In wireless sensor networks, security is one of the most challenging issues. An attack against sensors or the intruder intervention in the zone of interest can deny the integrity of the exchanged data between the sensors and the base station. In this paper, we propose a technique of data integrity protection using a novel method of shared cryptography for wireless sensor networks. Our proposal considers a cluster-based network. Sensor nodes belonging to a cluster are supervised by a cluster-head. The latter aggregates securely the sensed data and transmits them to the base station. Before sending the sensed data to the cluster-head, the sensor nodes encrypt partially the message using a shared cryptography protocol. The cluster-head reconstitutes the message in order to authenticate the integrity of the transmitted data. We have developed simulations, in which the obtained results show the performances of our protocol in terms of communication overhead and energy consumption.