1. A method of authenticating a text document with links to a plurality of files by modifying at least a selected attribute of invisible characters on a plurality of inter-word intervals of said text document; said method comprising the steps of: a) computing (step 10 or 22 ) a one-way hash function of each file of said plurality of files in order to obtain a hash value composed of a subset of hash digits for each one, b) encoding (step 16 or 24 ) each subset of a plurality of subsets of space characters in said text document by replacing in each subset of space characters, the value of said selected attribute for each space character by a corresponding encoded hash digit of each subset of hash digits corresponding to each one of said files, c) computing (step 18 ) the electronic signature of the encoded text document by using a public-key algorithm composed of a subset of signature digits, and d) encoding (step 20 ) another subset of space characters in said encoded text document by replacing the value of said selected attribute for each space character by a corresponding encoded signature digit.