Gergely Kalman - Freelance Python Developer for Hire

Co-founder, CTO, CEO

2014 - PRESENT

Buffered.com

Single-handedly designed and implemented a MVP of a VPN SaaS provider with desktop clients, supporting APIs, and server architecture.
Ran the company as Managing Director (CEO) during its existence.

Technologies: OpenVPN, Django, Python, wxPython, Kivy, Linux

Software Engineer, Interviewer

2011 - 2014

Toptal.com

Implemented several simple websites for personal projects using Django and Jinja2.
Implemented OpenVPN based desktop software using wxPython, OpenVPN, and OpenSSL.
Interviewed a large number of candidates and overhauled the interview process.

Technologies: wxPython, OpenVPN, OpenSSL, Django, Jinja2

Head of Media Platform Development

2010 - 2011

DuoDecad LLC, Media Platform Division

Worked as the only developer (for the first 8 months) on an alternative video streaming platform to Adobe Flash Media Server (primary goal of The Media Platform Division (MPD)).
Achieved our goal within a year using unofficial documentation of the protocol and manual reversing.
Designed and implemented live stream distribution and conversion architecture in Python3.
Optimized to allow one node to serve more than 100k clients using ~10Gbit/s.
Supported on-the-fly transcoding of incoming audio and video.
Benchmarked performance and moved heavy-lifting code to C.
Integrated several libav* libraries into Python for stream conversion.
Researched and assisted in hardware acquisitions for the project.
Devised custom event-driven interface with custom socket handling for Python, including FLV format handlers.
Detected bugs in Adobe formats and in libavformat.
Administered Media Platform Division's machines (about 80).
Tuned machines for maximum network performance.
Lectured on IT-Security, MPD's project, and Python programming.
Iterated until peak performance of the cluster was almost 100Gb. With 30 machines, it would have been capable of completely taking over the existing streaming cluster (100+ nodes).

Technologies: libav* libraries, Python3, C, Linux, Bonding, RTMP, FLV, AMF

IT Security Specialist

2008 - 2010

DuoDecad LLC, IT-Security Division

Performed software audits, penetration tests, and stress tests.
Implemented failover architecture for the main website.
Assisted our partner company in acquiring Payment Card Industry Data Security Standard (PCI-DSS) compliance.
Devised company policies for PCI-DSS, developed architecture, and held educational sessions as part of IT Security staff.
Benchmarked Linux kernel's behavior when presented with high volumes of DDoS traffic. Tuned and patched the kernel to achieve maximum resilience.
Worked as a member of the incident response team.
Developed a network analyzer in C which created real-time statistics of incoming HTTP requests and pinpointed attackers.
Ported old OpenSSH fork modifications to the latest version.

Technologies: Linux, IPtables, Keepalived, LVS, C, NetBoot

IT Operator

2008 - 2008

DuoDecad LLC, IT-Security Division

Helped with administration of several hundred Linux machines.
Led support for kernel and network-related issues.
Wrote small scripts in bash for administrative purposes.

Technologies: Linux

Instructor

2007 - 2007

SZAMALK Educational Institution

Taught a course for a single semester titled Linux, Networking, and System Administration.

Technologies: Linux

System Administrator

2005 - 2007

Dorm System Administrator Group ELTE

Helped with general Linux system administration tasks in my university dorm.
Implemented load balancing.
Administered web proxies.
Created minimal NetBoot architecture.

Technologies: NetBoot, Linux

PCI-DSS Consultant (Other amazing things)

Consultation and architectural help provided for Lalibco, which processed more than $500,000 daily for an Alexa top 50 website. Several bugs and security holes were uncovered in their systems. I prepared it for the PCI-DSS audit, which passed successfully.

Online Payment Architect, PCI-DSS Consultant (Other amazing things)

Helped design Escalion's (Lalib successor) system architecture from networking to services to policies and procedures. Advised on secure software practices and developed policies and procedures to keep cardholder data secure. Escalion passed PCI-DSS test and took over Lalib's transactions, which were around $500,000 each day.

Real Estate Scraper (Development)

I wrote my own scraper for the largest Hungarian real estate website to get amazing deals.

Buffered.com (Development)

https://buffered.com

I have created my own VPN startup called buffered.com, which I ran as CTO for 3 years and CEO for 1 year.

10 Most Common Web Security Vulnerabilities (Publication)

https://www.toptal.com/security/10-most-common-web-security-vulnerabilities

For all too many companies, it's not until after a breach has occurred that security becomes a priority. An effective approach to IT security must, by definition, be proactive and defensive. This post focuses on 10 common and significant web-related IT security pitfalls to be aware of, including recommendations on how they can be avoided.

Fixing the “Heartbleed” OpenSSL Bug: A Tutorial for Sys Admins (Publication)

https://www.toptal.com/freelance/the-heartbleed-openssl-bug-what-you-need-to-know

A potentially critical problem, nicknamed "Heartbleed", has surfaced in the widely-used OpenSSL cryptographic library. The vulnerability is particularly dangerous in that potentially critical data can be leaked and the attack leaves no trace. As a user, chances are that sites you frequent regularly are affected and your data may have been compromised. As a developer or sys admin, sites or servers you're responsible for are likely to have been affected. Here are the key facts you need to know about this dangerous bug and how to mitigate your vulnerability.

With a Filter Bypass and Some Hexadecimal, Hacked Credit Card Numbers Are Still, Still Google-able (Publication)

https://www.toptal.com/web/with-a-filter-bypass-credit-card-numbers-are-still-still-google-able

In 2007, Bennett Haselton revealed a minor hack with major implications: querying ranges of numbers on Google would return pages of sensitive information, including Credit Card numbers, Social Security numbers, and more. While Haselton's hack was addressed and patched, I was able to tweak his original technique to bypass Google's filter and return the same old dangerous results.

How I Made Porn 20x More Efficient with Python Video Streaming (Publication)

https://www.toptal.com/python/how-i-made-porn-20x-more-efficient-with-python

Porn is a big industry. There aren’t many sites on the Internet that can rival the traffic of its biggest players. And juggling this immense traffic is tough. To make things even harder, much of the content served from porn sites is made up of low latency live streams rather than simple static video content. But for all of the challenges involved, rarely have I read about the developers who take them on. So I decided to write about my own experience on the job.

Languages

C, Python, Bash, C++, PHP, Assembler x86

Frameworks

Django, Jinja, Scrapy, Qt Quick, Qt

Libraries/APIs

Libav, PyQt

Tools

OpenVPN, iptables, Scraping Hub

Paradigms

Object-oriented Programming (OOP), Imperative programming, Event-driven Programming, DevOps

Platforms

Linux, Windows, Mac OS

Storage

Memcached, MySQL

Other

Software Architecture, Scraping, Ethernet, TCP, UDP, ICMP, RTMP, SSH, Security, Code Auditing

Bachelor's degree in Computer Science

2005 - 2007

Eotvos Lorand Science University - Hungary