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Steven Allen edited this page Nov 26, 2012 · 1 revision

Definitions

  • Group Key Pair (Kpg, Ksg): The group's key pair (controlled by the producer).
  • User Key Pair (Kpu, Ksu): The user's key pair.
  • Membership Signature (Sm): The group key's signature on the member's public key Sm = Ksg(Kpu)

Questions

  1. Are the membership signatures sensitive information? That is, if one knows A signature, is one able to determine: a. The group that produced the signature. b. The signed public key.
  2. Is there any way to have expiring subkeys for user keys? That is, can membership signatures be generated on a master key and be verified with an expiring subkey? This would make using untrusted user agents (browsers) less of a security risk.

Knowledge

Consumer

  • Unless different group key pairs are used per resource, the client will be able to tell if a two resources are guarded by the same ACL.
  • The members of a group are not inherently known to the client. However, ensuring this, the membership signatures may need to be kept private/encrypted (Q1).
  • The client must know where to find member signatures. This could potentially leak information about who is publishing the content.

Relying Party

  • Unless different group key pairs are used, the relying party will be able to determine if two resources are guarded by the same ACL.
  • Unless different group key pairs are used, the relying party will be able to infer a consumer's access to other resources guarded by the same ACL.
  • The relying party cannot determine the identities of the group members or the clients requesting content.
  • The relying party should not need to know who is publishing the resource.
  • The relying party will not know the members of a group. However, this may require that the membership signatures be kept private (Q1)
  • All requests from a client for a resource will appear to be independent. That is, the relying party will not be able to track/identify consumers.

Obtaining Membership Signatures *

A consumer must be able to obtain his/her membership signature for a group. However, other parties must not be able to determine if a consumer is a member of a group. Additionally, consumers should not need to download all of the membership signatures for a group.

Online Services

  • There must be a method for transferring membership signatures to clients. Preferably, these signatures would not be private information (Q1) and could be distributed publicly (distributed key servers).