Solution – Challenge 56 – Cryptography Challenge 5 – Fully Functional Caesar’s Shift Cipher Decrypter

Below is a possible solution to Challenge 56 – Cryptography Challenge 5 – Fully Functional Caesar’s Shift Cipher Decrypter

1. Make a backup of your workbook
2. Open your workbook and ALT+F11
3. Locate your Workbook name in Project Explorer Window
4. Right click on your workbook name > Insert > Module
5. Copy paste the Macro code given below
6. Save your file as .xlsm
7. Call your function as =DecryptCS(A2,$C$2)

Function DecryptCS(CText, Shift) As String
    Dim Ws As Worksheet
    Dim i As Long
    Dim PText As String
    Dim PArr, CArr
    Application.Volatile
    CArr = Split(StrConv(CText, vbUnicode), vbNullChar)
    ReDim PArr(UBound(CArr) - 1)
    For i = LBound(CArr) To UBound(CArr) - 1
        If Abs(77.5 - Asc(UCase(CArr(i)))) < 13 Then
            If Asc(LCase(CArr(i))) - Shift < 97 Then
                PArr(i) = Chr(Asc(CArr(i)) - Shift + 26)
                Else
                PArr(i) = Chr(Asc(CArr(i)) - Shift)
            End If
        Else
            PArr(i) = CArr(i)
        End If
    Next i
    DecryptCS = Join(PArr, "")
End Function

The Excel file illustrating the above solution can be downloaded from Solution – Challenge 56 – Cryptography Challenge 5 – Decryption – Fully Functional Caesar’s Shift Cipher