In most digital transmission systems, the data stream is first encoded, then sent to an interleaver that rearranges the encoded symbols in order to provide protection against error bursts. In this paper, we consider analysis of an interleaved stream in a non cooperative context (i.e. military or spectrum surveillance application). In this context, the encoder and the interleaver used by the transmitter are unknown. We propose an approach that is able to estimate useful information, such as the interleaver period and the code rate. The method uses only the intercepted interleaved stream. Furthermore, we are able to perform a blind synchronization on the interleaver blocks. The approach is based on linear algebra theory: we show that the normalized rank of a matrix Z (whose columns are analysis blocks taken from the interleaved stream) decreases when the size of the analysis blocks is a multiple of the interleaver period. Furthermore, we show that the maximum decrease is obtained when the analysis blocks are synchronized with the interleaver blocks, and that it is linked to the code rate.