In modern society, there is an ever growing demand for improving the security levels of communication networks. Most of the internet security nowadays is based on powerful algorithms that distribute keys between remote users. These algorithms, however, are often vulnerable to implementation flaws which tamper their security. Quantum key distribution is an alternative approach, which takes advantage of the fundamental laws of quantum mechanics to guarantee unconditional security. However, it is technically challenging to implement and difficult to integrate with telecommunication networks. We have recently developed a new key distribution method, which relies on classical light and a multimode optical fiber. We utilize the strong mode mixing in the fiber to encrypt the key, and the optical reciprocity principle to decrypt it. In the talk I will explain the basic concepts of our method, and present its implementation using telecommunication compatible components.