Chilkat2-Python

Decrypt File in Chunks using 256-bit AES

See more Encryption Examples

Shows how to decrypt a file chunk-by-chunk using FirstChunk/LastChunk properties and accumulate the results in memory with a Chilkat BinData object. Chilkat2-Python

import sys
import chilkat2

success = False

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

# This example decrypts the file previously encrypted in this example:
# Encrypt File in Chunks using AES CBC

crypt = chilkat2.Crypt2()

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

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

fileToDecrypt = "c:/temp/qa_output/hamlet.enc"
facIn = chilkat2.FileAccess()
success = facIn.OpenForRead(fileToDecrypt)
if (success != True):
    print("Failed to open file to be decrytped.")
    sys.exit()

# Let's decrypt in 32000 byte chunks.
chunkSize = 32000
numChunks = facIn.GetNumBlocks(chunkSize)

crypt.FirstChunk = True
crypt.LastChunk = False

bd = chilkat2.BinData()
bdDecrypted = chilkat2.BinData()

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

    # Decrypt this chunk.
    crypt.DecryptBd(bd)
    # Accumulate the decrypted chunks.
    bdDecrypted.AppendBd(bd)

    crypt.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.FirstChunk = True
crypt.LastChunk = True

facIn.FileClose()

# The fully decrypted file is contained in bdDecrypted.
# You can save to a file if desired, or use the decrypted data in your application directly from bdDecrypted.
bdDecrypted.WriteFile("c:/temp/qa_output/hamlet_decrypted.xml")