Successful marketing and acceptance of On-The-Fly Computing systems require dealing with their security. The highly dynamic and heterogeneous nature of the visioned system as well as data protection and further legal requirements pose a challenge for modern cryptography and require novel cryptographic solutions.
During the course of the project we intend to design solutions for confidential and authenticated communication in dynamic groups based on identity-based and attribute-based cryptography. This requires key revocation and reduction of power of authority for identity-based schemes. Efficient allocation of services and data access control in On-The-Fly Computing systems also require novel cryptographic schemes, which we intend to realize based on the attribute-based encryption schemes.
Another important market mechanism in On-The-Fly Computing Systems is an anonymous reputation system which enables clients to rate products and services and gives incentives to providers to improve their services. Hence, in this part of the project we develop new models of security and schemes to build a highly flexible and secure reputation system.
Anonymous Group Signatures and Reputation Systems
In standard signature schemes, the sender computes a signature on his message using his secret key. The receiver can check, using the signature and the sender's public key, that the message was indeed composed by the sender and that it was not modified in transit. To achieve this, the public key must uniquely identify the sender. However, in many scenarios this strict identification is not necessary or even desirable. Whenever an application only needs assurance that the sender belongs to a certain group of possible senders, anonymous group signatures can be used.
Anonymous group signatures allow each member of a group to sign messages without disclosing their identity. For this, each group member gets their own private key that is associated to the group's public key. In contrast to standard digital signature schemes, the message receiver can only check whether some group member signed the message, but not which specific member did it. The actual signer can only be determined by a special entity in the system (the group manager).
Besides anonymity, other properties of group signatures play an important role in some applications. For example, it may be useful to restrict the number of messages that each group member can sign. Furthermore, techniques for revoking group membership are important. In particular, these and other extensions of group signatures can be used to construct anonymous reputation systems.
Reputation systems are an important tool to allow customers and providers of goods and services to gather useful information about past transactions. In order to receive trustworthy, reliable, and honest ratings, a reputation system should guarantee the customer anonymity and at the same ensure that no customer can submit more than one rating. Of course the ratings should be publicly verifiable by third parties.