Past Meetup

Camilo Aguilar on the rsync algorithm & a PWLMini by David Ashby

This Meetup is past

191 people went

Two Sigma

101 Ave. of the Americas, 23rd Fl. J · New York

How to find us

Cross Streets: Watt and Grand. Note: Please make sure you’re signed-up for the meetup, including your first and last name. Without this info you won’t be allowed into the building by security.

Location image of event venue


We're thrilled to host Camilo Aguilar, software engineer at Enigma and fellow PWL organizer (of the Medellín chapter (, presenting on the rsync algorithm ( by A. Tridgell and P. Mackerras.

In addition to Camilo's talk, PWLNYC Organizer David Ashby will be opening the event with a lightning talk on the Secure Hash Standard (, specifically SHA256, called SHAmwow: Poorly Re-implementing SHA256 for Fun and Profit.


• Camilo Aguilar on the rsync algorithm:

Modern computers are very powerful. These days, mobile phones are packed with multi core CPUs and even GPUs. Despite these advances in hardware, internet connections in most parts of the world are still surprisingly slow and unreliable. This creates a challenge: how can files be efficiently transferred between computers over a low-bandwidth, high latency network connection? In 1996, Andrew Tridgell and Paul Mackerras developed a simple solution which powers one of the most useful UNIX tools, rsync. The algorithm remains relevant 21 years after its invention because it solves a timeless problem.

This talk will take you step by step through the rsync algorithm. You will learn that PhD theses are not always scary or unapproachable. Hopefully, you will also leave with a better intuition about the inner workings of rsync, as well as ideas for how its principles can be building blocks for solving many other different problems.

Other References:

- Efficient Algorithms for Sorting and Synchronization (

• David Ashby on SHA256:

While most of us use hash functions on a daily basis, few people can say that they truly understand what’s actually going on when they call SHA2("hello world"). Even fewer can say they’ve bothered to implement the function themselves, considering every introduction to cryptography starts off with a big warning saying to never, ever implement cryptographic primitives and just use vetted libraries due to the security implications. Of course, that important warning didn’t stop me from digging into the FIPS 180-4 spec ( to scratch the itch to understand how exactly it works, and along the way get a much better intuition about what bitwise operators actually do, what a bit rotation is, and why hex notation actually matters.


Camilo Aguilar is a Software Engineer at Enigma ( and a founding member of Papers We Love Medellín ( When not working, he travels to unknown places with his wife. He believes writing a bio is a lot more difficult than explaining rsync.

David Ashby ( is a self-taught programmer and systems engineer who sometimes spends his weekends implementing hash functions in high-level languages. He also helps organize the meetup, but no nepotism was to blame for the existence of this presentation.


Doors open at 6:30 pm; the presentations will begin right around 7:00 pm; and, yes, there will be refreshments of all kinds and pizza.

You'll have to check-in with security with your Name/ID. Definitely sign-up if you’re going to attend–unfortunately people whose names aren’t entered into the security system in advance won’t be allowed in.

After Camilo's presentation, we will open up the floor to discussion and questions.

We hope that you'll read some of the papers and references before the meetup, but don't stress if you can't. If you have any questions, thoughts, or related information, please visit #pwlnyc ( on slack (, our GitHub repository (, or add to the discussion on this event's thread.

Additionally, if you have any papers you want to add to the repository above (papers that you love!), please send us a pull request ( Also, if you have any ideas/questions about this meetup or the Papers-We-Love org, just open up an issue.


TwoSigma ( - Platinum Sponsor of the New York chapter