Method and device for protecting documents or for verifying authenticity of a document using an encrypted information produced by said method, and documents protected by said encrypted information

A device for protecting documents or for verifying the authenticity of a document that comprises means for entering and storing strings of characters and of numeric values of a determined length representing entries to be protected, for the purpose of identifying falsifications of administrative documents or documents issued by public authorities;

• a means for condensing the string of characters by performing a first computational algorithm on a value obtained by conversion to a determined and fixed computational base enabling the device to generate a plurality of numeric values which are stored and represent stored strings in the form of a plurality of intermediate results;
• means for transforming that plurality of results to a finite succession of digits by using an algorithm from a set of computational algorithms;
• means for transforming the numeric result obtained by using a transformation base randomly selected from a plurality thereof, those transformation means thereby generating an encrypted identifier formed from digits and letters and stored, means for inserting into the encrypted identifier a first character, representing an identifier of the computational base, in a random position determined by a second character inserted in a fixed position in the encrypted identifier, in order to define, on the one hand, the position of the first character and, on the other hand, the number of the algorithm randomly selected from a plurality thereof.