加密程序为何+32 才显示可打印字符

Private Sub Command1_Click()
    cleartext = Text1.Text
    If Len(cleartext) = 0 Then
        cleartext = "": Text2.Text = ""
        Exit Sub                                    
     End If
 Dim tmpbuf() As Byte
Dim inval As Long, xorval As Long, outval As Long
Dim i As Long, j As Long

Randomize (Rnd((-1) * Abs(keycode) * Len(cleartext)))   '生成固定序列组

tmpbuf = StrConv(cleartext, vbFromUnicode) '-----------tmpbuf转成西文单字节

For i = LBound(tmpbuf) To UBound(tmpbuf)
    xorval = Int(128 * Rnd) '----------------------------固定的整数组，0-128之间不含128
    inval = Int(tmpbuf(i))   ' ---------------------------对原码的ANSI码提取码的字符值
    tmpbuf(i) = converttoprintablechar(xorval, inval Xor xorval)   '对输入的密码进行加密inval Xor xorval

Next i

ciphertext = StrConv(tmpbuf, vbUnicode)
Text2.Text = ciphertext                             '加密后的字符串   
End Sub
Private Function converttoprintablechar(ByVal xorval As Long, ByVal calaval As Long) As Byte
    Dim k As Long, i As Long
    For i = 32 To 126     '-------------------------可打印字符是32-126之间，含32，126
        If (i Xor xorval) < calaval Then            '可打印字符与固定序列随机数逐个XOR
            k = k + 1
        End If
    Next i      
    converttoprintablechar = CByte(32 + k) '------------------为什么+32      
End Function
以上程序是加密程序，返回值为什么要+32？？？不解？？？？