A receiving method for a digital stream, the stream including frames having each a body composed of a variable number c of symbols and preceded by a header including d symbols, a field composed of a fixed number e of symbols unknown to the receiver and defining the number c. A locking phase of the receiving method includes receiving a series of e symbols of the stream; performing a correlation computation for pairs of symbols received, the correlation computation being used to verify a predefined relationship if the e symbols form the unknown field; determining a correlation level and determining whether the e symbols form the unknown field on the basis of the correlation level; repeating the steps until it is determined that the e symbols form the unknown field.