Computer-implemented method for maintaining the validity of a file by two users, that are a receiver and a validating instance, said method comprising the sequential realization of the following set of steps for each of a plurality of users: (a) providing said file to the user; (b) searching a publisher-related file signature in a blockchain, said publisher-related file signature belonging to said file; (c) confirming a validity of said publisher-related file signature; (d) determining an identification string belonging to said file based on said file and/or optionally based on said publisher-related file signature, comprising the step of calculating a hash from said file by means of a cryptographic hash function, in which said identification string is determined based on at least said hash; (e) establishing a renewed file signature based on at least both said identification string belonging to said file and a private key belonging to the user; (f) registering said renewed file signature in said blockchain; in which said publisher-related file signature comprises a publisher identity belonging to a publisher; in which said publisher is different of each of said two users; in which said confirming of the validity in step (c) comprises determining the validity of said publisher identity; in which said renewed file signature at least allows to identify said file in a unique way with respect to the blockchain; in which said establishing in step (e) comprises encrypting said identification string by means of said private key belonging to a key pair belonging to said user for obtaining a signed identification string, said key pair comprising said private key and a public key; in which said renewed file signature comprises said signed identification string; in which said renewed file signature comprises a user identity for finding said public key; in which a renewed file signature is obtained by another hash function and/or another key pair and/or another technology for signing than previously utilized for said file; and in which said maintaining is done as soon as step (f) has been carried out for each user. (a) providing said file to the user; (b) searching a publisher-related file signature in a blockchain, said publisher-related file signature belonging to said file; (c) confirming a validity of said publisher-related file signature; (d) determining an identification string belonging to said file based on said file and/or optionally based on said publisher-related file signature, comprising the step of calculating a hash from said file by means of a cryptographic hash function, in which said identification string is determined based on at least said hash; (e) establishing a renewed file signature based on at least both said identification string belonging to said file and a private key belonging to the user; (f) registering said renewed file signature in said blockchain; in which said publisher-related file signature comprises a publisher identity belonging to a publisher; in which said publisher is different of each of said two users; in which said confirming of the validity in step (c) comprises determining the validity of said publisher identity; in which said renewed file signature at least allows to identify said file in a unique way with respect to the blockchain; in which said establishing in step (e) comprises encrypting said identification string by means of said private key belonging to a key pair belonging to said user for obtaining a signed identification string, said key pair comprising said private key and a public key; in which said renewed file signature comprises said signed identification string; in which said renewed file signature comprises a user identity for finding said public key; in which a renewed file signature is obtained by another hash function and/or another key pair and/or another technology for signing than previously utilized for said file; and in which said maintaining is done as soon as step (f) has been carried out for each user.