Patent ID: 6934845

Claim:
A computer implemented method of marking an original text document said original text document comprising words separated by inter-word intervals, said inter-word intervals including one or more blank characters having numbers, said numbers being altered, said method of altering said numbers of said blank characters, comprising the sequence of steps of: applying a reversible transform over said original text document in order that all said inter-word intervals become exclusively comprised of odd numbers of said blank characters; splitting and transforming said original text document into a first subset and a second subset of said words including trailing blanks of said inter-word intervals of said words; and over said first subset: computing from said original text document and a secret-key, an authentication pattern that fits the number of said intervals of said first subset; adding inter-word blank characters in positions corresponding to said authentication pattern; generating a canonical form of said first subset; computing, from said canonical form of said first subset and said secret-key, a blurring pattern that fits the number of said intervals of said first subset; modifying the numbers of inter-word blank characters according to said blurring pattern; and over said second subset: generating canonical form of said second subset; computing, from said canonical form of said second subset and said secret-key, a blurring pattern that fits the number of said intervals of said second subset; modifying the numbers of inter-word blank characters according to said blurring pattern; recombining said first subset and said second subset thereby, obtaining a marked text for authentication.