〉 ::= 〈e〉 = 〈e〉 | 〈e〉 ≠ 〈e〉 | 〈e〉 ≤ 〈e〉 | 〈e〉 ≥ 〈e〉 | 〈e〉

〈e〉 | 〈c〉, 〈c〉
(15) Expression 〈e〉 ::= 〈constant〉 | 〈var〉 | 〈dc〉 | f(〈list of var〉) | 〈e〉 - 〈e〉 | 〈e〉 + 〈e〉 | 〈e〉 ∪ 〈e〉

⊃ 〈e〉 | 〈e〉 ⊆

y dR is a distributed role, e.g. dR (org, member) represents all the members in org.
In the rest of this paper, roles denote distributed roles by default.
y aR is an administrative role, representing the authority defined in section 2.2,
e.g. aR (org, member) is the administrative role for dR(org, member). Given a
role dr, its administrative role is denoted as aR (dr).
y sR is a session role, representing the capability defined in section 2.2, e.g.
sR(org, sid012) is the capability holding by the session identified by session ID
“sid012”. A user has to log on the server successfully before he can get a session
role.
Delegation Constraint . The delegation constraint (10) is a logical term and defines
the spacial constraint in section 2.3. Spacial constraint acts as parameters in predicates
when specifying policies. 〈scope〉 and 〈depth〉 can be “*”, which means no constraint.
〈dc〉 can be ∅ , which is equivalent to the constant sc ({}, 0, *).

Constraint . The constraints (14) are composed of constraint expressions (15) and
constraint predicates. The type of constants and variables in (15) can be integer, float,
entity and set of entities. Constraint expression can also be delegation constraints and
return values of functions. Constraint predicates include “=”, “≠”, “≤”, “≥”, “ ⊆ ” and

“ ⊃ ”, where “ ⊆ ” and “ ⊃ ” are binary predicates on entity sets and 〈dc〉 respectively.

Predicates . The predicates (2) are the policy items used to express authorization and
delegation policies. REAL05 has six reserved predicates:

y x.canRequest(y, pm) means that x allows entity y to access the resources con-
trolled by permission pm.
y x.canHold(dr, pm) means that x assigns role dr with permission pm.
y x.canActivate(y, dr) means that x allows entity y to activate the role dr, and y
will be assigned with all the permissions hold by dr.
y x.hasActivated(y, dr) means that entity y has logged on x and activated the role
dr successfully.