My bullet proof advanced math captcha

No robots can resolve this captcha, prove me wrong.

REST API

Parsing HTML can be boring, here is the REST API.

The server gives a challenge, and a secret (the crypted response).

{
    "challenge": "seven + sixteen",
    "secret": "gAAAAABo3UlwKjJ9nZDynItpjxCnJDy4-VmIVOmqLbr2jOexjYFLtOK9dmte3VtF9p19SRjdYHFLZWabYEmRgqy80Gl507xtKw=="
}

POST your response with the previous secret. The server answers true or false.

{
    "response": 23,
    "secret":"gAAAAABo3UlwKjJ9nZDynItpjxCnJDy4-VmIVOmqLbr2jOexjYFLtOK9dmte3VtF9p19SRjdYHFLZWabYEmRgqy80Gl507xtKw=="
}