Interactive coding with nearly optimal round and communication blowup

The problem of constructing error-resilient interactive protocols was introduced in the seminal works of Schulman (FOCS 1992, STOC 1993). These works show how to convert any two-party interactive protocol into one that is resilient to constant-fraction of error, while blowing up the communication by only a constant factor. Since these seminal works, there have been many follow-up works which improve the error rate, the communication rate, and the computational efficiency.

All these works assume that in the underlying protocol, in each round, each party sends a *single* bit. This assumption is without loss of generality, since one can efficiently convert any protocol into one which sends one bit per round. However, this conversion may cause a substantial increase in *round* complexity, which is what we wish to minimize in this work. Moreover, all previous works assume that the communication complexity of the underlying protocol is *fixed* and a priori known, an assumption that we wish to remove.

In this work, we consider protocols whose messages may be of *arbitrary* lengths, and where the length of each message and the length of the protocol may be *adaptive*, and may depend on the private inputs of the parties and on previous communication. We show how to efficiently convert any such protocol into another protocol with comparable efficiency guarantees, that is resilient to constant fraction of adversarial error, while blowing up both the *communication* complexity and the *round* complexity by at most a constant factor. Moreover, as opposed to most previous work, our error model not only allows the adversary to toggle with the corrupted bits, but also allows the adversary to *insert* and *delete* bits. In addition, our transformation preserves the computational efficiency of the protocol. Finally, we try to minimize the blowup parameters, and give evidence that our parameters are nearly optimal.

This is joint work with Klim Efremenko and Elad Haramaty.