A study on read-write protection of a digital document by cryptographic techniques

Sensitive information, e.g., privacy information or company secret, should be carefully managed and it is desired that only privileged users can read and edit these kinds of information. For these needs, this paper proposes cryptographic schemes for a proper use of digital document and a concrete construction for the proposed schemes. Note that the proposed schemes are called ldquocontent protection schemes (CPSs)rdquo in this paper. The proposed schemes enable a sender to decide an access control, i.e., read-write protection, on a document by public keys of recipients and a recipient can read or edit a part of the document according to the access control without any help of neither the sender nor any trusted entity. The concrete construction proposed in this paper consists of only standard cryptographic techniques. This means that the proposed construction can be easily implemented by a standard cryptographic library and that users do not need to prepare a special key set for the proposed schemes. Since the proposed schemes control the read-write protection on a digital document by private keys of recipients, they can promote proper use of digital document even if we could not manage them on a server.