(VB.NET) Encrypt Already Existing Zip

To encrypt an already existing non-encrypted .zip, the application must open the .zip, set the encryption related properties, and then re-write.

Chilkat .NET Downloads Chilkat .NET Framework Chilkat for .NET Core

' This requires the Chilkat Zip API to have been previously unlocked.
' See Unlock Chilkat Zip for sample code.

Dim zip As New Chilkat.Zip

' Open an unencrypted .zip
Dim success As Boolean = zip.OpenZip("qa_data/zips/test.zip")
If (success <> True) Then
    Debug.WriteLine(zip.LastErrorText)
    Exit Sub
End If


' Unzip to a temp directory.
Dim numFilesUnzipped As Integer = zip.Unzip("qa_output/tmp")
If (numFilesUnzipped < 0) Then
    Debug.WriteLine(zip.LastErrorText)
    Exit Sub
End If


' Clear the zip object.
zip.NewZip("qa_output/aesTest.zip")

' Indicate that 128-bit AES encryption is to be used when writing the .zip
zip.Encryption = 4
zip.EncryptKeyLength = 128

' Set the password.
zip.EncryptPassword = "secret"

' Append the files.
zip.AppendFromDir = "qa_output/tmp"
success = zip.AppendFiles("*.*",True)
If (success <> True) Then
    Debug.WriteLine(zip.LastErrorText)
    Exit Sub
End If


' Write the .zip and close it.
success = zip.WriteZipAndClose()
If (success <> True) Then
    Debug.WriteLine(zip.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Success.")