We consider reliable and secure communication over intersymbol interference wiretap channels (ISI-WTCs). In particular, we first derive an achievable secure rate for ISI-WTCs without imposing any constraints on the input distribution. Afterwards, we focus on the setup where the input distribution of the ISI-WTC is constrained to be a time-invariant finite-order Markov chain. Optimizing the parameters of this Markov chain toward maximizing the achievable secure rates is a computationally intractable problem in general, and so, toward finding a local maximum, we propose an iterative algorithm that at every iteration replaces the secure rate function with a suitable~surrogate function whose maximum can be found efficiently. Although the secure rates achieved in the unconstrained setup are potentially larger than the secure rates achieved in the constrained setup, the latter setup has the advantage of leading to efficient algorithms for estimating and optimizing the achievable secure rates, and also has the benefit of being the basis of efficient coding schemes.

翻译：我们研究在符号间干扰窃听信道上的可靠和安全通信。具体而言，我们首先推导了在输入分布无任何约束条件下，符号间干扰窃听信道可达安全速率的表达式。随后，我们聚焦于输入分布被约束为时不变有限阶马尔可夫链的设定。优化该马尔可夫链参数以最大化可达安全速率通常是一个计算上不可解的问题；因此，为寻求局部最优解，我们提出一种迭代算法，该算法在每次迭代中用合适的替代函数替换安全速率函数，并能高效地求得该替代函数的最大值。尽管无约束设定下获得的安全速率可能大于约束设定下的结果，但后者具有以下优势：可导出估计和优化可达安全速率的高效算法，并可作为高效编码方案的设计基础。