Public Class clsCrypt
    Public Function Encrypt(ByVal sCrypt As String) As String
        On Error GoTo Err_RaiseErrorClass
        Dim tmp As String
        Dim sVal As String
        Dim l As Long
        For l = 1 To Len(sCrypt)
            sVal = HexValue(Mid(sCrypt, l, 1))
            If Len(sVal) > 4 Then
                If Left(sVal, 4) = "ERR:" Then
                    tmp = sVal
                    Exit For
                End If
            End If
            If Len(sVal) = 1 Then sVal = "0" & sVal
            tmp = tmp & sVal
        Next l
        Encrypt = tmp
Exit_RaiseErrorClass:
        Exit Function
Err_RaiseErrorClass:
        MsgBox(Err.Number & ": " & Err.Description)
        Resume Exit_RaiseErrorClass
    End Function

    Public Function Decrypt(ByVal sCrypt As String) As String
        On Error GoTo Err_RaiseErrorClass
        Dim tmp As String
        Dim sVal As String
        Dim str As String
        Dim l As Long
        sVal = UCase(sCrypt)
        Do Until sVal = ""
            If Len(sVal) < 2 Then
                str = ChrValue(sVal)
                If Len(str) > 4 Then
                    If Left(str, 4) = "ERR:" Then
                        tmp = str
                        Exit Do
                    End If
                End If
                tmp = tmp & str
                sVal = ""
            Else
                str = Left(sVal, 2)
                If Left(str, 1) = "0" Then str = Right(str, 1)
                str = ChrValue(str)
                If Len(str) > 4 Then
                    If Left(str, 4) = "ERR:" Then
                        tmp = str
                        Exit Do
                    End If
                End If
                tmp = tmp & str
                sVal = Right(sVal, Len(sVal) - 2)
            End If
        Loop
        Decrypt = tmp
Exit_RaiseErrorClass:
        Exit Function
Err_RaiseErrorClass:
        MsgBox(Err.Number & ": " & Err.Description)
        Resume Exit_RaiseErrorClass
    End Function

    Private Function HexValue(ByVal sChr As String) As String
        On Error GoTo Err_HexValue
        Dim iDec As Integer
        iDec = Asc(sChr)
        HexValue = Hex(iDec)
Exit_HexValue:
        Exit Function
Err_HexValue:
        HexValue = "ERR:" & Err.Number
        Resume Exit_HexValue
    End Function

    Private Function ChrValue(ByVal sHex As String) As String
        On Error GoTo Err_ChrValue
        Dim sChr As String
        Dim dblVal As Double
        Dim i As Integer
        Const cIdx = 16
        For i = 1 To Len(sHex)
            sChr = Mid(sHex, i, 1)
            If sChr <> " " Then
                If sChr <= "9" Then
                    dblVal = dblVal + CInt(sChr)
                Else
                    dblVal = dblVal + ((Asc(sChr) - 55) Mod 32)
                End If
                If i < Len(sHex) Then dblVal = dblVal * cIdx
            End If
        Next i
        ChrValue = Chr(dblVal)
Exit_ChrValue:
        Exit Function
Err_ChrValue:
        ChrValue = "ERR:" & Err.Number
        Resume Exit_ChrValue
    End Function
End Class

I noticed alot of your code is legacy VB 6.0 based code. I would optimize it for .NET which should have a positive impact and probably increase performance as well. Maybe use Try/Catch/Finally/End Try error handling as well.

Otherwise it looks pretty good.

Jason

can you please post a comment maybe per line? about what each line does so that beginners, like me, could understand.. :) hehehe.. thanks.

Public Class HexCrypt
    Public Shared Function StringToHex(ByVal sCrypt As String) As String
        Dim Retorno As String = ""
        Dim sVal As String
        Dim l As Long

        Try
            For l = 1 To Len(sCrypt)
                sVal = CharToHex(Mid(sCrypt, l, 1))

                'El valor hex debe tener una logitud mayor que 1.
                Retorno = Retorno & IIf(Len(sVal) = 1, "0", "") & sVal
            Next l
        Catch ex As Exception

        End Try
        Return Retorno

    End Function

    Public Shared Function HexToString(ByVal sCrypt As String) As String
        Dim Retorno As String = ""
        Dim sVal As String
        Dim str As String
        Dim l As Long = 0

        sVal = sCrypt.ToUpper
        Try
            Do Until sVal = ""
                If Len(sVal) < 2 Then
                    str = HexToChar(sVal)

                    Retorno = Retorno & str
                    sVal = ""
                Else
                    str = Left(sVal, 2)
                    If Left(str, 1) = "0" Then str = Right(str, 1)
                    str = HexToChar(str)

                    Retorno = Retorno & str
                    sVal = Right(sVal, Len(sVal) - 2)
                End If
            Loop
        Catch ex As Exception

        End Try

        Return Retorno

    End Function

    Private Shared Function CharToHex(ByVal sChr As Char) As String
        Return Hex(Asc(sChr))
    End Function

    Private Shared Function HexToChar(ByVal sHex As String) As String
        Return Convert.ToInt32(sHex, 16)
    End Function
End Class
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