Boneh-Franklin Identity-based Encryption Research Articles

Enabling privacy and leakage resistance for dynamic blockchain-based access control systems

With rise of 5G/6G network, low-storage devices usually outsource data for higher rate and less latency. Non-controlled outsourcing and complex communications incur security issues for IoT applications. Specially, user privacy and access reliability pose technical challenges for sensitive data outsourcing and sharing. In this paper, we harmonize functional encryption and blockchain to propose a reliable and privacy-aware access control system named R-PAC. It allows a result-form access without learning raw information and fair interaction against malicious users. With a combination of all-or-nothing encapsulation technology, R-PAC supports users’ dynamic joining and key leakage resistance. We design R-PAC from Boneh–Franklin identity-based encryption, with forward-coverable encryption and reverse-discoverable decryption, and formally prove its indistinguishability security. We implement a R-PAC prototype and deploy it to a simulated Ethereum network to evaluate its performance. Experiments from both data access and transaction overhead show that R-PAC is with reasonable cost and has a trade-off between efficiency and strong security/functionality.

Identity-based encryption with security against the KGC: A formal model and its instantiations

The key escrow problem is one of the main barriers to the widespread real-world use of identity-based encryption (IBE). Specifically, a key generation center (KGC), which generates secret keys for a given identity, has the power to decrypt all ciphertexts. At PKC 2009, Chow defined a notion of security against the KGC, that relies on assuming that it cannot discover the underlying identities behind ciphertexts. However, this is not a realistic assumption since, in practice, the KGC manages an identity list, and hence it can easily guess the identities corresponding to given ciphertexts. Chow later amended this issue by introducing a new entity called an identity-certifying authority (ICA) and proposed an anonymous key-issuing protocol. Essentially, this allows the users, KGC, and ICA to interactively generate secret keys without users ever having to reveal their identities to the KGC. Unfortunately, since Chow separately defined the security of IBE and that of the anonymous key-issuing protocol, his IBE definition did not provide any formal treatment when the ICA is used to authenticate the users. Effectively, all of the subsequent works following Chow lack the formal proofs needed to determine whether or not it delivers a secure solution to the key escrow problem.In this paper, based on Chow's work, we formally define an IBE scheme that resolves the key escrow problem and provide formal definitions of security against corrupted users, KGC, and ICA. Along the way, we observe that if we are allowed to assume a fully trusted ICA, as in Chow's work, then we can construct a trivial (and meaningless) IBE scheme that is secure against the KGC. Finally, we present two instantiations in our new security model: a lattice-based construction based on the Gentry–Peikert–Vaikuntanathan IBE scheme (STOC 2008) and Rückert's lattice-based blind signature scheme (ASIACRYPT 2010), and a pairing-based construction based on the Boneh–Franklin IBE scheme (CRYPTO 2001) and Boldyreva's blind signature scheme (PKC 2003).

Identity-based authenticated encryption with identity confidentiality

After two decades of research on signcryption, recently a new cryptographic primitive, named higncryption, was proposed at ACM CCS'16. Higncryption can be viewed as privacy-enhanced signcryption, which integrates public key encryption, digital signature and identity concealment (which is not achieved in signcryption) into a monolithic primitive. Here, identity concealment means that the transcript of protocol runs should not leak participants' identity information.In this work, we propose the first identity-based higncryption (IBHigncryption, for short). We present the formal security model for IBHigncryption, under which security proof of the proposed scheme is conducted. The most impressive feature of IBHigncryption, besides other desirable properties it offers, is its simplicity and efficiency, which might be somewhat surprising in retrospect. Our IBHigncryption has a much simpler setup stage with smaller public parameters and particularly no need of computing master public key. It is essentially as efficient as (if not more than) the fundamental CCA-secure Boneh-Franklin identity-based encryption scheme [14], and has significant efficiency advantage over the IEEE 1363.3 standard of identity-based signcryption [8].

Reflections on the security proofs of Boneh-Franklin identity-based encryption scheme

In this paper, we first review the existing proofs of the Boneh-Franklin identity-based encryption scheme (BF-IBE for short), and show how to admit a new proof by slightly modifying the specifications of the hash functions of the original BF-IBE. Compared with prior proofs, our new proof provides a tighter security reduction and minimizes the use of random oracles, thus indicates BF-IBE has better provable security with our new choices of hash functions. The techniques developed in our proof can also be applied to improving security analysis of some other IBE schemes. As an independent technical contribution, we also give a rigorous proof of the Fujisaki-Okamoto (FO) transformation in the case of CPA-to-CCA, which demonstrates the efficiency of the FO-transformation (CPA-to-CCA), in terms of the tightness of security reduction, has long been underestimated. This result can remarkably benefit the security proofs of encryption schemes using the FO-transformation for CPA-to-CCA enhancement.

Another look at automated theorem-proving II

I continue the discussion initiated in [22] of whether or not computer-assisted proofs are a promising approach to preventing errors in reductionist security arguments. I examine some recent papers that describe automated security proofs for hashed ElGamal encryption, Boneh-Franklin identity-based encryption, and OAEP.

The Twin Diffie–Hellman Problem and Applications

We propose a new computational problem called the twin Diffie–Hellman problem. This problem is closely related to the usual (computational) Diffie–Hellman problem and can be used in many of the same cryptographic constructions that are based on the Diffie–Hellman problem. Moreover, the twin Diffie–Hellman problem is at least as hard as the ordinary Diffie–Hellman problem. However, we are able to show that the twin Diffie–Hellman problem remains hard, even in the presence of a decision oracle that recognizes solutions to the problem—this is a feature not enjoyed by the Diffie–Hellman problem, in general. Specifically, we show how to build a certain “trapdoor test” that allows us to effectively answer decision oracle queries for the twin Diffie–Hellman problem without knowing any of the corresponding discrete logarithms. Our new techniques have many applications. As one such application, we present a new variant of ElGamal encryption with very short ciphertexts, and with a very simple and tight security proof, in the random oracle model, under the assumption that the ordinary Diffie–Hellman problem is hard. We present several other applications as well, including a new variant of Diffie and Hellman’s non-interactive key exchange protocol; a new variant of Cramer–Shoup encryption, with a very simple proof in the standard model; a new variant of Boneh–Franklin identity-based encryption, with very short ciphertexts; a more robust version of a password-authenticated key exchange protocol of Abdalla and Pointcheval.

A variant of Boneh-Franklin IBE with a tight reduction in the random oracle model

The first practical identity based encryption (IBE) scheme was published by Boneh and Franklin at Crypto 2001, based on the elliptic curve pairing. Since that time, many other IBE schemes have been...

Provably Secure Timed-Release Public Key Encryption

A timed-release cryptosystem allows a sender to encrypt a message so that only the intended recipient can read it only after a specified time. We formalize the concept of a secure timed-release public-key cryptosystem and show that, if a third party is relied upon to guarantee decryption after the specified date, this concept is equivalent to identity-based encryption; this explains the observation that all known constructions use identity-based encryption to achieve timed-release security. We then give several provably-secure constructions of timed-release encryption: a generic scheme based on any identity-based encryption scheme, and two more efficient schemes based on the existence of cryptographically admissible bilinear mappings. The first of these is essentially as efficient as the Boneh-Franklin Identity-Based encryption scheme, and is provably secure and authenticated in the random oracle model; the final scheme is not authenticated but is provably secure in the standard model (i.e., without random oracles).

Protecting against key-exposure: strongly key-insulated encryption with optimal threshold

Key-insulated encryption schemes use a combination of key splitting and key evolution to protect against key exposure. Existing schemes, however scale poorly, having cost proportional to the number t of time periods that may be compromised by the adversary, and thus are practical only for small values of t. Yet in practice t might be large.This paper presents a strongly key-insulated encryption scheme with optimal threshold. In our scheme, t need not be known in advance and can be as large as one less than the total number of periods, yet the cost of the scheme is not impacted. This brings key-insulated encryption closer to practice. Our scheme is based on the Boneh-Franklin identity-based encryption (IBE) scheme [9], and exploits algebraic properties of the latter.Another contribution of this paper is to show that (not strongly) key-insulated encryption with optimal threshold and allowing random-access key updates (which our scheme and all others known allow) is equivalent to a restricted form of IBE. This means that the connection between key-insulated encryption and IBE is not accidental.