Organizational Cryptography for Access Control

A cryptosystem for granting/rescinding access permission is proposed, based on elliptic curve cryptography. The `Organizational Cryptosystem\u27 grants access permission not by giving secret (decription) key to the corresponding user but by converting the ciphertext so that the user can decript with their secret key. The `conversion key\u27 for the document, which is created from the secret key which the ciphertext has been originally encrypted for, the public key of the member who shall be permitted to read the ciphertext, and a part of the ciphertext. Therefore it is not possible to decrypt the ciphertext with the conversion key. Nor, for the administrator who issues the conversion key, to obtain any information about the plaintext

Enhanced STS using Check Equation --Extended Version of the Signature scheme proposed in the PQCrypt2010--

We propose solutions to the problems which has been left in the Enhanced STS, which was proposed in the PQCrypto 2010. Enhanced STS signature scheme is dened as the public key with the Complementary STS structure, in which two STS public keys are symmetrically joined together. Or, the complementary STS is the public key where simply two STS public keys are joined together, without the protection with Check Equation. We discuss the following issues left in the Enhanced STS, which was prosented in the PQCrypt2010: (i) We implied that there may exist a way to cryptanalyze the Complementary STS structure. Although it has been proposed that the system be protected by Check Equations [35][37], in order to cope with an unknown attack, we did not show the concrete procedure. We show the actual procedure to cryptanalyze it and forge a signature. (ii) We assumed that the Check Equation should be changed every time a document is signed. This practice is not always allowed. We improved this matter. The Check Equation which was proposed in the PQCrypto 2010 dened the valid life as a function of the number of times the documents are signed, because the secret key of Check Equation is analyzed by collecting valid signatures. Now we propose a new method of integrating the Check Equation into the secret key and eliminate the risk of the hidden information drawn from the existing signature

Hidden Pair of Bijection Signature Scheme

A new signature system of multivariate public key cryptosys- tem is proposed. The new system, Hidden Pair of Bijection (HPB), is the advanced version of the Complementary STS system. This system real- ized both high security and quick signing. Experiments showed that the cryptanalysis of HPB by Gröbner bases has no less complexity than the random polynomial systems. It is secure against other way of cryptanalysis effective for Complementary STS. On the other hand, since it is based on bijections, signatures exist for any message, unlike other cryptosystems based on non-bijections such as HFE or Unbalanced Oil and Vinegar

Proposal of Multivariate Public Key Cryptosystem Based on Modulus of Numerous Prime Numbers and CRT with Security of IND-CPA

We have proposed before a multivariate public key cryptosystem (MPKC) that does not rely on the difficulty of prime factorization, and whose modulus is the product of many small prime numbers. In this system, the prime factorization by the attackers is self-trivial, and the structure of the secret key is based on CRT (Chinese Remainder Theorem). In this paper we propose MPKC with security of IND-CPA by adding random numbers to central transformation vectors in the system proposed before

Nonlinear Piece In Hand Perturbation Vector Method for Enhancing Security of Multivariate Public Key Cryptosystems

Abstract. The piece in hand (PH) is a general scheme which is applicable to any reasonable type of multivariate public key cryptosystems for the purpose of enhancing their security. In this paper, we propose a new class PH method called NLPHPV (NonLinear Piece in Hand Perturbation Vector) method. Although our NLPHPV uses similar perturbation vectors as is used for the previously known internal perturbation method, this new method can avoid redundant repetitions in decryption process. With properly chosen parameter sizes, NLPHPV achieves an observable gain in security from the original multivariate public key cryptosystem. We demonstrate these by both theoretical analyses and computer simulations against major known attacks and provides the concrete sizes of security parameters, with which we even expect the grater security against potential quantum attacks

Proposal of a Signature Scheme based on STS Trapdoor

A New digital signature scheme based on Stepwise Triangular Scheme (STS) is proposed. The proposed trapdoor has resolved the vulnerability of STS and secure against both Gröbner Bases and Rank Attacks. In addition, as a basic trapdoor, it is more efficient than the existing systems. With the efficient implementation, the Multivariate Public Key Cryptosystems (MPKC) signature public key has the signature longer than the message by less than 25 %, for example

Construction of the Tsujii-Shamir-Kasahara (TSK) Type Multivariate Public Key Cryptosystem, which relies on the Difficulty of Prime Factorization

A new multivariate public-key cryptosystem (MPKC) with the security based on the difficulty of the prime factoring is proposed. Unlike conventional cryptosystems such as RSA, most MPKCs are expected secure against quantum computers, and their operation of encryption and decryption is expected quick, because they do not need exponential operation. However, their security against quantum computers is very difficult to prove mathematically. We propose a new MPKC based on sequential solution method, assuming the security against von Neumann computers, whose attack seems as difficult as prime factoring. This cryptosystem is applicable to both encryption and signature

Security Enhancement of Various MPKCs by 2-layer Nonlinear Piece In Hand Method

Following the last proposal of the nonlinear Piece in Hand method, which has 3-layer structure, 2-layer nonlinear Piece in Hand method is proposed. Both of them aim at enhancing the security of existing and future multivariate public key cryptosystems. The new nonlinear Piece in Hand is compared with the 3-layer method and PMI+, which was proposed by Ding, et al

Proposal of PPS Multivariate Public Key Cryptosystems

In this paper we propose a new MPKC, called PPS, based on (i) the 2-layer nonlinear piece in hand method, (ii) PMI, and (iii) STS. The PPS is a specific MPKC obtained by applying the 2-layer nonlinear piece in hand method to STS, in the manner that the rank and randomness of the lower rank steps in the original secret polynomial vector of STS are enhanced by adding a perturbation polynomial vector and moreover PMI is used in the auxiliary part. The PPS overcomes the drawbacks of the three schemes by the advantage of the three schemes themself. Thus, PPS can be thought to be immune simultaneously from the algebraic attacks, such as the Groebner bases attacks, from the rank attacks, and from the differential attacks

Wie nicht-lineare Zeitrepräsentationen zukunftsbezogene Urteile und Entscheidungen beeinflussen können : ein entwicklungspsychologischer Ansatz

Die vorliegende Arbeit untersuchte in drei Experimenten den Einfluss der Zeit auf Bewertungen und Entscheidungen in unterschiedlichen Altersstufen. Experiment 1 beschäftigte sich mit dem Einfluss des Zeithorizontes auf die Beurteilung der Riskantheit einer Investition sowie auf das Investitionsverhalten bei 12-Jährigen. Im Gegensatz zu typischen Ergebnissen von Erwachsenen führte bei den Kindern eine lange Zeitspanne zwischen Investition und Erfolgsfeedback zur Annahme eines höheren Risikos und damit zu geringeren Investitionen. In Experiment 2 wurde die Bewertung materieller und nicht-materieller Werte, deren Erhalt verzögert war, bei 12-Jährigen und Erwachsenen untersucht. Dabei zeigte sich, dass Erwachsene Geld als materiellen Wert und Hilfe als nicht-materiellen Wert in ähnlicher Weise mit zunehmender Verzögerung abwerteten. Die Kinder hingegen werteten das verzögerte Geld deutlich stärker ab als Erwachsene, die Hilfe jedoch gar nicht. In Experiment 3 wurde die Entwicklung des Wissens über exponentielles Mengenwachstum in verschiedenen Altersgruppen untersucht. So schätzten 13-Jährige ein solches Wachstum normativ, doch bereits 9-Jährige unterschieden in ihren Schätzungen bedeutsam zwischen exponentiellem und linearem Wachstum, was für ein frühes intuitives Wissen in diesem Bereich spricht. Im Anschluss wurde ein Modell zur altersabhängigen Zeitrepräsentation entwickelt, das versucht, den Einfluss der Zeitrepräsentation in allen drei Experimenten zu erklären. Three experiments were conducted to examine the role of time on judgments and decisions in different age groups. Experiment 1 investigated the influence of the time horizon on 12-year-olds judgments of riskiness and amount of investment into an endeavour. In contrast to typical results of adults, a long time span between the investment and a feedback about its success yielded judgments of higher riskiness and, thus, lower investments in children. Experiment 2 assessed 12-year-olds and adults evaluation of material and immaterial values, whose receipt was either immediate or delayed. Results showed similar subjective discount rates for delayed money (i.e. material value) and delayed help (i.e. immaterial value) in adults. However, children discounted the delayed money more than adults, but they devaluated the delayed help not at all. Experiment 3 investigated the development of knowledge about exponential growth in children, aged 7 to 13 years, and adults. Only 13-year-olds showed a normative estimation of exponential growth. However, 9-year-olds already differentiated between exponential and linear growth in their estimations. This result points to an early intuitive knowledge in this domain. Finally, a model of age-related time representation was proposed to explain the role of time representation in the three experiments