Xbase++

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. Xbase++

LOCAL nSuccess
LOCAL oCrypt
LOCAL cFileToEncrypt
LOCAL oFacIn
LOCAL cOutputEncryptedFile
LOCAL oFacOutEnc
LOCAL nChunkSize
LOCAL nNumChunks
LOCAL oBd
LOCAL i
LOCAL cDecryptedFile
LOCAL nBSame

nSuccess := 0

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

oCrypt := CreateObject("Chilkat.Crypt2")

oCrypt:CryptAlgorithm := "aes"
oCrypt:CipherMode := "cbc"
oCrypt:KeyLength := 256

oCrypt:SetEncodedKey("000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F", "hex")
oCrypt:SetEncodedIV("000102030405060708090A0B0C0D0E0F", "hex")

cFileToEncrypt := "qa_data/hamlet.xml"
oFacIn := CreateObject("Chilkat.FileAccess")
nSuccess := oFacIn:OpenForRead(cFileToEncrypt)
IF (nSuccess != 1)
    ? "Failed to open file that is to be encrytped."
    oCrypt:destroy()
    oFacIn:destroy()
    RETURN
ENDIF

cOutputEncryptedFile := "c:/temp/qa_output/hamlet.enc"
oFacOutEnc := CreateObject("Chilkat.FileAccess")
nSuccess := oFacOutEnc:OpenForWrite(cOutputEncryptedFile)
IF (nSuccess != 1)
    ? "Failed to encrypted output file."
    oCrypt:destroy()
    oFacIn:destroy()
    oFacOutEnc:destroy()
    RETURN
ENDIF

//  Let's encrypt in 10000 byte chunks.
nChunkSize := 10000
nNumChunks := oFacIn:GetNumBlocks(nChunkSize)

oCrypt:FirstChunk := 1
oCrypt:LastChunk := 0

oBd := CreateObject("Chilkat.BinData")

i := 0
DO WHILE i < nNumChunks
    i := i + 1
    IF (i == nNumChunks)
        oCrypt:LastChunk := 1
    ENDIF

    //  Read the next chunk from the file.
    //  The last chunk will be whatever amount remains in the file..
    oBd:Clear()
    oFacIn:FileReadBd(nChunkSize, oBd)

    //  Encrypt.
    oCrypt:EncryptBd(oBd)

    //  Write the encrypted chunk to the output file.
    oFacOutEnc:FileWriteBd(oBd, 0, 0)

    oCrypt: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.
oCrypt:FirstChunk := 1
oCrypt:LastChunk := 1

oFacIn:FileClose()
oFacOutEnc:FileClose()

//  Decrypt the encrypted output file in a single call using CBC mode:
cDecryptedFile := "qa_output/hamlet_dec.xml"
nSuccess := oCrypt:CkDecryptFile(cOutputEncryptedFile, cDecryptedFile)
//  Assume success for the example..

//  Compare the contents of the decrypted file with the original file:
nBSame := oFacIn:FileContentsEqual(cFileToEncrypt, cDecryptedFile)
? "bSame = " + Str(nBSame)

oCrypt:destroy()
oFacIn:destroy()
oFacOutEnc:destroy()
oBd:destroy()