(Visual FoxPro) Encrypt File in Chunks using AES CBC

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

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loCrypt
LOCAL lcFileToEncrypt
LOCAL loFacIn
LOCAL lnSuccess
LOCAL lcOutputEncryptedFile
LOCAL loFacOutEnc
LOCAL lnChunkSize
LOCAL lnNumChunks
LOCAL loBd
LOCAL i
LOCAL lcDecryptedFile
LOCAL lnBSame

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Crypt2')
loCrypt = CreateObject('Chilkat.Crypt2')

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

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

lcFileToEncrypt = "qa_data/hamlet.xml"
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.FileAccess')
loFacIn = CreateObject('Chilkat.FileAccess')
lnSuccess = loFacIn.OpenForRead(lcFileToEncrypt)
IF (lnSuccess <> 1) THEN
    ? "Failed to open file that is to be encrytped."
    RELEASE loCrypt
    RELEASE loFacIn
    CANCEL
ENDIF

lcOutputEncryptedFile = "qa_output/hamlet.enc"
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.FileAccess')
loFacOutEnc = CreateObject('Chilkat.FileAccess')
lnSuccess = loFacOutEnc.OpenForWrite(lcOutputEncryptedFile)
IF (lnSuccess <> 1) THEN
    ? "Failed to encrypted output file."
    RELEASE loCrypt
    RELEASE loFacIn
    RELEASE loFacOutEnc
    CANCEL
ENDIF

* Let's encrypt in 10000 byte chunks.
lnChunkSize = 10000
lnNumChunks = loFacIn.GetNumBlocks(lnChunkSize)

loCrypt.FirstChunk = 1
loCrypt.LastChunk = 0

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.BinData')
loBd = CreateObject('Chilkat.BinData')

i = 0
DO WHILE i < lnNumChunks
    i = i + 1
    IF (i = lnNumChunks) THEN
        loCrypt.LastChunk = 1
    ENDIF

    * Read the next chunk from the file.
    * The last chunk will be whatever amount remains in the file..
    loBd.Clear()
    loFacIn.FileReadBd(lnChunkSize,loBd)

    * Encrypt.
    loCrypt.EncryptBd(loBd)

    * Write the encrypted chunk to the output file.
    loFacOutEnc.FileWriteBd(loBd,0,0)

    loCrypt.FirstChunk = 0
ENDDO

* Make sure both FirstChunk and LastChunk are restored to 1 after
* encrypting or decrypting in chunks.  Otherwise subsequent encryptions/decryptions
* will produce unexpected results.
loCrypt.FirstChunk = 1
loCrypt.LastChunk = 1

loFacIn.FileClose()
loFacOutEnc.FileClose()

* Decrypt the encrypted output file in a single call using CBC mode:
lcDecryptedFile = "qa_output/hamlet_dec.xml"
lnSuccess = loCrypt.CkDecryptFile(lcOutputEncryptedFile,lcDecryptedFile)
* Assume success for the example..

* Compare the contents of the decrypted file with the original file:
lnBSame = loFacIn.FileContentsEqual(lcFileToEncrypt,lcDecryptedFile)
? "bSame = " + STR(lnBSame)

RELEASE loCrypt
RELEASE loFacIn
RELEASE loFacOutEnc
RELEASE loBd