VBA で Base64 エンコードと Base64 デコードを実現し、暗号化された URL の処理を非常に便利にします。
VBA Base64 エンコード / 暗号化関数：
'VBA Base64 エンコード / 暗号化関数：
Function Base64Encode (StrA As String) As String 'Base64 エンコード
On Error GoTo over ' エラーハンドリング
Dim buf() As Byte, length As Long, mods As Long
Dim Str() As Byte
Dim i, kk As Integer
kk = Len(StrA) - 1
ReDim Str(kk)
For i = 0 To kk
Str(i) = Asc(Mid(StrA, i + 1, 1))
Next i
Const B64_CHAR_DICT = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
mods = (UBound (Str) + 1) Mod 3 '3 で割った余り
length = UBound(Str) + 1 - mods
ReDim buf(length / 3 * 4 + IIf(mods <> 0, 4, 0) - 1)
For i = 0 To length - 1 Step 3
buf(i / 3 * 4) = (Str(i) And &HFC) / &H4
buf(i / 3 * 4 + 1) = (Str(i) And &H3) * &H10 + (Str(i + 1) And &HF0) / &H10
buf(i / 3 * 4 + 2) = (Str(i + 1) And &HF) * &H4 + (Str(i + 2) And &HC0) / &H40
buf(i / 3 * 4 + 3) = Str(i + 2) And &H3F
Next
If mods = 1 Then
buf(length / 3 * 4) = (Str(length) And &HFC) / &H4
buf(length / 3 * 4 + 1) = (Str(length) And &H3) * &H10
buf(length / 3 * 4 + 2) = 64
buf(length / 3 * 4 + 3) = 64
ElseIf mods = 2 Then
buf(length / 3 * 4) = (Str(length) And &HFC) / &H4
buf(length / 3 * 4 + 1) = (Str(length) And &H3) * &H10 + (Str(length + 1) And &HF0) / &H10
buf(length / 3 * 4 + 2) = (Str(length + 1) And &HF) * &H4
buf(length / 3 * 4 + 3) = 64
End If
For i = 0 To UBound(buf)
Base64Encode = Base64Encode + Mid(B64_CHAR_DICT, buf(i) + 1, 1)
Next
over:
End Function
VBA Base64 デコード / 復号関数：
'VBA Base64 デコード / 復号関数：
Function Base64Decode (B64 As String) As String 'Base64 デコード
On Error GoTo over ' エラーハンドリング
Dim OutStr() As Byte, i As Long, j As Long
Const B64_CHAR_DICT = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
If InStr (1, B64, "=") <> 0 Then B64 = Left (B64, InStr (1, B64, "=") - 1) 'Base64 の実際の長さを判断し、パディングを除く
Dim kk, length As Long, mods As Long
mods = Len(B64) Mod 4
length = Len(B64) - mods
ReDim OutStr(length / 4 * 3 - 1 + Switch(mods = 0, 0, mods = 2, 1, mods = 3, 2))
For i = 1 To length Step 4
Dim buf(3) As Byte
For j = 0 To 3
buf (j) = InStr (1, B64_CHAR_DICT, Mid (B64, i + j, 1)) - 1 ' 文字の位置に基づいてインデックス値を取得
Next
OutStr((i - 1) / 4 * 3) = buf(0) * &H4 + (buf(1) And &H30) / &H10
OutStr((i - 1) / 4 * 3 + 1) = (buf(1) And &HF) * &H10 + (buf(2) And &H3C) / &H4
OutStr((i - 1) / 4 * 3 + 2) = (buf(2) And &H3) * &H40 + buf(3)
Next
If mods = 2 Then
OutStr(length / 4 * 3) = (InStr(1, B64_CHAR_DICT, Mid(B64, length + 1, 1)) - 1) * &H4 + ((InStr(1, B64_CHAR_DICT, Mid(B64, length + 2, 1)) - 1) And &H30) / 16
ElseIf mods = 3 Then
OutStr(length / 4 * 3) = (InStr(1, B64_CHAR_DICT, Mid(B64, length + 1, 1)) - 1) * &H4 + ((InStr(1, B64_CHAR_DICT, Mid(B64, length + 2, 1)) - 1) And &H30) / 16
OutStr(length / 4 * 3 + 1) = ((InStr(1, B64_CHAR_DICT, Mid(B64, length + 2, 1)) - 1) And &HF) * &H10 + ((InStr(1, B64_CHAR_DICT, Mid(B64, length + 3, 1)) - 1) And &H3C) / &H4
End If
For i = 0 To UBound(OutStr)
Base64Decode = Base64Decode & Chr(OutStr(i))
Next i ' デコード結果を読み取る
over:
End Function
参考：http://club.excelhome.net/forum.php?mod=viewthread&tid=1239744&ordertype=1