We comment on the recent Letter, by Liu et al. [Opt. Lett. 38, 1651 (2013)] in which a method to improve the security strength of the asymmetric cryptosystem (ACS) by Qin and Peng [Opt. Lett. 35, 118 (2010)] was proposed. However, in accordance with Liu’s methodology, we could easily find other more efficient ways to achieve their purpose. More importantly, we think it is vitally necessary to point out that there exists a widespread, fundamental misunderstanding on the concept of ACS, which has also been studied in a series of related works.
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