Visual FoxPro

AES Encrypt and Decrypt a File

_LANGUAGE_ demonstrates how to AES encrypt a file of any size, and then decrypt. Visual FoxPro

LOCAL lnSuccess
LOCAL loCrypt
LOCAL lcIvHex
LOCAL lcKeyHex
LOCAL lcInFile
LOCAL lcOutFile
LOCAL loDecrypt

lnSuccess = 0

* 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"

* CipherMode may be "ecb" or "cbc"
loCrypt.CipherMode = "cbc"

* KeyLength may be 128, 192, 256
loCrypt.KeyLength = 256

* The padding scheme determines the contents of the bytes
* that are added to pad the result to a multiple of the
* encryption algorithm's block size.  AES has a block
* size of 16 bytes, so encrypted output is always
* a multiple of 16.
loCrypt.PaddingScheme = 0

* An initialization vector is required if using CBC mode.
* ECB mode does not use an IV.
* The length of the IV is equal to the algorithm's block size.
* It is NOT equal to the length of the key.
lcIvHex = "000102030405060708090A0B0C0D0E0F"
loCrypt.SetEncodedIV(lcIvHex,"hex")

* The secret key must equal the size of the key.  For
* 256-bit encryption, the binary secret key is 32 bytes.
* For 128-bit encryption, the binary secret key is 16 bytes.
lcKeyHex = "000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F"
loCrypt.SetEncodedKey(lcKeyHex,"hex")

* Encrypt a file, producing the .aes as output.
* The input file is unchanged, the output .aes contains the encrypted
* contents of the input file.

* Note: The .aes output file has no file format.  It is simply a stream
* of bytes that resembles random binary data.
lcInFile = "/Users/chilkat/testData/pdf/sample.pdf"
lcOutFile = "/Users/chilkat/testData/p7m/sample.pdf.aes"
lnSuccess = loCrypt.CkEncryptFile(lcInFile,lcOutFile)
IF (lnSuccess <> 1) THEN
    ? loCrypt.LastErrorText
    RELEASE loCrypt
    CANCEL
ENDIF

* For demonstration purposes, a different instance of the object will be used
* for decryption.
loDecrypt = CreateObject('Chilkat.Crypt2')

* All settings must match to be able to decrypt:
loDecrypt.CryptAlgorithm = "aes"
loDecrypt.CipherMode = "cbc"
loDecrypt.KeyLength = 256
loDecrypt.PaddingScheme = 0
loDecrypt.SetEncodedIV(lcIvHex,"hex")
loDecrypt.SetEncodedKey(lcKeyHex,"hex")

* Decrypt the .aes
lcInFile = "/Users/chilkat/testData/p7m/sample.pdf.aes"
lcOutFile = "/Users/chilkat/testData/pdf/recovered.pdf"
lnSuccess = loDecrypt.CkDecryptFile(lcInFile,lcOutFile)
IF (lnSuccess = 0) THEN
    ? loDecrypt.LastErrorText
    RELEASE loCrypt
    RELEASE loDecrypt
    CANCEL
ENDIF

? "Success!"

RELEASE loCrypt
RELEASE loDecrypt