plaidCTF 2014 - rendezvous (misc250)

For PlaidCTF2014, Eindbazen and fail0verflow joined forces as 0xffa, the Final Fail Alliance.
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This challenge was about establishing a connection to a hidden tor service which is rather picky in accepting connections. We were given the following description:

Misc (250 pts)
The Plague has a friend called Alice who has some secrets on a tor
service (http://6c4dm56aer6xn2h2.onion/). We think if we can talk to
her, we can learn some useful things about The Plague. Unfortunately
she will only rendezvous with "chandler" when he brings a cookie with
"beef" baked into it. Can you help us find her secret?

Getting Started

The first thing we did was of course trying to connect to the service. Whether using a tor to web gateway as for example or a local tor instance, the result was the same: no connection could be established. Using curl -v –socks5-hostname localhost:9050 http://6c4dm56aer6xn2h2.onion/ showed that curl didn’t even send the request, confirming that the problem is at the tor layer and not at the HTTP layer. Thus getting a tor connection to the hidden service is actually part of the challenge.