Security element, corresponding engraved intaglio printing plate, and methods and devices for producing, decoding and authenticating security marking of said security element

A security element comprising a substrate and a security marking, the security marking comprising a two-dimensional intaglio pattern printed on a surface of the substrate via intaglio printing with intaglio ink, the two-dimensional intaglio pattern having an associated color and comprising at least one base intaglio pattern comprising a plurality of intaglio modules, each base intaglio pattern only comprises intaglio modules of which tones belong to a corresponding set of two distinct allowed tones forming a pair of allowed tones, each intaglio module having one tone of said associated color, a tone of an intaglio module being selected from a tone palette of a plurality of distinct reference tones of the associated color, a CIE color difference ΔE* between the tones being greater than or equal to 2.0, a width & of an intaglio module being greater than 20 μm and less than or equal to 50 μm,

• wherein the two-dimensional intaglio pattern is produced based on an associated two-dimensional encoded pattern comprising at least one reference pattern, wherein each of the at least one base intaglio pattern is based on an associated reference pattern of the at least one reference pattern, each base intaglio pattern and an associated reference pattern encoding a same portion of information, which specifies a unique identification number of the associated reference pattern,
• wherein each reference pattern includes a specific arrangement of a plurality of symbols, each symbol in the arrangement allowing to encode data according to a state of said symbol, the state of each symbol consisting in a specific arrangement of a first two-dimensional element E1 and a second distinct two-dimensional element E2 within the symbol, each element E having a corresponding value of a parameter p(E), the parameter of the first element E1 having a positive value different from a zero value of the parameter of the second element E2,
• wherein each reference pattern only comprises dark symbols and light symbols, the parameter value of the first element of a dark symbol corresponding to the darker tone of the pair of allowed tones of an associated base intaglio pattern, and the parameter value of the first element of a light symbol corresponding to the lighter tone of said associated pair of allowed tones,
• wherein each intaglio module of each base intaglio pattern of the two-dimensional intaglio pattern is printed
• either as a separate intaglio module corresponding to a first element of a symbol of an associated reference pattern of the two-dimensional encoded pattern and its location in the reference pattern;
• or
• as a portion of an intaglio line corresponding to a line connecting two first elements having a same parameter value p, respectively belonging to two distinct adjacent symbols of an associated reference pattern of the two-dimensional encoded pattern, and a location of the line in the reference pattern.