vba - 为什么此代码会禁用工作表保护？

Question

以下代码由 this website 提供我用它来取消保护我不知道密码的工作表。

Sub DisableSheetProtection()
Dim password As String
On Error Resume Next
For i = 65 To 66: For j = 65 To 66
For k = 65 To 66: For l = 65 To 66
For m = 65 To 66: For n = 65 To 66
For o = 65 To 66: For p = 65 To 66
For q = 65 To 66: For r = 65 To 66
For S = 65 To 66: For t = 32 To 126
ActiveSheet.Unprotect Chr(i) & _
Chr(j) & Chr(k) & Chr(l) & _
Chr(m) & Chr(n) & Chr(o) & _
Chr(p) & Chr(q) & Chr(r) & _
Chr(S) & Chr(t)

Next t: Next S: Next r: Next q
Next p: Next o: Next n: Next m
Next l: Next k: Next j: Next i
MsgBox "Sheet protection disabled."
End Sub

问题是: 它是如何或为什么起作用的？ Chr(65) 是 A，Chr(66) 是 B，Chr(32) 到 Chr(126) 是整个字母表和特殊字符。

基本上，如果您想尝试所有可能性，则需要这样做:

Sub DisableSheetProtection()
    Dim password As String
    On Error Resume Next
    For i = 32 To 126: For j = 32 To 126
    For k = 32 To 126: For l = 32 To 126
    For m = 32 To 126: For n = 32 To 126
    For o = 32 To 126: For p = 32 To 126
    For q = 32 To 126: For r = 32 To 126
    For S = 32 To 126: For t = 32 To 126
    ActiveSheet.Unprotect Chr(i) & _
    Chr(j) & Chr(k) & Chr(l) & _
    Chr(m) & Chr(n) & Chr(o) & _
    Chr(p) & Chr(q) & Chr(r) & _
    Chr(S) & Chr(t)

    Next t: Next S: Next r: Next q
    Next p: Next o: Next n: Next m
    Next l: Next k: Next j: Next i
    MsgBox "Sheet protection disabled."
    End Sub

但是该代码可以正常工作，因为它用于取消保护并且您无法打印出正确的密码。我认为这与 VBA 取消保护/保护方法有关。

Answer 1

Internal XL passwords are about as useful for security as tissuepaper. The reason is that the passwords you enter (i.e., withTools/Protect/Protect Worksheet or /Protect Workbook) are not useddirectly in protection.Instead they are hashed (mathematicallytransformed) into a much less secure code. Effectively, any passwordof any length is transformed into a string of 12 characters, the first11 of which have one of only two possible values. The remainingcharacter can have up to 95 possible values, leading to only

2^11 * 95 = 194,560 potential passwords.

This may seem like a lot, but it only takes a few seconds for a modern computer >to try them all. As a comparison, a 4-character password containing just the 26lower case alphabet characters has 456,976 combinations, and a3-character password consisting of lower case, upper case and thedigits 0-9 will have 238,328 combinations.

Again, it doesn't matter what your original password is, one of those194K strings will unlock your sheet or workbook.

更多阅读 this 。