Crypto Seminar
— 5:30pm
Location:
In Person and Virtual - ET
-
Group Viewing, Blelloch-Skees Conference Room, Gates Hillman 8115 and Zoom
Speaker:
ALPER ÇAKAN
,
Ph.D. Student, Computer Science Department, Carnegie Mellon University
https://csd.cmu.edu/people/doctoral-student/alper-cakan
Unclonable Cryptography with Unbounded Collusions
Quantum no-cloning theorem gives rise to the intriguing possibility of quantum copy protection where we encode a program in a quantum state such that a user in possession of k such states cannot create (k+1) working copies. Introduced by Aaronson (CCC'09) over a decade ago, copy protection has proven to be notoriously hard to achieve.
In this work, we construct public-key encryption and functional encryption schemes whose secret keys are copy-protected against unbounded collusions in the plain model (i.e. without any idealized oracles), assuming (post-quantum) subexponentially secure iO, one-way functions and LWE. This resolves a long-standing open question of constructing fully collusion-resistant copy-protected functionalities raised by multiple previous works.
Prior to our work, copy-protected functionalities were known only in restricted collusion models where either an a-priori bound on the collusion size was needed, in the plain model with the same assumptions as ours (Liu, Liu, Qian, Zhandry [TCC'22]), or adversary was only prevented from doubling their number of working programs, in a structured quantum oracle model (Aaronson [CCC'09]).
We obtain our results through a novel technique which uses identity-based encryption to construct unbounded collusion resistant copy-protection schemes from 1-to-2 secure schemes. This is analogous to the technique of using digital signatures to construct full-fledged quantum money from single banknote schemes (also called mini-schemes) (Lutomirski et al. [ICS'09], Farhi et al. [ITCS'12], Aaronson and Christiano [STOC'12]). We believe our technique is of independent interest.
Along the way, we also construct a functional encryption scheme whose master secret key can be punctured at all functions f such that f(m_0) != f(m_1). This might also be of independent interest.
Group Viewing and Zoom Participation. See announcement.
Event Website:
https://sites.google.com/view/crypto-seminar/home