Use of des symmetric encryption

Encryption in the Web site using cookies or storing data to the database often use encryption and decryption, MD5 very useful, but sometimes need to inverse. Then the DES symmetric encryption is more useful. Set a key, and then encrypt all the data. Code introduction as follows, the prior declaration only for the younger brother personal understanding, please advise
Imports System
Imports System.IO
Imports System.Text
Imports System.Diagnostics
Imports System.Security.Cryptography
Imports System.Text.RegularExpressions

' Symmetric encryption using standard des
Public Function encryptdes (ByVal sourcestr As String) as String

' Get Encodekey string from web.config
Dim Skey as String
Skey = ConfigurationSettings.AppSettings ("Encodekey")

' Put the input string into the byte array
Dim des as DESCryptoServiceProvider = New DESCryptoServiceProvider ()
Dim Inputbytearray as Byte ()
Inputbytearray = Encoding.Default.GetBytes (SOURCESTR)

' Set Encrypt object and Skey
Des. Key = ASCIIEncoding.ASCII.GetBytes (skey)
DES.IV = ASCIIEncoding.ASCII.GetBytes (skey)
Dim ms as MemoryStream = New MemoryStream ()
Dim cs as CryptoStream = New CryptoStream (MS, Des. CreateEncryptor (), CryptoStreamMode.Write)
Dim SW As StreamWriter = New StreamWriter (CS)
Sw. Write (SOURCESTR)
Sw. Flush ()
Cs. FlushFinalBlock ()
Ms. Flush ()
Return convert.tobase64string (Ms. GetBuffer (), 0, Ms. Length)

End Function

' Symmetric decryption using standard des
Public Function decryptdes (ByVal sourcestr As String) as String

' Get Encodekey string from web.config
Dim SKey as String
SKey = ConfigurationSettings.AppSettings ("Encodekey")

' Put the input string into the byte array
Dim des as DESCryptoServiceProvider = New DESCryptoServiceProvider ()

Des. Key = ASCIIEncoding.ASCII.GetBytes (SKey)
DES.IV = ASCIIEncoding.ASCII.GetBytes (SKey)

Dim buffer as Byte () = convert.frombase64string (SOURCESTR)

Dim ms as MemoryStream = New MemoryStream (buffer)
Dim cs as CryptoStream = New CryptoStream (MS, Des. CreateDecryptor (), CryptoStreamMode.Read)
Dim sr as StreamReader = New StreamReader (CS)
return Sr. ReadToEnd ()

End Function