We use sensor technologies in many areas of everyday life. We use sensors to check and study various phenomena and to improve our lives. Hence, the sensors are used in medicine, industry, sports, and many other aspects of everyday life. Interconnected sensors and other wireless devices and servers form Wireless Sensor Networks. During communication between the nodes of such networks, we often send private and sensitive data. These data should be properly secured. Securing communication in a Wireless Sensor Network mainly affects the reconciliation and distribution of session keys and authentication. Specially designed protocols must protect both methods. In turn, the protocols may be exposed to dishonest users of such networks and thus exposed to various attacks (for example, replay attacks and smart card stolen attacks). This article surveys the existing session key negotiation, distribution, and authentication protocols. We will explain the security problems and threats to which the sensor networks are exposed. We will discuss the security levels implemented by the protocols currently used in sensor networks. We will analyze the challenges and requirements faced by the newly designed protocols.