CkPython

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. CkPython

import sys
import chilkat

success = False

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

crypt = chilkat.CkCrypt2()

crypt.put_CryptAlgorithm("aes")
crypt.put_CipherMode("cbc")
crypt.put_KeyLength(256)

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

fileToEncrypt = "qa_data/hamlet.xml"
facIn = chilkat.CkFileAccess()
success = facIn.OpenForRead(fileToEncrypt)
if (success != True):
    print("Failed to open file that is to be encrytped.")
    sys.exit()

outputEncryptedFile = "c:/temp/qa_output/hamlet.enc"
facOutEnc = chilkat.CkFileAccess()
success = facOutEnc.OpenForWrite(outputEncryptedFile)
if (success != True):
    print("Failed to encrypted output file.")
    sys.exit()

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

crypt.put_FirstChunk(True)
crypt.put_LastChunk(False)

bd = chilkat.CkBinData()

i = 0
while i < numChunks :
    i = i + 1
    if (i == numChunks):
        crypt.put_LastChunk(True)

    # 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.put_FirstChunk(False)

# 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.put_FirstChunk(True)
crypt.put_LastChunk(True)

facIn.FileClose()
facOutEnc.FileClose()

# Decrypt the encrypted output file in a single call using CBC mode:
decryptedFile = "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:
bSame = facIn.FileContentsEqual(fileToEncrypt,decryptedFile)
print("bSame = " + str(bSame))