Identity based signcryption schemes without random oracles

Signcryption is a cryptographic primitive which performs encryption and signature in a single logical step with the cost lower than signature-then-encryption approach.. In this paper we gave attacks on confidentiality and unforgeability of two identity based signcryption schemes without random oracles. Further we proposed an improved identity based signcryption scheme without random oracles. We also proposed an identity based public verifiable signcryption scheme with third party verification without random oracles

Constant-Size Hierarchical Identity-Based Signature/Signcryption without Random Oracles

We construct the first constant-size hierarchical identity-based signature (HIBS) without random oracles - the signature size is $O(\lambda_s)$ bits, where $\lambda_s$ is the security parameter, and it is independent of the number of levels in the hierarchy. We observe that an efficient hierarchical identity-based signcryption (HIBSC) scheme without random oracles can be compositioned from our HIBS and Boneh, Boyen, and Goh\u27s hierarchical identity-based encryption (HIBE). We further optimize it to a constant-factor efficiency improvement. This is the first constant-size HIBSC without random oracles

Signcryption schemes with threshold unsigncryption, and applications

The final publication is available at link.springer.comThe goal of a signcryption scheme is to achieve the same functionalities as encryption and signature together, but in a more efficient way than encrypting and signing separately. To increase security and reliability in some applications, the unsigncryption phase can be distributed among a group of users, through a (t, n)-threshold process. In this work we consider this task of threshold unsigncryption, which has received very few attention from the cryptographic literature up to now (maybe surprisingly, due to its potential applications). First we describe in detail the security requirements that a scheme for such a task should satisfy: existential unforgeability and indistinguishability, under insider chosen message/ciphertext attacks, in a multi-user setting. Then we show that generic constructions of signcryption schemes (by combining encryption and signature schemes) do not offer this level of security in the scenario of threshold unsigncryption. For this reason, we propose two new protocols for threshold unsigncryption, which we prove to be secure, one in the random oracle model and one in the standard model. The two proposed schemes enjoy an additional property that can be very useful. Namely, the unsigncryption protocol can be divided in two phases: a first one where the authenticity of the ciphertext is verified, maybe by a single party; and a second one where the ciphertext is decrypted by a subset of t receivers, without using the identity of the sender. As a consequence, the schemes can be used in applications requiring some level of anonymity, such as electronic auctions.Peer ReviewedPostprint (author's final draft

Lightweight certificateless and provably-secure signcryptosystem for the internet of things

International audienceIn this paper, we propose an elliptic curve-based signcryption scheme derived from the standardized signature KCDSA (Korean Certificate-based Digital Signature Algorithm) in the context of the Internet of Things. Our solution has several advantages. First, the scheme is provably secure in the random oracle model. Second, it provides the following security properties: outsider/insider confidentiality and unforgeability; non-repudiation and public verifiability, while being efficient in terms of communication and computation costs. Third, the scheme offers the certificateless feature, so certificates are not needed to verify the user's public keys. For illustration, we conducted experimental evaluation based on a sensor Wismote platform and compared the performance of the proposed scheme to concurrent scheme

SIGNCRYPTION ANALYZE

The aim of this paper is to provide an overview for the research that has been done so far in signcryption area. The paper also presents the extensions for the signcryption scheme and discusses the security in signcryption. The main contribution to this paper represents the implementation of the signcryption algorithm with the examples provided.ElGamal, elliptic curves, encryption, identity-based, proxy-signcryption, public key, ring-signcryption, RSA, signcryption

The zheng-seberry public key cryptosystem and signcryption

In 1993 Zheng-Seberry presented a public key cryptosystem that was considered efficient and secure in the sense of indistinguishability of encryptions (IND) against an adaptively chosen ciphertext adversary (CCA2). This thesis shows the Zheng-Seberry scheme is not secure as a CCA2 adversary can break the scheme in the sense of IND. In 1998 Cramer-Shoup presented a scheme that was secure against an IND-CCA2 adversary and whose proof relied only on standard assumptions. This thesis modifies this proof and applies it to a modified version of the El-Gamal scheme. This resulted in a provably secure scheme relying on the Random Oracle (RO) model, which is more efficient than the original Cramer-Shoup scheme. Although the RO model assumption is needed for security of this new El-Gamal variant, it only relies on it in a minimal way

Signcryption with Proxy Re-encryption

Confidentiality and authenticity are two of the most fundamental problems in cryptography. Many applications require both confidentiality and authenticity, and hence an efficient way to get both together was very desirable. In 1997, Zheng proposed the notion of ``signcryption\u27\u27, a single primitive which provides both confidentiality and authenticity in a way that\u27s more efficient than signing and encrypting separately. Proxy re-encryption is a primitive that allows a semi-trusted entity called the ``proxy\u27\u27 to convert ciphertexts addressed to a ``delegator\u27\u27 to those that can be decrypted by a ``delegatee\u27\u27, by using some special information given by the delegator, called the ``rekey\u27\u27. In this work, we propose the notion of signcryption with proxy re-encryption (SCPRE), and motivate the same. We define security models for SCPRE, and also propose a concrete unidirectional, non-interactive identity-based SCPRE construction. We also provide complete proofs of security for the scheme in the security models defined. We finally provide directions for further research in this area