The Bitcoin Piñata

Published: 2017-09-15 (last updated: 2018-04-16)


The Bitcoin Piñata is a unikernel which serves as bug bounty system to test TLS and the underlying implementations. Its communication endpoints are a website describing the setup, and both a TLS client and a TLS server listening on a port. The total size, including TLS, X.509, TCP/IP, of the virtual machine image is 4MB, which is less than 4% of a comparable system using a Linux kernel and OpenSSL.

When a TLS handshake with the Piñata is successful including mutual authentication, the Piñata transmits the private key to a Bitcoin wallet which initially contained 10BTC. The project started on February 10th 2015. Our lender transferred on March 18th 2018 the 10BTC and repurposed them for other projects.

On startup, the Piñata generates its certificate authority on the fly, including certificates and private keys. This means that only the Piñata itself contains private keys which can authenticate successfully, and an attacker has to find an exploitable flaw in any software layer (OCaml runtime, virtual network device, TCP/IP stack, TLS library, X.509 validation, or elsewhere) to complete the challenge.

The Piñata is online since February 10th 2015, and even though hundreds of thousands of connections and initiated TLS handshakes, no Bitcoins were taken.

By using a Bitcoin wallet, the Piñata is a transparent bug bounty. Everybody can observe (by looking into the blockchain) whether it has been compromised and the money has been transferred to another wallet. It is also self-serving: when an attacker discovers a flaw, they don't need to fill out any forms to retrieve the bounty, instead they can take the wallet, without any questions asked.