(VB.NET) Streaming Encryption

Encrypt and decrypt using a stream.

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' This example assumes the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim crypt As New Chilkat.Crypt2

' Setup encryption using the chacha20 algorithm...
crypt.CryptAlgorithm = "chacha20"
crypt.KeyLength = 256
crypt.EncodingMode = "hex"
Dim ivHex As String = "000000000000000000000002"
crypt.SetEncodedIV(ivHex,"hex")
crypt.InitialCount = 42
Dim keyHex As String = "1c9240a5eb55d38af333888604f6b5f0473917c1402b80099dca5cbc207075c0"
crypt.SetEncodedKey(keyHex,"hex")

Dim plainText As String = "The quick brown fox jumped over the lazy dog." & vbCrLf

Dim stream As New Chilkat.Stream

' We'll save the encrypted output in eStrings to demonstrate streaming decryption next.
Dim eStrings As New Chilkat.StringArray

' Start a background task that will encrypt a stream.
Dim task As Chilkat.Task = crypt.EncryptStreamAsync(stream)
Dim success As Boolean = task.Run()

' Write plainText to the stream, and read chacha20 encrypted text..
Dim cipherText As String
Dim i As Integer
For i = 1 To 10
    ' Note: An encryption algorithm's block size will cause buffering,
    ' and therefore not every loop iteration will produce output.
    success = stream.WriteString(plainText)
    If (stream.DataAvailable = True) Then
        cipherText = stream.ReadBytesENC("hex")
        Debug.WriteLine(cipherText)
        success = eStrings.Append(cipherText)
    End If

Next

' Tell the background task that the stream has ended.
success = stream.WriteClose()

' Let's make sure the background task finished.
' It should already be the case that the task is finished.
While (task.Finished <> True)
    task.SleepMs(20)
End While

' Get any remaining data available from the stream.
If (stream.DataAvailable = True) Then
    cipherText = stream.ReadBytesENC("hex")
    Debug.WriteLine(cipherText)
    success = eStrings.Append(cipherText)
End If


If (task.TaskSuccess <> True) Then
    Debug.WriteLine("async encryption failed:")
    Debug.WriteLine(task.ResultErrorText)
    success = False
End If




Debug.WriteLine("-- encrypt finished --")

' Now decrypt to return the original.

' Reset the stream object so it can be used again.
stream.Reset()

' Start a background task that will decrypt a stream.
task = crypt.DecryptStreamAsync(stream)
success = task.Run()

Dim n As Integer = eStrings.Count
For i = 0 To n - 1
    success = stream.WriteBytesENC(eStrings.GetString(i),"hex")
    If (stream.DataAvailable = True) Then
        plainText = stream.ReadString()
        Debug.WriteLine(plainText)
    End If

Next

' Tell the background task that the stream has ended.
success = stream.WriteClose()

' Let's make sure the background task finished.
' It should already be the case that the task is finished.
While (task.Finished <> True)
    task.SleepMs(20)
End While

' Get any remaining data available from the stream.
If (stream.DataAvailable = True) Then
    plainText = stream.ReadString()
    Debug.WriteLine(plainText)
End If



If (task.TaskSuccess <> True) Then
    Debug.WriteLine("async decryption failed:")
    Debug.WriteLine(task.ResultErrorText)
    success = False
End If





Debug.WriteLine("-- decrypt finished --")