Identity Based Public Verifiable Signcryption Scheme

Signcryption as a single cryptographic primitive offers both confidentiality and authentication simultaneously. Generally in signcryption schemes, the message is hidden and thus the validity of the ciphertext can be verified only after unsigncrypting the ciphertext. Thus, a third party will not be able to verify whether the ciphertext is valid or not. Signcryption schemes that allow any user to verify the validity of the ciphertext without the knowledge of the message are called public verifiable signcryption schemes. Third Party verifiable signcryption schemes allow the receiver to convince a third party, by providing some additional information along with the signcryption other than his private key with/without exposing the message. In this paper, we show the security weaknesses in three existing schemes \cite{BaoD98}, \cite{TsoOO08} and \cite{ChowYHC03}. The schemes in \cite{BaoD98} and \cite{TsoOO08} are in the Public Key Infrastructure (PKI) setting and the scheme in \cite{ChowYHC03} is in the identity based setting. More specifically, \cite{TsoOO08} is based on elliptic curve digital signature algorithm (ECDSA). We also, provide a new identity based signcryption scheme that provides public verifiability and third party verification. We formally prove the security of the newly proposed scheme in the random oracle model

A New Pairing-Free Certificateless Signcryption Scheme

Signcryption is a cryptographic primitive which provides unforgeability and confidentiality for digital communications. Many signcryption schemes have been constructed in the literature for secure communication between smart objects. But, many of these existing schemes are not secure and inefficient for resource constrained applications like WSNs, Mobile computing, VANETs and IoT applications. To enrich the security and efficiency issues, in this paper, we propose a new signcryption scheme in certificateless based framework and prove its security under the CDHP and ECDLP assumptions. The efficiency analysis indicates that our scheme is more efficient than other existing signcryption schemes and is well suitable for resource-constrained applications

Breaking and Fixing of an Identity Based Multi-Signcryption Scheme

Signcryption is a cryptographic primitive that provides authentication and confidentiality simultaneously in a single logical step. It is often required that multiple senders have to signcrypt a single message to a certain receiver. Obviously, it is inefficient to signcrypt the messages separately. An efficient alternative is to go for multi-signcryption. The concept of multi-signcryption is similar to that of multi-signatures with the added property - confidentiality. Recently, Jianhong et al. proposed an identity based multi-signcryption scheme. They claimed that their scheme is secure against adaptive chosen ciphertext attack and it is existentially unforgeable. In this paper, we show that their scheme is not secure against chosen plaintext attack and is existentially forgeable, we also provide a fix for the scheme and prove formally that the improved scheme is secure against both adaptive chosen ciphertext attack and existential forgery

Efficient identity based signcryption scheme and solution of key-escrow problem

In cryptography for sending any information from sender to receiver, we have to ensure about the three types of security policies i.e. integrity, confidentiality and authentication. For confidentiality purpose, encryption-decryption technique is used and for authentication purpose digital signature is used, so to ensure this three properties, first sender encrypt the message and then sign the message. Same process done at the receiver end that means first message is decrypted then verified, so it's two step process that increases the communication as well as computation cost. But in many real life applications where more speed and less cost is required like e-commerce applications, we can't use signature then encryption technique, so signcryption is the cryptographic primitives that provides signature as well as encryption at the same time on a single step. First signcryption scheme is proposed by Yullian Zheng in 1997, Since then many signcryption scheme is proposed based on elliptic discrete logarithm problem (ECDLP) , Bilinear pairing, Identity Based and certificateless environment. Many of the Signcryption scheme used Random Oracle Model for their security proofs and few are based on standard model

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

Certificateless KEM and Hybrid Signcryption Schemes Revisited

Often authentication and confidentiality are required as simultaneous key requirements in many cryptographic applications. The cryptographic primitive called signcryption effectively implements the same and while most of the public key based systems are appropriate for small messages, hybrid encryption (KEM-DEM) provides an efficient and practical way to securely communicate very large messages. Recently, Lippold et al. \cite{GCJ09} proposed a certificateless KEM in the standard model and the first certificateless hybrid signcryption scheme was proposed by Fagen Li et al. \cite{LST09}. The concept of certificateless hybrid signcryption has evolved by combining the ideas of signcryption based on tag-KEM and certificateless cryptography. In this paper, we show that \cite{GCJ09} is not Type-I CCA secure and \cite{LST09} is existentially forgeable. We also propose an improved certificateless hybrid signcryption scheme and formally prove the security of the improved scheme against both adaptive chosen ciphertext attack and existential forgery in the appropriate security models for certificateless hybrid signcryption

Improvements and Generalisations of Signcryption Schemes

In this work, we study the cryptographic primitive: signcryption, which combines the functionalities of digital signatures and public-key encryption. We first propose two generic transforms from meta-ElGamal signature schemes to signcryption schemes. These constructions can be thought of as generalisations of the signcryption schemes by Zheng and Gamage et al. Our results show that a large class of signcryption schemes arc outsider IND-CCA2 secure and insider UF-CMA secure. As a by-product, we also show that the meta-EIGamal signature schemes, for which no previous formal security proofs have been shown, arc UF-CMA secure. \Ve then propose a modification of one of the transforms in order to achieve insider IXD-CCA2 security in addition to insider UF-CMA security. This modification COStS just one extra exponential operation. In particular, we can apply this modification to the Zheng signcryption scheme to make it fully insider secure. Finally, we propose a generic transform from a two-key signcryption scheme to a one-key signcryption scheme while preserving both confidentiality and unforgeability. Our result shows that if we have an insider I)JD•CCA2 and CFC1A secure two-key signcryption scheme, then it can be turned into an insider IND-CCA2 and CF•CMA secure one• key signcryption scheme. We also show that an insider IND•CCA2 and UF-CMA secure one• key signcryption scheme induces a secure combined public• key scheme; that is, a combination of a signature scheme and a public• key encryption scheme that can securely share the same key pair. Combining previous results suggests that we can obtain a large class of insider secure one-key signcryption schemes from meta-ElGamal signature schemes, and that each of them can induce a secure combined public-key scheme.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

CASE: A New Frontier in Public-Key Authenticated Encryption

We introduce a new cryptographic primitive, called Completely Anonymous Signed Encryption (CASE). CASE is a public-key authenticated encryption primitive, that offers anonymity for senders as well as receivers. A case-packet should appear, without a (decryption) key for opening it, to be a blackbox that reveals no information at all about its contents. To decase a case-packet fully - so that the message is retrieved and authenticated - a verifcation key is also required. Defining security for this primitive is subtle. We present a relatively simple Chosen Objects Attack (COA) security definition. Validating this definition, we show that it implies a comprehensive indistinguishability-preservation definition in the real-ideal paradigm. To obtain the latter definition, we extend the Cryptographic Agents framework of [2, 3] to allow maliciously created objects. We also provide a novel and practical construction for COA-secure CASE under standard assumptions in public-key cryptography, and in the standard model. We believe CASE can be a staple in future cryptographic libraries, thanks to its robust security guarantees and efficient instantiations based on standard assumptions

A new identity based signcryption scheme from pairings

We present a new identity based scheme using pairings over elliptic curves. It combines the functionalities of signature and encryption and is provably secure in the random oracle model. We compare it with J. Malone-Lee's scheme from the points of view of security and efficiency. We give a proof of semantic security under the decisional bilinear Diffie-Hellman assumption for this new scheme.Anglai