The Legic Prime system uses proprietary RFIDs to secure building access and micropayment applications. The employed algorithms rely on obscurity and consequently did not withstand scrutiny. This paper details how the algorithms were found from opening silicon chips as well as interacting with tags and readers. The security of the tags is based on several secret check-sums but no secret keys are employed that could lead to inherent security on the cards. Cards can be read, written to and spoofed using an emulator. Beyond these card weaknesses, we find that Legic’s trust delegation model can be abused to create master tokens for all Legic installations.

The Legic Prime system uses proprietary RFIDs to secure building access and micropayment applications. The employed algorithms rely on obscurity and consequently did not withstand scrutiny. This paper details how the algorithms were found from opening silicon chips as well as interacting with tags and readers. The security of the tags is based on several secret check-sums but no secret keys are employed that could lead to inherent security on the cards. Cards can be read, written to and spoofed using an emulator. Beyond these card weaknesses, we find that Legic’s trust delegation model can be abused to create master tokens for all Legic installations.

The DECT Standard Cipher (DSC) is a proprietary 64-bit stream cipher based on irregularly clocked LFSRs and a non-linear output combiner. The cipher is meant to provide confidentiality for cordless telephony. This paper illustrates how the DSC was reverse-engineered from a hardware implementation using custom firmware and information on the structure of the cipher gathered from a patent. Beyond disclosing the DSC, the paper proposes a practical attack against DSC that recovers the secret key from 2(15) keystreams on a standard PC with a success rate of 50% within hours; somewhat faster when a CUDA graphics adapter is available.

Nachdem Sicherheitslücken im veralteten DECT-Standards bereits auf dem CCC-Kongress im Dezember 2008 erkennbar wurden, präsentierten die Autoren dieses Jahr eine Kryptoanalyse der DECT Verschlüsselung. Der Beitrag illustriert die derzeitige durch DECT verschuldete Bedrohungslage und gibt Handlungsempfehlungen zum sicheren Telefonieren.

Cryptography ensures the confidentiality and authenticity of information but often relies on unproven assumptions. SAT solvers are a powerful tool to test the hardness of certain problems and have successfully been used to test hardness assumptions. This paper extends a SAT solver to efficiently work on cryptographic problems. The paper further illustrates how SAT solvers process cryptographic functions using automatically generated visualizations, introduces techniques for simplifying the solving process by modifying cipher representations, and demonstrates the feasibility of the approach by solving three stream ciphers. To optimize a SAT solver for cryptographic problems, we extended the solver’s input language to support the XOR operation that is common in cryptography. To better understand the inner workings of the adapted solver and to identify bottlenecks, we visualize its execution. Finally, to improve the solving time significantly, we remove these bottlenecks by altering the function representation and by pre-parsing the resulting system of equations. The main contribution of this paper is a new approach to solving cryptographic problems by adapting both the problem description and the solver synchronously instead of tweaking just one of them. Using these techniques, we were able to solve a well-researched stream cipher 26 times faster than was previously possible.

Radio Frequency Identification (RFID) technology bridges the physical and virtual worlds by enabling computers to track the movement of objects. Within a few years, RFID tags will replace barcodes on consumer items to increase the efficiency in logistics processes. The same tags, however, can be used to monitor business processes of competitors and to track individuals by the items they carry or wear. This work seeks to diminish this loss of privacy by adding affordable privacy protection to RFID systems. Technical privacy measures should be integrated in RFID tags in order to thwart rogue scanning and preserve the privacy of individuals and corporations. To be available for the upcoming deployment of item-level tags, protection measures must not substantially increase the costs of RFID systems. Previously proposed solutions, however, would unacceptably increase the costs of RFID tags, because the solutions use building blocks which were not optimized for privacy applications. Privacy, therefore, has been considered too expensive to be included in low-cost tags. This dissertation instead argues that privacy can be achieved at very low cost within the tight constraints of the smallest RFID tags and the largest installations. Designing more economical protection systems requires a better understanding of what properties are crucial for privacy. By modeling the incentives of attackers and measuring the extent to which different protection measures rescind these incentives, protection systems can be found that prevent different attacks. Sufficient protection is achieved if the cost of rogue scanning exceeds its expected return for all likely attackers. Perfect protection is neither possible nor necessary to achieve strong privacy. Protection can be realized through the combination of purposefully designed cryptographic primitives and optimized private identification protocols. These protocols achieve privacy only probabilistically, but—when parameterized well—disclose very little information. Adding noise to tag responses is one example for a protocol-level measure that provides a tradeoff between privacy and cost. The noise makes most tags indistinguishable to rogue readers while only modestly increasing the workload for the backend system. Privacy protocols rely on cryptographic functions, but all available functions are too expensive for RFID tags. New functions should not provide expensive properties that are not necessary for privacy, but be an order of magnitude cheaper. Adapting small noise-based hash functions proposed for authentication is one alternative to achieving some of the properties of cryptographic functions without incurring their costs. Another alternative is designing new cryptographic primitives to share resources with functions already present on RFID tags. Such functions can be found through automated tests that measure the cryptographic strength of a large number of possible designs. To achieve maximal privacy within a given cost budget, all design choices need to be considered concurrently, as similar tradeoffs often exist in different building blocks. This dissertation provides the building blocks needed to achieve strong privacy at low cost as well as a design method for building private systems from these building blocks. Towards this end, contributions are made in modeling the value of information, measuring privacy, optimizing privacy protocols, and designing cryptographic primitives.

To protect privacy in large systems, users should be able to authenticate against a central server without disclosing their identity to others. Private identification protocols based on public key cryptography are computationally expensive and cannot be implemented on small devices like RFID tags. Symmetric key protocols, on the other hand, provide only modest levels of privacy, but can be efficiently executed on servers and cheaply implemented on devices. The privacy of symmetric-key privacy protocols derives from the fact that an attacker only ever knows a small fraction of the keys in a system while the legitimate reader knows all keys. We propose to amplify this gap in the ability to distinguish users by adding noise to user responses. We focus on scenarios where an attacker is not able to acquire multiple different reads known to be from the same device, and justify this threat model by proposing a simple modification to RFID tag designs. In such scenarios, we can use noise to blur the borders between groups of users that the attacker would otherwise be able to distinguish. We evaluate the effectiveness and cost of this randomization and find that the information leakage from the tree protocol can be decreased to two thousandths of its original value with 150 times the number of server-side cryptographic operations and minimal cost to the tag. Degrees of privacy up to those achieved by public key protocols can be reached while staying well below the cost of public key cryptography.

The security of embedded devices often relies on the secrecy of proprietary cryptographic algorithms. These algorithms and their weaknesses are frequently disclosed through reverse-engineering software, but it is commonly thought to be too expensive to reconstruct designs from a hardware implementation alone. This paper challenges that belief by presenting an approach to reverse-engineering a cipher from a silicon implementation. Using this mostly automated approach, we reveal a cipher from an RFID tag that is not known to have a software or micro-code implementation. We reconstruct the cipher from the widely used Mifare Classic RFID tag by using a combination of image analysis of circuits and protocol analysis. Our analysis reveals that the security of the tag is even below the level that its 48-bit key length suggests due to a number of design flaws. Weak random numbers and a weakness in the authentication protocol allow for pre-computed rainbow tables to be used to find any key in a matter of seconds. Our approach of deducing functionality from circuit images is mostly automated, hence it is also feasible for large chips. The assumption that algorithms can be kept secret should therefore to be avoided for any type of silicon chip.

MiFare Crypto 1 is a lightweight stream cipher used in London’s Oyster card, Netherland’s OV-Chipcard, US Boston’s CharlieCard, and in numerous wireless access control and ticketing systems worldwide. Recently, researchers have been able to recover this algorithm by reverse engineering [11, 13]. We have examined MiFare from the point of view of the so called algebraic attacks. We can recover the full 48-bit key of the MiFare algorithm in 200 seconds on a PC, given 1 known IV (from one single encryption). The security of this cipher is therefore close to zero. This is particularly shocking, given the fact that, according to the Dutch press, 1 billion of MiFare Classic chips are used worldwide, including many government security systems.

Many applications inherently disclose information because perfect privacy protection is prohibitively expensive. RFID tags, for example, cannot be equipped with the cryptographic primitives needed to completely shield their information from unauthorized reads. All known privacy protocols that scale to the anticipated sizes of RFID systems achieve at most modest levels of protection. Previous analyses found the protocols to have weak privacy, but relied on simplifying attacker models and did not provide insights into how to improve privacy. We introduce a new general way to model privacy through probability distributions, that capture how much information is leaked by different users of a system. We use this metric to examine information leakage for an RFID tag from the a scalable privacy protocol and from a timing side channel that is observable through the tag's random number generator. To increase the privacy of the protocol, we combine our results with a new model for rational attackers to derive the overall value of an attack. This attacker model is also based on distributions and integrates seamlessly into our framework for information leakage. Our analysis points to a new para meterization for the privacy protocol that significantly improves privacy by decreasing the expected attack value while maintaining reasonable scalability at acceptable cost.

Radio Frequency Identification (RFID) systems promise large scale, automated tracking solutions but also pose a threat to customer privacy. The tree-based hash protocol proposed by Molnar and Wagner presents a scalable, privacy-preserving solution. Previous analyses of this protocol concluded that an attacker who can extract secrets from a large number of tags can compromise privacy of other tags. We propose a new metric for information leakage in RFID protocols along with a threat model that more realistically captures the goals and capabilities of potential attackers. Using this metric, we measure the information leakage in the tree-based hash protocol and estimate an attacker's probability of success in tracking targeted individuals, considering scenarios in which multiple information sources can be combined to track an individual. We conclude that an attacker has a reasonable chance of tracking tags when the tree-based hash protocol is used.