Effectiveness of plaintext encoding in knapsack PKC

Knapsack public-key cryptosystem is known to be vulnerable to the low-density attack (LDA) when the density is low. Nasako and Murakami proposed the method of realizing high density by plaintext encoding over finite fields. However, little is known about the effectiveness of plaintext encoding against LDA in the knapsack cryptosystem. In this paper, we confirm that the plaintext encoding is very effective in order to be secure against LDA.