最大的问题是如何明确地指出在字符串中哪些是合法的。

The biggest problem is figuring out exactly what should be legal in the string.

youdao

同样，对于字符串您也要确定哪些是合法的，并拒绝所有其他的字符串。

Again, with strings you need to identify what is legal, and reject any other string.

youdao

此外，现在还有第二项检查，目的是让证书标识匹配某个字符串，管理员已将该字符串设计为过滤出除已知合法用户之外的所有用户。

In addition, there is now a second check so that the identity of the certificate matches some string that the administrator has designed to filter out all but a known set of legitimate users.

youdao