(AutoIt) Example: Crypt2.RandomizeIV method

Demonstrates using a random initialization vector for AES GCM encryption.

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.

$oCrypt = ObjCreate("Chilkat.Crypt2")

$oCrypt.CryptAlgorithm = "aes"
$oCrypt.CipherMode = "gcm"
$oCrypt.KeyLength = 256

Local $sK = "000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F"
Local $sAAD = "feedfacedeadbeeffeedfacedeadbeefabaddad2"
Local $sPT = "This is the text to be AES-GCM encrypted."

; Generate a random IV.
$oCrypt.RandomizeIV 
Local $sIV = $oCrypt.GetEncodedIV("hex")

$oCrypt.SetEncodedKey $sK,"hex"

Local $bSuccess = $oCrypt.SetEncodedAad($sAAD,"hex")

; Return the encrypted bytes as base64
$oCrypt.EncodingMode = "base64"
$oCrypt.Charset = "utf-8"
Local $sCipherText = $oCrypt.EncryptStringENC($sPT)
If ($oCrypt.LastMethodSuccess <> True) Then
    ConsoleWrite($oCrypt.LastErrorText & @CRLF)
    Exit
EndIf

; Get the GCM authenticated tag computed when encrypting.
Local $sAuthTag = $oCrypt.GetEncodedAuthTag("base64")

ConsoleWrite("Cipher Text: " & $sCipherText & @CRLF)
ConsoleWrite("Auth Tag: " & $sAuthTag & @CRLF)

; Let's send the IV, CipherText, and AuthTag to the decrypting party.
; We'll send them concatenated like this: [IV || Ciphertext || AuthTag]
; In base64 format.
$oBdEncrypted = ObjCreate("Chilkat.BinData")
$oBdEncrypted.AppendEncoded($sIV,"hex")
$oBdEncrypted.AppendEncoded($sCipherText,"base64")
$oBdEncrypted.AppendEncoded($sAuthTag,"base64")

Local $sConcatenatedGcmOutput = $oBdEncrypted.GetEncoded("base64")
ConsoleWrite("Concatenated GCM Output: " & $sConcatenatedGcmOutput & @CRLF)

; Sample output so far:

; -------------------------------------------------------------------------------------
; Now let's GCM decrypt...
; -------------------------------------------------------------------------------------

$oDecrypt = ObjCreate("Chilkat.Crypt2")

; The values shared and agreed upon by both sides beforehand are: algorithm, cipher mode, secret key, and AAD.
; Sometimes the IV can be a value already known and agreed upon, but in this case the encryptor sends the IV to the decryptor.
$oDecrypt.CryptAlgorithm = "aes"
$oDecrypt.CipherMode = "gcm"
$oDecrypt.KeyLength = 256
$oDecrypt.SetEncodedKey $sK,"hex"
$oDecrypt.SetEncodedAad($sAAD,"hex")

$oBdFromEncryptor = ObjCreate("Chilkat.BinData")
$oBdFromEncryptor.AppendEncoded($sConcatenatedGcmOutput,"base64")

Local $iSz = $oBdFromEncryptor.NumBytes

; Extract the parts.
Local $sExtractedIV = $oBdFromEncryptor.GetEncodedChunk(0,16,"hex")
Local $sExtractedCipherText = $oBdFromEncryptor.GetEncodedChunk(16,$iSz - 32,"base64")
Local $sExpectedAuthTag = $oBdFromEncryptor.GetEncodedChunk($iSz - 16,16,"base64")

; Before GCM decrypting, we must set the authenticated tag to the value that is expected.
; The decryption will fail if the resulting authenticated tag is not equal to the expected result.
$bSuccess = $oDecrypt.SetEncodedAuthTag($sExpectedAuthTag,"base64")

; Also set the IV.
$oDecrypt.SetEncodedIV $sExtractedIV,"hex"

; Decrypt..
$oDecrypt.EncodingMode = "base64"
$oDecrypt.Charset = "utf-8"
Local $sDecryptedText = $oDecrypt.DecryptStringENC($sExtractedCipherText)
If ($oDecrypt.LastMethodSuccess <> True) Then
    ; Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    ConsoleWrite($oDecrypt.LastErrorText & @CRLF)
    Exit
EndIf

ConsoleWrite("Decrypted: " & $sDecryptedText & @CRLF)