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为什么输入错误密码时会有延迟？

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为什么输入错误密码时会有延迟？

当输入正确的密码时，应用程序或操作系统（没有特定的应用程序，几乎所有地方都是如此）会立即接受，但当输入错误的密码时，会有 1-2 秒的短暂延迟。这是为什么呢？

答案1

延迟是为了减慢自动软件的破解尝试。如果没有延迟，破解尝试将运行得更快。

文档：参见pam_fail_delay 函数

理由

   It is often possible to attack an authentication scheme by exploiting
   the time it takes the scheme to deny access to an applicant user. In
   cases of short timeouts, it may prove possible to attempt a brute force
   dictionary attack -- with an automated process, the attacker tries all
   possible passwords to gain access to the system. In other cases, where
   individual failures can take measurable amounts of time (indicating the
   nature of the failure), an attacker can obtain useful information about
   the authentication process. These latter attacks make use of procedural
   delays that constitute a covert channel of useful information.

   To minimize the effectiveness of such attacks, it is desirable to
   introduce a random delay in a failed authentication process. Preferable
   this value should be set by the application or a special PAM module.
   Standard PAM modules should not modify the delay unconditional.

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