International Association for Cryptologic Research

International Association
for Cryptologic Research


Bhaskar Roberts


Security Analysis of Quantum Lightning 📺
Bhaskar Roberts
Zhandry recently defined a new cryptographic object called quantum lightning, which has a number of useful applications, including a strong form of quantum money. Further, they proposed a construction of quantum lightning based on superpositions of low-rank matrices. The scheme is unusual, so it is difficult to base the scheme's security on any widespread computational assumptions. So instead, they proposed a new hardness assumption that, if true, could be used to prove security. In this work, we show that the hardness assumption is in fact false, so the proof of security does not hold. However, we note that the proposal for quantum lightning has not been proven insecure. This work is the first step in analyzing the security of Zhandry's proposal and moving toward a scheme that we can prove to be secure.
Franchised Quantum Money 📺
Bhaskar Roberts Mark Zhandry
The construction of public key quantum money based on standard cryptographic assumptions is a longstanding open question. Here we introduce franchised quantum money, an alternative form of quantum money that is easier to construct. Franchised quantum money retains the features of a useful quantum money scheme, namely unforgeability and local verification: anyone can verify banknotes without communicating with the bank. In franchised quantum money, every user gets a unique secret verification key, and the scheme is secure against counterfeiting and sabotage, a new security notion that appears in the franchised model. Finally, we construct franchised quantum money and prove security assuming one-way functions.


Mark Zhandry (1)