In vehicular communications, a balance between privacy and anonymity from one side and responsibility and non repudiation from the other side is very important. In this paper, a security framework for VANETs to achieve privacy and non-repudiation is proposed. We present the safety requirements in the context of accident and reporting problem. We build a platform to provide security to safety messages in an accident scenario based on Identity-based cryptography (IBC). An analytical evaluation and performance measurement are achieved to validate this platform. This study confirms that identity-based cryptography and elliptic curves are very useful to make light communications.