Hierarchical And Dynamic Threshold Paillier Cryptosystem Without Trusted Dealer

We propose the first hierarchical and dynamic threshold Paillier cryptosystem without trusted dealer and prove its security in the malicious adversary model. The new cryptosystem is fully distributed, i.e., public and private key generation is performed without a trusted dealer. The private key is shared with a hierarchical and dynamic secret sharing scheme over the integers. In such a scheme not only the amount of shareholders, but also their levels in the hierarchy decide whether or not they can reconstruct the secret and new shareholders can be added or removed without reconstruction of the secret.