# Secure Polar Coding with Delayed Wiretapping Information

## TL;DR

This paper develops secure polar coding schemes for wiretap channels with delayed channel state information, achieving near-optimal secrecy capacity under different channel conditions.

## Contribution

It introduces explicit weak and strong security polar coding schemes for delay CSI scenarios, extending secure coding theory to more realistic, time-varying wiretap channels.

## Key findings

- The weak security scheme approaches secrecy capacity with delay CSI.
- The strong security scheme guarantees strong security with delay CSI.
- Simulations confirm the effectiveness of both schemes.

## Abstract

In this paper, we investigate the secure coding issue for a wiretap channel model with fixed main channel and varying wiretap channel, by assuming that legitimate parties can obtain the wiretapping channel state information (CSI) after some time delay. For the symmetric degraded delay CSI case, we present an explicit weak security scheme by constructing secure polar codes on a one-time pad chaining structure, and prove its weak security, reliability and capability of approaching the secrecy capacity of perfect CSI case with delay CSI assumption. Further for the symmetric no-degraded delay CSI case, we present a modified multi-block chaining structure in which the original subset of frozen bit is designed for conveying functional random bits securely. Then we combine this modified multi-block chaining structure with the weak security scheme to construct an explicit strong security polar coding scheme, and prove its strong security, reliability and also the capability of approaching the secrecy capacity of perfect CSI case with delay CSI assumption. At last, we carry out stimulations to prove the performance of both secure schemes.