Visual Basic 6.0

AES Encrypt and Decrypt a File

_LANGUAGE_ demonstrates how to AES encrypt a file of any size, and then decrypt. Visual Basic 6.0

Dim success As Long
success = 0

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

Dim crypt As New ChilkatCrypt2

crypt.CryptAlgorithm = "aes"

' CipherMode may be "ecb" or "cbc"
crypt.CipherMode = "cbc"

' KeyLength may be 128, 192, 256
crypt.KeyLength = 256

' The padding scheme determines the contents of the bytes
' that are added to pad the result to a multiple of the
' encryption algorithm's block size.  AES has a block
' size of 16 bytes, so encrypted output is always
' a multiple of 16.
crypt.PaddingScheme = 0

' An initialization vector is required if using CBC mode.
' ECB mode does not use an IV.
' The length of the IV is equal to the algorithm's block size.
' It is NOT equal to the length of the key.
Dim ivHex As String
ivHex = "000102030405060708090A0B0C0D0E0F"
crypt.SetEncodedIV ivHex,"hex"

' The secret key must equal the size of the key.  For
' 256-bit encryption, the binary secret key is 32 bytes.
' For 128-bit encryption, the binary secret key is 16 bytes.
Dim keyHex As String
keyHex = "000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F"
crypt.SetEncodedKey keyHex,"hex"

' Encrypt a file, producing the .aes as output.
' The input file is unchanged, the output .aes contains the encrypted
' contents of the input file.

' Note: The .aes output file has no file format.  It is simply a stream
' of bytes that resembles random binary data.
Dim inFile As String
inFile = "/Users/chilkat/testData/pdf/sample.pdf"
Dim outFile As String
outFile = "/Users/chilkat/testData/p7m/sample.pdf.aes"
success = crypt.CkEncryptFile(inFile,outFile)
If (success <> 1) Then
    Debug.Print crypt.LastErrorText
    Exit Sub
End If

' For demonstration purposes, a different instance of the object will be used
' for decryption.
Dim decrypt As New ChilkatCrypt2

' All settings must match to be able to decrypt:
decrypt.CryptAlgorithm = "aes"
decrypt.CipherMode = "cbc"
decrypt.KeyLength = 256
decrypt.PaddingScheme = 0
decrypt.SetEncodedIV ivHex,"hex"
decrypt.SetEncodedKey keyHex,"hex"

' Decrypt the .aes
inFile = "/Users/chilkat/testData/p7m/sample.pdf.aes"
outFile = "/Users/chilkat/testData/pdf/recovered.pdf"
success = decrypt.CkDecryptFile(inFile,outFile)
If (success = 0) Then
    Debug.Print decrypt.LastErrorText
    Exit Sub
End If

Debug.Print "Success!"