B4J Code Snippet ROT13 Function

Hello everybody.

I'm posting this simple function here, I needed it today and I hadn't found it here on the forum.

ROT13 (Rotate by 13 places) is a simple letter substitution cipher that replaces a letter with the 13th letter after it in the alphabet. It is a special case of the Caesar cipher which was developed in ancient Rome. ROT13 is not a secure encryption method, but rather a form of obfuscation used to hide text, especially spoilers or punchlines in online forums. It works by shifting each letter 13 positions in the alphabet, looping back to the beginning if needed (e.g., 'Z' becomes 'M', 'A' becomes 'N'). The same function is used for both encoding and decoding, as ROT13 is its own inverse.

'encrypt = true (encrypt), encrypt = false (Decrypt)
Sub Rot13(input As String, encrypt As Boolean) As String
    Dim output As StringBuilder
    output.Initialize
    Dim alphabet As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
    Dim rot13Alphabet As String = "NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm"
  
    Dim sourceAlphabet As String
    Dim targetAlphabet As String
  
    If encrypt Then
        sourceAlphabet = alphabet
        targetAlphabet = rot13Alphabet
    Else
        sourceAlphabet = rot13Alphabet
        targetAlphabet = alphabet
    End If
  
    For i = 0 To input.Length - 1
        Dim c As Char = input.CharAt(i)
        Dim index As Int = sourceAlphabet.IndexOf(c)
        If index <> -1 Then
            output.Append(targetAlphabet.CharAt(index))
        Else
            output.Append(c)
        End If
    Next
    Return output.ToString
End Sub

thx