Xbase++

AEAD AES 128-bit GCM

See more Encryption Examples

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". Xbase++

LOCAL nSuccess
LOCAL oCrypt
LOCAL K
LOCAL cIV
LOCAL cAAD
LOCAL cPT
LOCAL cCT
LOCAL T
LOCAL cCtResult
LOCAL cTResult
LOCAL cPtResult
LOCAL cTInvalid

nSuccess := 0

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

oCrypt := CreateObject("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)
K := "feffe9928665731c6d6a8f9467308308"

//  This is the 16-byte initialization vector:
cIV := "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.
cAAD := "feedfacedeadbeeffeedfacedeadbeefabaddad2"

//  The plain-text bytes (in hex format) to be encrypted.
cPT := "d9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39"

//  The expected cipher text (in hex format)
cCT := "42831ec2217774244b7221b784d0d49ce3aa212f2c02a4e035c17e2329aca12e21d514b25466931c7d8f6a5aac84aa051ba30b396a0aac973d58e091"

//  The expected authenticated tag given the above inputs.
T := "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(cIV, "hex")
oCrypt:SetEncodedKey(K, "hex")

//  Set the additional authenticated data (AAD)
nSuccess := oCrypt:SetEncodedAad(cAAD, "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.
cCtResult := oCrypt:EncryptEncoded(cPT)
IF (oCrypt:LastMethodSuccess != 1)
    ? oCrypt:LastErrorText
    oCrypt:destroy()
    RETURN
ENDIF

//  Examine the result.  It should be the same (case insensitive) as our expected result:
? "computed result: " + cCtResult
? "expected result: " + cCT

//  Examine the authenticated tag. It should be the same (case insensitive) as our expected authenticated tag:
cTResult := oCrypt:GetEncodedAuthTag("hex")
? "computed authTag: " + cTResult
? "expected authTag: " + T

//  -------------------------------------------------------------------------------------
//  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.
nSuccess := oCrypt:SetEncodedAuthTag(T, "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.
cPtResult := oCrypt:DecryptEncoded(cCT)
IF (oCrypt:LastMethodSuccess != 1)
    //  Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    ? oCrypt:LastErrorText
    oCrypt:destroy()
    RETURN
ENDIF

//  Examine the decrypted result.  It should be the same as our expected plaintext (case insensitive)
? "plaintext decrypted: " + cPtResult
? "plaintext expected:  " + cPT

//  Let's intentionally set the expected authenticated tag to an incorrect value. 
//  The decrypt operation should fail:
cTInvalid := "ffaabbbc3221a5db94fae95ae7121a47"

nSuccess := oCrypt:SetEncodedAuthTag(cTInvalid, "hex")

cPtResult := oCrypt:DecryptEncoded(cCT)
IF (oCrypt:LastMethodSuccess != 1)
    //  Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    ? oCrypt:LastErrorText
ENDIF

oCrypt:destroy()