knapsack cipher

例句：

1. 1. The military used a rucksack cipher to send secret messages during World War II.
   二战期间，军队使用背包密码发送秘密信息。
2. 2.This rucksack cipher is designed to be easy to use and understand for people who are not familiar with cryptography.
   这个背包密码设计得易于使用和理解，适合不熟悉密码学的人。
3. 3.The rucksack cipher was one of the earliest forms of encryption used in warfare.
   背包密码是战争初期使用的一种加密形式之一。