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AEAD AES 128-bit GCM

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Demonstrates AES encryption using the Galois/Counter Mode (GCM). GCM is an authenticated encryption mode with "additional data" (often referred to as AEAD). GCM is a cipher mode that can be applied to any symmetric encryption algorithm with a 16-byte block size, such as AES and Twofish. In GCM mode, the block encryption algorithm is transformed into a stream encryption algorithm, and therefore no padding occurs (and the PaddingScheme property does not apply). The "additional data" (known as the AAD) does not get encrypted but plays a role in the computation of the resulting "authenticated tag". AutoIt

Local $bSuccess = False

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

$oCrypt = ObjCreate("Chilkat.Crypt2")

;  Set the encryption algorithm to "AES"	
$oCrypt.CryptAlgorithm = "aes"

;  Indicate that the Galois/Counter Mode (GCM) should be used:
$oCrypt.CipherMode = "gcm"

;  KeyLength may be 128, 192, 256
$oCrypt.KeyLength = 128

;  This is the 128-bit AES secret key (in hex format)
Local $sK = "feffe9928665731c6d6a8f9467308308"

;  This is the 16-byte initialization vector:
Local $sIV = "cafebabefacedbaddecaf888"

;  This is the additional data to be used as input to the GCM AEAD algorithm,
;  but is not included in the output.  It plays a role in the computation of the
;  resulting authenticated tag.
Local $sAAD = "feedfacedeadbeeffeedfacedeadbeefabaddad2"

;  The plain-text bytes (in hex format) to be encrypted.
Local $sPT = "d9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39"

;  The expected cipher text (in hex format)
Local $sCT = "42831ec2217774244b7221b784d0d49ce3aa212f2c02a4e035c17e2329aca12e21d514b25466931c7d8f6a5aac84aa051ba30b396a0aac973d58e091"

;  The expected authenticated tag given the above inputs.
Local $sT = "5bc94fbc3221a5db94fae95ae7121a47"

;  Note: The above data are the values for test vector #4 from 
;  the PDF document at: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf

;  EncodingMode specifies the encoding of the output for
;  encryption, and the input for decryption.
;  It may be "hex", "url", "base64", or "quoted-printable".
$oCrypt.EncodingMode = "hex"

;  Set the secret key and IV
$oCrypt.SetEncodedIV $sIV,"hex"
$oCrypt.SetEncodedKey $sK,"hex"

;  Set the additional authenticated data (AAD)
$bSuccess = $oCrypt.SetEncodedAad($sAAD,"hex")

;  For the purpose of duplicating the test vectors, we are using the EncryptEncoded method.
;  This method decodes the input string according to the encoding specified by the EncodingMode
;  property, which in this case is "hex".  The decoded bytes are encrypted using the mode specified
;  by the CipherMode property.  The resulting
;  encrypted bytes are encoded (again using the encoding mode specified by EncodingMode),
;  and the result is returned.
;  <b>Note:</b> The CipherMode property sets the block mode of operation (gcm, cfb, cbc, ofb, ecb, etc.) 
;  for any of the Chilkat encryption/decryption methods (such as EncryptBytes, EncryptString, 
;  CkEncryptFile, etc.)   Just because GCM mode is demonstrated with EncryptEncoded/DecryptEncoded,
;  does not imply that GCM mode is specific to only these methods.
Local $sCtResult = $oCrypt.EncryptEncoded($sPT)
If ($oCrypt.LastMethodSuccess <> True) Then
    ConsoleWrite($oCrypt.LastErrorText & @CRLF)
    Exit
EndIf

;  Examine the result.  It should be the same (case insensitive) as our expected result:
ConsoleWrite("computed result: " & $sCtResult & @CRLF)
ConsoleWrite("expected result: " & $sCT & @CRLF)

;  Examine the authenticated tag. It should be the same (case insensitive) as our expected authenticated tag:
Local $sTResult = $oCrypt.GetEncodedAuthTag("hex")
ConsoleWrite("computed authTag: " & $sTResult & @CRLF)
ConsoleWrite("expected authTag: " & $sT & @CRLF)

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

;  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 (case insensitive) to 
;  the expected result.
;  Note: The return value of SetEncodedAuthTag indicates whether the string passed was a valid
;  representation of the encoding specified in the 2nd arg.
$bSuccess = $oCrypt.SetEncodedAuthTag($sT,"hex")

;  All of our properties (IV, secret key, cipher mode, and AAD) are already set from the code above...

;  So let's decrypt CT to and check to see if we get PT.
Local $sPtResult = $oCrypt.DecryptEncoded($sCT)
If ($oCrypt.LastMethodSuccess <> True) Then
    ;  Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    ConsoleWrite($oCrypt.LastErrorText & @CRLF)
    Exit
EndIf

;  Examine the decrypted result.  It should be the same as our expected plaintext (case insensitive)
ConsoleWrite("plaintext decrypted: " & $sPtResult & @CRLF)
ConsoleWrite("plaintext expected:  " & $sPT & @CRLF)

;  Let's intentionally set the expected authenticated tag to an incorrect value. 
;  The decrypt operation should fail:
Local $sTInvalid = "ffaabbbc3221a5db94fae95ae7121a47"

$bSuccess = $oCrypt.SetEncodedAuthTag($sTInvalid,"hex")

$sPtResult = $oCrypt.DecryptEncoded($sCT)
If ($oCrypt.LastMethodSuccess <> True) Then
    ;  Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    ConsoleWrite($oCrypt.LastErrorText & @CRLF)
EndIf