In this paper we propose a new cryptosystem, based on a new time-delayed chaotic system. Two chaotic signals are sent by the transmitter: the first one is aimed at synchronizing the receiver, which is proved through the resolution of a Linear Matrix Inequality (LMI). The transmission of a second chaotic signal enables the design of a new way to encrypt a message: we perform a kind of modulation of the frequency of a chaotic signal generated by the transmitter, depending on the message and we propose a method to recover the message. The efficiency of this new cryptosystem is illustrated by the encryption, transmission and recovery of a picture. The security of the proposed cryptosystem is discussed at the end of the article.