The popular technology Wireless sensor networks (WSNs) are used in many fields of the application such as the medical, the military, the industry, the agricultural, etc. In this paper, explains the security issues in the WSNs. Firstly explain the challenges of wireless sensor networks, the security requirements such as confidentiality, integrity, authenticity, data freshness, and availability and the attacks in the WSNs, the security issues are accomplished via these classes: [the encryption algorithms (symmetric, asymmetric, hybrid) , the security protocols such as (Tinysec, SPINS, LEDS, Minisec, LEAP, MASA, Lightweight LCG, MiniSec, VEBEK of WSN), the secure data aggregation, and the key management, etc.]. Also, this paper concentrates on the study researches that fulfill the high level of the security in the WSNs.