A method of reading at least one bar code carried by a substrate, the method including: a) generating, especially in an automatic manner, when presenting the bar code to a system for reading the bar code, at least one authentication cue related to an intrinsic physical characteristic of the substrate and independent of the data contained in the bar code, and b) allowing the reading of the bar code, only in the event of a positive authentication of the substrate or reading the bar code regardless of the result of the authentication of the substrate and in the event of negative authentication of the substrate, preventing access to just one part of the data contained in the bar code and/or to any data that may be associated with the bar code, and which is stored on a separate data medium from the substrate.