Carl Löndahl

Carl Löndahl

We propose a polynomial-time attack on the hHB protocol, showing that the protocol does not attain the claimed security. Our attack is based on the GRS attack.

Qian Guo, Thomas Johansson, Carl Löndahl

The LPN (Learning Parity with Noise) problem has recently proved to be of great importance in cryptology. A special and very useful case is the RING-LPN problem, which typically provides improved efficiency in the constructed cryptographic primitive. We present a new algorithm for solving the RING-LPN problem in the case when the polynomial used is reducible. It greatly outperforms previous algorithms for solving this problem. Using the algorithm, we can break the Lapin authentication protocol for the proposed instance using a reducible polynomial, in about 2^70 bit operations.