We consider the problem of hiding information in a steganographic framework, i.e. embedding a binary message within an apparently innocuous content, in order to establish a `suspicion-free' digital communication channel. The adversary is passive as no intentional attack is foreseen. The only threat is that she discovers the presence of a hidden communication. The main goal of this article is to find if the calar Costa Scheme, a recently published embedding method exploiting side information at the encoder, is suitable for that framework. We justify its use assessing its security level with respect to the Cachin's criterion. We derive a public-key stegosystem following the ideas of R. Anderson and P. Petitcolas. This technique is eventually applied to PCM audio contents. Experimental performances are detailed in terms of bit-rate and Kullback-Leibler distance.