Lua

Decrypt 256-bit AES GCM Produced by Something Unknown

See more Encryption Examples

Demonstrates how to decrypt something produced elsewhere (unknown) with 256-bit AES GCM. Lua

local chilkat = require("chilkat")

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

-- We have the following to decrypt:

-- Key (Base64):
local keyBase64 = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

-- IV (Base64Url):
local ivBase64Url = "xrvaINMLqotAbWRK"

-- ciphertext (base64url):
local cipherBase64Url = "RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY="

local crypt = chilkat.Crypt2.new()

crypt.crypt_algorithm = "aes"
crypt.cipher_mode = "gcm"
crypt.key_length = 256

local success = crypt:set_encoded_aad("random", "ascii")
crypt:set_encoded_key(keyBase64, "base64")
crypt:set_encoded_iv(ivBase64Url, "base64url")

-- The cipher text contains the 16-byte auth tag at the end.
-- get it separately..
local bdEncrypted = chilkat.BinData.new()
local bdAuthTag = chilkat.BinData.new()
success = bdEncrypted:append_encoded(cipherBase64Url, "base64url")

local numBytes = bdEncrypted.num_bytes
local authTagHex = bdEncrypted:get_encoded_chunk(numBytes - 16, 16, "hex")

print("Auth tag in hex: " .. authTagHex)

success = bdAuthTag:append_encoded(authTagHex, "hex")
bdEncrypted:remove_chunk(numBytes - 16, 16)

-- Use this special value to tell Chilkat to ignore the auth tag.
success = crypt:set_encoded_auth_tag("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", "hex")

-- Decrypt
crypt.encoding_mode = "base64"
local originalText = crypt:decrypt_string_enc(bdEncrypted:get_encoded("base64"))
if not crypt.last_method_success then
    print(crypt.last_error_text)
else
    print(originalText)
    print("Success.")
end

-- Decrypted text