Hacking Cryptographic Protocols with Advanced Variational Quantum
  Attacks
Borja Aizpurua Pablo Bermejo Josu Etxezarreta Martinez Roman Orus
Here we introduce an improved approach to Variational Quantum Attack
Algorithms (VQAA) on crytographic protocols. Our methods provide robust quantum
attacks to well-known cryptographic algorithms, more efficiently and with
remarkably fewer qubits than previous approaches. We implement simulations of
our attacks for symmetric-key protocols such as S-DES, S-AES and Blowfish. For
instance, we show how our attack allows a classical simulation of a small
8-qubit quantum computer to find the secret key of one 32-bit Blowfish instance
with 24 times fewer number of iterations than a brute-force attack. Our work
also shows improvements in attack success rates for lightweight ciphers such as
S-DES and S-AES. Further applications beyond symmetric-key cryptography are
also discussed, including asymmetric-key protocols and hash functions. In
addition, we also comment on potential future improvements of our methods. Our
results bring one step closer assessing the vulnerability of large-size
classical cryptographic protocols with Noisy Intermediate-Scale Quantum (NISQ)
devices, and set the stage for future research in quantum cybersecurity.