encrypting/decrypting a password stored on a compact database - vb.net

Question

My project contains 2 forms, one to register users and one to login. I am using a compact local database to store the passwords. I wrote a function to encrypt the password when the user registers. I then wrote another to decrypt the same password when the user logs in.
The first part, encryption, works just fine. The user registers, and I can see the password encrypted on the database. However, when I try to log in, the password is not being decrypted. Here are my Functions.
Module EncryptionModule
Public Function base64Encode(ByVal sData As String) As String
Try
Dim encData_Byte As Byte() = New Byte(sData.Length - 1) {}
encData_Byte = System.Text.Encoding.UTF8.GetBytes(sData)
Dim encodedData As String = Convert.ToBase64String(encData_Byte)
Return (encodedData)
Catch ex As Exception
Throw (New Exception("Error is base64Encode" & ex.Message))
End Try
End Function
Public Function base64Decode(ByVal sData As String) As String
Dim encoder As New System.Text.UTF8Encoding()
Dim utf8Decode As System.Text.Decoder = encoder.GetDecoder()
Dim todecode_byte As Byte() = Convert.FromBase64String(sData)
Dim charCount As Integer = utf8Decode.GetCharCount(todecode_byte, 0, todecode_byte.Length)
Dim decoded_char As Char() = New Char(charCount - 1) {}
utf8Decode.GetChars(todecode_byte, 0, todecode_byte.Length, decoded_char, 0)
Dim result As String = New [String](decoded_char)
Return result
End Function
End Module
This is the routine to register a user and encrypting the password:
Private Sub btnRegister_Click(sender As Object, e As EventArgs) Handles btnRegister.Click
'If the username is taken or used on the
'database, then create account
If MasterTableAdapter.CheckUserName(txtUserName.Text) = Nothing Then
Dim pwd As String = base64Encode(Trim(txtConfirmPassword.Text))
MasterTableAdapter.CreateAccount(txtFName.Text, txtLName.Text, txtUserName.Text, pwd, int1)
MsgBox("An account has been created for: " & vbNewLine & _
"Employee: " & txtFName.Text & " " & txtLName.Text & vbNewLine & _
"User Name: " & txtUserName.Text & vbNewLine & _
"Access Level: " & strAccessLevel)
Me.Close()
Else
MessageBox.Show("The username is in use. Please select another username.", "Authentication Error", MessageBoxButtons.OK, _
MessageBoxIcon.Error)
End If
End Sub
Here is the routine to log in and decrypt the password from the Login Form:
Private Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.Click
Dim pwd As String = base64Decode(Trim(txtPassword.Text))
If Not MasterTableAdapter.Login(txtUserName.Text, pwd) = Nothing Then
'frmWelcomePage.Show()
MsgBox("SUCCESS")
Else
'If no match, display error, clear text boxes and send focus back to the username text box.
MessageBox.Show("Username or password do not match", "Authentication Failure", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
txtPassword.Text = Nothing
txtUserName.Text = Nothing
txtUserName.Focus()
End If
End if
End Sub
I am new to the whole encryption arena so I don't know what I am doing wrong here.

Answer 1

You shouldn't decrypyt the password.
When the user creates a password, you should generate a hash (ie: a value from which the password can not be reconstructed)
When the user attempts to login, you should compare the hash value of the given password with the stored hash.

Answer 2

First, Base64 encoding is not encryption. Many people can look at a B64 string and know what to do to unscramble it. You should look into hash techniques as podiluska suggested.
That said, since your Decode method cant unscramble what you encode, it means you have an error in one or the other. Simple encoding for what you are doing can be done:
Dim s As String = "MySecretPassword"
' convert to byte array
Dim bArry() As Byte = System.Text.Encoding.UTF8.GetBytes(s)
' convert bytes to Base64:
Dim sb64 As String = System.Convert.ToBase64String(barry)
To decode is just the reverse:
' Base64 -> Byte Array
Dim bOut() As Byte = System.Convert.FromBase64String(sb64)
' Byte Arry -> clear text
Dim sOut As String = System.Text.Encoding.UTF8.GetString(bOut)