Securing Yourself at DEF CON 26

That time of year is just around the corner again! DEF CON 26 is next week and we here at Tinfoil Security are super excited!

Over the next week the largest gathering of security professionals, researchers, and enthusiasts in the world will be taking place at Caesars Palace and Flamingo Hotels in Las Vegas, NV. The conference is incredible—it consistently ranks among the highlights of the year among nearly everyone I know—but it does have a reputation for being host to all sorts of nefariousness. So if this is your first time going, pay close attention to make sure you have a fun and safe time!

Why be cautious? Well just as an example, one year during DEF CON, hackers installed a fake ATM in the Rio hotel when it was held there, and used it to steal credit card information. Needless to say, don’t use ATMs at Caesars Palace and Flamingo Hotels if you can help it - bring cash with you. Every year people get owned at DEF CON, but with a little preparation, you can secure yourself against all but the most ludicrous of attacks. Incidentally, while our advice is most applicable to DEF CON and Blackhat, it is also applicable to any other conference you go to. Hackers don’t just hide in holes and hibernate until DEF CON every year - they are everywhere.


DEF CON is known for sporting the “world’s most hostile network.” A good rule of thumb is to assume that any communication going on within 1000 feet of Caesars Palace and Flamingo Hotels are going to be intercepted. If the idea of your phone calls being listened in on, your SMS messages being intercepted, or your web traffic being sniffed bothers you, leave your devices at home. If that’s not feasible, backup and wipe your electronics before the conference: the inconvenience garnered by using a clean laptop for a week is insignificant compared to the damage caused by accidentally leaking source code or other confidential information. This is also true of your mobile device - if you must bring it, back it up and wipe it before and after the conference.

Make sure you are completely up to date on patches, software updates, browser updates, and have the latest AV software. You want to make sure you do this far away from Las Vegas, as downloading anything while in Vegas is probably the worst possible idea. Do not download anything, turn off automatic updates, and be very wary of any “SSL Certificate Errors” you might otherwise have ignored.

Clear your cache, cookies, temporary files, and just about anything else. A lot of websites often cache very sensitive information that can be stolen if accessed by an attacker. Encrypt your data on-disk using full-disk encryption. On Mac, you can do this by setting up FileVault. On Windows, your best bet is probably BitLocker.


If you must bring a phone or a laptop to the conference, keep all of the radios disabled when not in use. Your phone should be in airplane mode, your WiFi should be disabled, and perhaps most importantly, your list of trusted network SSIDs should be cleared - tools like the WiFi Pineapple can spoof access points, trivially allowing an attacker to man-in-the-middle your network traffic. Even the RSA conference, widely regarded as one of the most “professional” security conferences, has had a pineapple as well a few years ago.

The best prevention mechanism for pineapples (if you must enable WiFi) is to disable auto-joining of known networks and delete all of your existing known networks. The way a pineapple works is by listening to your device broadcast its known networks: “Hey, is Tinfoil Security Wireless around?” Then, of course, the pineapple responds: “Yup, I’m right here! Just connect and enjoy your wonderful internet access!” And, by then, it’s game over.

An absolute necessity for network access at DEF CON is the use of a VPN. If you have access to one, use it. If you don’t have access to one, we can help you get set up in five minutes, at no charge. As far as we’re concerned, using a VPN is one of the most important things you can do to secure yourself at DEF CON (or anywhere, for that matter), but it also isn’t sufficient. Even if you’re using a VPN, you should still avoid accessing sensitive information while at the conference. Don’t log into internal services like your company wiki or source control, and avoid checking email at all costs. Be wary of relying on VPNs on mobile devices - it can be difficult to see how traffic is being routed, and whether the VPN is configured properly.

If your phone is acting weird, or wonky, or it looks like you have full LTE service but every call gets dropped: it is a safe bet that you are being intercepted. Turn your phone off immediately, walk somewhere else, and try again. A device “acting weird” at DEF CON is something to be concerned about.

Physical Attacks

Even charging your phone or laptop could result in your device being compromised. It’s not uncommon to see public charging stations scattered around the Caesars Palace and Flamingo Hotels, and as with nearly everything at DEF CON, it should be assumed that these are being used as a vector for exploitation: entire products have been built around protecting users from malicious USB ports.

If you can avoid it, don’t plug anything in at DEF CON, and if you must, bring your own cables: here is a great example of an exploit that was leaked which allows an attacker to eavesdrop on a computer using a modified VGA cable. It sounds absurd, but these are the kinds of attacks you need to be thinking about. Your best bet is to just minimize your exposure surface by reducing your usage of electronics as much as possible.

Social Engineering

Something as innocuous as a “promotional” USB stick giveaway might be an attempt to load malicious code onto your system. Even scanning a QR code might be the first stage in an exploit to root your device. There’s no limit to the creativity of hackers, and if anything is evidence of that, it’s the mind blowing hacks that crop up at DEF CON every year.

If this interests you, you should watch (or participate in!) the Social Engineering CTF. It is incredible what people will tell you if you ask them nicely, and talk with a little confidence. There's even  a Social Engineering CTF for Kids. That’s right - every year, Fortune 500 companies have data leaked and stolen by children. If it can happen to them, it can happen to you, so always be a little wary when meeting with new people - most of them will be great, but keep yours eyes out for anything fishy.

ID Badges

For some hackers, getting a free lunch from a company after cloning their VP of Engineering’s badge at DEF CON is the pinnacle of social engineering. There is no reason to bring your company badge or RFID / NFC enabled credit card (the kind you can tap) to DEF CON. If, for some reason, you absolutely have to take it with you to DEF CON, put it in a copper-lined envelope, and wrap it in six layers of aluminum foil (or, as the case may be, tinfoil).

This sounds insane, but these cloning devices are rampant all around the conference, and it's not unheard of for some to be sold on the premises.

Healthy Paranoia

We could go on for pages about the different types of attacks you might run into, and what you can do to protect yourself against them, but really it just comes down to having the right mindset about security - don’t take anything at face value, and assume that everyone is somehow out to exploit you. It sounds scary, but a little common sense goes a long way, and even amidst the fake ATM scares, and things like the Wall of Sheep, DEF CON is an experience that shouldn’t be missed. Nobody likes getting “owned” though, so if it’s your first time, take our advice to heart, and think twice before doing anything that might compromise your security.

If you are going to Blackhat or DEF CON, let us know and ping us at: and we would absolutely love to catch up and buy you a beverage. If there is anything else you’re doing to prepare, let us know: we’d love to hear about it!

Most importantly, have fun - and stay safe. :)

Shane Wilton

Shane Wilton is the Grand Magistrate of Security at Tinfoil Security, and the company's resident programming language theorist. When he isn't coding in a functional language like Elixir, he's probably hacking on an interpreter for an esolang of his own, or playing around with dependent types in Idris. Security is always at the forefront of his thoughts, and he enjoys building tools which make it easy for other engineers to write secure code. His love for security is matched only by his love for bad movies - and does he ever love bad movies.

Slim Docker Images for Rails

At Tinfoil we’ve been building and distributing our applications with Docker for a few years now. One aspect we value of our Docker images is keeping them small and nimble. By default it’s easy to have a Docker image become bloated because each command introduces a new layer and history of changes to the file system. Luckily there are some tricks to reducing the final image size without squashing all of the layers together.

We can start with a modern Rails application that uses Yarn in addition to Sprockets to manage JavaScript dependencies, Bundler to manage the Ruby gem dependencies, and an expectation that we'll be connecting to an external PostgreSQL database.

A simple starting Dockerfile might look like the one below. We need Node.JS and Yarn installed to precompile our JavaScript assets.

The final image size is 1.11GB! We can start off the weight loss program by combining the commands to install Node.js and Yarn, as well as cleaning up the apt package caches.

That made it a tiny bit smaller: 1.09GB. The ruby:2.5 image is based off of Debian, and has a lot of extra utilities and functionality preinstalled. We’ve found a lot of success making smaller images by basing the image off of Alpine Linux. Most ruby code works fine under Alpine, but since it uses musl instead of glibc, you have to be careful with some C dependencies or ruby gem extensions.

421MB now, so we’re making some nice improvements. We don’t need all of the NPM packages at runtime, so we can use a multi-stage Dockerfile to avoid storing those layers in the final image. Multiple stages split up the build and precompilation steps in their own Docker images, and we can copy out the build artifacts into our final image.

It’s now 231MB, a savings of around 75% 🎉. Note that the `uglifier` gem used by default in Rails 5.2 still requires you to have a Javascript runtime available, otherwise our final docker image could be even smaller.

For the next related post we’ll go over how to use multi-stage Dockerfiles for an Elixir Phoenix project for some more impressive size savings. 

Ben Sedat

Ben Sedat is the Engineering Wizard of Tinfoil Security. He's a bit of a blend between a traditional software engineer (builder) and security engineer (breaker). He spends a lot of time thinking about security: both detection as well as creating solutions for the security issues that exist in software and the internet. He also plays lots of video games. Lots.

Do good with your data at RSA, with Tinfoil Security!

It’s that time of year again! RSA is coming up on April 16th-20th at the Moscone Center in San Francisco and we’re looking forward to seeing you there! We’ll be at booth # 4532, and we’d love to show you our newly launched API Scanner.

This is Tinfoil Security’s second time attending the conference and, based on what we observed last year, we wanted to approach it with a twist. Our goal is to encourage you to think about how much data you share when your badge is scanned, and what you are willing to give up for it. We want you to ask yourself: “What is my data worth?”

At least once during this year’s conference, you’re likely to scan your badge for free swag - a pen, a beer, a t-shirt, or the chance to win a prize. Last year, we were astonished at how much companies had invested in items that would hopefully attract your attention so they could partake in a swag exchange to get hold of your data. Many items you might collect are fun and useful - we love the nerdy things! However, we noticed many people discarding unwanted swag at the end of the conference, only to be picked up by the local homeless population.

This gave us an idea.

We want to provide you with the opportunity to use your data to do good. For each badge we scan, Tinfoil Security will donate a meal to those in need, right here in San Francisco.

To help us with our mission, Tinfoil Security has partnered with the non-profit Curry Without Worry as our 2018 community partner. Curry Without Worry cooks and serves warm, healthy meals to those in need, just blocks from the Moscone Center, where RSA is being held. During our time volunteering with Curry Without Worry, the Tinfoil Security team was surprised to discover it was not just those who are homeless that are in need of a meal, but also college students, off-duty police officers with their children, and city workers. Hunger affects more community members than we realize!

Don’t want your badge scanned at all? Come to our booth (#4532) and we will show you a hack to protect your data! We will also be giving away free pens, stickers, and tattoos - no badge scan required!

In case this is your first time hearing about us: Tinfoil Security provides security tools for developers and DevOps teams. We integrate into your current development workflow, empowering developers to find and fix vulnerabilities as a part of their normal development process. Our goal is to increase bandwidth for your security teams while training developers to code more securely and treat vulnerabilities as normal bugs. Whether you’re building web applications or APIs powering mobile backend servers, IoT devices, and web services, we have a dynamic vulnerability scanner that’s right for you and your team.

More about our 2018 Community partner: Curry Without Worry

Curry Without Worry was founded in December of 2006, as a 501(c)(3) with the purpose of serving soul pleasing food to the hungry people of San Francisco. While they desire to feed people who are most in need, their philosophy is that hunger is not defined by an empty stomach. For this reason, Curry Without Worry is open to all who hunger to join them. The mix of those who accept a meal brings a sense of equality and peace to the experience, allowing those truly having a hard time in life to realize that there are people who care about bringing people from all walks of life together. They serve vegan meals at the Civic Center in San Francisco every Tuesday evening, rain or shine.

You can make a donation directly at:

Don’t forget to visit Tinfoil Security at our RSA Booth # 4532.

If you’ve not yet purchased your ticket, please enjoy a complimentary Guest Expo Pass on us. To sign up, please go to the RSA registration page and enter the expo passcode: X8ETINFO

Tinfoil RSA 2018

Neda Blocho

With a background in running the world's top accelerator program out of Stanford University and a tour as a seed stage investor in Silicon Valley, Neda has seen first hand the great need for solving issues around cyber security! Neda makes sure the world knows how much better and safer their DevOps lives can be by partnering with Tinfoil.

API Security Scanning: How is it done the right way?

We’re excited to announce our API Security Scanner has been officially launched and is now publicly available! It’s a much needed tool we’ve been building and rigorously testing for the past year and a half, and we can’t wait to start sharing it with the world. Before we go into the details on how the scanner works, it’s important to start by discussing the problem of API security in general, and why such a tool is needed in the first place.

First, when we say API, it’s worth clarifying that we’re talking about web-based APIs such as REST APIs, web services, mobile-backend APIs, and the APIs that power IoT devices. We are not targeting lower-level APIs like libraries or application binary interfaces. This is an important distinction to make, because the sorts of security vulnerabilities that affect web-based APIs are going to mirror the same categories of vulnerabilities we’ve spent the past seven years defending against, with our web application security scanner.

Just as web applications can be vulnerable to issues like Cross-Site Scripting (XSS) or SQL injection, APIs can also fall prey to similar attacks. As always, it isn’t quite that simple, and the nuances of how these vulnerabilities are actually exploited and detected can vary dramatically between the two types of applications. In the case of XSS, for example, the difference between a vulnerable API and a secure API depends not only on the presence of attacker controlled sinks in an HTTP response, but also on the content-types of the responses in question, how those responses are consumed by a client, and whether sufficient content-type sniffing mitigations have been enforced.

Also worthy of consideration is how APIs handle authentication, especially as compared to web applications. In the case of web applications, authentication is more or less a solved problem. For the most part, the user visits a page with a login form, enters their credentials, submits the form, and gets back a cookie. There are minor variations to this -- sometimes people store the session in local storage or session storage, for example -- but for the most part, every web application authenticates in pretty much the same way. APIs, on the other hand? Not so much. At an absolute minimum, you need to account for protocols like OAuth2 (and all of its associated grant types!), OpenID Connect, and increasingly, JSON Web Tokens (JWT). Beyond that, it’s also common to layer on other security requirements, like client certificates, or signed requests. Existing web application security scanners have no concept of any of these standards, and even if you managed to get a scanner to authenticate to your API, you’re not going to have much luck coercing it into properly signing your requests.

Lastly, unlike web applications, APIs aren’t discoverable. Unless you’re one of the dozen companies in the world with a HATEOAS based API, it simply isn’t possible for a security scanner to load up your API, follow all of the links, and automatically discover all of the endpoints in that API, let alone the parameters expected by those endpoints, and any constraints required of them. Without some way of programmatically acquiring this information, API security scanning simply can’t be automated in the same way that web scanning has been.

These are all solvable problems, but they mean that a dynamic security scanner needs to be built from the ground up to understand APIs, how APIs are used, and more importantly, how APIs are attacked. This means that simply repurposing an existing web-application security scanner won’t be sufficient (which is what most other solutions currently do). With this point in mind, our API scanner is an entirely new scanning engine (written in Elixir!), built off of everything we’ve learned over the past seven years of attacking web applications.

To handle the previously mentioned authentication issues, we’ve devised a clever system using something we like to call authenticators. Essentially, we’ve distilled API authentication down to its primitives: whether that’s as simple as adding a header or a parameter to a request, or performing an entire OAuth2 handshake and storing the received bearer token for later. From there, our scanner is able to chain together all of these authenticators together, incrementally transforming unauthenticated requests into authenticated requests. Furthermore, because our scanner has such a nuanced understanding of all the discrete steps of an authentication workflow, it becomes possible to detect when any of those steps have failed, and also when any of them aren’t being honored by the server. This uniquely enables us to fuzz the individual steps of an authentication flow, providing us a powerful tool for determining authorization and authentication bypasses.

To address the discoverability issues inherent with APIs, we approached the problem the same way humans do: with documentation! As a developer looking to use a third-party API, your first stop is always the documentation for that API. Historically, this documentation has almost always been presented as unstructured text, and in a form not conducive to being parsed by software. With standards like Swagger, RAML, and API Blueprint becoming more widespread over recent years, the idea of programmatically specifying an API’s behavior is becoming increasingly popular, and this offers an exciting opportunity for API security scanning. In our experience, we’ve found that Swagger in particular is beginning to win out as the de facto standard for API documentation, and so we’ve designed the first version of our API scanner to ingest Swagger documents, and use them to build a map of an API for scanning.

Reading in documentation like this nicely solves the issue of being unable to crawl an API, but it also allows us to scan APIs with a level of intelligence that black-box dynamic web application scanning has never had access to. In most variants of web application scanning, the scanning engine crawls the application to determine all available input vectors: forms, links, buttons, really anything that might trigger some login on the client or server. From there, these inputs are fuzzed to look for security vulnerabilities. The issue, then, is that because this is entirely black box scanning, it becomes difficult for a scanner to ensure it is generating good payloads to send to the web application. By this we mean payloads that, while still being malicious, conform to the format and structure expected by the application. We could send a server every variation of SQL we can think of, but if the server is blocking our requests because they fail the first level of input validation, then we’re never going to make any progress. Our web application scanner actually addresses this very problem by examining the context in which parameters are used, in order to infer their expected structure. By sidestepping this problem entirely with API scanning, we’ve found that we’re able to more easily achieve an even higher level of coverage typically reserved for highly-skilled, manual penetration testing.

By parsing Swagger documentation, though, this problem can be cleverly avoided. Now, in addition to knowing the endpoints to scan, and the parameters on those endpoints, we’re also aware of the types of those parameters and whatever other constraints are specified in the Swagger documentation. It becomes possible for us to know that a given parameter needs to be a string, resembling an email address, of a specific length, and possibly excluding certain characters. Given all of this information, we can begin intelligently generating attack payloads that conform to various subsets of these constraints, allowing us to audit for holes in the server’s intended validation logic, while also giving a suitable jumping off point for intentionally trying to bypass that validation logic with cleverly constructed payloads.

It’s been a long road to get to this point, but we’re proud to have finally built an API security scanner that approaches the problem from a strong foundation, and with careful thought put into what makes API security scanning difficult. We have a lot of enhancements to make, but what we’ve been shipping to customers over the past year has already filled an important gap in their application security program -- especially with our ever present focus on integrating security scanning into the DevOps process. Just as with our web application scanner, our API scanner is designed to be integrated directly into the software development life-cycle, so that developers can find and fix vulnerabilities as early as possible, and often without waiting for a dedicated security engineer to get involved. We facilitate this with first-party integrations for tools like Jenkins, and also by providing a REST API that can drive the entire scanning and reporting process, from start to finish.

Security is much too important to be dealt with as an afterthought. That’s why we always strive to enable our customers push their security up the stack, so they can empower their developers to find and fix vulnerabilities before they become a problem.

Interested in setting up a demo to see for yourself? Find a time that works for you, and schedule a demo right here.

Shane Wilton

Shane Wilton is the Grand Magistrate of Security at Tinfoil Security, and the company's resident programming language theorist. When he isn't coding in a functional language like Elixir, he's probably hacking on an interpreter for an esolang of his own, or playing around with dependent types in Idris. Security is always at the forefront of his thoughts, and he enjoys building tools which make it easy for other engineers to write secure code. His love for security is matched only by his love for bad movies - and does he ever love bad movies.

Tags: XSS security

Just Behave Already: Property Testing

What is property testing? In short, it can be described as a method of testing output of a program against the expected behavior, or properties, of a piece of code. Why should you care? The same reason we here at Tinfoil Security care: good testing goes beyond ensuring your code is functional. It can be crucial line of defense when it comes to the security of your applications, and property testing is a uniquely powerful tool in accomplishing these ends. But before we dive deeper, lets review more traditional testing.

it "finds the biggest element in the list" do
  assert 5 = biggest([5])
  assert 6 = biggest([6, 5])
  assert 100 =
    |> Enum.to_list()
    |> biggest()

The test above is fairly straightforward. It attempts to check that the biggest function will in fact return the biggest element of a provided list. It falls short in a few noticeable ways: What if the list is empty? What if it isn't sorted? What if there are duplicate integers?

Traditional testing very often focuses on specific examples and is dependent on the assumptions of the programmer. The function above may have been created with only positive integers in mind and it may not occur to the writer to test for cases involving negatives.

This example is a simple one, but it demonstrates a major drawback of traditional testing: it reveals the presence of expected bugs, rather than the absence of unexpected bugs. How would we pursue the latter? Enter property testing.

What is a Property?

Property testing is reliant on describing the properties of a function or piece of code. Very simply, these properties are general rules on how a program should behave. For the example function above, we might define the following:

  • "biggest returns the largest element of a list."

We might describe the properties of other well-known algorithms as such:

  • "sort returns a list with every element in ascending order."
  • "append returns a list with a length equal to the sum of the lengths of both lists passed to it."
  • "append returns a list with every element of of the first list, followed by every element of the second list."

Once we have defined the general properties of a program we can move beyond specific examples. From there we can use generators to test the output of our code against these properties using a variety of generated inputs.

How to Describe a Property?

This is easier said than done, however. Describing the properties of a program can be difficult, but there are a few general strategies, as described by Fred Herbert's excellent book on Property Testing in Erlang:

Modeling: Modeling involves reimplementing your algorithm with a simpler (though likely less efficient) one. Our biggest function for example could have it's output compared with an algorithm that uses sort to arrange a list in ascending order, then returns the final element. Sort is far less time-efficient, O(n log n) compared to the O(n) of our biggest function, but since it retains the same properties of biggest we can use it as a model to test our results against.

Equivalent Statements: Equivalent statements are used to reframe the property into a simpler one. For instance, we could say that the element returned by biggest is larger than or equal to any of the remaining elements of the input list. This simplified property is not quite the same but fundamentally equivalent to the one we had defined above.    

Symmetry: Some functions have natural inverses. The process of encrypting and decrypting data, for example, can be described by the following properties:

  • The input encrypted, then decrypted will return the original input.
  • The input decrypted, then encrypted will return the original input.

Oracles: Oracles involve using a reference implementation to compare your output against and, as such, are perhaps the best way to test the properties of your code. Oracles are most often used when porting existing code from language to another or when replacing a working implementation with an improved one.


Implementing property tests is not easy. It relies not only on describing the properties you wish to test against, but also on constructing generators to create the large, varied sets of randomized input to feed into your code. A single property may be tested hundreds of times, and generators will often create increasingly complicated inputs across these test iterations, or "generations" as they are called.

One can imagine that this randomly generated input could quickly become too unwieldy for the developer to make sense of. The failing case may contain large amounts of data irrelevant to what the actual cause of the failure. To help narrow things down to the true cause a property testing framework will often attempt to reduce, or "shrink", the failing case down to a minimal reproducible state. This usually involves shrinking integers down to zero, strings to "", and lists to [].

Fortunately, there are a variety of language-specific property testing libraries currently available. StreamData, for example, is an Elixir property testing library - and candidate to be included into Elixir proper - that provides built in generators for primitive data-types as well as tools to create custom ones. Generators can even be used to generate symbolic function calls, allowing the possibility to fuzz and test transitions on a state machine.


As a final note, it should be mentioned that while property testing is a powerful tool, it is not a perfect solution. Describing the properties of a piece of code can be difficult, as can coming up with tests for those properties. Furthermore, these tests are reliant on well-made generators to come up with the varied and unexpected input, which in itself can be a difficult and time consuming task.

It is also important to note that more traditional testing should not be entirely eschewed for property tests. The real strength of property testing is in using generated input to automate all the tedious work of thinking up unusual edge cases and writing individual tests for them, and it is at its best when used with unit tests that check for unique edge cases or document unusual behavior.

At Tinfoil Security, we understand that thorough and effective testing is an essential part of creating of efficient and secure technology. If you have any questions or would like to let us know how property testing has helped in your projects, feel free to reach out at

Peter Ludlum

Peter is a Software Engineering Intern at Tinfoil Security. A recent graduate of App Academy, he enjoys nothing more than bringing beautiful (and functional) web pages to life. When he isn't coding, Peter is usually lost in a book or strumming out a new tune on the ukulele.

Tags: security guide DevSec DevOps