Cryptography, Security and Privacy

An Information-Theoretic Proof of the Streaming Switching Lemma for Symmetric Encryption

Ido Shahaf, Or Ordentlich, Gil Segev

Date & Time

01:00 am – 01:00 am


Motivated by a fundamental paradigm in cryptography, we consider a recent variant of the classic problem of bounding the distinguishing advantage between a random function and a random permutation. Specifically, we consider the problem of deciding whether a sequence of $q$ values was sampled uniformly with or without replacement from $[N]$, where the decision is made by a streaming algorithm restricted to using at most $s$ bits of internal memory. In this work, the distinguishing advantage of such an algorithm is measured by the KL divergence between the distributions of its output as induced under the two cases. We show that for any $s=\Omega(\log N)$ the distinguishing advantage is upper bounded by $O(q \cdot s / N)$, and even by $O(q \cdot s / N \log N)$ when $q \leq N^{1 - \epsilon}$ for any constant $\epsilon > 0$ where it is nearly tight with respect to the KL divergence.


Ido Shahaf

Hebrew University of Jerusalem

Or Ordentlich

Hebrew University of Jerusalem

Gil Segev

Hebrew University of Jerusalem

Session Chair

Michael Langberg

State University of New York at Buffalo