McFly: Verifiable Encryption to the Future Made Practical

Nico Döttling; Lucjan Hanzlik; Bernardo Magri; Stella Wohnig

Paper 2022/433

McFly: Verifiable Encryption to the Future Made Practical

Nico Döttling, Helmholtz Center for Information Security

Lucjan Hanzlik, Helmholtz Center for Information Security

Bernardo Magri, University of Manchester

Stella Wohnig, Helmholtz Center for Information Security, Saarland University

Abstract

Blockchain protocols have revolutionized the way individuals and devices can interact and transact over the internet. More recently, a trend has emerged to harness blockchain technology as a catalyst to enable advanced security features in distributed applications, in particular fairness. However, the tools employed to achieve these security features are either resource wasteful (e.g., time-lock primitives) or only efficient in theory (e.g., witness encryption). We present McFly, a protocol that allows one to efficiently ``encrypt a message to the future'' such that the receiver can decrypt the message almost effortlessly. Towards this goal, we design and implement a novel primitive we call signature-based witness encryption and combine it with a BFT blockchain (or a blockchain finality layer) in such a way that the decryption of the message can be piggybacked on the tasks already performed by the blockchain committee, resulting in almost-for-free decryption. To demonstrate the practicality of the McFly protocol, we implemented our signature-based witness encryption scheme and evaluated it on a standard laptop with Intel i7 @2,3 GHz. For the popular BLS12-381 curve, a $381$-bit message and a committee of size $500$ the encryption time is $9.8s$ and decryption is $14.8 s$. The scheme remains practical for a committee of size $2000$ with an encryption time of $58 s$ and decryption time of $218 s$.

Note: We have added a small fix to our SWE scheme, which enables it to securely work also in the case of multiple identical reference messages by including additional randomness.

Metadata

Available format(s): PDF
Category: Cryptographic protocols
Publication info: Published elsewhere. Minor revision. Financial Cryptography 2023
Keywords: blockchain timed-release witness encryption identity-based encryption
Contact author(s): doettling @ cispa de
hanzlik @ cispa de
bernardo magri @ manchester ac uk
stella wohnig @ cispa de
History: 2023-07-26: revised; 2022-04-06: received; See all versions
Short URL: https://ia.cr/2022/433
License: CC BY

BibTeX

@misc{cryptoeprint:2022/433,
      author = {Nico Döttling and Lucjan Hanzlik and Bernardo Magri and Stella Wohnig},
      title = {McFly: Verifiable Encryption to the Future Made Practical},
      howpublished = {Cryptology ePrint Archive, Paper 2022/433},
      year = {2022},
      note = {\url{https://eprint.iacr.org/2022/433}},
      url = {https://eprint.iacr.org/2022/433}
}