加密两次好还是坏？ [英] Is encrypting twice good or bad?

问题描述

几个月前，我正在读书，如果你重新加密一个加密的消息，它不会提高其安全性，并且使得密码更不安全。但是当我现在搜索时，我找不到关于这个案例的任何具体的文章。如果你让我知道，这将是很棒的，它会很棒，你给我一个参考，所以我可以阅读。
提前感谢

解决方案

答案确实取决于正在使用的加密。

如果您 rot-13 你的明文两次，你会得到明文

如果您应用 DES 两次使用不同的键，您将获得更大的键盘空间的效果，以便攻击者进行搜索。 参见RSA。

区别在于加密函数是否在功能组合下形成代数组。就是说差异取决于是否应用于消息 m 的加密功能 F（）和密钥 Ki F（< k1>，F（< k2>，< em> m））== F（K3， / em>）针对某些 K3 ？

A few month ago I was reading somewhere that if you re-encrypt an encrypted message, it does not improve its security and it evens makes the cipher less secure. But as I search now, I cannot find any specific article regarding this case. It would be great if you let me know, and it would be awesome it you give me a reference so I can read about it. Thanks in advance.

解决方案

The answer really depends on the encryption being used.

If you rot-13 your plaintext twice, you get the plaintext back.

If you apply DES twice with different keys, you get the effect of a larger keyspace for an attacker to search. See reference at RSA.

The difference is whether the encryption function forms an algebraic group under functional composition. That is the same as saying the difference depends on whether, for an encryption function F() and keys Ki applied to a message m, does F( K1, F( K2, m)) == F( K3, m ) for some K3?

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