说明：  密码学介绍 双语版PDF 很不错的密码学入门知识，但发现中译本有些语句译得生涩别扭，故给出英文原版以便对照。 这个PDF里主要说加密的起源及其发展，并未提及高深的数学理论，只要是个合格的高中生，都能看
(Cryptography introduce bilingual PDF version is very good knowledge of cryptography entry, but found some of the translations awkward sentence translation was jerky, it gives the English original for comparison. The principal said encrypted PDF in the origin and development of advanced mathematical theory did not mention, as long as a qualified high school students, can look)