asked on

Security Encryption ( From encypt to decrypt )

Oh I took an example from microsoft, and i'm trying to Decrypt a string.

Dim ct As ICryptoTransform
Dim ms As MemoryStream
Dim cs As CryptoStream
Dim byt() As Byte
Dim IVbyt() As Byte
Dim KeyByt() As Byte

Try
ct = mCSP.CreateDecryptor(mCSP.Key, mCSP.IV)
Catch

KeyByt = Convert.FromBase64String(txtKey.Text)
IVbyt = Convert.FromBase64String(txtIV.Text)

--->> I added this part

mCSP.IV = IVbyt
mCSP.Key = KeyByt

ct = mCSP.CreateDecryptor(mCSP.Key, mCSP.IV)

End Try

byt = Convert.FromBase64String(Value)

ms = New MemoryStream
cs = New CryptoStream(ms, ct, CryptoStreamMode.Write)
cs.Write(byt, 0, byt.Length)
cs.FlushFinalBlock()

cs.Close()

Return Encoding.UTF8.GetString(ms.ToArray())

I wanted to make it so i could enter the two manditory keys in a text box and it would decrypt my string but i get this error!

Object reference not set to an instance of an object.

Any help would be awsome!!

Thanks!

S-Twilley

Which line do you get the error on?

===========

Also... where if the "Value" variable coming from... just incase this is the bit causing the error:

byt = Convert.FromBase64String(Value)

shutuplonnie

ASKER

Private Function DecryptString(ByVal Value As String) As String

That's where my value is coming from the example if you want to look at is from

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetsec/html/cryptosimplified.asp

The error line is ..

mCSP.IV = IVbyt

S-Twilley

My guess is that you haven't initialized your mCSP object using one of the lines given on that page you gave me... e.g:

mCSP = SetEnc()

------------------

Which relates to doing...

mCSP = New DESCryptoServiceProvider

or

mCSP = New TripleDESCryptoServiceProvider.

Im not sure which type you are using but let's say it's the first of the two:

=================

mCSP = New DESCryptoServiceProvider

Dim ct As ICryptoTransform
Dim ms As MemoryStream
Dim cs As CryptoStream
Dim byt() As Byte
Dim IVbyt() As Byte
Dim KeyByt() As Byte

Try
ct = mCSP.CreateDecryptor(mCSP.Key, mCSP.IV)
Catch

KeyByt = Convert.FromBase64String(txtKey.Text)
IVbyt = Convert.FromBase64String(txtIV.Text)

--->> I added this part

mCSP.IV = IVbyt
mCSP.Key = KeyByt

ct = mCSP.CreateDecryptor(mCSP.Key, mCSP.IV)

End Try

byt = Convert.FromBase64String(Value)

ms = New MemoryStream
cs = New CryptoStream(ms, ct, CryptoStreamMode.Write)
cs.Write(byt, 0, byt.Length)
cs.FlushFinalBlock()

cs.Close()

Return Encoding.UTF8.GetString(ms.ToArray())

ASKER CERTIFIED SOLUTION

S-Twilley

membership

This solution is only available to members.

To access this solution, you must be a member of Experts Exchange.

Start Free Trial

S-Twilley

This assumes that since mCSP has been intialized... that you've probably set a KEY/IV value to it, you can add more checking, and try catch blocks to it if you like:

If Not mCSP Is Nothing Then
Try
ct = mCSP.CreateDecryptor(mCSP.Key, mCSP.IV)
Catch
KeyByt = Convert.FromBase64String(txtKey.Text)
IVbyt = Convert.FromBase64String(txtIV.Text)

mCSP = New DESCryptoServiceProvider ' If you have implemented the SetEnc() function, you may want to use that instead of "New DESCryptoServiceProvider"

mCSP.IV = IVbyt
mCSP.Key = KeyByt

ct = mCSP.CreateDecryptor(mCSP.Key, mCSP.IV)
End Try
Else
KeyByt = Convert.FromBase64String(txtKey.Text)
IVbyt = Convert.FromBase64String(txtIV.Text)

mCSP = New DESCryptoServiceProvider ' If you have implemented the SetEnc() function, you may want to use that instead of "New DESCryptoServiceProvider"

mCSP.IV = IVbyt
mCSP.Key = KeyByt

ct = mCSP.CreateDecryptor(mCSP.Key, mCSP.IV)
End If

shutuplonnie

ASKER

Thanks Everything is working Well!!