On the Provable Security of Multi-Receiver Signcryption Schemes

In ATC 2007, an identity based signcryption scheme for multiple receivers was proposed by Yu et al. In this paper, we first show that Yu et al.\u27s signcryption scheme is insecure by demonstrating an universal forgeability attack - anyone can generate a valid signcryption on any message on behalf of any legal user for any set of legal receivers without knowing the secret keys of the legal users. Also, we point out a subtle flaw in the proof of confidentiality given by Yu et al. and show that the scheme does not provide confidentiality. Further, we propose a corrected version of Yu et al.\u27s scheme and formally prove its security (confidentiality and unforgeability) under the existing security model for signcryption.\\ In another direction, Fagen Li et al. have proposed a pairing based multi-recipient signcryption scheme which works in public key infrastructure (PKI). We show that, the scheme proposed by Fagen Li et al. is not adaptive chosen ciphertext secure. We propose a new PKI based multi-receiver signcryption scheme and formally prove confidentiality and unforgeability of the scheme. Since all the previously reported schemes are shown to have flaws either in this paper or else where, the schemes reported in this paper are the only correct and efficient ones (both identity based and PKI based) for multi-receiver signcryption

An efficient FIS and RSA based Signcryption Security Scheme

No Abstrac

A Multi-Receiver ID-Based Generalized Signcryption Scheme

Generalized signcryption(GSC) can adaptively work as an encryption scheme, a signature scheme or a signcryption scheme with only one algorithm. In this paper, the formal definition and security notions of multi-receiver identity-based generalized signcryption (MID-GSC) are defined. A concrete scheme is also proposed and proved to be confidential under the Bilinear Diffie-Hellman (BDH) assumption and existential unforgeable under the Computational Diffie-Hellman(CDH) assumption in the random oracle model, which only needs one pairing computation to generalized signcrypt a single message for n receivers using the randomness re-use technique. Compared with other multi-receiver ID-based signcryption schemes, the new scheme is also of high efficiency

nMIBAS: A Novel Multi-Receiver ID-Based Anonymous Signcryption with Decryption Fairness

Based on the ring signature technology, the multi-receiver ID-based anonymous signcryption (MIBAS) is proposed, and its goal is to protect the privacy of the sender or so-called signer. In an MIBAS scheme, every receiver can verify whether the sender is a member of a trusted group and thus ensure the reliability of the message source, but he could not get the real sender. However, MIBAS paid no attention to privacy of the receivers and has not taken the privacy of the receivers into account during its design. Our analyses show that there widely exist the receiver privacy exposure and decryption unfairness problems in the existing multi-receiver ID-based signcryption schemes. Motivated by these concerns, a new multi-receiver ID-based anonymous signcryption (nMIBAS) is proposed to protect the identity of the receivers. The nMIBAS scheme can not only solve the problem that the existing schemes cannot protect the privacy of receivers, but also meet the fairness of decryption to prevent the possible cheating behavior of the sender effectively. Analysis shows that this scheme is a secure and effective signcryption scheme

An Efficient identity based Multi-receiver Signcryption Scheme using ECC

ABSTRACT Signcryption is a technique of performing signature and encryption in a single logical step. It is a secure and efficient technique of providing security between the sender and the receiver so that the data send by the sender should be made secure from various types of attacks such as desynchronization attacks, identity disclosure attack and spoofing attacks. Although there are many technique implemented for the generation of signature and encryption. Here a new and efficient technique of signcryption has been implemented in a multireceiver environment on the basis of identity of the receiver. The proposed work given here is the implementation of signcryption scheme using elliptic curve cryptography where the authentication between sender and the receiver is based on the identity of the receiver

Contributions to secret sharing and other distributed cryptosystems

The present thesis deals with primitives related to the eld of distributed cryptography. First, we study signcryption schemes, which provide at the same time the functionalities of encryption and signature, where the unsigncryption operation is distributed. We consider this primitive from a theoretical point of view and set a security framework for it. Then, we present two signcryption schemes with threshold unsigncryption, with di erent properties. Furthermore, we use their authenticity property to apply them in the development of a di erent primitive: digital signatures with distributed veri cation. The second block of the thesis deals with the primitive of multi-secret sharing schemes. After stating some e ciency limitations of multi-secret sharing schemes in an information-theoretic scenario, we present several multi-secret sharing schemes with provable computational security. Finally, we use the results in multi-secret sharing schemes to generalize the traditional framework of distributed cryptography (with a single policy of authorized subsets) into a multipolicy setting, and we present both a multi-policy distributed decryption scheme and a multi-policy distributed signature scheme. Additionally, we give a short outlook on how to apply the presented multi-secret sharing schemes in the design of other multi-policy cryptosystems, like the signcryption schemes considered in this thesis. For all the schemes proposed throughout the thesis, we follow the same formal structure. After de ning the protocols of the primitive and the corresponding security model, we propose the new scheme and formally prove its security, by showing a reduction to some computationally hard mathematical problem.Avui en dia les persones estan implicades cada dia més en diferents activitats digitals tant en la seva vida professional com en el seu temps lliure. Molts articles de paper, com diners i tiquets, estan sent reemplaçats més i més per objectes digitals. La criptografia juga un paper crucial en aquesta transformació, perquè proporciona seguretat en la comunicació entre els diferents participants que utilitzen un canal digital. Depenent de la situació específica, alguns requisits de seguretat en la comunicació poden incloure privacitat (o confidencialitat), autenticitat, integritat o no-repudi. En algunes situacions, repartir l'operació secreta entre un grup de participants fa el procés més segur i fiable que quan la informació secreta està centralitzada en un únic participant; la criptografia distribuïda és l’àrea de la criptografia que estudia aquestes situacions. Aquesta tesi tracta de primitives relacionades amb el camp de la criptografia distribuïda. Primer, estudiem esquemes “signcryption”, que ofereixen a la vegada les funcionalitats de xifrat i signatura, on l'operació de “unsigncryption” està distribuïda. Considerem aquesta primitiva des d’un punt de vista teòric i establim un marc de seguretat per ella. Llavors, presentem dos esquemes “signcryption” amb operació de “unsigncryption” determinada per una estructura llindar, cada un amb diferents propietats. A més, utilitzem la seva propietat d’autenticitat per desenvolupar una nova primitiva: signatures digitals amb verificació distribuïda. El segon bloc de la tesi tracta la primitiva dels esquemes de compartició de multi-secrets. Després de demostrar algunes limitacions en l’eficiència dels esquemes de compartició de multi-secrets en un escenari de teoria de la informació, presentem diversos esquemes de compartició de multi-secrets amb seguretat computacional demostrable. Finalment, utilitzem els resultats obtinguts en els esquemes de compartició de multi-secrets per generalitzar el paradigma tradicional de la criptografia distribuïda (amb una única política de subconjunts autoritzats) a un marc multi-política, i presentem un esquema de desxifrat distribuït amb multi-política i un esquema de signatura distribuïda amb multi-política. A més, donem indicacions de com es poden aplicar els nostres esquemes de compartició de multi-secrets en el disseny d’altres criptosistemes amb multi-política, com per exemple els esquemes “signcryption” considerats en aquesta tesi. Per tots els esquemes proposats al llarg d’aquesta tesi, seguim la mateixa estructura formal. Després de definir els protocols de la primitiva primitius i el model de seguretat corresponent, proposem el nou esquema i demostrem formalment la seva seguretat, mitjançant una reducció a algun problema matemàtic computacionalment difícil

An Improved Certificateless Generalized Signcryption Scheme

Signcryption is basically a cryptographic primitive which provides both signature and encryption functions simultaneously, but it is not useful when only one of the function is required. Generalized Signcryption (GSC) is a special cryptographic primitive which can provide Signcryption function when security and authenticity are needed simultaneously, and can also provide encryption or signature function separately when any one of them is needed. The first Generalized Signcryption was proposed in 2006 by Han et al. Since then many Generalized Signcryption has been proposed based on ECDLP, based on Bilinear Pairing, Identity based and some are also proposed in Certificateless environment. Majority of the Generalized Signcryption schemes uses Random Oracle Model for their security proof and few are proposed based on Standard model. In this thesis we have surveyed the existing GSC schemes and compare their security properties and efficiency. Along with this we also have proposed two schemes of which first one is an Identity based Generalized Signcryption Scheme and second one is a Certificateless Generalized Signcryption Scheme which is a variation of Certificateless Signcryption Scheme by Barbosa et al. We begin by giving formal definition of GSC primitive and complete with comparative study with other models. Finally, we look ahead at what future progress might be made in the field

Anonymous ID Based Signcryption Scheme for Multiple Receivers

Anonymous signcryption is synonyms of ring signcryption which provides anonymity of the sender along with the advantages of signcryption. Multi receiver signcryption is suited for situation where a sender wants to send a message to multiple receivers in the confidential and authenticated way. This paper proposes an identity based anonymous signcryption scheme in multi-receiver setting. It also provides proofs of provable security of the proposed scheme under some computationally difficult problems