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旨在加强联邦数据加密标准(DES)的二次加密方法早已经提出,最新的建议指出,用两个56比特密钥进行三次加密(先用第一密钥加密,接着用第二密钥解密,然后再用第一密钥加密)可以提高简单二次加密的保密性。本文指出,虽然这两种方法都可以有效地改进一次加密的保密性,但是该新方法并不能有效地提高简单二次加密的保密性。用一个选定明文攻击来对112比特密钥进行密码分析,需要大约2~(56)次运算和2~56个存贮字。虽然我们用DES作为一个例子,但是这种方法可以应用于任何类似的密码。
A secondary encryption method aimed at strengthening the Federal Data Encryption Standard (DES) has long been proposed, and the latest proposal states that encryption is performed three times using two 56-bit keys (first encrypted with a first key followed by a second key , And then encrypted with the first key) can improve the confidentiality of simple secondary encryption. This paper points out that although these two methods can effectively improve the confidentiality of the first encryption, the new method can not effectively improve the confidentiality of the simple second encryption. Performing a cryptanalysis of a 112-bit key with a selected plaintext attack requires approximately 2 to 56 operations and 2 to 56 memory words. Although we use DES as an example, this method can be applied to any similar password.