Paper 2021/847
Dynamic Collusion Bounded Functional Encryption from IdentityBased Encryption
Rachit Garg, Rishab Goyal, George Lu, and Brent Waters
Abstract
Functional Encryption is a powerful notion of encryption in which each decryption key is associated with a function $f$ such that decryption recovers the function evaluation $f(m)$. Informally, security states that a user with access to function keys $\mathsf{sk}_{f_1}, \mathsf{sk}_{f_2}, \ldots$ (and so on) can only learn $f_1(m), f_2(m), \ldots$ (and so on) but nothing more about the message. The system is said to be $q$bounded collusion resistant if the security holds as long as an adversary gets access to at most $q = q(\lambda)$ function keys. A major drawback of such "statically" bounded collusion systems is that the collusion bound $q$ must be declared at setup time and is fixed for the entire lifetime of the system. We initiate the study of "dynamically" bounded collusion resistant functional encryption systems which provide more flexibility in terms of selecting the collusion bound, while reaping the benefits of statically bounded collusion FE systems (such as quantum resistance, simulation security, and general assumptions). Briefly, the virtues of a dynamically bounded scheme can be summarized as: (i) [Finegrained individualized selection.] It lets each encryptor select the collusion bound by weighing the tradeoff between performance overhead and the amount of collusion resilience. (ii) [Evolving encryption strategies.] Since the system is no longer tied to a single collusion bound, thus it allows to dynamically adjust the desired collusion resilience based on any number of evolving factors such as the age of the system, or a number of active users, etc. (iii) [Ease and simplicity of updatability.] None of the system parameters have to be updated when adjusting the collusion bound. That is, the same key $\mathsf{sk}_f$ can be used to decrypt ciphertexts for collusion bound $q = 2$ as well as $q = 2^\lambda$. We construct such a dynamically bounded functional encryption scheme for the class of all polynomialsize circuits under the general assumption of IdentityBased Encryption.
Metadata
 Available format(s)
 Category
 Publickey cryptography
 Publication info
 Preprint. MINOR revision.
 Keywords
 Functional Encryption
 Contact author(s)

rachg96 @ cs utexas edu
goyal @ utexas edu
gclu @ cs utexas edu
bwaters @ cs utexas edu  History
 20210719: revised
 20210622: received
 See all versions
 Short URL
 https://ia.cr/2021/847
 License

CC BY
BibTeX
@misc{cryptoeprint:2021/847, author = {Rachit Garg and Rishab Goyal and George Lu and Brent Waters}, title = {Dynamic Collusion Bounded Functional Encryption from IdentityBased Encryption}, howpublished = {Cryptology ePrint Archive, Paper 2021/847}, year = {2021}, note = {\url{https://eprint.iacr.org/2021/847}}, url = {https://eprint.iacr.org/2021/847} }