Under the assumption that the random high-density knapsack problem is infeasible, the proposed schemes are provably secure against ciphertext-only attack.

在高密度随机背包困难性假设下，可以证明方案在唯密文攻击下是安全的。

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Because the sensitive data is encrypted, any direct attack on the database file analysis, can only see the ciphertext.

由于敏感数据被加密，任何直接对数据库文件进行分析的攻击方式，都只能看到密文。

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Three are ciphers that can take input plaintexts of large and varying lengths and will output the ith block of the ciphertext after having processed only the first i blocks of the plaintext.

这些加密都可以对输入数据量很大并且长度可变的明文进行加密，但是只有在明文的前 个分组处理完毕后才输出密文的第 个分组。

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