Public-Key Revocation and Tracing Schemes with Subset Difference Methods Revisited

Broadcast encryption

is a very powerful primitive since it can send an encrypted message to a set of users excluding a set of revoked users.

Public-key broadcast encryption (PKBE)

is a special type of broadcast encryption such that anyone can run the encryption algorithm to create an encrypted message by using a public key. In this paper, we propose a new technique to construct an efficient PKBE scheme by using the subset cover framework. First, we introduce a new concept of public-key encryption named

single revocation encryption (SRE)

and propose an efficient SRE scheme in the random oracle model. A user in SRE is represented as a group that he belongs and a member in the group. In SRE, a sender can create a ciphertext for a specified group where one member in the group is revoked, and a receiver can decrypt the ciphertext if he belongs to the group in the ciphertext and he is not revoked in the group. Second, we show that the subset difference (SD) scheme (or the layered subset difference (LSD) scheme) and an SRE scheme can be combined to construct a public-key revocation encryption (PKRE) scheme such that a set of revoked users is specified in a ciphertext. Our PKRE scheme using the LSD scheme and our SRE scheme can reduce the size of private keys and public keys by log

N

factor compared with the previous scheme of Dodis and Fazio.