Greg Brockman

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The Stellar object model

Stellar attempts to encode a relatively direct model of real-world
finance. Here’s an overview of the main concepts you need to know to
start building using Stellar’s API.

 Credits

Think of the credit system as a graph. Each account is represented as
a node, and the credits are represented as per-currency weights
on the edges. For example, if Joyce owes me 10 GBP, then from my
perspective the balance between us is set to +10 GBP. If she later
gives me 15 GBP in person, then our balance should adjust down to -5
GBP.

From her perspective, everything is the same except the signs are
reverse.

Note that it’s possible to issue credits in arbitrary (even user-defined) currencies. The implications here are pretty interesting, and I’ll likely address them in a subsequent post.

 Trust

Trust lines are effectively permission for an edge’s nodes to move the balance in one direction. By default...

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System Design: Stripe Capture the Flag

We launched Stripe CTF 2.0 on Wednesday. Thus far we’ve had 14,000 signups, and over 500 people have captured the flag. Designing an architecture to handle this many users, all running their potentially malicious code on the level servers, was definitely a challenge, but it was also a ton of fun.

Our first and foremost design goal was pretty simple: don’t let people root the machines. It’s horrendously difficult to keep a shared Linux login machine secure, so the best you can do is apply all of the security countermeasures you can think of. Each level server is configured in the same way (maintaining multiple configurations is a great way to end up with an oversight due to increased complexity). All user-facing services run in a chroot with only /home, /tmp, /var/tmp, and /var/log writeable. This is implemented by mounting a filesystem (created using debootstrap) at /var/chroot and...

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