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The delegator dr can specify spacial constraint when it begins a delegation to direct
delegatee de, as shown in fig.3. In fact, dr can also specify constraints on each step of
delegation, which is called step-by-step control, see fig.3-I. O. Bandmann etc adopted
this kind of control in their delegation model [14]. The step-by-step control seems too
detailed to be useful in practical systems and may raise much difficulty in construct-
ing computation models [14].
According to the semantics of the relation ⇒ defined above, we can see that the
spacial constraint adopts the unitary control model, as shown in fig.3-II. The unitary
control model unifies the one-step constraint into more intuitionistic constraint and
overcomes the deficiencies of step-by-step control, while still provides enough flexi-
bility. Spacial constraint can be used both on DoA and DoC. Samples in section 4 will
illustrate the advantages of such constraint model. The semantics of valid delegation
path and relations of
and ⇒ will be defined by logic rules in section 3.
3 Rule-Based Policy Language
To validate the feasibility of our model, we design a policy specification language for
GCDM named REAL05 (Role-based Extensible Authorization Language, 2005 Ver-
sion). REAL05 is a declarative language based on Datalog C [15], which can be used
to specify policies as well as semantics.
Definition 6 (Rule). A rule in REAL05 takes the form of the following:
A.H ← A 1 .B 1 , A 2 .B 2 , … , A n .B n , Ψ,
where H, B 1 …B n are predicates with one or more parameters, A, A 1 ,…A n are entities.
H is the rule head, A i .B i (i=1…n) and Ψ constitute the rule body. Ψ is the constraint.
If n=0, the rule is called a constraint fact . The entity before each predicate is called
the principle of the predicate, which means the predicate is asserted by its principal.
The principle of the rule head is called the issuer of the rule. The rule can be read as:
to deduce A says H, we must deduce “A 1 says B 1 ”, “A 2 says B 2 ”, …, “A n says B n
and Ψ. The rules often need to be transferred across open networks and need to be
signed by its issuer. The signed rules are often called credentials .
3.1 Syntax
REAL05 can specify authorization, delegation and constrained delegation policies.
Table 1 shows the simplified syntax of REAL05. The undefined items such as 〈user-
defined-predicate〉, 〈entity〉, 〈name〉, 〈natural-number〉 〈constant〉 and 〈var〉 are user
defined predicate name, entity, name of permission or role, natural number and vari-
ables respectively.
Privileges . The privileges in REAL05 include permission (5) and roles (6). Permis-
sions have the same meaning as permissions defined in section 2.2. For example,
pm (read, file-a) may represent the privilege to read the file named “file-a”. The roles
group related permissions together and can express more scalable policies. There are
three types of roles in REAL05: dR, aR and sR.
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