conference paper published yes Hamza M Abusalah author 40297222-F248-11E8-B48F-1D18A9856A87 Georg Fuchsbauer author 46B4C3EE-F248-11E8-B48F-1D18A9856A87 Krzysztof Z Pietrzak author 3E04A7AA-F248-11E8-B48F-1D18A9856A870000-0002-9139-1654 KrPi department ACNS: Applied Cryptography and Network Security Provable Security for Physical Cryptography project Teaching Old Crypto New Tricks project 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 ∈ L, but hides the message if x ∈ 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 cur- rently 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 parame- ters 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. https://research-explorer.ista.ac.at/download/1229/5273/IST-2017-765-v1+1_838.pdf application/pdfno Springer2016Guildford, UK eng 00038632450001610.1007/978-3-319-39555-5_16 9696285 - 303 https://research-explorer.ista.ac.at/record/83 Abusalah, Hamza M., et al. <i>Offline Witness Encryption</i>. Vol. 9696, Springer, 2016, pp. 285–303, doi:<a href="https://doi.org/10.1007/978-3-319-39555-5_16">10.1007/978-3-319-39555-5_16</a>. Abusalah, H. M., Fuchsbauer, G., &#38; Pietrzak, K. Z. (2016). Offline witness encryption (Vol. 9696, pp. 285–303). Presented at the ACNS: Applied Cryptography and Network Security, Guildford, UK: Springer. <a href="https://doi.org/10.1007/978-3-319-39555-5_16">https://doi.org/10.1007/978-3-319-39555-5_16</a> Abusalah HM, Fuchsbauer G, Pietrzak KZ. 2016. Offline witness encryption. ACNS: Applied Cryptography and Network Security, LNCS, vol. 9696, 285–303. H.M. Abusalah, G. Fuchsbauer, K.Z. Pietrzak, in:, Springer, 2016, pp. 285–303. Abusalah HM, Fuchsbauer G, Pietrzak KZ. Offline witness encryption. In: Vol 9696. Springer; 2016:285-303. doi:<a href="https://doi.org/10.1007/978-3-319-39555-5_16">10.1007/978-3-319-39555-5_16</a> H. M. Abusalah, G. Fuchsbauer, and K. Z. Pietrzak, “Offline witness encryption,” presented at the ACNS: Applied Cryptography and Network Security, Guildford, UK, 2016, vol. 9696, pp. 285–303. Abusalah, Hamza M, Georg Fuchsbauer, and Krzysztof Z Pietrzak. “Offline Witness Encryption,” 9696:285–303. Springer, 2016. <a href="https://doi.org/10.1007/978-3-319-39555-5_16">https://doi.org/10.1007/978-3-319-39555-5_16</a>. 12292018-12-11T11:50:50Z2026-04-08T14:10:21Z