(Visual FoxPro) Streaming Encryption by Encrypting in Chunks

Encrypt data in chunks.

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

LOCAL loCrypt
LOCAL lcTxt1
LOCAL lcTxt2
LOCAL lcTxt3
LOCAL loSbEncrypted
LOCAL i
LOCAL lcDecryptedText

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

loCrypt = CreateObject('Chilkat.Crypt2')

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

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

loCrypt.EncodingMode = "hex"
lcTxt1 = "The quick brown fox jumped over the lazy dog." + CHR(13) + CHR(10)
lcTxt2 = "-" + CHR(13) + CHR(10)
lcTxt3 = "Done." + CHR(13) + CHR(10)

loSbEncrypted = CreateObject('Chilkat.StringBuilder')

* Encrypt the 1st chunk:
* (don't worry about feeding the data to the encryptor in 
* exact multiples of the encryption algorithm's block size.
* Chilkat will buffer the data.)
loCrypt.FirstChunk = 1
loCrypt.LastChunk = 0
loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt1))

* Encrypt the 2nd chunk
loCrypt.FirstChunk = 0
loCrypt.LastChunk = 0
loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt2))

* Now encrypt N more chunks...
* Remember -- we're doing this in CBC mode, so each call
* to the encrypt method depends on the state from previous
* calls...
loCrypt.FirstChunk = 0
loCrypt.LastChunk = 0

FOR i = 0 TO 4
    loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt1))
    loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt2))
NEXT

* Now encrypt the last chunk:
loCrypt.FirstChunk = 0
loCrypt.LastChunk = 1
loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt3))

? loSbEncrypted.GetAsString()

* Now decrypt in one call.
* (The data we're decrypting is both the first AND last chunk.)  
loCrypt.FirstChunk = 1
loCrypt.LastChunk = 1
lcDecryptedText = loCrypt.DecryptStringENC(loSbEncrypted.GetAsString())

? lcDecryptedText

* Note: You may decrypt in N chunks by setting the FirstChunk
* and LastChunk properties prior to calling the Decrypt* methods

RELEASE loCrypt
RELEASE loSbEncrypted