Lua

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". Lua

local chilkat = require("chilkat")

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

local crypt = chilkat.Crypt2.new()

-- Set the encryption algorithm to "AES"
crypt.crypt_algorithm = "aes"

-- Indicate that the Galois/Counter Mode (GCM) should be used:
crypt.cipher_mode = "gcm"

-- KeyLength may be 128, 192, 256
crypt.key_length = 128

-- This is the 128-bit AES secret key (in hex format)
local K = "feffe9928665731c6d6a8f9467308308"

-- This is the 16-byte initialization vector:
local IV = "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 AAD = "feedfacedeadbeeffeedfacedeadbeefabaddad2"

-- The plain-text bytes (in hex format) to be encrypted.
local PT = "d9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39"

-- The expected cipher text (in hex format)
local CT = "42831ec2217774244b7221b784d0d49ce3aa212f2c02a4e035c17e2329aca12e21d514b25466931c7d8f6a5aac84aa051ba30b396a0aac973d58e091"

-- The expected authenticated tag given the above inputs.
local 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".
crypt.encoding_mode = "hex"

-- Set the secret key and IV
crypt:set_encoded_iv(IV, "hex")
crypt:set_encoded_key(K, "hex")

-- Set the additional authenticated data (AAD)
local success = crypt:set_encoded_aad(AAD, "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 ctResult = crypt:encrypt_encoded(PT)
if not crypt.last_method_success then
    print(crypt.last_error_text)
    return
end

-- Examine the result.  It should be the same (case insensitive) as our expected result:
print("computed result: " .. ctResult)
print("expected result: " .. CT)

-- Examine the authenticated tag. It should be the same (case insensitive) as our expected authenticated tag:
local tResult = crypt:get_encoded_auth_tag("hex")
print("computed authTag: " .. tResult)
print("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.
success = crypt:set_encoded_auth_tag(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.
local ptResult = crypt:decrypt_encoded(CT)
if not crypt.last_method_success then
    -- Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    print(crypt.last_error_text)
    return
end

-- Examine the decrypted result.  It should be the same as our expected plaintext (case insensitive)
print("plaintext decrypted: " .. ptResult)
print("plaintext expected:  " .. PT)

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

success = crypt:set_encoded_auth_tag(tInvalid, "hex")

ptResult = crypt:decrypt_encoded(CT)
if not crypt.last_method_success then
    -- Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    print(crypt.last_error_text)
end