International Association for Cryptologic Research

International Association
for Cryptologic Research


Streaming Functional Encryption

Jiaxin Guan , Princeton University
Alexis Korb , UCLA
Amit Sahai , UCLA
DOI: 10.1007/978-3-031-38551-3_14 (login may be required)
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Presentation: Slides
Conference: CRYPTO 2023
Abstract: 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 . . . 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 st_i and output a value y_i and the next state st_{i+1}. For any k ≤ n, a user with a function key for a streaming function f can learn the first k output values y_1 . . . y_k where (y_i, st_{i+1}) = f (x_i, st_i) and st_1 = ⊥ given only ciphertexts for the first k elements x_1 . . . 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 P/Poly from a compact, secure FE scheme for 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 P/Poly from the polynomial hardness of well-studied assumptions.
  title={Streaming Functional Encryption},
  author={Jiaxin Guan and Alexis Korb and Amit Sahai},