We construct a short group signature scheme. Signatures in our scheme are approximately the size of a standard RSA signature with the same security. Security of our group signature is based on the Strong Diffie-Hellman assumption and a new assumption in bilinear groups called the Decision Linear assumption. We prove security of our system, in the random oracle model, using a variant of the security definition for group signatures recently given by Bellare, Micciancio, and Warinschi.

/pdf/short-group-signatures-1vel1tk9wi.pdf

Short Group Signatures

We construct two efficient Identity Based Encryption (IBE) systems that are selective identity secure without the random oracle model. Selective identity secure IBE is a slightly weaker security model than the standard security model for IBE. In this model the adversary must commit ahead of time to the identity that it intends to attack, whereas in the standard model the adversary is allowed to choose this identity adaptively. Our first secure IBE system extends to give a selective identity Hierarchical IBE secure without random oracles.

/pdf/efficient-selective-id-secure-identity-based-encryption-3f5rqiikeo.pdf

Efficient Selective-ID Secure Identity-Based Encryption Without Random Oracles

Short group signatures

We present a Hierarchical Identity Based Encryption (HIBE) system where the ciphertext consists of just three group elements and decryption requires only two bilinear map computations, regardless of the hierarchy depth. Encryption is as ecient as in other HIBE systems. We prove that the scheme is selective-ID secure in the standard model and fully secure in the random oracle model. Our system has a number of applications: it gives very ecient forward secure public key and identity based cryptosystems (with short ciphertexts), it converts the NNL broadcast encryption system into an ecient public key broadcast system, and it provides an ecient mechanism for encrypting to the future. The system also supports limited delegation where users can be given restricted private keys that only allow delegation to bounded depth. The HIBE system can be modified to support sublinear size private keys at the cost of some ciphertext expansion.

/pdf/hierarchical-identity-based-encryption-with-constant-size-3pkft9cvmf.pdf

Hierarchical Identity Based Encryption with Constant Size Ciphertext.

We present a Hierarchical Identity Based Encryption (HIBE) system where the ciphertext consists of just three group elements and decryption requires only two bilinear map computations, regardless of the hierarchy depth. Encryption is as efficient as in other HIBE systems. We prove that the scheme is selective-ID secure in the standard model and fully secure in the random oracle model. Our system has a number of applications: it gives very efficient forward secure public key and identity based cryptosystems (with short ciphertexts), it converts the NNL broadcast encryption system into an efficient public key broadcast system, and it provides an efficient mechanism for encrypting to the future. The system also supports limited delegation where users can be given restricted private keys that only allow delegation to bounded depth. The HIBE system can be modified to support sublinear size private keys at the cost of some ciphertext expansion.

/pdf/hierarchical-identity-based-encryption-with-constant-size-1otup5atzv.pdf

Hierarchical identity based encryption with constant size ciphertext

A New Traitor Tracing

/pdf/id-based-cryptosystems-with-pairing-on-elliptic-curve-1yemmc1ppr.pdf

ID based Cryptosystems with Pairing on Elliptic Curve.

A Construction of Public Key Cryptosystem for Realizing Ciphertext of Size 100 Bit and Digital Signature Scheme

Extensive studies have been made of the public key cryptosystems based on multivariate polynomials over F 2 . However most of the proposed public key cryptosystems based on multivariate polynomials, are proved not secure. In this paper, we propose several types of new constructions of public key cryptosystems based on randomly generated singular simultaneous equations. One of the features of the proposed cryptosystems is that the sets of random singular simultaneous equations significantly enlarges the size of the transformation.

Ryuichi Sakai

Papers

A New Traitor Tracing

ID based Cryptosystems with Pairing on Elliptic Curve.

A Construction of Public Key Cryptosystem for Realizing Ciphertext of Size 100 Bit and Digital Signature Scheme

A Construction of Public-Key Cryptosystem Based on Singular Simultaneous Equations

New Key Generation Algorithm for RSA Cryptosystem