crypt(): DES or MD5

DES 算法的 crypt() 函数最多只支持 8 个字符的 password, 超过 8 个字符的部分被忽略掉了; 而 MD5 算法的 crypt() 则没有这个限制. 因此现在的 passwd 命令一般用 MD5 加密方式.

From crypt's man page:
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The glibc2 version of this function has the following additional features. If salt is a character string starting with the three characters "$1$" followed by at most eight characters, and optionally terminated by "$", then instead of using the DES machine, the glibc crypt function uses an MD5-based algorithm, and outputs up to 34 bytes, namely "$1$$", where "" stands for the up to 8 characters following "$1$" in the salt, followed by 22 bytes chosen from the set [a-zA-Z0-9./]. The entire key is significant here (instead of only the first 8 bytes).