(Visual Basic 6.0) Compress and Encrypt a Large File (Low and Constant Memory Footprint)

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Demonstrates how to compress and encrypt a large file such that the memory footprint remains low and constant.

Note: This example requires Chilkat v9.5.0.99 or greater.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

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

Dim compress As New ChilkatCompression
compress.Algorithm = "deflate"

Dim success As Long

' Set encryption params.
' The possible values are the same as for the corresponding properties in the Chilkat Crypt2 class/object.
' The encoded IV and Key must be specified as hex.
Dim json As New ChilkatJsonObject
success = json.UpdateString("cryptAlgorithm","aes")
success = json.UpdateString("cipherMode","cbc")
success = json.UpdateInt("keyLength",128)
success = json.UpdateInt("paddingScheme",0)
success = json.UpdateString("encodedIV","000102030405060708090A0B0C0D0E0F")
success = json.UpdateString("encodedKey","000102030405060708090A0B0C0D0E0F")

' Do file-to-file compression+encryption in a single call.
Dim inPath As String
inPath = "qa_data/largeFile.dat"
Dim outPath As String
outPath = "c:/temp/qa_output/compressed_encrypted.dat"
success = compress.CompressEncryptFile(json,inPath,outPath)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' We can do file-to-file decrypt/decompress like this:
Dim inPath2 As String
inPath2 = outPath
Dim outPath2 As String
outPath2 = "c:/temp/qa_output/restored.dat"
success = compress.DecryptDecompressFile(json,inPath2,outPath2)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' Note: The above decrypt + decompress is the equivalent of doing the same in these two steps:
Dim crypt As New ChilkatCrypt2
crypt.CryptAlgorithm = "aes"
crypt.CipherMode = "cbc"
crypt.KeyLength = 128
crypt.PaddingScheme = 0
crypt.SetEncodedIV "000102030405060708090A0B0C0D0E0F","hex"
crypt.SetEncodedKey "000102030405060708090A0B0C0D0E0F","hex"

Dim decryptedPath As String
decryptedPath = "c:/temp/qa_output/decrypted.dat"
success = crypt.CkDecryptFile(inPath2,decryptedPath)
If (success = 0) Then
    Debug.Print crypt.LastErrorText
    Exit Sub
End If

Dim outPath3 As String
outPath3 = "c:/temp/qa_output/restored_in_two_steps.dat"
success = compress.DecompressFile(decryptedPath,outPath3)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

Debug.Print "Success."