International Association for Cryptologic Research

International Association
for Cryptologic Research


M. Choudary Gorantla


One Round Group Key Exchange with Forward Security in the Standard Model
Constructing a one round group key exchange (GKE) protocol that provides forward secrecy is an open problem in the literature. In this paper, we investigate whether or not the security of one round GKE protocols can be enhanced with any form of forward secrecy without increasing the number of rounds. We apply the {\em key evolving} approach used for forward secure encryption/signature schemes and then model the notion of forward security for the first time for key exchange protocols. This notion is slightly weaker than forward secrecy, considered traditionally for key exchange protocols. We then revise an existing one round GKE protocol to propose a GKE protocol with forward security. In the security proof of the revised protocol we completely avoid reliance on the random oracle assumption that was needed for the proof of the base protocol. Our security proof can be directly applied to the base protocol, making it the most efficient one round GKE protocol secure in the standard model. Our one round GKE protocol is generically constructed from the primitive of forward secure encryption. We also propose a concrete forward secure encryption scheme with constant size ciphertext that can be used to efficiently instantiate our protocol.
Attribute-based Authenticated Key Exchange
We introduce the concept of attribute-based authenticated key exchange (AB-AKE) within the framework of ciphertext policy attribute-based systems. A notion of AKE-security for AB-AKE is presented based on the security models for group key exchange protocols and also taking into account the security requirements generally considered in the ciphertext policy attribute-based setting. We also extend the paradigm of hybrid encryption to the ciphertext policy attribute-based encryption schemes. A new primitive called encapsulation policy attribute-based key encapsulation mechanism (EP-AB-KEM) is introduced and a notion of chosen ciphertext security is defined for EP-AB-KEMs. We propose an EP-AB-KEM from an existing attribute-based encryption scheme and show that it achieves chosen ciphertext security in the generic group and random oracle models. We present a generic one-round AB-AKE protocol that satisfies our AKE-security notion. The protocol is generically constructed from any EP-AB-KEM that satisfies chosen ciphertext security. Instantiating the generic AB-AKE protocol with our EP-AB-KEM will result in a concrete one-round AB-AKE protocol also secure in the generic group and random oracle models.
Verifiably Encrypted Signature Scheme with Threshold Adjudication
M. Choudary Gorantla Ashutosh Saxena
Verifiably encrypted signature is useful in handling the fair exchange problem especially, online contract signing. In this paper, we propose a verifiably encrypted signature scheme using bilinear pairings. Our scheme facilitates the adjudication to be done in a threshold manner to achieve robustness. We show that the distribution of adjudication capability is robust and unforgeable. Our scheme is secure against extraction and existential forgery in the random oracle model.
A Survey on ID-Based Cryptographic Primitives
M. Choudary Gorantla Raju Gangishetti Ashutosh Saxena
ID-based cryptosystem has been, for a few years, the most active area of research and currently is of great interest to the cryptographic society. In this work we survey three fundamental ID-based cryptographic primitives Digital Signature, Encryption and Key Agreement, which are based on the mathematical concepts Integer Factorization, Quadratic Residues and Bilinear Pairings. We review several schemes along with their efficiency and security considerations. The survey helps in understanding the research work carried out in the area of ID-based cryptosystems from the year 1984 to 2004.