[Resource Topic] 2022/1599: Streaming Functional Encryption

Welcome to the resource topic for 2022/1599

Streaming Functional Encryption

Authors: Jiaxin Guan, Alexis Korb, Amit Sahai


We initiate the study of streaming functional encryption (sFE) which is designed for scenarios in which data arrives in a streaming manner and is computed on in an iterative manner as the stream arrives. Unlike in a standard functional encryption (FE) scheme, in an sFE scheme, we (1) do not require the entire data set to be known at encryption time and (2) allow for partial decryption given only a prefix of the input. More specifically, in an sFE scheme, we can sequentially encrypt each data point x_i in a stream of data x = x_1\ldots x_n as it arrives, without needing to wait for all n values. We can then generate function keys for streaming functions which are stateful functions that take as input a message x_i and a state \mathsf{st}_i and output a value y_i and the next state \mathsf{st}_{i+1}. For any k \leq n, a user with a function key for a streaming function f can learn the first k output values y_1\ldots y_k where (y_i, \mathsf{st}_{i+1}) = f(x_i, \mathsf{st}_i) and \mathsf{st}_1 = \bot given only ciphertexts for the first k elements x_1\ldots x_k.

In this work, we introduce the notion of sFE and show how to construct it from FE. In particular, we show how to achieve a secure sFE scheme for \mathsf{P/Poly} from a compact, secure FE scheme for \mathsf{P/Poly}, where our security notion for sFE is similar to standard FE security except that we require all function queries to be made before the challenge ciphertext query. Furthermore, by combining our result with the FE construction of Jain, Lin, and Sahai (STOC, 2022), we show how to achieve a secure sFE scheme for \mathsf{P/Poly} from the polynomial hardness of well-studied assumptions.

ePrint: https://eprint.iacr.org/2022/1599

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