  Vehicular communications play a substantial role in providing safety
transportation by means of safety message exchange. Researchers have proposed
several solutions for securing safety messages. Protocols based on a fixed key
infrastructure are more efficient in implementation and maintain stronger
security in comparison with dynamic structures. The purpose of this paper
present a method based on a fixed key infrastructure for detection
impersonation attack, in other words, Sybil attack, in the vehicular ad hoc
network. This attack, puts a great impact on performance of the network. The
proposed method, using an cryptography mechanism to detection Sybil attack.
Finally, using Mat lab simulator the results of this approach are reviewed,
This method it has low delay for detection Sybil attack, because most
operations are done in Certification Authority, so this proposed schema is a
efficient method for detection Sybil attack.
