Paper 2015/371

Constant-Round MPC with Fairness and Guarantee of Output Delivery

S. Dov Gordon, Feng-Hao Liu, and Elaine Shi


We study the round complexity of multiparty computation with fairness and guaranteed output delivery, assuming existence of an honest majority. We demonstrate a new lower bound and a matching upper bound. Our lower bound rules out any two-round fair protocols in the standalone model, even when the parties are given access to a common reference string (CRS). The lower bound follows by a reduction to the impossibility result of virtual black box obfuscation of arbitrary circuits. Then we demonstrate a three-round protocol with guarantee of output delivery, which in general is harder than achieving fairness (since the latter allows the adversary to force a fair abort). We develop a new construction of a threshold fully homomorphic encryption scheme, with a new property that we call ``flexible'' ciphertexts. Roughly, our threshold encryption scheme allows parties to adapt flexible ciphertexts to the public keys of the non-aborting parties, which provides a way of handling aborts without adding any communication.

Available format(s)
Publication info
Preprint. MINOR revision.
MPCThreshold FHELearning with error
Contact author(s)
fenghao @ cs umd edu
2015-04-23: received
Short URL
Creative Commons Attribution


      author = {S.  Dov Gordon and Feng-Hao Liu and Elaine Shi},
      title = {Constant-Round MPC with Fairness and Guarantee of Output Delivery},
      howpublished = {Cryptology ePrint Archive, Paper 2015/371},
      year = {2015},
      note = {\url{}},
      url = {}
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