Method of securing a given original digital file (A 1,...,A 8) belonging to a batch of a plurality of original digital files (A 1,...,A 8) against forgery or tampering, each original digital file (A 1,...,A 8) including its own digital data (D 1,...,D 8), comprising the steps of: for each original digital file (A 1,...,A 8) of the batch, calculating by means of a one-way function an associated digital file signature (x 1,...,x 8) of its digital data (D 1,...,D 8); forming a tree based on the plurality of calculated digital file signatures (x 1,...,x 8) for the original digital files (A 1,...,A 8) of the batch and comprising nodes arranged according to a given nodes ordering in the tree, said tree comprising node levels from the leaf nodes, corresponding to the plurality of digital file signatures (x 1,...,x 8) respectively associated to the plurality of original digital files (A 1,...,A 8) in the batch, to the root node of the tree, every non-leaf node of the tree corresponding to a digital signature by means of the one-way function of a concatenation of the respective digital signatures of its child nodes according to a tree concatenation ordering, the root node corresponding to a reference root digital signature, i.e. a digital signature by means of the one-way function of a concatenation of the digital signatures of the nodes of a penultimate nodes level in the tree according to said tree concatenation ordering; associating with the given original digital file (A 1,...,A 8) a corresponding digital verification key (k 1,...k 8) being a sequence of the respective digital signatures, from the leaf nodes level to the penultimate nodes level, of every other leaf node having the same parent node in the tree that the leaf-node corresponding to the digital file signature (x 1,...,x 8) of the given original digital file (A 1,...,A 8), and successively at each next level in the tree, of every non-leaf node having the same parent node in the tree that the previous same parent node considered at the preceding level; making available to a user the reference root digital signature of the tree; and characterized by including in the given original digital file (A 1,...,A 8) a corresponding machine readable digital security marking comprising a representation of its digital data (D 1,...,D 8) and its corresponding digital verification key (k 1,...k 8), thereby obtaining a marked original digital file (A 1,...,A 8) of which digital data (D 1,...,D 8) are secured against forgery or tampering. for each original digital file (A 1,...,A 8) of the batch, calculating by means of a one-way function an associated digital file signature (x 1,...,x 8) of its digital data (D 1,...,D 8); forming a tree based on the plurality of calculated digital file signatures (x 1,...,x 8) for the original digital files (A 1,...,A 8) of the batch and comprising nodes arranged according to a given nodes ordering in the tree, said tree comprising node levels from the leaf nodes, corresponding to the plurality of digital file signatures (x 1,...,x 8) respectively associated to the plurality of original digital files (A 1,...,A 8) in the batch, to the root node of the tree, every non-leaf node of the tree corresponding to a digital signature by means of the one-way function of a concatenation of the respective digital signatures of its child nodes according to a tree concatenation ordering, the root node corresponding to a reference root digital signature, i.e. a digital signature by means of the one-way function of a concatenation of the digital signatures of the nodes of a penultimate nodes level in the tree according to said tree concatenation ordering; associating with the given original digital file (A 1,...,A 8) a corresponding digital verification key (k 1,...k 8) being a sequence of the respective digital signatures, from the leaf nodes level to the penultimate nodes level, of every other leaf node having the same parent node in the tree that the leaf-node corresponding to the digital file signature (x 1,...,x 8) of the given original digital file (A 1,...,A 8), and successively at each next level in the tree, of every non-leaf node having the same parent node in the tree that the previous same parent node considered at the preceding level; making available to a user the reference root digital signature of the tree; and characterized by including in the given original digital file (A 1,...,A 8) a corresponding machine readable digital security marking comprising a representation of its digital data (D 1,...,D 8) and its corresponding digital verification key (k 1,...k 8), thereby obtaining a marked original digital file (A 1,...,A 8) of which digital data (D 1,...,D 8) are secured against forgery or tampering.