VBA-LocalStorage

Note: Under development

Store key-value information for Workbooks/Documents locally with moderate security. This can be useful for cases such as user-specific preferences, application state, and, in trusted environments, authentication information.

Stored values are encrypted with either an ApplicationKey, which is stored in VBA with the workbook, or a user-supplied password:

• ApplicationKey: the values are secure while at-rest when separate from the workbook, but if someone gains access to the computer and the workbook is unprotected, they will be able to access the stored values. This is a reasonable baseline for security and generally matches the approach used with browsers.
• If additional security is desired, the user can elect to use a user-supplied password for encryption which would secure the values at-rest and would require entering the password to decrypt the values even with access to the computer and workbook.

Overview

User Flow:

1. Request Local Storage On first access, a dialog is displayed requesting usage of local storage for the given workbook/document. If the user rejects local storage, this preference is saved and in-memory storage will be used. If the user accepts, encryption with ApplicationKey will be used. Finally, the user has an option to accept with user-supplied password
2. On workbook/document re-open, if encrypted with user-supplied password, display Unlock Local Storage user form, otherwise decrypts automatically

Usage

Follows browser's localStorage approach with GetItem, SetItem, RemoveItem, and Clear

Private Token As String

Sub Login()
  Token = LocalStorage.GetItem("token")

  If Token = "" Then
    Token = "..."
    LocalStorage.SetItem "token", Token
  End If
End Sub

Sub Logout()
  Token = ""
  LocalStorage.RemoveItem "token"
End Sub

Sub Cleanup()
  LocalStorage.Clear
End Sub

Installation

1. Import LocalStorage.bas, RequestLocalStorage.frm, and UnlockLocalStorage.frm
2. Set unique and strong value for ApplicationKey constant in LocalStorage.bas