Advice regarding encryption - asp.net

Question

I have a class called tdes which looks like this:
Imports Microsoft.VisualBasic
Imports System
Imports System.Collections.Generic
Imports System.Text
Imports System.Security.Cryptography
Imports System.IO
Namespace security
Public Class tdes
Private des As New TripleDESCryptoServiceProvider()
Private utf8 As New UTF8Encoding()
Private keyValue As Byte()
Private iVValue As Byte()
Public Property Key() As Byte()
Get
Return keyValue
End Get
Set(ByVal value As Byte())
keyValue = value
End Set
End Property
Public Property iV() As Byte()
Get
Return iVValue
End Get
Set(ByVal value As Byte())
iVValue = value
End Set
End Property
Public Sub New(ByVal key As Byte(), ByVal iV As Byte())
Me.keyValue = key
Me.iVValue = iV
End Sub
Public Function ByteDecrypt(ByVal bytes As Byte()) As String
Dim output As Byte()
output = Transform(bytes, des.CreateDecryptor(Me.keyValue, Me.iVValue))
'Return Convert.ToBase64String(output)
Return utf8.GetString(output)
End Function
Public Function ByteEncrypt(ByVal bytes As Byte()) As Byte()
Return Transform(bytes, des.CreateEncryptor(Me.keyValue, Me.iVValue))
End Function
Public Function StringDecrypt(ByVal text As String) As String
Dim input As Byte() = Convert.FromBase64String(text)
Dim output As Byte() = Transform(input, des.CreateDecryptor(Me.keyValue, Me.iVValue))
Return utf8.GetString(output)
End Function
Public Function StringEncrypt(ByVal text As String) As String
Dim input As Byte() = utf8.GetBytes(text)
Dim output As Byte() = Transform(input, des.CreateEncryptor(Me.keyValue, Me.iVValue))
Return Convert.ToBase64String(output)
End Function
Public Function StringEncryptByte(ByVal text As String) As Byte()
Dim input As Byte() = utf8.GetBytes(text)
Dim output As Byte() = Transform(input, des.CreateEncryptor(Me.keyValue, Me.iVValue))
'Return Convert.ToBase64String(output)
Return output
End Function
Private Function Transform(ByVal input As Byte(), ByVal cryptoTransform As ICryptoTransform) As Byte()
' Create the necessary streams
Dim memory As New MemoryStream()
Dim stream As New CryptoStream(memory, cryptoTransform, CryptoStreamMode.Write)
' Transform the bytes as requesed
stream.Write(input, 0, input.Length)
stream.FlushFinalBlock()
' Read the memory stream and convert it back into byte array
memory.Position = 0
Dim result As Byte() = New Byte(memory.Length - 1) {}
memory.Read(result, 0, result.Length)
' Clean up
memory.Close()
stream.Close()
' Return result
Return result
End Function
End Class
End Namespace
And it works well encrypting and decrypting things. I want to encrypt some existing passwords in a database table, so I've run a little script on them which encrypt them like so (lots missing for brevity):
Dim key As Byte() = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24}
Dim iv As Byte() = {8, 7, 6, 5, 4, 3, 2, 1}
Dim enc As New security.tdes(key, iv)
Dim i As Integer = 0
Using oConn As New SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings("pitstopConnectionString").ConnectionString)
Using cmd As New SqlCommand("doUpdatePasswords", oConn)
cmd.CommandType = CommandType.StoredProcedure
cmd.Parameters.AddWithValue("#userid", userid)
cmd.Parameters.AddWithValue("#newpassword", enc.StringEncryptByte(currentPassword))
oConn.Open()
Try
i = cmd.ExecuteNonQuery()
Catch ex As Exception
Exit Sub
End Try
End Using
End Using
This has successfully encrypted all my passwords for all the records in the table. Now, when I allow someone to login, I want to compare the two values (what was typed in, to what the stored password is) and I assumed the best way would be to decrypt the stored and compare using strings? Like so:
If (enc.ByteDecrypt(pwdenc).ToString() = pitstop.doMakeSafeForSQL(txtPassword.Text.ToString.ToLower)) Then
However, I get all sorts of bizarre errors; Unable to cast object of type 'System.String' to type 'System.Byte[]'. is one, Invalid character in a Base-64 string. is another based on how I call the password in the proceeding SQLDataReader:
Using oConn As New SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings("pitstopConnectionString").ConnectionString)
Using cmd As New SqlCommand("doGetEncryptedForLogin", oConn)
cmd.CommandType = CommandType.StoredProcedure
cmd.Parameters.AddWithValue("#email", pitstop.doMakeSafeForSQL(txtEmail.Text.ToString.ToLower))
oConn.Open()
Using dr As SqlDataReader = cmd.ExecuteReader()
If dr.HasRows() = True Then
While dr.Read()
pwdenc = dr("password_b")
End While
Else
pitstop.doLogIt("Denied login for [" & txtEmail.Text & "]")
litError.Text = "The details you have provided are incorrect. Please try again."
pnlDenied.Visible = True
Exit Sub
End If
dr.Close()
End Using
End Using
End Using
Help or advice welcomed, as I'm stumped here...

Answer 1

Since noone else seems to answer, I'll give you my own two cents. I remember having experienced a similiar situation when I started "playing" with encryption, more than three years ago; in my case the problem was somehow related with the Base64 conversion, though I cannot remember the exact details now.
I suggest you going through a calm and patient debugging session, tracking down all the values of the strings, the byte arrays before and after crypting and decrypting.
I understand it's not a great help, but I hope at least can direct you in the right direction.

Answer 2

I fixed this error by replacing my 'encryption' class with Jeff Atwood's (www.codinghorror.com) fantastic encryption tools.
I did want to salt the passwords and store the salt, but I run out of time to implement that and will have to return to it. In the meantime, I've used this code as my encrypt and decrypt functions - I hope this is of some assistance to someone:
Dim key As String = System.Configuration.ConfigurationManager.AppSettings("key").ToString()
Dim salty As String = pitstop.doMakeSafeForSQL(txtEmail.Text.ToString().ToLower())
Dim p As Encryption.Symmetric.Provider = Encryption.Symmetric.Provider.TripleDES
Dim sym As New Encryption.Symmetric(p)
sym.Key.Text = key
Dim encryptedData As Encryption.Data
encryptedData = sym.Encrypt(New Encryption.Data(pitstop.doMakeSafeForSQL(txtPassword.Text.ToString().ToLower())))
Decryption:
Dim decryptedData As Encryption.Data
Dim pr As Encryption.Symmetric.Provider = Encryption.Symmetric.Provider.TripleDES
Dim sym2 As New Encryption.Symmetric(pr)
sym2.Key.Text = System.Configuration.ConfigurationManager.AppSettings("key").ToString()
Try
decryptedData = sym2.Decrypt(encryptedData)
Catch ex As Exception
// removed for brevity //
End Try
If anyone has any articles or advice on how to create, store and retrieve salted passwords, I'd love to see it.
Chris