In the vehicular ad hoc network, moving vehicles can keep communicating with each other by entering or leaving the network at any time to establish a new connection. However, since many users transmit a substantial number of messages, it may cause reception delays and affect the entire system. A certificateless aggregate signature scheme can provide a signature compression that keeps the verification cost low. Therefore, it is beneficial for environments constrained by time, bandwidth, and storage, such as vehicular ad hoc network. In recent years, several certificateless aggregate signature schemes have been proposed. Unfortunately, some of them still have some security and privacy issues under specific existing attacks. This article offers an authentication scheme that can improve security, privacy, and efficiency. First, we apply the certificateless aggregate signature method to prevent the onboard unit devices from leaking sensitive information when sending messages. The scheme is proven to be secure against the Type-1 [ ] and Type-2 [ ] adversaries in the random oracle model under the computational Diffie–Hellman problem assumption. Then, the performance evaluation demonstrates that our proposed scheme is more suitable for deployment in vehicular ad hoc network environments.

The proposed scheme groups three pixels as an embedding unit to conceal three bits of secret data in which the possible modification for each pixel is at most +1 or −1. With our new scheme, the probability of altering one pixel by adding 1 or subtracting 1 is 6/8; it is 1/8 when altering two pixels, and 1/8 when preserving pixels without any modification. In conventional algorithms, the expected number of modification per pixel (ENMPP) mostly ranges from 0.375 to 0.5 on average when the embedding capacity of each pixel is one bit of secret message. In contrast, our new scheme groups three pixels together to convey three bits of secret message. The ENMPP is reduced at least by 0.333 on average. As a result, our algorithm offers higher visual quality for the stego image. The experimented results have verified that our scheme is super to the previous algorithms.