B4X

AES Encrypt and Decrypt a File

_LANGUAGE_ demonstrates how to AES encrypt a file of any size, and then decrypt. B4X

Dim success As Boolean = False

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

Dim crypt As ChilkatCrypt2
crypt.Initialize("crypt")

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 = "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 = "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 = "/Users/chilkat/testData/pdf/sample.pdf"
Dim outFile As String = "/Users/chilkat/testData/p7m/sample.pdf.aes"
success = crypt.CkEncryptFile(inFile, outFile)
If success <> True Then
    Log(crypt.LastErrorText)
    Return
End If


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

'  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 = False Then
    Log(decrypt.LastErrorText)
    Return
End If


Log("Success!")