ID Based Signcryption Scheme in Standard Model

Designing an ID based signcryption scheme in the standard model is among the most interesting and important problems in cryptography. However, all the existing systems in the ID based setting, in the standard model, do not have either the unforgeability property or the indistinguishability property or both of them. In this paper, we present the first provably secure ID based signcryption scheme in the standard model with both these properties. The unforgeability property of this scheme is based on the hardness of Computational Diffie-Hellman problem and the indistinguishability property of this scheme is based on the hardness of Decisional Bilinear Diffie-Hellman problem. Our scheme is strongly unforgeable in the strong attack mode called insider security. Moreover, our scheme possess an interesting property called public verifiability of the ciphertext. Our scheme integrates cleverly, a modified version of Waters\u27 IBE and a suitably modified version of the ID based signature scheme in the standard model proposed by Paterson et al. However, our security reductions are more efficient. Specifically, while the security reductions for indistinguishability is similar to the bounds of Waters\u27 scheme, the unforgeability reductions are way better than the bounds for Paterson et al.\u27s scheme

Signcryption schemes based on elliptic curve cryptography

Signcryption is cryptographic primitive which simultaneously provide both the function of digital signature and public key encryption in a single logical step. Identity based cryptography is an alternative to the traditional certificate based cryptosystem. Its main idea is that each user uses his identity information as his public key. Many identity based signcryption scheme have been proposed so, far. However, all the schemes were proven using bilinear pairing. Elliptic curve cryptosystem (ECC) have recently received significant attention by research due to their low computational and communicational overhead. Elliptic curve cryptography (ECC) is the hardest computational problems; the elliptic curve discrete logarithm problem and elliptic curve Deffie-Hellman problem are the most reliable cryptographic technique in ECC. The advantages of ECC that it requires shorter key length compared to other public-key algorithms. So, that its use in low-end systems such as smart cards because of its efficiency and limited computational and communicational overhead. We introduce new signcryption schemes based on elliptic curve cryptography. The security of proposed schemes is based on elliptic curve discrete logarithm problem (ECDLP) and elliptic curve Diffie-Hellman problem (ECDHP). The proposed schemes provide various desirable security requirements like confidentiality, authenticity, non-repudiation and forward security as well as chosen ciphertext attack and unforgeability

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