A system and method concerns a secure transmission of a file fragmentable into a plurality of fragments, and comprises (a) initially fixing a global encryption key; (b) encrypting the fragmentable file based on said global key to form a first encrypted file; (c) encrypting the global key by means of an asymmetric encryption algorithm using a public key to obtain a global encrypted key; (d) inserting values representing the global encrypted key among the fragments of said encrypted file to form a second encrypted file; and (e) transmitting the second encrypted file.