Experimenting with SSL Vulnerabilities in Android Apps

As the number of always-on, always-connected smartphones increase, so does the amount of personal and sensitive information they collect and transmit. Thus, it is crucial to secure traffic exchanged by these devices, especially considering that mobile users might connect to open Wi-Fi networks or even fake cell towers. The go-to protocol to secure network connection is HTTPS i.e., HTTP over SSL/TLS.

In the Android ecosystem, applications (apps for short), support HTTPS on sockets by relying on the android.net, android.webkit, java.net, javax.net, java.security, javax.security.cert, and org.apache.http packages of the Android SDK. These packages are used to create HTTP/HTTPS connections, administer and verify certificates and keys, and instantiate TrustManager and HostnameVerifier interfaces, which are in turn used in the SSL certificate validation logic.

A TrustManager manages the certificates of all Certificate Authorities (CAs) used to assess a certificate’s validity. Only root CAs trusted by Android are contained in the default TrustManager. A HostnameVerifier performs hostname verification whenever a URL’s hostname does not match the hostname in the peer’s identification credentials.

While browsers provide users with visual feedback that their communication is secured (via the lock symbol) as well as certificate validation issues, non-browser apps do so less extensively and effectively. This shortcoming motivates the need to scrutinize the security of network connections used by apps to transmit user sensitive data. We found that some of the most popular Android apps insufficiently secure these connections, putting users’ passwords, credit card details and chat messages at risk.

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Teaching Privacy Enhancing Technologies at UCL

Last term I had the opportunity and pleasure to prepare and teach the first course on Privacy Enhancing Technologies (PETs) at University College London, as part of the MSc in Information Security.

The course covers principally, and in some detail, engineering aspects of PETs and caters for an audience of CS / engineering students that already understands the basics of information security and cryptography (although these are not hard prerequisites). Students were also provided with a working understanding of legal and compliance aspects of data protection regimes, by guest lecturer Prof. Eleni Kosta (Tilburg); as well as a world class introduction to human aspects of computing and privacy, by Prof. Angela Sasse (UCL). This security & cryptographic engineering focus sets this course apart from related courses.

The taught part of the course runs for 20 hours over 10 weeks, split in 10 topics:

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Measuring Internet Censorship

Norwegian writer Mette Newth once wrote that: “censorship has followed the free expressions of men and women like a shadow throughout history.” Indeed, as we develop innovative and more effective tools to gather and create information, new means to control, erase and censor that information evolve alongside it. But how do we study Internet censorship?

Organisations such as Reporters Without Borders, Freedom House, or the Open Net Initiative periodically report on the extent of censorship worldwide. But as countries that are fond of censorship are not particularly keen to share details, we must resort to probing filtered networks, i.e., generating requests from within them to see what gets blocked and what gets through. We cannot hope to record all the possible censorship-triggering events, so our understanding of what is or isn’t acceptable to the censor will only ever be partial. And of course it’s risky, or even outright illegal, to probe the censor’s limits within countries with strict censorship and surveillance programs.

This is why the leak of 600GB of logs from hardware appliances used to filter internet traffic in and out of Syria was a unique opportunity to examine the workings of a real-world internet censorship apparatus.

Leaked by the hacktivist group Telecomix, the logs cover a period of nine days in 2011, drawn from seven Blue Coat SG-9000 internet proxies. The sale of equipment like this to countries such as Syria is banned by the US and EU. California-based manufacturer Blue Coat Systems denied making the sales but confirmed the authenticity of the logs – and Dubai-based firm Computerlinks FZCO later settled on a US$2.8m fine for unlawful export. In 2013, researchers at the University of Toronto’s Citizen Lab demonstrated how authoritarian regimes in Saudi Arabia, UAE, Qatar, Yemen, Egypt and Kuwait all rely on US-made equipment like those from Blue Coat or McAfee’s SmartFilter software to perform filtering.

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One-out-of-Many Proofs: Or How to Leak a Secret and Spend a Coin

I’m going to EUROCRYPT 2015 to present a new zero-knowledge proof that I’ve developed together with Markulf Kohlweiss from Microsoft Research. Zero-knowledge proofs enable you to demonstrate that a particular statement is true without revealing anything else than the fact it is true. In our case the statements are one-out-of-many statements, intuitively that out of a number of items one of them has a special property, and we greatly reduce the size of the proofs compared to previous works in the area. Two applications where one-out-of-many proofs come in handy are ring signatures and Zerocoin.

Ring signatures can be used to sign a message anonymously as a member of a group of people, i.e., all a ring signature says is that somebody from the group signed the message but not who it was. Consider for instance a whistleblower who wants to leak her company is dumping dangerous chemicals in the ocean, yet wants to remain anonymous due to the risk of being fired. By using a ring signature she can demonstrate that she works for the company, which makes the claim more convincing, without revealing which employee she is. Our one-out-of-many proofs can be used to construct very efficient ring signatures by giving a one-out-of-many proof that the signer holds a secret key corresponding to a public key for one of the people in the ring.

Zerocoin is a new virtual currency proposal where coins gain value once they’ve been accepted on a public bulletin board. Each coin contains a commitment to a secret random serial number that only the owner knows. To anonymously spend a coin the owner publishes the serial number and gives a one-out-of-many proof that the serial number corresponds to one of the public coins. The serial number prevents double spending of a coin; nobody will accept a transaction with a previously used serial number. The zero-knowledge property of the one-out-of-many proof provides anonymity; it is not disclosed which coin the serial number corresponds to. Zerocoin has been suggested as a privacy enhancing add-on to Bitcoin.

The full research paper is available on the Cryptology ePrint Archive.

A Digital Magna Carta?

I attended two privacy events over the past couple of weeks. The first was at the Royal Society, chaired by Prof Jon Crowcroft.

All panelists talked about why privacy is necessary in a free, democratic society, but also noted that individuals are ill equipped to achieve this given the increasing number of technologies collecting data about us, and the commercial and government interests in using those.

During the question & answer session, one audience member asked if we needed a Digital Charter to protect rights to privacy. I agreed, but pointed out that citizens and consumers would need to express this desire more clearly, and be prepared to take collective action to stop the gradual encroachment.

The second panel – In the Digital Era – Do We Still Have Privacy? – organised in London by Lancaster University this week as part of its 50th Anniversary celebrations, chaired by Sir Edmund Burton.

One of the panelists – Dr Mike Short from Telefonica O2 – stated that it does not make commercial sense for a company to use data in a way that goes against their customer’s privacy preferences.

But there are service providers that force users to allow data collection – you cannot have the service unless you agree to your data being collected (which goes against the OECD principles for informed consent) or the terms & conditions so long that users don’t want to read them – and even if they were prepared to read them, they would not understand them without a legal interpreter.

We have found in our research at UCL (e.g. Would You Sell Your Mother’s Data, Fairly Truthful) that consumers have a keen sense of ‘fairness’ about how their data is used – and they definitely do not think it ‘fair’ for them to be used against their express preferences and life choices.

In the Q & A after the panel the question of what can be done to ensure fair treatment for consumers, and the idea of a Digital Charter, was raised again. The evening’s venue was a CD’s throw away from the British Library, where the Magna Carta is exhibited to celebrate its 800th anniversary. The panelists reminded us that last year, Sir Tim Berners-Lee called for a ‘Digital Magna Carta’ – I think this is the perfect time for citizens and consumers to back him up, and unite behind his idea.

Is sending shoppers ads by Bluetooth just a bit creepy?

Using Bluetooth wireless networking to send information to nearby smartphones, beacon technology could transform how retailers engage with their customers. But customers will notice how their information is used to personalise these unsolicited adverts, and companies that fail to respect their privacy may get burned.

UK retailer House of Fraser is to introduce beacon-equipped mannequins to its Aberdeen store, which will deliver details about the clothes and accessories the mannequin is wearing to the smartphones of customers within 50 metres. In London’s Regent Street, around 100 stores have installed Apple’s iBeacons, able to send adverts to smartphones to entice passers-by to come inside.

A sort of precursor to the “internet of things”, beacon technology has great potential to enhance consumer experience: providing access to relevant information more quickly, or offering rewards and discounts for loyal shoppers. Some retailers may rearrange their store based on analysing data from customers’ shopping habits. It has uses outside of marketing too, such as providing contactless payments, tourist information at museums, or gate information at airports.

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On-line lecture: DP5 Private Presence @ 31C3

During the break I attended the 31st Chaos Communications Congress (31C3) in Hamburg, Germany. There I had the pleasure of giving a presentation on “DP5: PIR for Privacy-preserving Presence” along with my colleague from Waterloo, Ian Goldberg. The Audio/Video Chaos Angels did a nice job of capturing the event, and making it available for all to view (I come in at 26:23).

Other resources around DP5 include:

  • Technical Report (pdf)
  • Talk Slides (pdf)
  • Event Page (html)
  • Git code repository (git)

Sequencing your genome is becoming an affordable reality – but at what personal cost?

Genomics is increasingly hailed by many as the turning point in modern medicine. Advances in technology now mean we’re able to make out the full DNA sequence of an organism and decipher its entire hereditary information, bringing us closer to discovering the causes of particular diseases and disorders and drugs that can be targeted to the individual.

Buzzwords like “whole genome sequencing” and “personalised medicine” are everywhere – but how are they enabling a powerful medical and societal revolution?

It all started in the 1990’s with the Human Genome Project – a very ambitious venture involving 20 international partners and an investment of US$3 billion. In 2003, 13 years after it began, the project yielded the first complete human genome. Today, the cost of sequencing whole genomes is plummeting fast and it is now possible to do the job for less than US$1,000, meaning a whole host of applications both in research and in treatments.

Variants and mutations

Genetic mutations are often linked to disorders, predisposition to diseases and response to treatment. For instance, inherited genetic variants can cause blood disorders such as thalassaemia or others such as cystic fibrosis or sickle cell anaemia.

Genome sequencing is being used today in diagnostic and clinical settings to find rare variants in a patient’s genome, or to sequence cancers’ genomes (to point out genomic differences between solid tumours and develop a more effective therapeutic strategy). It is also possible to test for known simple mutations via a process called genotyping, which can find genetic differences through a set of biomarkers. In the case of thalassemia, for example, there are mutations in the HBB gene on chromosome 11.

A number of drugs, including blood-thinners like warfarin, have already been commercialised with genetic markers (such as a known location on a chromosome) linked to effectiveness and correct dosage.

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Tor: the last bastion of online anonymity, but is it still secure after Silk Road?

The Silk Road trial has concluded, with Ross Ulbricht found guilty of running the anonymous online marketplace for illegal goods. But questions remain over how the FBI found its way through Tor, the software that allows anonymous, untraceable use of the web, to gather the evidence against him.

The development of anonymising software such as Tor and Bitcoin has forced law enforcement to develop the expertise needed to identify those using them. But if anything, what we know about the FBI’s case suggests it was tip-offs, inside men, confessions, and Ulbricht’s own errors that were responsible for his conviction.

This is the main problem with these systems: breaking or circumventing anonymity software is hard, but it’s easy to build up evidence against an individual once you can target surveillance, and wait for them to slip up.

The problem

A design decision in the early days of the internet led to a problem: every message sent is tagged with the numerical Internet Protocol (IP) addresses that identify the source and destination computers. The network address indicates how and where to route the message, but there is no equivalent indicating the identity of the sender or intended recipient.

This conflation of addressing and identity is bad for privacy. Any internet traffic you send or receive will have your IP address attached to it. Typically a computer will only have one public IP address at a time, which means your online activity can be linked together using that address. Whether you like it or not, marketers, criminals or investigators use this sort of profiling without consent all the time. The way IP addresses are allocated is geographically and on a per-organisation basis, so it’s even possible to pinpoint a surprisingly accurate location.

This conflation of addressing and identity is also bad for security. The routing protocols which establish the best route between two points on the internet are not secure, and have been exploited by attackers to take control of (hijack) IP addresses they don’t legitimately own. Such attackers then have access to network traffic destined for the hijacked IP addresses, and also to anything the legitimate owner of the IP addresses should have access to.

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