  The notion of linear finite transducer (LFT) plays a crucial role in some
cryptographic systems. In this paper we present a way to get an approximate
value, by random sampling, for the number of non-equivalent injective LFTs. By
introducing a recurrence relation to count canonical LFTs, we show how to
estimate the percentage of $\tau$-injective LFTs. Several experimental results
are presented, which by themselves constitute an important step towards the
evaluation of the key space of those systems.
