CSI4SAP

gangof4

不知做ＩＴ　ＡＵＤＩＴＯＲ　的ＤＸ有么有用过　ＣＳＩ４ＳＡＰ　的Ａｕｔｈｏｒｉｚａｉｔｏｎ　ａｕｄｉｔｏｒ

huaiyueliang

3 Attack and Its Solution\r\n3.1 Re-watermarking Attack\r\nIn common case, we can assume that there is only one watermark in image for\r\nownership dispute. It is not unreasonable to assume that multiple watermarked\r\nversions of the same image may indeed exist. But, if there are multiple watermark\r\nin one image, how can we decide the original watermark? And if we\r\ncannot find out which so-called original image is the true original, how can we\r\ndecide which watermarked version of an image is the truely watermarked version\r\nin circulation? Bob is free to create as many watermarked versions with his\r\nown watermarks embedded after he has reverse-engineered a counterfeit original\r\nfrom Alice’s watermarked version. To counter the claims, Bob has to prove the\r\npresence of his watermark in these watermarked images and the watermarked\r\nversion of Alice, in addition to the presence of his watermark in Alice’s original.\r\nS. Craver solves this problems as follows. He define non-invertible watermark\r\nand advanced non-quasi-invertible watermark scheme. By using this concepts,\r\nDesignated Verification of Digital Watermark 1073\r\nhe can do prevent multiple watermark attacks. But there are some unsolved\r\nproblems in above mechanism.\r\n3.2 Solution: Undeniable Verification\r\nMultiple watermarking problem must be solved easily if we consider it in verifi-\r\ncation process. In case of several attack proposed by S. Craver, we only review\r\nits robustness on verification module. Therefore, we can solve proposed attack\r\nproblems from different directions compared with S. Craver’s mechanism. In\r\nproposed system, if there are multiple watermarked image, the owner(pseudoowner:\r\nprover) can cooperate its verification process. So, in case that the examined\r\nwatermark (pseudo-watermark) can also be matched with the verifier’s input\r\nmessage on true-watermark, we can trust the pseudo-owner as really true-owner.\r\n3.3 Undeniable Property of Digital Watermark\r\nDigital watermarks are verified as authentic by anyone using the verification process.\r\nHowever, this self-verification property is unsuitable from many applications\r\nsuch as watermark based commercial digital contents distribution system.\r\nThe validity or invalidity of an undeniable watermark can be ascertained by\r\nconducting a verification process with original watermarker. If a confirmation\r\nprocess is needed, the cooperating original watermarker gives exponentially-high\r\ncertainty to the verifier that the watermark does correspond to the legal one.\r\nWe can use undeniable scheme in the watermarking process. This is because the\r\nconfidence measure relies on the fact that the watermark vector can be later\r\nextracted, and using a commitment mechanism make designated verifier can\r\ncertificate the legal owner on embedded watermark information.\r\nMultimedia image company could embed the watermark which they signed\r\nusing an undeniable scheme. Only someone who had directly purchased the image\r\nfrom that company could verify the watermark and be certain that the\r\nimage were right. Undeniable watermark verification could also be useful in any\r\nsituation in which an individual wishes to sign a data anonymously.\r\n3.4 New Verification Mechanism\r\nWe can propose a new verification mechanism by using designated verification\r\nmechanism as Fig. 1. In first case, the original watermarker can embed his\r\nown secret(true watermark) on cover data and generate watermarked data.\r\nAnd it is distrubuted to the buyer by using network protocol. And then the\r\nauthorized user can buy or get this data. However, the attacker can also\r\nmultiply re-watermark his own fabricated watermark on distributed data. In\r\nthis case, illegal data can be generated by attacker. So, if this data will be used\r\nby unauthorized user, we must verify and proof its legality and correctness on\r\ncopied data. Therefore, we can suggest a new designated verification mechanism\r\non watermarked data as the authorized user can verify its correctness by doing\r\na undeniable-style proof with original watermarker.