Stream randomness extraction against quantum side information

TL;DR

This paper introduces a generalized stream-processing method for quantum randomness extractors, enabling real-time data processing while maintaining security guarantees, thus improving efficiency in quantum cryptography.

Contribution

It extends stream-processing to a broader class of extractors based on universal hashing, shifting computation offline and enabling on-the-fly processing.

Findings

Stream implementation preserves security guarantees of block-wise extractors.

Transformed three typical extractor constructions from block to stream.

Benchmark results show practical performance on quantum data.

Abstract

Randomness extraction is indispensable for quantum random number generators, serving to eliminate bias and potential information leakage from raw measurement data. Conventional extractors operate in a block-wise fashion, requiring the complete accumulation of raw data before processing. To circumvent the latency and buffering overheads that hinder real-time random number generation, recent work introduced a stream-cipher implementation for the randomness extractor based on the Toeplitz matrix hashing. In this work, we generalize this stream-processing paradigm to the broader family of randomness extractors based on (almost dual) universal$_2$ random hashing. Specifically, we shift the computational burden from a time-consuming block-wise post-processing stage into an offline pre-processing stage that generates a pseudo-random mask. This allows the raw data to be processed by the mask on the fly using a simple bitwise exclusive-OR operation. Crucially, we prove that this stream implementation strictly preserves the security guarantees of the original block-wise protocols. We detail the transformation of three typical constructions -- based on standard Toeplitz, circulant, and modified Toeplitz matrices -- from block to stream implementations, and benchmark their practical performance using realistic quantum experimental data. We anticipate our framework will enhance the efficiency of real-time quantum cryptographic systems.