54 | | Encoding the policies may require more expressive ABAC rules than a GENI credential can encode. In the very short term, we can use the X.509 based formats to encode those more complex ABAC rules. In very short order we will define types of the existing credential formats to encode these rules. |
55 | | |
56 | | The rest of this page discusses the short term modifications to libabac that will be needed to support the existing GENI credentials. |
57 | | |
58 | | == GENI "privilege" credentials == |
59 | | |
60 | | The only type of GENI credential currently in use is the "privilege" credential. This credential assigns a principal (called the owner) one or more privileges with respect to another principal (called the target). The credential has an implicit issuer, the signer of the credential. The privileges are strings meaningful to the implementation. There is also a bit that allows delegation of the privilege. This section describes how to represent the semantics of the GENI credentials in ABAC statements. Libabac will import a GENI credential into ABAC statements internally and use those statements to make authorization decisions; the AM (relying party) will import the credentials and policy into libabac and ask libabac for the authorization decision. |
61 | | |
62 | | The AM's decision to allow Owner to exercize privilege on Target is expressed in ABAC as asking the prover if Owner has the AM.privilege(Target) attribute. For each Issuer that the AM trusts to authorize privilege(Target) the AM's policy includes the rule: |
| 55 | Aggregate Managers do not issue these credentials to users. They are elements of the local policy, encoded in a configuration file. While ABAC allows delegation here, for now lets assume a series of simple delegations. There are a set of issuers that each Aggregate Manager believes. For each Issuer that AM believes, it has a rule like this: |
77 | | Encoding these in ABAC is accomplished in two ways: |
78 | | * the right to delegate is encoded in an ABAC credential |
79 | | * the rules for valid delagation (that the delegator must have the privilege and the right to delegate) is expressed in the AM policies. |
80 | | |
81 | | An undelegated credential that can be delegated expands into ABAC statements of the form: |
82 | | |
83 | | {{{ |
84 | | Issuer.privilege(Target) <- Owner |
85 | | Issuer.can_delegete_privilege(Target) <- Owner |
86 | | }}} |
87 | | |
88 | | Each AM will include this line in its policy: |
89 | | |
90 | | {{{ |
91 | | Issuer.privilege(Target) <- Issuer.can_delegate_privilege(Target).privilege(Target) |
92 | | }}} |
93 | | |
94 | | That says that AM will treat a statement from a delegator as a statement from the issuer with respect to privilege on target. |
95 | | |
96 | | When converting a delegated credential into ABAC, both the credential itself and the credential in the parent element are imported using the rules above. This recurses. |
97 | | |
98 | | This can be expressed in [http://groups.geni.net/geni/attachment/wiki/GEC11Authorization/chase-abac-gec11.ppt "RT0 lite"] |
99 | | |
100 | | == "Speaks-For" and Delegation == |
101 | | |
102 | | Existing GENI credentials support delegation of privileges. Each privilege in a credential has a flag indicating whether the owner can further delegate the privilege to others by creating a similar credential and signing it. The new credential includes the credential that is the basis for delegation in the new credential's parent element. This recurses. |
103 | | |
104 | | One can imagine a system where a user gets only delegatable resources from Slice Authorities, AMs and other resource controllers and delegates them to tools for use. This has two major drawbacks: |
105 | | |
106 | | * Resource controllers must issue delegatable resources or force users to share identity with tools |
107 | | * Asking a tool to summarize the data about all resouces a user holds at a given source would require delegating rights to access each resource individually, which is cumbersome |
108 | | |
109 | | The solution that GENI is adopting is a "speaks-for" privilege. A credential bestowing that privilege from a user to a tool (a principal with a GID) allows the tool to act as the user. As with all privileges, it has an expiration, so this is not a complete aliasing. "Speaks-for" is independent of delegation, and by default GENI resource controllers will support it. |
110 | | |
111 | | == Expressing GENI privileges with speaks-for in ABAC == |
112 | | |
113 | | Here we describe the ABAC rules that describe the GENI policy as it stands. |
114 | | This section assumes one knows the [wiki:TIEDABACModel ABAC definitions], and the [http://groups.geni.net/geni/attachment/wiki/GEC11Authorization/chase-abac-gec11.ppt "RT0 lite"] encoding of RT1 single parameter attributes. (In a nutshell, an RT0 lite encoding of the RT1 credential Principal.Attribute(parameter) is Principal.attribute_parameter). |
115 | | |
116 | | For a given request at an Aggregate Manager, the Manager knows the principal making the request, the target of the request, and which privilege is required to execute it. It has a prover initialized with its policy (an ABAC context in [http://abac.deterlab.net libabac] terms). It adds any credentials in the request and asks the prover a yes/no question - "does the principal making this request have the proper privilege?" |
117 | | |
118 | | The first thing to encode in ABAC is "the proper privilege." The ABAC attribute {{{AM.privilege(Target)}}} means that AM believes principals in that set have privilege with respect to Target. For example, the resolve on a slice S would be {{{AM.resolve(S)}}}. When a principal (P) requests an operation that requires resolve rights on slice S, the Manager (AM) asks the prover if P is a member of {{{AM.resolve(S)}}} (or in other words, if P has the {{{AM.resolve(S)}}} attribute). |
119 | | |
120 | | Aggregate Managers do not issue these credentials themselves, so there are rules about who they believe. While ABAC allows delegation here, for now lets assume a series of simple delegations. There are a set of issuers that each Aggregate Manager believes. For each Issuer that AM believes, it has a rule like this: |
121 | | |
122 | | {{{ |
123 | | AM.privilege(Target) <- Issuer.privilege(Target) |
124 | | }}} |
125 | | |
126 | | Issuers, such as Slice Authorities and Clearinghoses, issue credentials to users. Because GENI allows all privileges to be passed around by "speaks-for" the ABAC for issuing a privilege to a user (P) looks like: |
| 71 | Because GENI allows all privileges to be passed around by "speaks-for" the ABAC for issuing a privilege to a user (P) looks like: |
142 | | To be concrete: if (in GENI terms) AM trusts Issuer about {{{resolve}}} on {{{Target}}}, Issuer has handed P a GENI credential assigning {{{resolve}}} on {{{Target}}}, and P has issued a "speaks-for" credential to tool T, and T makes a request including both credentials, AM has the following ABAC rules: |
| 87 | Note that this interprets the same credential format (GENI privilege credential) differently depending on the privilege being assigned (speaks-for). This is because of the implicit semantics of "speaks-for" buried in its definition. |
| 88 | |
| 89 | To be concrete: if (in GENI terms) AM trusts Issuer about {{{resolve}}} on {{{Target}}}, Issuer has handed P a GENI credential assigning {{{resolve}}} on {{{Target}}}, and P has issued a "speaks-for" credential to tool T, and T makes a request including both credentials, AM has the following ABAC rules in its prover: |
145 | | AM.resolve(Target) <- Issuer.resolve(Target) |
146 | | Issuer.resolve(Target) <- Issuer.speaks_for(P) |
147 | | Issuer.speaks_for(P) <- P |
148 | | Issuer.speaks_for(P) <- P.speaks_for(P) |
149 | | P.speaks_for(P) <- T |
| 92 | AM.resolve(Target) <- Issuer.resolve(Target) /* from static policy and RT1 lite expansion */ |
| 93 | Issuer.resolve(Target) <- Issuer.speaks_for(P) /* From Issuer GENI privilege credential */ |
| 94 | Issuer.speaks_for(P) <- P /* From Issuer GENI privilege credential */ |
| 95 | Issuer.speaks_for(P) <- P.speaks_for(P) /* From Issuer GENI privilege credential */ |
| 96 | P.speaks_for(P) <- T /* From User GENI privilege credential (speaks_for) */ |