Vehicular ad-hoc networks differ from the wired networks and behave in a highly dynamic context, e.g. frequently changing signal-to-noise ratio (SNR) and security risks, which undoubtedly affects the experienced quality-of-service (QoS) and security. In this paper, we propose to dynamically balance the anticipated QoS and security for adapting to the varying vehicular context and the served applications with aims to attain a satisfactory performance rating but without compromising any security. To this end, a variant of IKEv2 called Vehicular Internet Key Exchange (VIKE) is put forward to autonomously negotiate the optimal encryption and integrity algorithms and the related profile that particularly suit to the current context with respect to the confronted SNR, security risk and application requirements. We theoretically derive the relations between the QoS and security for analytical solutions in terms of four categories of vehicular applications. The extensive numerical calculations are conducted to comprehensively investigate how the proposed VIKE responses to the various combinations of the SNR, modulation scheme and key length. The results show that the VIKE is capable of self-adapting to the vehicular context, and of contributing to the quality of communication performance without compromising any security. The proposed VIKE is expected to port the mass-deployed IKE into securing the emerging numerous vehicular applications and services.