International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Susan Hohenberger

Publications

Year
Venue
Title
2023
EUROCRYPT
Registered Attribute-Based Encryption
Susan Hohenberger George Lu Brent Waters David J. Wu
Attribute-based encryption (ABE) generalizes public-key encryption and enables fine-grained control to encrypted data. However, ABE upends the traditional trust model of public-key encryption by requiring a single trusted authority to issue decryption keys. If an adversary compromises the central authority and exfiltrates its secret key, then the adversary can decrypt every ciphertext in the system. This work introduces registered ABE, a primitive that allows users to generate secret keys on their own and then register the associated public key with a "key curator" along with their attributes. The key curator aggregates the public keys from the different users into a single compact master public key. To decrypt, users occasionally need to obtain helper decryption keys from the key curator which they combine with their own secret keys. We require that the size of the aggregated public key, the helper decryption keys, the ciphertexts, as well as the encryption/decryption times to be polylogarithmic in the number of registered users. Moreover, the key curator is entirely transparent and maintains no secrets. Registered ABE generalizes the notion of registration-based encryption (RBE) introduced by Garg et al. (TCC 2018), who focused on the simpler setting of identity-based encryption. We construct a registered ABE scheme that supports an a priori bounded number of users and policies that can be described by a linear secret sharing scheme (e.g., monotone Boolean formulas) from assumptions on composite-order pairing groups. Our approach deviates sharply from previous techniques for constructing RBE and only makes black-box use of cryptography. All existing RBE constructions (a weaker notion than registered ABE) rely on heavy non-black-box techniques. The encryption and decryption costs of our construction are comparable to those of vanilla pairing-based ABE. Two limitations of our scheme are that it requires a structured reference string whose size scales quadratically with the number of users (and linearly with the size of the attribute universe) and the running time of registration scales linearly with the number of users. Finally, as a feasibility result, we construct a registered ABE scheme that supports general policies and an arbitrary number of users from indistinguishability obfuscation and somewhere statistically binding hash functions.
2020
CRYPTO
Chosen Ciphertext Security from Injective Trapdoor Functions
Susan Hohenberger Venkata Koppula Brent Waters
We provide a construction of chosen ciphertext secure public-key encryption from (injective) trapdoor functions. Our construction is black box and assumes no special properties (e.g. ``lossy'', ``correlated product secure'') of the trapdoor function.
2018
EUROCRYPT
2017
TCC
2015
JOFC
2015
EUROCRYPT
2015
ASIACRYPT
2015
ASIACRYPT
2014
EUROCRYPT
2014
PKC
2013
PKC
2013
CRYPTO
2012
TCC
2012
EUROCRYPT
2012
PKC
2012
JOFC
Batch Verification of Short Signatures
With computer networks spreading into a variety of new environments, the need to authenticate and secure communication grows. Many of these new environments have particular requirements on the applicable cryptographic primitives. For instance, a frequent requirement is that the communication overhead inflicted be small and that many messages be processable at the same time. In this paper, we consider the suitability of public key signatures in the latter scenario. That is, we consider (1) signatures that are short and (2) cases where many signatures from (possibly) different signers on (possibly) different messages can be verified quickly. Prior work focused almost exclusively on batching signatures from the same signer.We propose the first batch verifier for messages from many (certified) signers without random oracles and with a verification time where the dominant operation is independent of the number of signatures to verify. We further propose a new signature scheme with very short signatures, for which batch verification for many signers is also highly efficient. Combining our new signatures with the best known techniques for batching certificates from the same authority, we get a fast batch verifier for certificates and messages combined. Although our new signature scheme has some restrictions, it is very efficient and still practical for some communication applications.
2011
TCC
2011
JOFC
2010
EUROCRYPT
2009
PKC
2009
EUROCRYPT
2009
CRYPTO
2008
ASIACRYPT
2007
ASIACRYPT
2007
ASIACRYPT
2007
EUROCRYPT
2007
TCC
2005
EUROCRYPT
2005
TCC

Program Committees

Crypto 2024
Crypto 2022
Eurocrypt 2020
Crypto 2019
PKC 2014
TCC 2014
Crypto 2012
Crypto 2010
TCC 2010
TCC 2008
Crypto 2008