Decryption function gives wrong result with special characters

问题

I'm building an encryption/decryption function in VBScript / Classic ASP. It all works as long as the string to be encrypted/decrypted does not contain special characters.

' str = "Bayern München"
' key = "ab34ehyd67hy6752daskjh"

Function EncryptString(val, key)

    valLen = Len(val)
    keyLen = Len(key)
    keyPos = 1
    newVal = ""
    revVal = val

    For x = 1 To valLen
        calc = AscW(Mid(revVal, x, 1)) + AscW(Mid(key, keyPos, 1))
        'Response.Write ":" & AscW(Mid(revVal, x, 1)) & " + " & AscW(Mid(key, keyPos, 1)) & " = " & calc & "<br />"
        newVal = newVal & Hex(calc)
        keyPos = keyPos + 1
        If keyPos > keyLen Then keyPos = 1
    Next

    EncryptString = newVal

End Function

Function DecryptString(val, key)

    ' The workaround - start
    For i = 160 To 255
        val = Replace(val, Chr(i), "&#" & i & ";")
    Next
    ' The workaround - end

    valLen = Len(val)
    keyLen = Len(key)
    keyPos = 1
    newVal = ""
    revVal = val
    chrVal = ""

    ' I suspect this to be the error
    For y = 1 To valLen Step 2
        chrVal = chrVal & ChrW("&h" & Mid(revVal, y, 2))
    Next

    For x = 1 To Len(chrVal)
        calc = AscW(Mid(chrVal, x, 1)) - AscW(Mid(key, keyPos, 1))
        'Response.Write "::" & AscW(Mid(chrVal, x, 1)) & " - " & AscW(Mid(key, keyPos, 1)) & " = " & calc & "<br />"
        newVal = newVal & ChrW(calc)
        keyPos = keyPos + 1
        If keyPos > keyLen Then keyPos = 1
    Next

    DecryptString = newVal

End Function

If I do an encryption of the string "Bayern München" and afterwards call the DecryptString function on the encrypted string, it returns Bayern M?À?vU?.

If I output the data (the Response.Write's in the example), the decryption function returns a negative number for the character ü, so I'm doing something wrong - but what?

The system encoding is Windows-1252.

UPDATE:

I did this workaround in the DecryptString function. I'm not sure if it covers all possible problems, but from my testing so far it does:

For i = 160 To 255
    val = Replace(val, Chr(i), "&#" & i & ";")
Next

来源：https://stackoverflow.com/questions/60151047/decryption-function-gives-wrong-result-with-special-characters

标签

vbscript

asp-classic