假设两个密钥分别是K1和K2，以下（ ）是正确使用三重DES加密算法对明文M进行加密的过程。
①使用K1对M进行DES加密得到C1
②使用K1对C1进行DES解密得到C2
③使用K2对C1进行DES解密得到C2
④使用K1对C2进行DES加密得到C3
⑤使用K2对C2进行DES加密得到C3。
- A.①②⑤
- B.①③④
- C.①②④
- D.①③⑤
正确答案及解析
正确答案
解析
3DES是三重数据加密算法的通称。它相当于是对每个数据块应用三次DES加密算法，密钥长度达到168位，但在软考中是112位，主要是因为第一次加密和第三次加密用的相同的密钥。3DES通过增加DES的密钥长度来避免类似的攻击，而不是设计一种全新的块密码算法。
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