[RESOLVED] [2005] Decryption Algorithm Please Help!

[IssaFram]

My teacher has given me code for an encryption code and has challenged us to find a working decryption function. I am having a very hard time with this. Can anyone help me out? Here is the Encryption algorithm:

Public Function Encrypt(ByVal strData As String, ByVal strKey As String) As String
        Dim k1 As Integer
        Dim strCompleteEncrypted As String
        Dim s3 As String
        Dim intI As Integer
        Dim blnFlag As Boolean
        Dim intJ As Integer
        k1 = 0
        strCompleteEncrypted = ""
        s3 = ""
        intI = strData.Length
        blnFlag = False
        intJ = intI
        For intJ = intI To 1 Step -1
            If k1 = strKey.Length Then k1 = 0
            Dim intSingleASCValue As Integer
            intSingleASCValue = Asc(strKey.Substring(k1, 1))
            Dim i1 As Integer
            i1 = (intSingleASCValue Mod 13) + 1
            If k1 < strKey.Length - 1 Then
                Dim k As Integer
                k = Asc(strKey.Substring(k1 + 1, 1)) + k1 + 1
                If k > 122 Then k = 65 + (122 - k)
                Dim intArrayASCValue(0 To strKey.Length - 1) As Integer
                Dim intCounter As Integer
                For intCounter = 0 To strKey.Length - 1
                    intArrayASCValue(intCounter) = Asc(strKey.Substring(intCounter, 1))
                Next
                intArrayASCValue(k1 + 1) = k
                Dim intKeyTemp As Integer
                intKeyTemp = strKey.Length - 1
                strKey = ""
                For intCounter = 0 To intKeyTemp
                    strKey = strKey & Chr(intArrayASCValue(intCounter))
                Next
            End If
            Dim str4 As String
            str4 = strData.Substring(intJ - 1, 1)
            intSingleASCValue = Asc(str4)
            Dim intEncryptedASC2 As Integer
            intEncryptedASC2 = intSingleASCValue \ 11
            intEncryptedASC2 = 122 - intEncryptedASC2 - i1
            Dim intEncryptedASC1 As Integer
            intEncryptedASC1 = intSingleASCValue Mod 11
            intEncryptedASC1 = 65 + intEncryptedASC1 + i1
            Dim strEncrypted1 As String
            Dim strEncrypted2 As String
            strEncrypted1 = Chr(intEncryptedASC1)
            strEncrypted2 = UCase(Chr(intEncryptedASC2))
            strCompleteEncrypted = strCompleteEncrypted + strEncrypted1 + strEncrypted2
            k1 = k1 + 1
        Next
        Return strCompleteEncrypted
    End Function

Here is a demonstration:

Encrypt("Some Test Encryption Text", "issa_fram")

It returns: INXCDPRITOELFLHPHOENBNHMNDNCMKUNOHQEEOJQPSFNOMCOJP
I realized that the encrypted text length is twice the length of the original data.
When decrypting, the key ("issa_fram") will be provided. Can anyone help me out? I would really appreciate it