Paper Info
Title
Offline Witness Encryption.
Abstract
Witness encryption (WE) was introduced by Garg et al. [GGSW13]. A WE scheme is defined for some NP language L and lets a sender encrypt messages relative to instances x. A ciphertext for x can be decrypted using w witnessing x is an element of L, but hides the message if x is not an element of L. Garg et al. construct WE from multilinear maps and give another construction [GGH+13b] using indistinguishability obfuscation (iO) for circuits. Due to the reliance on such heavy tools, WE can currently hardly be implemented on powerful hardware and will unlikely be realizable on constrained devices like smart cards any time soon. We construct a WE scheme where encryption is done by simply computing a Naor-Yung ciphertext (two CPA encryptions and a NIZK proof). To achieve this, our scheme has a setup phase, which outputs public parameters containing an obfuscated circuit (only required for decryption), two encryption keys and a common reference string (used for encryption). This setup need only be run once, and the parameters can be used for arbitrary many encryptions. Our scheme can also be turned into a functional WE scheme, where a message is encrypted w.r.t. a statement and a function f, and decryption with a witness w yields f(m, w). Our construction is inspired by the functional encryption scheme by Garg et al. and we prove (selective) security assuming iO and statistically simulation-sound NIZK. We give a construction of the latter in bilinear groups and combining it with ElGamal encryption, our ciphertexts are of size 1.3 kB at a 128-bit security level and can be computed on a smart card.
Year
DOI
Venue
2016
10.1007/978-3-319-39555-5_16
Lecture Notes in Computer Science
Keywords
DocType
Volume
Witness encryption,Indistinguishability obfuscation,NIZK,Groth-Sahai proofs
Conference
9696
ISSN
Citations 
PageRank 
0302-9743
0
0.34
References 
Authors
0
3
Name
Order
Citations
PageRank
Hamza Abusalah131.74
Georg Fuchsbauer2203.07
Krzysztof Pietrzak3151372.60