Decrypt and encrypt text - in Korean

I have the following routines:

Public Function DecryptText(ByVal in_text As String) As String
Dim strKey As String = "ROCK"
Dim i As Integer
Dim c As Integer
Dim out_buff As String

For i = 1 To Len(RTrim(in_text))
c = Asc(Mid$(in_text, i, 1))
c -= Asc(Mid(strKey, (i Mod Len(strKey)) + 1, 1))
out_buff &= Chr(c And &HFF)
Next
Return RTrim(out_buff)
End Function

Public Function EncryptText(ByVal in_text As String) As String
Dim strKey As String = "ROCK"
Dim i As Integer
Dim c As Integer
Dim out_buff As String

For i = 1 To Len(RTrim(in_text))
c = Asc(Mid$(in_text, i, 1))
c += Asc(Mid(strKey, (i Mod Len(strKey)) + 1, 1))
out_buff &= Chr(c And &HFF)
Next
Return out_buff
End Function

They work fine on all computers the have ever been used on. Now, we sold
the software to a company and their computers (WinXP Pro) have the
korean language on them, and it is displaying windows messages in
Korean. How can these routines get messed up when the user has Korean?

Darin

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