Here is my test code.
   local key = "AAAAAAAAAAAAAAAA"
  local iv = "0123456789abcdef" 
  local str = Cryptography.aesEncrypt("Hello, world!", key, iv, 1)
  local str_2 = Cryptography.aesDecrypt(str, key, iv, 1) 
  print(str, str_2)
The string is encrypted, but when it's decrypted there are 3 extra characters at the end. These characters are EXT (end of text) codes.
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Comments
Testing by concatenating to the ends of the string:
:Hello, world!: