What are the main differences between capability lists and access lists

Capability lists and access control lists (ACLs) are both methods used in computer security to control access to resources, but they differ in their approach and implementation. Here are the main differences between capability lists and access control lists:

1. Authorization Model:

   • Capability Lists: Capability lists follow the "capabilities-based" authorization model. In this model, each user or process holds a list of capabilities that grant specific permissions to access resources. These capabilities are typically unforgeable tokens or keys that can be presented to the system to prove authorization.
   • Access Control Lists: Access control lists follow the "discretionary access control" (DAC) model. In this model, each resource (such as a file or object) has an associated access control list specifying which users or groups are granted specific permissions (e.g., read, write, execute) on the resource.

2. Ownership:

   • Capability Lists: In capability-based systems, ownership of a capability implies authority over the associated resource. Users or processes can delegate capabilities to others, granting them access to resources.
   • Access Control Lists: Access control lists are typically associated with the resource itself rather than with individual users or processes. The owner of the resource can control the permissions granted to other users or groups through the ACL.

3. Granularity:

   • Capability Lists: Capability lists tend to be more fine-grained in terms of access control, as each capability grants specific permissions to access individual resources or perform specific operations.
   • Access Control Lists: Access control lists can be fine-grained or coarse-grained, depending on the granularity defined in the ACL entries. ACLs can specify permissions at the level of individual users, groups, or other entities.

4. Dynamic vs. Static:

   • Capability Lists: Capability-based systems often involve dynamic capabilities that can be created, transferred, and revoked dynamically during runtime. This flexibility allows for more dynamic access control policies.
   • Access Control Lists: Access control lists are typically static and defined at the time of resource creation or configuration. Changes to ACLs usually require administrative privileges and may involve modifying the resource's metadata.

5. Revocation:

   • Capability Lists: Capability-based systems can revoke access to a resource by simply removing or invalidating the associated capability from the user's or process's capability list.
   • Access Control Lists: Revoking access in ACL-based systems may require modifying the ACL entries or changing ownership of the resource, which may be more complex and may not be as immediate.

In summary, capability lists and access control lists represent different approaches to access control, with capability lists focusing on granting specific capabilities to users or processes and access control lists focusing on specifying permissions directly on resources. Each approach has its advantages and trade-offs, and the choice between them depends on the specific security requirements and design considerations of the system.