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In-vehicle electronic control unit (ECU) communications generally count on private protocols (defined by the manufacturers) under controller area network (CAN) specifications. Parsing the private protocols for a particular vehicle model would be of great significance in testing the vehicle’s resistance to various attacks, as well as in designing efficient intrusion detection and prevention systems (IDPS) for the vehicle. This paper proposes a suite of methods for parsing ECU private protocols on in-vehicle CAN network. These methods include an algorithm for parsing discrete variables (encoded in a discrete manner, e.g., gear state), an algorithm for parsing continuous variables (encoded in a continuous manner, e.g., vehicle speed), and a parsing method based on upper-layer protocols (e.g., OBD and UDS). Extensive verifications have been performed on five different brands of automobiles (including an electric vehicle) to demonstrate the universality and the correctness of these parsing algorithms. Some parsing tips and experiences are also presented. Our continuous-variables parsing algorithm could run in a semi-automatic manner and the parsing algorithm from upper-layer protocols could execute in a completely automatic manner. One might view the results obtained by our parsing algorithms as an important indicator of penetration testing on in-vehicle CAN network.

Modern vehicles are generally equipped with dozens of (or even hundreds of) electronic and intelligent devices and bloom into more involved information hub in enabling V2X networking. Protecting this increasingly complex vehicle ecosystem can be an arduous task, especially as the proliferation of data across distinct connected devices makes them more vulnerable than ever before. Intrusion detection systems (IDSs) have been found extremely rewarding in monitoring in-vehicle network traffic and detecting potential intrusions. The paper presents WLOF-InV, a novel unsupervised method based on local density for IDS on in-vehicle network. Given historical in-vehicle data of message identifiers, WLOF-InV first segments the traffic into a slice of (e.g., m) sliding windows. For each sliding window, WLOF-InV exerts information gain to select features for dimensionality reduction and squeezes out n features which are then bundled together to form a row vector and eventually gets an $m\times n$ matrix. WLOF-InV then adaptively determines the hyperparameters for local outlier factor (LOF) model (optimizing the scores for ranking the training data and the cutoff position for anomalies). In online detection, WLOF-InV determines the features by the information gain and invokes abnormal score weighting mode (which weights the LOF value of each dimension data by entropy method) to obtain the complete LOF score (of the overall traffic), and thereby grabs the anomaly traffic by resorting to the adjusted model. WLOF-InV is validated on the real data of three attack types (DoS, fuzzy, and impersonation). Experimental results demonstrate that WLOF-InV contrives next to optimal performance.

There are many disparate conceptualizations to secure a cryptocurrency network. Bitcoin relies on the proof-of-work mechanism and heterogeneous altcoins use proof-of-stake. Delegated Proof-of-Stake (DPoS), known to be a fast, efficient, decentralized, and highly flexible blockchain design, further offers some interesting reshaping that are well worth deliberating. In DPoS consensus, a panel of trusted parties (called committee of producers in the paper) has to be established, with all of its members eligible to create blocks and prevent non-trusted parties from participating. Deterministic selection of block producers allows transactions to be confirmed in an expected average of 1 second. The paper revisits the security properties of DPoS and reinforces the fairness and randomness for the algorithm without sacrificing its performance. We first scrutinize the limitations of the DPoS consensus, including predictability of producers, bribing producers, and lack of task incentivizing. We then introduce a cascade progressive-like ranking to judge the behaviour of the producers, and the producer who does not contribute to the network at the current interaction will be committed to a lower chance of being qualified for the coming involvement. More specifically, we conceptualize the tweaking parameters and the weights for the producers and bring in the weighted committee to measure the contributions of the producers. The weighted committee is a multiset derived from the committee and the weights specify the multiplicities of the elements (the producers). A pseudo-random process is also formulated to squeeze out the producer probabilistically from the weighted committee for creating the blocks. This unpredictability of the producers amplifies the randomness of the network and gives rise to a more secure and reliable cryptocurrency system. The proposal aspires to be beneficial for practical applications and the practitioners are as well encouraged to customize case-by-case the tweaking parameters and the pseudo-random process.

Connected vehicles are generally equipped with many (dozens of, or even hundreds of) electronic and intelligent devices so that drivers can gain a more comfortable driving experience. Despite their numerous benefits, these technological developments have also created serious safety/security concerns. This article recapitulates the diversified attack surfaces of connected vehicles related to the technological developments from the perspective of the in-vehicle network. For each of the attacks, we discuss the rationale and the concrete methods presented in the literature. In particular, we illustrate how to launch successful attacks through the controlled area network (CAN) bus, electronic control units (ECUs), and in-vehicle infotainment system. The article also suggests some feasible solutions to the attacks demonstrated by the community. Considering the fact that vehicles are safety- critical, more practical and effective steps should be taken within the connected vehicle network toward securing connected vehicles and protecting drivers and passengers. Introduction

Keeping the public keys in contradiction of foe is extraordinarily imperative in public key cryptosystems. The greater part of the authentication protocols require at least one establishments to au...

Bitcoin is promoted as decentralized cryptocurrency by using pseudonym to achieve anonymity. Unfortunately, numerous seminal works have demonstrated that Bitcoin only offers weak anonymity in practice. Indeed, the practical technologies of clustering and flow analysis are much effective for tracing Bitcoin transaction and thereby revealing the owner involved. Otherwise said, user's privacy in Bitcoin has been sadly degenerated to be linkable. In this paper, we propose a completely decentralized scheme that can provide full anonymity in Bitcoin. The idea behind the output is to exploit a secure escrow address, which is consensual by all the involved users. The escrow address is generated from the trick of cryptographically secure distributed key generation and can then be used for mixing transactions in Bitcoin. Our protocol is secure against malicious adversaries. The users can jointly perform the protocol and successfully accomplish the transaction without the help of any (trusted) third party and no extra fees. Besides, our proposal is completely compatible with the current Bitcoin architecture.

Password-based authentication is the current dominant technology for online service providers to confirm the (claimed) identities of legitimate users. Semantic patterns reflect how people choose their passwords, and understanding the patterns is useful in developing policies, guidelines and good practices to secure the password-based mechanism. Semantic patterns are hard to recognize in general and they may vary for people of different spoken languages, cultures, and ethnicity groups, etc. However, it is possible to investigate them in a specific context. In this paper, we manage to characterize the Pinyin semantics of passwords from the Chinese Netizens (up to 591 million), thanks to the well-defined structures of the Pinyin phonetic system.We perform a comprehensive analysis on the (publicly available) compromised password datasets from several leading Chinese sites for social networking, (micro)blogging, Internet forums, gaming, dating, and various other online service providers in China. The number of passwords in total sums to over 141 million, of which the largest site leaks more than 30 million on its own. Our findings show that over 4% of passwords from our datasets represent Pinyin (including names), another nearly 5% of passwords represent concatenations of Pinyin and date (i.e., Pinyin with a date prefix/suffix), and the next 17% of passwords are combinations of Pinyin and numeric (non-date) prefix/suffix. A majority (over 93%) of pure Pinyin passwords are transcribed from only 24 Chinese characters. The pure numeric pattern and the pattern containing special symbols are also studied. Over 76% of the passwords can be covered by the patterns of pure numeric and concatenation of Pinyin and digits. Special symbols appear in only 2.66% of the passwords, and they are most likely (with a percentage of 82.85%) in the middle. To the best of our knowledge, this is the first large scale study of its kind, and might yield other interesting insights into the semantic role Pinyin plays (either as good practice guidance on strengthening password security, or for improving password guessing attack). HighlightsSemantic patterns are hard to recognize in general.The work manages to characterize the Pinyin semantics of passwords from the Chinese Netizens (up to 591 million).The number of passwords in total sums to over 141 million.This is the first large scale study of its kind, and might yield other interesting insights into the semantic role Pinyin plays.

The paper focuses on the comparative analysis of deep learning algorithms and traditional probabilistic models on strings of short lengths (typically, passwords). The password is one of the dominant methods used in user authentication. Compared to the traditional brute-force attack and dictionary attack, password guessing models use the leaked password datasets to generate password guesses, expecting to cover as many accounts as possible while minimizing the number of guesses. In this paper, we analyze the password pattern of leaked datasets and further present a comparative study on two dominant probabilistic models (i.e., Markov-based model and Probabilistic Context-Free Grammars (PCFG) based model) and the PassGAN model (which is a representative deep-learning-based method).

Rainbow is an effective multivariate digital signature scheme proposed by Ding and Schmidt. However, a lot of attacks against it have been proposed. To resist all these attacks, designer should be very careful with its choice of parameters. In this study, the authors will propose a new approach to build a secure variant of Rainbow. According to our security analysis, it could resist all the existing attacks against Rainbow and save some memory in the meantime.

We revisit the problem of basing signcryption SC tag key encapsulation mechanism KEM on standard assumptions and standard model and present direct constructions of SC-KEM/tag-KEM, which satisfy confidentiality and unforgeability with respect to adversarially chosen keys where the adversary is given more advantageous attack environment than existing models in the literature;are based on the standard decisional bilinear Diffie-Hellman and computational Diffie-Hellman assumptions without random oracle;do not use strongly unforgeable signature schemes as building blocks; andprovide comparable performance to existing SC-KEM/tag-KEM schemes.

It has been widely adopted to minimize the maintenance cost by predicting potential vulnerabilities before code audits in academia and industry. Most previous research dedicated to file/component level vulnerability prediction models is coarse- grained and may suffer from cost-prohibitive and impractical security testing activities. In this paper, we focus on a cost- aware vulnerability prediction model and present a just-in-time change-level code review tool called VulDigger to dig suspicious ones from a sea of code changes. Our contributions benefit from the case study of Mozilla Firefox by constructing a large-scale vulnerability-contributing changes (VCCs) dataset in a semi-automatic fashion. We then further manifest a classification tool with a mixture of established and new metrics derived from both software defect prediction and vulnerability prediction. Consequently, the precision of such tool is extremely promising (i.e., 92%) for an effort-aware software team. We also examine the return on investment by training a regression model to locate most skeptical changes with fewer lines to inspect. Our findings suggest that such model is capable of pinpointing 31% of all VCCs with only 20% of the effort it would take to audit all changes (i.e., 55% better than random predictor). Our outputs can assist as an early step of continuous security inspections as it provides immediate feedback once developers submit changes to their code base.

Zhang et al. proposed recently a group-oriented multisigncryption scheme with threshold designcryption and affirmed that their scheme is secure under standard complexity assumptions. However, the note elaborates concrete attacks on its indistinguishability and unforgeability under their security models. We also provide the impossibility result of public ciphertext authenticity for the scheme.

An internet of vehicles allows intelligent automobiles to interchange messages with other cars, traffic management departments, and data analysis companies about vehicle identification, accident detection, and danger warnings. The implementation of these features requires Internet of Things system support. Smart cars are generally equipped with many (hundreds or even thousands of) sensors and microcomputers so that drivers gain more information about travel. The connection between the in-vehicle network and the Internet can be leveraged by the attackers in a malicious manner and thus increases the number of ways the in-vehicle network can now be targeted. Protecting increasingly intelligent vehicle systems becomes more difficult, especially because a network of many different devices makes the system more vulnerable than ever before. The paper assumes a generic threat model in which attackers can access the controller area network (CAN) bus via common access points (e.g., Bluetooth, OBD-II, Wi-Fi, physical access, and cellular communication, etc). A machine learning based simplified attention (SIMATT)-security control unit (SECCU) symmetry framework is proposed towards a novel and lightweight anomaly detecting mechanism for the in-vehicle network. For this framework, we propose two new models, SECCU and SIMATT, and obtain state-of-the-art anomaly detecting performance when fusing the former to the latter. Regardless of the training phase or the detection phase, we strive to minimize the computational cost and thereby obtain a lightweight anomaly detection method. In particular, the SECCU model has only one layer of 500 computing cells and the SIMATT model has been improved to reduce its computational costs. Through substantial experiment comparisons (with various classical algorithms, such as LSTM, GRU, GIDS, RNN, or their variations), it is demonstrated that the SIMATT-SECCU framework achieves an almost optimal accuracy and recall rate.

In password-based or two-factor password and smart card authentications, password changing is one of common techniques used to improve the security of the systems protected by the password. However, the password-changing operations in existing password authentications either depend on the login phase or violate the common practice that an old password should not be valid for subsequent login after being updated. On the other hand, password mistyping is very common in reality, which may be random or be skewed by the adversary via technical means or social engineering manipulation [i.e., a kind of denial-of-service DoS attack]. In human-centric authentication mechanisms, password changing and DoS resilience are not marginal issues. The paper addresses the requirements of robust password changing in authentication and presents SPCA, a password authentication scheme with robust password changing, DoS resilience, and card-compromise security. Thus, the proposal can be viewed as a suitable candidate instantiation for authentication services of human-centric security, by embedding in the computer and software systems. SPCA also achieves other appealing features, such as self-healing ability and strong privacy protection, which may be useful for human-centric applications. Copyright © 2013 John Wiley & Sons, Ltd.

Key-insulated cryptography is an important technique to protect private keys in identity-based (IB) cryptosytems. Despite the flurry of recent results on IB key-insulated encryption (IBKIE) and signature (IBKIS), a problem regarding the security and efficiency of practicing IBKIE and IBKIS as a joint IB key-insulated signature/encryption scheme with a common set of parameters and keys remains open. To deal with the above question, we propose an identity-based key-insulated signcryption (IBKISC) scheme. Compared with the Sign-then-Encrypt (StE) and Encrypt-then-Sign (EtS) using IBKIE and IBKIS in the standard model, our proposed IBKISC scheme is the fastest with the shortest ciphertext size.

Multisignature scheme allows a group of signers to generate a compact signature on a common document that certifies they endorsed the message. However, the existing state of the art multisignatures often suffers from the following problems: impractical key setup assumptions, loose security reductions and inefficient signature verification. In this paper, we propose a non-interactive multisignature scheme with tight security reduction in the random oracle model. Our proposed multisignatures address the above three problems by achieving: provable security in the plain public key model; tight security reduction under the standard Computational Diffie–Hellman (CDH) assumption and O(1) computational time for signature verification through pre-computation. Hence, our non-interactive multisignatures are of great use in routing authentication of networks.

To tackle the key-exposure problem in signature settings, this paper introduces a new cryptographic primitive named threshold key-insulated signature (TKIS) and proposes a concrete TKIS scheme. For a TKIS system, at least k out of n helpers are needed to update a user’s temporary private key. On the one hand, even if up to k−1 helpers are compromised in addition to the exposure of any of temporary private keys, security of the non-exposed periods is still assured. On the other hand, even if all the n helpers are compromised, we can still ensure the security of all periods as long as none of temporary private keys is exposed. Compared with traditional key-insulated signature (KIS) schemes, the proposed TKIS scheme not only greatly enhances the security of the system, but also provides flexibility and efficiency.

Certificateless signcryption is a useful primitive which simultaneously provides the functionalities of certificateless encryption and certificateless signature. Recently, Liu et al. [15] proposed a new certificateless signcryption scheme, and claimed that their scheme is provably secure without random oracles in a strengthened security model, where the malicious-but-passive KGC attack is considered. Unfortunately, by giving concrete attacks, we indicate that Liu et al. certificateless signcryption scheme is not secure in this strengthened security model.

By exploiting a smart card, this paper presents a robust and efficient password-authenticated key agreement scheme. This paper strengthens the security of the scheme by addressing untraceability property such that any third party over the communication channel cannot tell whether or not he has seen the same (unknown) smart card twice through the authentication sessions. The proposed remedy also prevents a kind of denial of service attack found in the original scheme. High performance and other good functionalities are preserved.

Recently, democratic group signatures (DGSs) particularly catch our attention due to their great functionalities, i.e., no group manager, anonymity, and individual traceability. In existing DGS schemes, individual traceability says that any member in the group can reveal the actual signer's identity from a given signature. In this paper, we strengthen the security notions of DGS by taking insider attack against anonymity into account, and present a concrete DGS construction with collective traceability. The idea behind collective traceability is that a sender can first choose (ad-hoc) a set of n members (including himself), and then sign a message by using the public keys of all the members, in such a way that his identity would be recovered, in case of disputes, if and only if all n members collectively cooperate. The security properties of our scheme are formally proved under reasonable assumptions.

This paper presents a concrete democratic group signature scheme which holds (t, n)-threshold traceability. In the scheme, the capability of tracing the actual signer is distributed among n group members. It gives a valid democratic group signature such that any subset with more than t members can jointly reconstruct a secret and reveal the identity of the signer. Any active adversary cannot do this even if he can corrupt up to t − 1 group members.

Democratic group signatures (DGSs) attract many researchers due to their appealing properties, i.e., anonymity, traceability and no group manager. Security results of existing work are based on decisional Diffie-Hellman (DDH) assumption. In this paper, we present a democratic group signature scheme based on any gap Diffie-Hellman (GDH) group where DDH problem is easily but computational Diffe-Hellman (CDH) problem is hard to be solved. Besides the properties of ordinary DGSs, our scheme also provides the property of linkability, i.e., any public verifier can tell whether two group signatures are generated using the same private key. Security properties of our scheme employ a new and independently interesting decisional product Diffie-Hellman (DPDH) assumption which is weaker than DDH one.

We analyze the relationship between the notion of certificateless public key cryptography (CL-PKC) and identity-based schemes without a trusted private key generator (PKG), formally define the security of certificateless threshold signatures, and propose a concrete implementation based on bilinear pairings. To exhibit the security of our proposal, we develop the theory of simulatability and relationship between the certificateless threshold signatures and the underlying (non-threshold) ID-based signatures. We show that the proposed scheme is robust and existentially unforgeable against adaptively chosen message attacks under CDH assumption in the random oracle model.

In electronic world, proxy signature is a solution of delegation of signing capabilities. Proxy signatures can combine other special signatures to obtain some new types of proxy signatures. Due to the various applications of the bilinear pairings in cryptography, many identity based signature schemes have been proposed. In this paper, we propose an identity based multi-proxy signature scheme and an identity based proxy multi-signature scheme from bilinear pairings. Both of them can be regarded as a special case of corresponding variants of identity based threshold signature scheme. Based on these two schemes, we propose an identity based multi-proxy multi-signature scheme.

Democratic group signature (DGS) is a group-oriented primitive with great flexibilities, i.e., no group manager, anonymity, and traceability. In a DGS scheme with (t, n)-threshold traceability, any subset of not less than t members can jointly reveal the identity of the signer while preserving security even in the presence of an active adversary can corrupt up to t − 1 group members. This paper proposes an efficient DGS scheme. We use publicly verifiable secret sharing (PVSS) to distribute the trapdoor via which the real signer is revealed. The computation cost and communication overhead of our DGS signatures are greatly reduced, compared with the existing work. For example, the size of the resulting signature contains only 2n + 1 elements of Z q , except the PVSS output.

Graphical password methods rely on human experience and hand selection (not well-quantified metric) to evaluate the appropriateness and the confusion of the challenge images. In this paper we propose to use for authentication Chinese characters, for which the entropy can be up to 9.65 (much larger than other languages). We first show an algorithmic framework to authenticate a user and then present an empirical analysis conducted at a university. The advantages of the framework include the following: the storage overhead is low; no personal experience or hand selection is involved; there is no predefined dictionary of likely choices; and it can be easily referenced by personal-style cues. Our study shows that the number of participants that prefer our framework is much close to that in favor of graphical passwords, with an interesting outcome that the two groups of participants present significantly distinct backgrounds. Our framework and graphical passwords can be used as candidate authentication methods for users with different backgrounds. We also measure user choices of patterns and find that there is a slight preference of the 3$\times$3 grid to the circle patterns. While the proposed framework prescribes the challenge characters, the users have the option to define challenge characters of their own.

The paper presents a direct construction of signcryption tag-KEM under the standard DBDH and CDH assumptions in the standard model, without using strongly unforgeable signature schemes as building blocks. We prove its confidentiality and unforgeability with respect to adversarially-chosen keys where the adversary is given more advantageous attack environment than existing models in the literature. The performance of our construction is comparable to existing signcryption tag-KEM schemes.

Cloud computing provides users and companies a cost-efficient and flexible service. However, for a cloud computing client, one of most worrying problems is that IT infrastructure is under control of the cloud provider. To secure cloud users' computation, efficient remote attestation protocol is required. In this paper, by combining trusted computing and dynamic accumulators, we put forward an anonymous remote attestation scheme for cloud computing service provider. Under the help of online or offline trusted third parties, a user can attest remote trusted nodes and establish a secure communication. In addition, the scheme can also protect privacy of trusted nodes and greatly reduce the cost of storage and management.

The nonlinear filter generator (NLFG) is a powerful building block commonly used in stream ciphers. In this paper, we present the direct sum decomposition of the NLFG output sequence that leads to a system of linear equations in the initial state of the NLFG and further to an efficient algebraic attack. The coefficients of the equation system rely only on the NLFG structure. The attack is operated in an online/offline manner, doing most of the work (determining the coefficients of the equation system) in the offline phase. Thus the online phase is very fast, requiring only four multiplications and one diagonalization of n×n matrices. Compared with related works, our attack has the advantages in both online computation cost and success probability. On the one hand, far fewer output bits and significantly less matrix computation are required in our attack, although the online computation complexity O(LC) (LC is the linear complexity of the output sequence) is the same as in the known Ronjom-Helleseth attack. On the other hand, the success probability of the attack is analyzed in this paper, different from most prior work. The success probability of this algebraic attack is $1-2^{-\phi(2^n-1)}$ (φ(·) is the Euler function), which is much greater than 1−2−n, the success probability of the Ronjom-Helleseth attack.

Cloud Storage systems provide user a safe and consistent place to save user's valuable data and documents. However, user's files are not encrypted on some open source cloud storage systems, such as Hadoop and Sector. The storage service provider can easily access the user's files. This brings a big concern about user's privacy. This paper describes a cloud storage system named YI Cloud. This system allows the users to encrypt their files in the cloud storage. User's primary encryption key is shared between trusted entities using secret sharing algorithm. The primary key can be recovered when the user loses it. User's privacy is protected because user's files are encrypted in cloud storage. Using secret sharing algorithm, the YI Cloud also decreases the risk that user may lose all his/her encrypted files if he/she loses the encryption key.

A multisignature scheme allows an ad hoc set of users to sign a message so that the resulting single signature certifies that the users endorsed the message. However, all known multisignatures are either at the price of complexity and additional trust of Certificate Authority (CA), or sacrificing efficiency of computation and communication (including both bandwidth and round). This paper proposes a new multisignature scheme with efficient verification in the plain public key model. Our multisignatures enjoys the most desired features: (1) Our plain public key model-based multisignatures do not impose any impractical key setup or PKI requirements; (2) Our multisignature scheme is non-interactive, which saves computation and communication in signature generation; (3) Through pre-computation, our scheme achieves O(1) verification in the plain public key model; (4) Provable tighter security under the standard CDH assumption ensures high level of security in both practice and theory. Hence, our non-interactive multisignatures are of great use in authentication of routes in networks.

Standard identity-based (ID-based) signature schemes typically rely on the assumption that secret keys are kept perfectly secure. However, with more and more cryptographic primitives are deployed on insecure devices (e.g. mobile devices), key-exposure seems inevitable. This problem is perhaps the most devastating attack on a cryptosystem since it typically means that security is entirely lost. To minimize the damage caused by key-exposure in ID-based signatures scenarios, Zhou et al. [32] applied Dodis et al.'s key-insulation mechanism [12] and proposed an ID-based key-insulated signature (IBKIS) scheme. However, their scheme is not strong key-insulated, i.e, if an adversary compromises the helper key, he can derive all the temporary secret keys and sign messages on behalf the legitimate user. In this paper, we re-formalize the definition and security notions for IBKIS schemes, and then propose a new IBKIS scheme with secure key-updates. The proposed scheme is strong key-insulated and perfectly key-insulated. Our scheme also enjoys desirable properties such as unbounded number of time periods and random-access key-updates.

A conference key distribution system can provide a session key of a conference with more than three participants via network. In this paper,we propose an ID-based conference key distribution scheme from pairings. The proposed scheme provides user anonymity. At the same time, we also show that the proposed scheme is secure against replaying attacks and conspiratorial impersonation attacks.

Authentication protocols are essential for security in many systems. However, authentication protocols are error-prone and difficult to design. In pervasive computing, the inherent characteristics such as mobility and restricted resources make it even harder to design suitable authentication protocols. In this paper we propose an authentication protocol to solve an open problem in pervasive computing, that is secure use of public information utilities without accessing a trusted third party (TTP). Our solution not only provides authentication, but also establishes a secure communication channel between the user and the service provider without the participation of TTP. The authentication protocol can be built with any secure symmetric and asymmetric cryptographic algorithm. We show the protocol can resist passive and active attacks. We also discuss how the protocol can be extended to an applicable scheme with payment support.

An identity-based cryptosystem is a novel type of public cryptographic scheme in which the public keys of the users are their identities or strings derived from their identities. A signcryption is a primitive that provides private and authenticated delivery of messages between two parties. Proxy signature schemes are variations of ordinary digital signature schemes and have been shown to be useful in many applications. We proposed an identity-based proxy-signcryption scheme from pairings. Also we analyze the proposed scheme from efficiency and security points of view. Heuristic arguments have been given for those security properties. We have shown that the proxy-signcryption scheme is as efficient as ordinary identity-based signcryption schemes under certain circumstances.

In electronic world, proxy signature is a solution of delegation of signing capabilities. Proxy signatures can combine other special signatures to obtain some new types of proxy signatures. Due to the various applications of the bilinear pairings in cryptography, many pairing-based signature schemes have been proposed. In this paper, we propose a multi-proxy signature scheme and a proxy multi-signature scheme from bilinear pairings. We also show that both of them satisfy all the security properties required by proxy signatures.