Dr. Choi解答

本文主要是介绍Dr. Choi解答，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1、来由

网络安全课学习加解密，问了老师几个问题，老师给出了解答

2、问题

Please, find my answers to your questions I received on Cryptography

1. Is RSA an algorithm or procedure?
   Answer: RSA is a procedure to cover Public Key Infrastructure encryption and decryption mechanism. Strictly speaking, it is not a single mathematical algorithm. Rather, it is a crypto system for the whole PKI procedures. Of course, the term, RSA algorithm is sometimes used to describe the individual encryption and decryption mechanism.
   RSA是算法还是一个可以follow的过程？
   答：是一个cover PKI 加解密的过程。严格来讲不是一个简单的算法，而是一个整个 PKI 程序。当然 RSA 算法有时专指由三个科学家名字命名的那个加解密算法（PS：老师补充RSA甚至是一个安全公司名字）。

2. Are there different ways to implement digital signature? What is the relationship between RSA PKI and RSA digital signature?
   Answer: There are many different schemes to implement digital signature and RSA digital signature is just one of them. When you use the term RSA for digital signature, it implies a scheme which is based on RSA procedure/algorithm for PKI. In short, RSA PKI echo system and RSA digital signature are two separate but related notions.
   有不同方式实现数字签名吗？ RSA PKI 和 RSA 数字签名关系是什么
   答：有多种方式，RSA 数字签名只是其中一个，RSA 数字签名专指使用RSA 过程/算法的公私钥数字签名。两者相互关联又有不同

3. Why is HMAC less costly than Digital Signature even though both use hash? What is the advantage of using HMAC?
   Answer: HMAC does not use added procedure of digital signing (i.e. encrypting hashed message digest with the sender’s private key). Refer to the next question about the necessary steps for digital signature.
   为什么 HMAC 比数字签名代价少，虽然都用了hash，用HMAC有什么优势？
   答：HMAC 没有“MD后使用发送者私钥加密”那一步。

4. Is hashing a part of digital signature process?
   Answer: If you use RSA digital signature process and RSA algorithm, hashing is a mandatory part of digital signature because RSA algorithm used for digital signing requires extremely short length of string. However, the mechanism we discussed in the class is algorithm-neutral, meaning that it can be applied to other signing algorithms which do not require such a short string. In theory, the hashing procedure is not the essential part of digital signature and can serve other purposes like integrity checking.
   hash是数字签名必须的一步吗？
   答：如果使用 RSA 数字签名，那 hash 就是必须的一步，这是一个定义好的概念，另外 RSA 算法用于数字签名只能用于很短的字符串。当然，也有不强制 hash 的数字签名，但是 hash 也可以用来检测完整性。

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