METHOD FOR MARKING AND METHOD FOR MARKING CHECK OF LINES OF ANSWERS TO USER DATABASE REQUESTS USING DIGITAL WATERMARKS Russian patent published in 2008 - IPC G06F21/24 

FIELD: computer engineering.

SUBSTANCE: data introduction is performed by substitution of text line characters with identical in style characters from other character set; unique identifier is assigned to each user which identifier is transmitted to marking unit when request is sent to database control system. Value of signature bit for answer text line is calculated using one-bit hash function against key sequence corresponding to user identifier. To check the selected line, original line is taken and marked, the result is compared with checked line; to check the entire watermark it will be enough to check several arbitrarily selected lines which accelerates check procedure and do not impose limitations on line order. Using of one-bit hash function and key sequence allows to raise protection level.

EFFECT: enhancement of efficiency of surveillance system for processing, transmitting and distributing confidential information which is stored in text form in multiuser database.

2 cl, 4 dwg