B4X

Encrypt File in Chunks using AES CBC

See more Encryption Examples

Demonstrates how to use the FirstChunk/LastChunk properties to encrypt a file chunk-by-chunk. B4X

Dim success As Boolean = False

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

Dim crypt As ChilkatCrypt2
crypt.Initialize("crypt")

crypt.CryptAlgorithm = "aes"
crypt.CipherMode = "cbc"
crypt.KeyLength = 256

crypt.SetEncodedKey("000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F", "hex")
crypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F", "hex")

Dim fileToEncrypt As String = "qa_data/hamlet.xml"
Dim facIn As ChilkatFileAccess
facIn.Initialize
success = facIn.OpenForRead(fileToEncrypt)
If success <> True Then
    Log("Failed to open file that is to be encrytped.")
    Return
End If


Dim outputEncryptedFile As String = "c:/temp/qa_output/hamlet.enc"
Dim facOutEnc As ChilkatFileAccess
facOutEnc.Initialize
success = facOutEnc.OpenForWrite(outputEncryptedFile)
If success <> True Then
    Log("Failed to encrypted output file.")
    Return
End If


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

crypt.FirstChunk = True
crypt.LastChunk = False

Dim bd As ChilkatBinData
bd.Initialize

Dim i As Int = 0
Do 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
Loop

'  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)
Log("bSame = " & bSame)