Simple Caesar Cipher Function

For no particular reason, I wanted to create a function that would take a string and "encrypt" it via Caesar cipher. This function takes a string and shifts the letters left or right (in the alphabet) depending on the input. Shift right(2) for instance would be -

ABCDEFGHIJKLMNOPQRSTUVWXYZ
CDEFGHIJKLMNOPQRSTUVWXYZAB

The UDF:

Option Explicit

Public Function CaesarCipher(ByVal TextToEncrypt As String, ByVal CaesarShift As Long) As String

    'Positive means shift to right e.g. "A" Shift 1 returns "B"
    Dim IsPositive As Boolean
    IsPositive = True
    If CaesarShift  26 Then
        CaesarShift = CaesarShift Mod 26
    End If

    If IsPositive Then
          OutputText = ShiftRight(TextToEncrypt, CaesarShift)
    Else: OutputText = ShiftLeft(TextToEncrypt, CaesarShift)
    End If

    CaesarCipher = OutputText
End Function

The shifting functions:

Private Function ShiftRight(ByVal ShiftString As String, ByVal ShiftQuantity As Long) As String

    Dim TextLength As Long
    TextLength = Len(ShiftString)

    Dim CipherText As String
    Dim CharacterCode As Long
    Dim AsciiIndex As Long
    Dim AsciiIdentifier() As Long
    ReDim AsciiIdentifier(1 To TextLength)

    For AsciiIndex = 1 To TextLength
        CharacterCode = Asc(Mid(ShiftString, AsciiIndex, 1))
        If CharacterCode + ShiftQuantity > 90 Then
            CharacterCode = CharacterCode - 26 + ShiftQuantity
        ElseIf CharacterCode = 32 Then GoTo Spaces
        Else:  CharacterCode = CharacterCode + ShiftQuantity
        End If
Spaces:
        AsciiIdentifier(AsciiIndex) = CharacterCode
    Next

        For AsciiIndex = 1 To TextLength
            CipherText = CipherText & Chr(AsciiIdentifier(AsciiIndex))
        Next
    ShiftRight = CipherText
End Function

```
Private Function ShiftLeft(ByVal ShiftString As String, ByVal ShiftQuantity As Long) As String

Dim TextLength As Long
TextLength = Len(ShiftString)

Dim CipherText As String
Dim Character

Just some things that jump out at me:

Standard VBA Naming conventions have camelCase for local variables, and PascalCase only for sub/function names and Module/Global Variables. This allows you to tell at a glance if the variable you're looking at is local to your procedure, or coming from somewhere else.

I would probably use EncryptUsingCaesarCypher as your function name. It's more descriptive and closer to what it actually does.

`Text = CaesarCypher(text)

versus

`Text = EncryptUsingCaesarCypher(text)

Other than that, your naming is pretty solid.

Why separate functions for ShiftLeft and ShiftRight? The code in both is heavily-repeated and could be easily combined into a Shift(ByVal shiftValue as Long) function that handles positive and negative. This also lets you cut out all that messing around with isPositve and Abs(shift)

StackExchange Code Review Q#118247, answer score: 5