(VB.NET) Encrypt File in Chunks using AES CBC

Demonstrates how to use the FirstChunk/LastChunk properties to encrypt a file chunk-by-chunk.

Chilkat .NET Downloads Chilkat .NET Framework Chilkat for .NET Core

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

Dim crypt As New Chilkat.Crypt2

crypt.CryptAlgorithm = "aes"
crypt.CipherMode = "cbc"
crypt.KeyLength = 128

crypt.SetEncodedKey("000102030405060708090A0B0C0D0E0F","hex")
crypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex")

Dim fileToEncrypt As String = "qa_data/hamlet.xml"
Dim facIn As New Chilkat.FileAccess
Dim success As Boolean = facIn.OpenForRead(fileToEncrypt)
If (success <> True) Then
    Debug.WriteLine("Failed to open file that is to be encrytped.")
    Exit Sub
End If


Dim outputEncryptedFile As String = "qa_output/hamlet.enc"
Dim facOutEnc As New Chilkat.FileAccess
success = facOutEnc.OpenForWrite(outputEncryptedFile)
If (success <> True) Then
    Debug.WriteLine("Failed to encrypted output file.")
    Exit Sub
End If


' Let's encrypt in 10000 byte chunks.
Dim chunkSize As Integer = 10000
Dim numChunks As Integer = facIn.GetNumBlocks(chunkSize)

crypt.FirstChunk = True
crypt.LastChunk = False

Dim bd As New Chilkat.BinData

Dim i As Integer = 0
While i < numChunks
    i = i + 1
    If (i = numChunks) Then
        crypt.LastChunk = True
    End If


    ' Read the next chunk from the file.
    ' The last chunk will be whatever amount remains in the file..
    bd.Clear()
    facIn.FileReadBd(chunkSize,bd)

    ' Encrypt.
    crypt.EncryptBd(bd)

    ' Write the encrypted chunk to the output file.
    facOutEnc.FileWriteBd(bd,0,0)

    crypt.FirstChunk = False
End While

' Make sure both FirstChunk and LastChunk are restored to True after
' encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
' will produce unexpected results.
crypt.FirstChunk = True
crypt.LastChunk = True

facIn.FileClose()
facOutEnc.FileClose()

' Decrypt the encrypted output file in a single call using CBC mode:
Dim decryptedFile As String = "qa_output/hamlet_dec.xml"
success = crypt.CkDecryptFile(outputEncryptedFile,decryptedFile)
' Assume success for the example..

' Compare the contents of the decrypted file with the original file:
Dim bSame As Boolean = facIn.FileContentsEqual(fileToEncrypt,decryptedFile)
Debug.WriteLine("bSame = " & bSame)