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cryptographie, nombres aléatoires, random numbers

Cryptography: what are the random numbers for?

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Hervé Debar, Télécom SudParis – Institut Mines-Télécom and Olivier Levillain, Télécom SudParis – Institut Mines-Télécom

The original purpose of cryptography is to allow two parties (traditionally referred to as Alice and Bob) to exchange messages without another party (traditionally known as Eve) being able to read them. Alice and Bob will therefore agree on a method to exchange each message, M, in an encrypted form, C. Eve can observe the medium through which the encrypted message (or ciphertext) C is sent, but she cannot retrieve the information exchanged without knowing the necessary secret information, called the key.

This is a very old exercise, since we speak, for example, of the ‘Julius Caesar Cipher’. However, it has become very important in recent years, due to the increasing need to exchange information. Cryptography has therefore become an essential part of our everyday lives. Besides the exchange of messages, cryptographic mechanisms are used in many everyday objects to identify and authenticate users and their transactions. We find these mechanisms in phones, for example, to encrypt and authenticate communication between the telephone and radio antennas, or in car keys, and bank cards.

The internet has also popularized the ‘padlock’ in browsers to indicate that the communication between the browser and the server are protected by cryptographic mechanisms. To function correctly, these mechanisms require the use of random numbers, the quality (or more precisely, the unpredictability) thereof contributes to the security of the protocols.

Cryptographic algorithms

To transform a message M into an encrypted message C, by means of an algorithm A, keys are used. In so-called symmetric algorithms, we speak of secret keys (Ks), which are shared and kept secret by Alice and Bob. In symmetric algorithms, there are public (KPu) and private (KPr) key pairs. For each user, KPu is known to all, whereas KPr must be kept safe by its owner. Algorithm A is also public, which means that the secrecy of communication relies solely on the secrecy of the keys (secret or private).

Sometimes, the message M being transmitted is not important in itself, and the purpose of encrypting said message M is only to verify that the correspondent can decrypt it. This proof of possession of Ks or KPr can be used in some authentication schemes. In this case, it is important never to use the same message M more than once, since this would allow Eve to find out information pertaining to the keys. Therefore, it is necessary to generate a random message NA, which will change each time that Alice and Bob want to communicate.

The best known and probably most widely used example of this mechanism is the Diffie-Helman algorithm.  This algorithm allows a browser (Alice) and a website (Bob) to obtain an identical secret key K, different for each connection, by having exchanged their respective KPu beforehand. This process is performed, for example, when connecting to a retail website. This allows the browser and the website to exchange encrypted messages with a key that is destroyed at the end of each session. This means that there is no need to keep it (allowing for ease of use and security, since there is less chance of losing the key). It also means that not much traffic will be encrypted with the same key, which makes cryptanalysis attacks more difficult than if the same key were always used.

Generating random numbers

To ensure Eve is unable obtain the secret key, it is very important that she cannot guess the message NA. In practice, this message is often a large random number used in the calculations required by the chosen algorithm.

Initially, generating random variables was used for a lot of simulation work. To obtain relevant results, it is important not to repeat the simulation with the same parameters, but to repeat the simulation with different parameters hundreds or even thousands of times. The aim is to generate numbers that respect certain statistical properties, and that do not allow the sequence of numbers to be differentiated from a sequence that would be obtained by rolling dice, for example.

To generate a random number NA that can be used in these simulations, so-called pseudo-random generators are normally used, which apply a reprocessing algorithm to an initial value, known as the ‘seed’.  These pseudo-random generators aim to produce a sequence of numbers that resembles a random sequence, according to these statistical criteria. However, using the same seed twice will result in obtaining the same sequence twice.

The pseudo-random generator algorithm is usually public. If an attacker is able to guess the seed, he will be able to generate the random sequence and thus obtain the random numbers used by the cryptographic algorithms. In the specific case of cryptography, the attacker does not necessarily even need to know the exact value of the seed. If they are able to guess a set of values, this is enough to quickly calculate all possible keys and to crack the encryption.

In the 2000s, programmers used seeds that could be easily guessed, that were based on time, for example, making systems vulnerable. Since then, to avoid being able to guess the seed (or a set of values for the seed), operating systems rely on a mixture of the physical elements of the system (e.g. processing temperature, bus connections, etc.). These physical elements are impossible for an attacker to observe, and vary frequently, and therefore provide a good seed source for pseudo-random generators.

What about vulnerabilities?

Although the field is now well understood, random number generators are still sometimes subject to vulnerabilities. For example, between 2017 and 2021, cybersecurity researchers found 53 such vulnerabilities (CWE-338). This represents only a small number of software flaws (less than 1 in 1000). Several of these flaws, however, are of a high or critical level, meaning they can be used quite easily by attackers and are widespread.

A prime example in 2010 was Sony’s error on the PS3 software signature system. In this case, the reuse of a random variable for two different signatures allowed an attacker to find the manufacturer’s private key: it then became possible to install any software on the console, including pirated software and malware.

Between 2017 and 2021, flaws have also affected physical components, such as Intel Xeon processors, Broadcom chips used for communications and Qualcom SnapDragon processors embedded in mobile phones. These flaws affect the quality of random number generation.  For example, CVE-2018-5871 and CVE-2018-11290 relate to a seed generator whose periodicity is too short, i.e. that repeats the same sequence of seeds quickly. These flaws have been fixed and only affect certain functions of the hardware, which limits the risk.

The quality of random number generation is therefore a security issue. Operating systems running on newer processors (less than 10 years old) have random number generation mechanisms that are hardware-based. This generally ensures a good quality of the latter and thus the proper functioning of cryptographic algorithms, even if occasional vulnerabilities may arise. On the other hand, the difficulty is especially prominent in the case of connected objects, whose hardware capacities do not allow the implementation of random generators as powerful as those available on computers and smartphones, and which often prove to be more vulnerable.

Hervé Debar, Director of Research and Doctoral Training, Deputy Director, Télécom SudParis – Institut Mines-Télécom and Olivier Levillain, Assistant Professor, Télécom SudParis – Institut Mines-Télécom

This article has been republished from The Conversation under a Creative Commons license. Read the original article.

cybersécurité, attaques informatiques, attacks

Governments, banks, and hospitals: all victims of cyber-attacks

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Hervé Debar, Télécom SudParis – Institut Mines-Télécom

Cyber-attacks are not a new phenomenon. The first computer worm distributed via the Internet, known as the “Morris worm” after its creator, infected 10% of the 60,000 computers connected to the Internet at the time.

Published back in 1989, the novel The Cuckoo’s Egg was based on a true story of computer espionage. Since then, there have been any number of malicious events, whose multiple causes have evolved over time. The initial motivation of many hackers was their curiosity about this new technology that was largely out of the reach of ordinary people at the time. This curiosity was replaced by the lure of financial reward, leading firstly to messaging campaigns encouraging people to buy products online, and subsequently followed by denial-of-service attacks.

Over the past few years, there have been three main motivations:

  • Direct financial gain, most notably through the use of ransomware, which has claimed many victims.
  • Espionage and information-gathering, mostly state-sponsored, but also in the private sphere.
  • Data collection and manipulation (normally personal data) for propaganda or control purposes.

These motivations have been associated with two types of attack: targeted attacks, where hackers select their targets and find ways to penetrate their systems, and large-scale attacks, where the attacker’s aim is to claim as many victims as possible over an extended period of time, as their gains are directly proportional to their number of victims.

The era of ransomware

Ransomware is a type of malware which gains access to a victim’s computer through a back door before encrypting their files. A message is then displayed demanding a ransom in exchange for decrypting these files.

Kaseya cash register software

In July 2021, an attack was launched against Kaseya cash register software, which is used by several store chains. It affected the Cloud part of the service and shut down the payment systems of several retail chains.

The Colonial Pipeline attack

One recent example is the attack on the Colonial Pipeline, an oil pipeline which supplies the eastern United States. The attack took down the software used to control the flow of oil through the pipeline, leading to fuel shortages at petrol stations and airports.

This is a striking example because it affected a visible infrastructure and had a significant economic impact. However, other infrastructure – in banks, factories, and hospitals – regularly fall victim to this phenomenon. It should also be noted that these attacks are very often destructive, and that paying the ransom is not always sufficient to guarantee the recovery of one’s files.

Unfortunately, such attacks look set to continue, at least in the short-term, given the financial rewards for the perpetrators: some victims pay the ransom despite the legal and ethical questions this raises. Insurance mechanisms protecting against cyber-crime may have a detrimental effect, as the payment of ransoms only encourages hackers to continue. Governments have also introduced controls on cryptocurrencies, which are often used to pay these ransoms, in order to make payments more difficult. Paradoxically, however, payments made using cryptocurrency can be traced in a way that would be impossible with traditional methods of payment. We can therefore hope that this type of attack will become less profitable and riskier for hackers, leading to a reduction in this type of phenomenon.

Targeted, state-sponsored attacks

Infrastructure, including sovereign infrastructure (economy, finance, justice, etc.), is frequently controlled by digital systems. As a result, we have seen the development of new practices, sponsored either by governments or extremely powerful players, which implement sophisticated methods over an extended time frame in order to attain their objectives. Documented examples include the Stuxnet/Flame attack on Iran’s nuclear program, and the SolarWinds software hack.

SolarWinds

The attack targeting Orion and its SolarWinds software is a textbook example of the degree of complexity that can be employed by certain perpetrators during an attack. As a network management tool, SolarWinds plays a pivotal role in the running of computer systems and is used by many major companies as well as the American government.

The initial attack took place between January and September of 2019, targeting the SolarWinds compilation environment. Between the fall of 2019 and February 2020, the attacker interacted with this environment, embedding additional features. In February 2020, this interaction enabled the introduction of a Trojan horse called “Sunburst”, which was subsequently incorporated into SolarWinds’ updates. In this way, it became embedded in all of Orion’s clients’ systems, infecting as many as 18,000 organizations. The exploitation phase began in late 2020 when further malicious codes downloaded by Sunburst were injected, and the hacker eventually managed to breach the Office365 cloud used by the compromised companies. Malicious activity was first detected in December 2020, with the theft of software tools from the company FireEye.

This has continued throughout 2021 and has had significant impacts, underlining both the complexity and the longevity of certain types of attack. American intelligence agencies believe this attack to be the work of SVR, Russia’s foreign intelligence service, which has denied this accusation. It is likely that the strategic importance of certain targets will lead to future developments of this type of deep, targeted attack. The vital role played by digital tools in the running of our critical infrastructure will doubtless encourage states to develop cyber weapons, a phenomenon that is likely to increase in the coming years.

Social control

Revelations surrounding the Pegasus software developed by NSO have shown that certain countries can benefit significantly from compromising their adversaries’ IT equipment (including smartphones).

The example of Tetris

Tetris is the name given to a tool used (potentially by the Chinese government) to infiltrate online chat rooms and reveal the identities of possible opponents. This tool has been used on 58 sites and uses relatively complex methods to steal visitors’ identities.

“Zero-click” attacks

The Pegasus revelations shed light on what are known as “zero-click” attacks. Many attacks on messaging clients or browsers assume that an attacker will click a link, and that this click will then cause the victim to be infected. With zero-click attacks, targets are infected without any activity on their part. One ongoing example of this hack is the ForcedEntry or CVE-2021-30860 vulnerability, which has affected the iMessage app on iPhones.

Like many others, this application accepts data in a wide range of formats and must carry out a range of complex operations in order to present it to users in an elegant way, despite its reduced display format. This complexity has extended the opportunities for attacks. An attacker who knows a victim’s phone number can send them a malicious message, which will trigger an infection as it is processed by the phone. Certain vulnerabilities even make it possible to delete any traces (at least visible traces) that the message was received, in order to avoid alerting the target.

Despite the efforts to make IT platforms harder to hack, it is likely that certain states and private companies will remain capable of hacking into IT systems and connected objects, either directly (via smartphones, for example) or via the cloud services to which they are connected (e.g. voice assistants). This takes us into the world of politics, and indeed geopolitics.

The biggest problem with cyber-attacks remains identifying the origin of the attack and who was behind it. This is made even more difficult by attackers trying to cover their tracks, which the Internet gives them multiple opportunities to do.

How can you prevent an attack?

The best way of preventing an attack is to install the latest updates for systems and applications, and perhaps ensure that they are installed automatically. The majority of computers, phones and tablets can be updated on a monthly basis, or perhaps even more frequently. Another way is to activate existing means of protection such as firewalls or anti-virus software, which will eliminate most threats.

Saving your work on a regular basis is essential, whether onto a hard drive or in the Cloud, as is disconnecting from these back-ups once they have been completed. Back-up copies are only useful if they are kept separate from your computer, otherwise ransomware will attack your back-up drive as well as your main drive. Backing up twice, or saving key information such as the passwords to your main applications (messenger accounts, online banking, etc.) in paper form, is another must.

Digital tools should also be used with caution. Follow this simple rule of thumb: if it seems too good to be true in the real world, then there is every chance that it is also the case in the virtual world. By paying attention to any messages that appear on our screens and looking out for spelling mistakes or odd turns of phrase, we can often identify unusual behavior on the part of our computers and tablets and check their status.

Lastly, users must be aware that certain activities are risky. Unofficial app stores or downloads of executables in order to obtain software without a license often contain malware. VPNs, which are widely used to watch channels from other regions, are also popular attack vectors.

What should you do if your data is compromised?

Being compromised or hacked is highly stressful, and hackers constantly try to make their victims feel even more stressed by putting pressure on them or by sending them alarming messages. It is crucial to keep a cool head and find a second device, such as a computer or a phone, which you can use to find a tool that will enable you to work on the compromised machine.

It is essential to return to a situation in which the compromised machine is healthy again. This means a full system recovery, without trying to retrieve anything from the previous installation in order to prevent the risk of reinfection. Before recovery, you must analyze your back-up to make that sure no malicious code has been transferred to it. This makes it useful to know where the infection came from in the first place.

Unfortunately, the loss of a few hours of work has to be accepted, and you simply have to find the quickest and safest way of getting up and running again. Paying a ransom is often pointless, given that many ransomware programs are incapable of decrypting files. When decryption is possible, you can often find a free program to do it, provided by security software developers. This teaches us to back up our work more frequently and more extensively.

Finally, if you lack in-house cybersecurity expertise, it is highly beneficial to obtain assistance with the development of an approach that includes risk analyses, the implementation of protective mechanisms, the exclusive use of certified cloud services, and the performance of regular audits carried out by certified professionals capable of detecting and handling cybersecurity incidents.

Hervé Debar, Director of Research and PhDs, Deputy Director of Télécom SudParis.

This article has been republished from The Conversation under a Creative Commons licence. Read the original article (in French).

zero-click attacks

Zero-click attacks: spying in the smartphone era

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Zero-click attacks exploit security breaches in smartphones in order to hack into a target’s device without the target having to do anything. They are now a threat to everyone, from governments to medium-sized companies.

“Zero-click attacks are not a new phenomenon”, says Hervé Debar, a researcher in cybersecurity at Télécom SudParis. “In 1988 the first computer worm, named the “Morris worm” after its creator, infected 6,000 computers in the USA (10% of the internet at the time) without any human intervention, causing damage estimated at several million dollars.” By connecting to messenger servers which were open access by necessity, this program exploited weaknesses in server software, infecting it. It could be argued that this was one of the very first zero-click attacks, a type of attack which exploits security breaches in target devices without the victim having to do anything.

There are two reasons why this type of attack is now so easy to carry out on smartphones. Firstly, the protective mechanisms for these devices are not as effective as those on computers. Secondly, more complex processes are required in order to present videos and images, meaning that the codes enabling such content to be displayed are often more complex than those on computers. This makes it easier for attackers to hack in and exploit security breaches in order to spread malware. As Hervé Debar explains, “attackers must, however, know certain information about their target – such as their mobile number or their IP address – in order to identify their phone. This is a targeted type of attack which is difficult to deploy on a larger scale as this would require collecting data on many users.”

Zero-click attacks tend to follow the same pattern: the attacker sends a message to their target containing specific content which is received in an app. This may be a sound file, an image, a video, a gif or a pdf file containing malware. Once the message has been received, the recipient’s phone processes it using apps to display the content without the user having to click on it. While these applications are running, the attacker exploits breaches in their code in order to run programs resulting in spy software being installed on the target device, without the victim knowing.

Zero-days: vulnerabilities with economic and political impact

Breaches exploited in zero-click attacks are known as “zero-days”, vulnerabilities which are unknown to the manufacturer or which have yet to be corrected. There is now a global market for the detection of these vulnerabilities: the zero-day market, which is made up of companies looking for hackers to identify these breaches. Once the breach has been identified, the hacker will produce a document explaining it in detail, with the company who commissioned the document often paying several thousand dollars to get their hands on it. In some cases the manufacturer themselves might buy such a document in an attempt to rectify the breach. But it may also be bought by another company looking to sell the breach to their clients – often governments – for espionage purposes. According to Hervé Debar, between 100 and 1,000 vulnerabilities are detected on devices each year. 

Zero-click attacks are regularly carried out for theft or espionage purposes. For theft, the aim may be to validate a payment made by the victim in order to divert their money. For espionage, the goal might be to recover sensitive data about a specific individual. The most recent example was the Pegasus affair, which affected around 50,000 potential victims, including politicians and media figures. “These attacks may be a way of uncovering secret information about industrial, economic or political projects. Whoever is responsible is able to conceal themselves and to make it difficult to identify the origin of the attack, which is why they’re so dangerous”, stresses Hervé Debar. But it is not only governments and multinationals who are affected by this sort of attack – small and medium-sized companies are too. They are particularly vulnerable in that, owing to a lack of financial resources, they don’t have IT professionals running their systems, unlike major organisations.

Also read on I’MTech Cybersecurity: high costs for companies

More secure computer languages

But there are things that can be done to limit the risk of such attacks affecting you. According to Hervé Debar, “the first thing to do is use your common sense. Too many people fall into the trap of opening suspicious messages.” Personal phones should also be kept separate from work phones, as this prevents attackers from gaining access to all of a victim’s data. Another handy tip is to back up your files onto an external hard drive. “By transferring your data onto an external hard drive, it won’t only be available on the network. In the event of an attack, you will safely be able to recover your data, provided you disconnected the disc after backing up.” To protect against attacks, organisations may also choose to set up intrusion detection systems (IDS) or intrusion prevention systems (IPS) in order to monitor flows of data and access to information.

In the fight against cyber-attacks, researchers have developed alternative computing languages. Ada, a programming language which dates back to the 1980s, is now used in the aeronautic industry, in railways and in aviation safety. For the past ten years or so the computing language Rust has been used to solve problems linked to the management of buffer memory which were often encountered with C and C++, languages widely used in the development of operating systems. “These new languages are better controlled than traditional programming languages. They feature automatic protective mechanisms to prevent errors committed by programmers, eliminating certain breaches and certain types of attack.” However, “writing programs takes time, requiring significant financial investment on the part of companies, which they aren’t always willing to provide. This can result in programming errors leading to breaches which can be exploited by malicious individuals or organisations.”

Rémy Fauvel

Facebook

Facebook: a small update causes major disruption

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Hervé Debar, Télécom SudParis – Institut Mines-Télécom

Late on October 4, many users of Facebook, Instagram and WhatsApp were unable to access their accounts. All of these platforms belong to the company Facebook and were all affected by the same type of error: an accidental and erroneous update to the routing information for Facebook’s servers.

The internet employs various different types of technology, two of which were involved in yesterday’s incident: BGP (border gateway protocol) and DNS (domain name system).

In order to communicate, each machine must have an IP address. Online communication involves linking two IP addresses together. The contents of each communication are broken down into packets, which are exchanged by the network between a source and a destination.

How BGP (border gateway protocol) works

The internet is comprised of dozens of “autonomous systems”, or AS, some very large, and others very small. Some AS are interconnected via exchange points, enabling them to exchange data. Each of these systems is comprised of a network of routers, which are connected using either optical or electrical communication links. Communication online circulates using these links, with routers responsible for transferring communications between links in accordance with routing rules. Each AS is connected to at least one other AS, and often several at once.

When a user connects their machine to the internet, they generally do so via an internet service provider or ISP. These ISPs are themselves “autonomous systems”, with address ranges which they allocate to each of their clients’ machines. Each router receiving a packet will analyse both the source and the destination address before deciding to transfer the packet to the next link, following their routing rules.

In order to populate these routing rules, each autonomous system shares information with other autonomous systems describing how to associate a range of addresses in their possession with an autonomous system path. This is done step by step through the use of the BGP or border gateway protocol, ensuring each router has the information it needs to transfer a packet.

DNS (domain name system)

The domain name system was devised in response to concerns surrounding the lack of transparency with IP addresses for end users. For available servers on the internet, this links “facebook.com” with the IP address “157.240.196.35”.

Each holder of a domain name sets up (or delegates) a DNS server, which links domain names to IP addresses. They are considered to be the most reliable source (or authority) for DNS information, but are also often the first cause of an outage – if the machine is unable to resolve a name (i.e. to connect the name requested by the user to an address), then the end user will be sent an error message.

Each major internet operator – not just Facebook, but also Google, Netflix, Orange, OVH, etc. – has one or more autonomous systems and coordinates the respective BGP in conjunction with their peers. They also each have one or more DNS servers, which act as an authority over their domains.

The outage

Towards the end of the morning of October 4, Facebook made a modification to its BGP configuration which it then shared with the autonomous systems it is connected to. This modification resulted in all of the routes leading to Facebook disappearing, across the entire internet.

Ongoing communications with Facebook’s servers were interrupted as a result, as the deletion of the routes spread from one autonomous system to the next, since the routers were no longer able to transfer packets.

The most visible consequence for users was an interruption to the DNS and an error message, followed by the DNS servers of ISPs no longer being able to contact the Facebook authoritative server as a result of the BGP error.

This outage also caused major disruption on Facebook’s end as it rendered remote access and, therefore, teleworking, impossible. Because they had been using the same tools for communication, Facebook employees found themselves unable to communicate with each other, and so repairs had to be carried out at their data centres. With building security also online, access proved more complex than first thought.

Finally, with the domain name “facebook.com” no longer referenced, it was identified as free by a number of specialist sites for the duration of the outage, and was even put up for auction.

Impact on users

Facebook users were unable to access any information for the duration of the outage. Facebook has become vitally important for many communities of users, with both professionals and students using it to communicate via private groups. During the outage, these users were unable to continue working as normal.

Facebook is also an identity provider for many online services, enabling “single sign-on”, which involves users reusing their Facebook accounts in order to access services offered by other platforms. Unable to access Facebook, users were forced to use other login details (which they may have forgotten) in order to gain access.

Throughout the outage, users continued to request access to Facebook, leading to an increase in the number of DNS requests made online and a temporary but very much visible overload of DNS activity worldwide.

This outage demonstrated the critical role played by online services in our daily lives, while also illustrating just how fragile these services still are and how difficult it can be to control them. As a consequence, we must now look for these services to be operated with the same level of professionalism and care as other critical services.

Banking, for example, now takes place almost entirely online. A breakdown like the one that affected Facebook is less likely to happen to a bank given the standards and regulations in place for banking, such as the Directive On Network And Service Security, the General Data Protection Regulation or PCI-DSS.

In contrast, Facebook writes its own rules and is partially able to evade regulations such as the GDPR. Introducing service obligations for these major platforms could improve service quality. It is worth pointing out that no bank operates a network as impressive as Facebook’s infrastructure, the size of which exacerbates any operating errors.

More generally, after several years of research and standardisation, safety mechanisms for BGP and DNS are now being deployed, the aim being to prevent attacks which could have a similar impact. The deployment of these security mechanisms will need to be accelerated in order to make the internet more reliable.

Hervé Debar, Director of Research and PhDs, Deputy director, Télécom SudParis – Institut Mines-Télécom

This article has been republished from The Conversation under a Creative Commons licence. Read the original article.