Pensions, Education and Life Expectancy

In a two-period model with agent heterogeneity we analyze a pension reform toward a stronger link between contributions and benefits (as recently observed in several countries) in a pension system with a Bismarckian and a Beveridgian component. We show that such a policy change reduces the educational level in an economy. The life expectancy differential between skilled and unskilled individuals drives this result. Furthermore, we investigate the consequences on the intragenerational redistribution characteristics of the pension system – in the sense of the number of net-recipients relative to net-payers – as well as welfare effects.social security, education, life expectancy, pension reform, redistribution

Cryptanalysis and Design of Symmetric Primitives

Der Schwerpunkt dieser Dissertation liegt in der Analyse und dem Design von Block- chiffren und Hashfunktionen. Die Arbeit beginnt mit einer Einführung in Techniken zur Kryptoanalyse von Blockchiffren. Wir beschreiben diese Methoden und zeigen wie man daraus neue Techniken entwickeln kann, welche zu staerkeren Angriffen fuehren. Im zweiten Teil der Arbeit stellen wir eine Reihe von Angriffen auf eine Vielzahl von Blockchiffren dar. Wir haben dabei Angriffe auf reduzierte Versionen von ARIA und dem AES entwickelt. Darueber hinaus praesentieren wir im dritten Teil Angriffe auf interne Blockchiffren von Hashfunktionen. Wir entwickeln Angriffe, welche die inter- nen Blockchiffren von Tiger und HAS-160 auf volle Rundenanzahl brechen. Die hier vorgestellten Angriffe sind die ersten dieser Art. Ein Angriff auf eine reduzierte Ver- sion von SHACAL-2 welcher fast keinen Speicherbedarf hat, wird ebenfalls vorgestellt. Der vierte Teil der Arbeit befasst sich mit den Design und der Analyse von kryp- tographischen Hashfunktionen. Wir habe einen Slide Angriff, eine Technik welche aus der Analyse von Blockchiffren bekannt ist, im Kontext von Hashfunktionen zur Anwendung gebracht. Dabei praesentieren wir verschiedene Angriffe auf GRINDAHL und RADIOGATUN. Aufbauend auf den Angriffen des zweiten und dritten Teils dieser Arbeit stellen wir eine neue Hashfunktion vor, welche wir TWISTER nennen. TWISTER wurde fuer den SHA-3 Wettbewerb entwickelt und ist bereits zur ersten Runde angenommen.This thesis focuses on the cryptanalysis and the design of block ciphers and hash func- tions. The thesis starts with an overview of methods for cryptanalysis of block ciphers which are based on differential cryptanalysis. We explain these concepts and also sev- eral combinations of these attacks. We propose new attacks on reduced versions of ARIA and AES. Furthermore, we analyze the strength of the internal block ciphers of hash functions. We propose the first attacks that break the internal block ciphers of Tiger, HAS-160, and a reduced round version of SHACAL-2. The last part of the thesis is concerned with the analysis and the design of cryptographic hash functions. We adopt a block cipher attack called slide attack into the scenario of hash function cryptanalysis. We then use this new method to attack different variants of GRINDAHL and RADIOGATUN. Finally, we propose a new hash function called TWISTER which was designed and pro- posed for the SHA-3 competition. TWISTER was accepted for round one of this com- petition. Our approach follows a new strategy to design a cryptographic hash function. We also describe several attacks on TWISTER and discuss the security issues concern- ing these attack on TWISTER

New Related-Key Boomerang Attacks on AES

In this paper we present two new attacks on round reduced versions of the AES. We present the first application of the related-key boomerang attack on 7 and 9 rounds of AES-192. The 7-round attack requires only 2^{18} chosen plaintexts and ciphertexts and needs 2^{67.5} encryptions. We extend our attack to nine rounds of AES-192. This leaves to a data complexity of 2^{67} chosen plaintexts and ciphertexts using about 2^{143.33} encryptions to break 9 rounds of AES-192

Some Observations on SHAMATA

In this note we discuss some observation of the SHA-3 candidate SHAMATA. We observe that its internal block cipher is very weak, which could possibly lead to an attack on the hash function

Security of Cyclic Double Block Length Hash Functions including Abreast-DM

We provide the first proof of security for Abreast-DM, one of the oldest and most well-known constructions for turning a block cipher with $n$-bit block length and $2n$-bit key length into a 2n-bit cryptographic hash function. In particular, we prove that when Abreast-DM is instantiated with AES-256, i.e. a block cipher with 128-bit block length and 256-bit key length, any adversary that asks less than 2^124.42 queries cannot find a collision with success probability greater than 1/2. Surprisingly, this about 15 years old construction is one of the few constructions that have the desirable feature of a near-optimal collision resistance guarantee. We generalize our techniques used in the proof of Abreast-DM to a huge class of double block length (DBL) hash functions that we will call Cyclic-DM. Using this generalized theorem we are able to derive several DBL constructions that lead to compression functions that even have a higher security guarantee and are more efficient than Abreast-DM. Furthermore we give DBL constructions that have the highest security guarantee of all DBL compression functions currently known in literature. We also provide an analysis of preimage resistance for Cyclic-DM compression functions. Note that this work has been already presented at Dagstuhl \u2709

Some Observations on Indifferentiability

At Crypto 2005, Coron et al. introduced a formalism to study the presence or absence of structural flaws in iterated hash functions: If one cannot differentiate a hash function using ideal primitives from a random oracle, it is considered structurally sound, while the ability to differentiate it from a random oracle indicates a structural weakness. This model was devised as a tool to see subtle real world weaknesses while in the random oracle world. In this paper we take in a practical point of view. We show, using well known examples like NMAC and the Mix-Compress-Mix (MCM) construction, how we can prove a hash construction secure and insecure at the same time in the indifferentiability setting. These constructions do not differ in their implementation but only on an abstract level. Naturally, this gives rise to the question what to conclude for the implemented hash function. Our results cast doubts about the notion of “indifferentiability from a random oracle” to be a mandatory, practically relevant criterion (as e.g., proposed by Knudsen [16] for the SHA-3 competition) to separate good hash structures from bad ones

Related-Key Rectangle Attack of the Full 80-Round HAS-160 Encryption Mode

In this paper we investigate the security of the encryption mode of the HAS-160 hash function. HAS-160 is a Korean hash standard which is widely used in Korea\u27s industry. The structure of HAS-160 is similar to SHA-1 but includes some improvements. The encryption mode of HAS-160 is defined similarly as the encryption mode of SHA-1 that is called SHACAL-1. In 2006, Dunkelman et. al. successfully broke the full 80-round SHACAL-1. In this paper, we present the first cryptographic attack that breaks the encryption mode of the full 80-round HAS-160. SHACAL-1 and the encryption mode of HAS-160 are both blockciphers with key size 512 bits and plain-/ciphertext size of 160 bits. We will apply a key recovery attack that needs about 2^{155} chosen plaintexts and 2^{375.98} 80-round HAS-160 encryptions. The attack does not aim for a collision, preimage or 2nd-preimage attack, but it shows that HAS-160 used as a block cipher can be differentiated from an ideal cipher faster than exhaustive search

Attacking Reduced Rounds of the ARIA Block Cipher

ARIA is a block cipher proposed at ICISC\u2703. Its design is very similar to the advanced encryption standard (AES). The authors propose that on 32-bit processors, the encryption speed is at least 70% of that of the AES. They claim to offer a higher security level than AES. In this paper we present two attacks of reduced round ARIA which shows some weaknesses of the cipher. Moreover, our attacks have the lowest memory requirements compared to existing attacks on ARIA with an increase in the time complexity

Automatic Personalization of User Interfaces based on User Interaction Analytics

The default user interface (UI) of software applications is the same for all users, even though users differ in terms of their needs and preferences for using the software. UI customization is typically limited to the most advanced and/or highly active users. As a result, a significant proportion of users of a software do not reap the benefits of having a UI that is personalized to them. This disclosure describes techniques to determine and present a personalized UI to each user or an application, with the user’s permission. UI personalization is performed based on analytics of user-permitted data of user interaction and other relevant information. The analysis can be performed by a suitably trained machine learning model which outputs the optimal personalized UI for each user. Model training and execution is performed on the user device, and if the user permits, on a server that trains the model based on aggregated, non-identifiable user data

Why Do Developers Get Password Storage Wrong? A Qualitative Usability Study

Passwords are still a mainstay of various security systems, as well as the cause of many usability issues. For end-users, many of these issues have been studied extensively, highlighting problems and informing design decisions for better policies and motivating research into alternatives. However, end-users are not the only ones who have usability problems with passwords! Developers who are tasked with writing the code by which passwords are stored must do so securely. Yet history has shown that this complex task often fails due to human error with catastrophic results. While an end-user who selects a bad password can have dire consequences, the consequences of a developer who forgets to hash and salt a password database can lead to far larger problems. In this paper we present a first qualitative usability study with 20 computer science students to discover how developers deal with password storage and to inform research into aiding developers in the creation of secure password systems