Xojo Plugin

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. Xojo Plugin

Dim success As Boolean
success = False

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

Dim crypt As New Chilkat.Crypt2

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

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

Dim fileToEncrypt As String
fileToEncrypt = "qa_data/hamlet.xml"
Dim facIn As New Chilkat.FileAccess
success = facIn.OpenForRead(fileToEncrypt)
If (success <> True) Then
    System.DebugLog("Failed to open file that is to be encrytped.")
    Return
End If

Dim outputEncryptedFile As String
outputEncryptedFile = "c:/temp/qa_output/hamlet.enc"
Dim facOutEnc As New Chilkat.FileAccess
success = facOutEnc.OpenForWrite(outputEncryptedFile)
If (success <> True) Then
    System.DebugLog("Failed to encrypted output file.")
    Return
End If

// Let's encrypt in 10000 byte chunks.
Dim chunkSize As Int32
chunkSize = 10000
Dim numChunks As Int32
numChunks = facIn.GetNumBlocks(chunkSize)

crypt.FirstChunk = True
crypt.LastChunk = False

Dim bd As New Chilkat.BinData

Dim i As Int32
i = 0
While i < numChunks
    i = i + 1
    If (i = numChunks) Then
        crypt.LastChunk = True
    End If

    // Read the next chunk from the file.
    // The last chunk will be whatever amount remains in the file..
    success = bd.Clear()
    success = facIn.FileReadBd(chunkSize,bd)

    // Encrypt.
    success = crypt.EncryptBd(bd)

    // Write the encrypted chunk to the output file.
    success = facOutEnc.FileWriteBd(bd,0,0)

    crypt.FirstChunk = False
Wend

// 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 
facOutEnc.FileClose 

// Decrypt the encrypted output file in a single call using CBC mode:
Dim decryptedFile As String
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:
Dim bSame As Boolean
bSame = facIn.FileContentsEqual(fileToEncrypt,decryptedFile)
System.DebugLog("bSame = " + Str(bSame))