DIGITAL WATERMARKING PDF
Digital watermarking is the act of hiding a message related to a digital signal (i.e. the watermark embedded in a digital work can be used to record one or more. PDF | On Jan 9, , Sri Vadana and others published DIGITAL WATERMARKING. PDF | While formal definitions and security proofs are well Key-based digital watermarking model: (a) watermark encoding and (b) watermark.
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that has been attracting increasing interest is based on digital watermarking watermarking is the process of embedding information into digital multimedia. Because of these shortcomings, digital watermarking is sometimes referred to as being .. pixia-club.info~fapp2/publications/pixia-club.info ABSTRACT. Digital media is the need of a people now a day as the alternate of paper media. As the technology grown up digital media required protection while .
The most powerful technique which is used to protect the information from unauthorized users is Digital Watermarking. Digital watermarking is very efficient in Data security and robustness.
Digital water marking is the promising solution for safeguard the information. The information may be a text, audio, video. To protect the data from unauthorized users there are many techniques used such as Cryptography, steganography, Digital watermarking is used.
In cryptography, encryption and decryption is used for sending and receiving the data. If the secret key is known to the hackers they can easily hack the data and in steganography the message is hiding inside the image.
If it comes to know that message is hidden in the image the interceptors crack the image and hack the information. To overcome this, a technology which is used to protect data is Digital Watermarking. The information which is hidden using digital watermarking can be known to all.
Once the information is watermarked it is not possible to remove or modify the secret information. Hence Digital Watermarking provides data security, copyright, authentication etc. Digital water marking is widely used now a days for hiding information. Digital watermarking is the practice of embedding extra information within digital content, also called host data, in a manner that does not interfere with the normal usage of data. An example is Google Maps images that are obtained from satellites used for applications such as urban planning, environmental protection, and defense, S.
The "digital watermarking" of covert communication technology has the capacity to meet these requirements, because it not only protects the content of the communicating information, but more important it hides the existence of communication facts, and thus confuse interceptors Li Qiuyan et. By embedding confidential information ,watermarking in original data, it affirms the ownership of the data, verifies integrity of data, tracks the source of data, controls usage of data and delivery of confidential information.
According to goal and requirement of covert information, digital watermarking should have the following basic characteristics: 1. Hide: watermark information and source data integrate together, without changing the data storage space; besides the source data must not has obvious change phenomenon.
Robustness: It means that embedded watermarking data after going through various processing operation and against operation, which avoid losing or damage the watermarking information. Security: it refers the now location and content of watermarking information is unknown, which needs to apply covert arithmetic and take measures like adopting pretreatment for example, encryption to watermarking. All digital watermarking systems compose two essential parts: watermarking embedding system and watermarking detection system.
The information you want to embed in can be all kinds of nature, such as number, image and text so forth. The use of password is to enhance the security by protecting non-authorized people from reading messages. The output of watermarking embedding process is image works with embedded watermarking. Watermarking Detecting Process The input of the watermarking detection process is the image be tested, it may not be watermarking embedded, or it may be images been watermarking embedded and then attacked.
Because of different watermarking algorithm, the input of watermarking detection process can also be password, intact face and so on.
The Input of the watermarking detection process may be the watermarking been detected, or a confidence value about whether watermarking is involved in the detected signals.
When the radios transfer confidential information, they embed confidential information as watermarking in a carrier which can be put in public.
The carrier can be digital signals like text, picture and sound. In radio watermarking encryption scheme, it should use double or multiple watermarking mechanism: in carriers except for embedding robustness watermarking in order to hide information, it also embeds half fragile watermarking unrelated to contents, fragile watermarking, in the use of distinguishing from enemy and recognizing if the information are attacked or distorted.
Digital Watermarking Techniques is mainly classified into two types they are a. Spatial domain watermarking b. Frequency domain watermarking a. Spatial domain watermarking The term spatial domain defines an aggregate of pixels composing an image.
This technique directly modifies the intensity or color values of the selected pixels. This is an earliest and the simplest watermarking technique. Frequency domain watermarking The frequency domain technique first transforms an image into a set of frequency domain coefficients.
Sometimes the Fourier transform is used to make over the signal from time domain to frequency domain or from frequency domain to time domain.
The DCT is a very popular transform function used in manipulating the signals. It transforms a signal from spatial domain to frequency domain. Owing to good performance, it has been used in JPEG standard for image compression.
DCT has been useful in many fields such as data compression, pattern recognition, and image processing, and so on. The DCT manipulate the original image into the smallest low frequency coefficient and also it can ground the image blocking effect which can realize the high-quality concession between the information centralizing and the computing complications DCT-based watermarking is based on two essentials.
The first is that most of the signal energy lies at low-frequencies sub band which contains the most imperative visual parts of the image. The second is that high frequency components of the image are usually detached through compression and noise attacks. This document is then saved, and shared with the individual whose username matches the watermark.
If a leak occurs, it should be obvious that this individual is the source. An example of such a watermark on a PDF document opened in Adobe Reader can be seen below: PDF Document containing a semi-transparent watermark containing identifying company and user information. When an image is added as an additional layer, or object, it can typically be removed relatively easily.
Multiple open source software applications can be used to this end, including ghostscript , pdftk , and qpdf. In our case, we will be using ghostscript to programmatically remove all images from our PDF document. In this case we will be using the pdfwrite device to generate the output file.
The final parameter, in our case page1-wm. The time required for this command to execute will depend on the size of the document being modified.
Digital Watermarking Seminar PPT with pdf report
In our case, the PDF is a single page, so the process is completed in less than one second. The result is an identical PDF document, but with all images removed, including the security-critical watermark. This technique works fine for our document, as the only images present in the document are the watermarks.
If a user attempting to strip an image-based watermark wishes to do so while also retaining all other images in the document, then additional steps can be taken.
Fortunately for the PDF document creator, and unfortunately for the user, this process is more complicated than simply removing all images with ghostscript. This situation involves gaining a better understanding of the PDF specification and how information is represented within a PDF document. A PDF file can be thought of as a series of objects. An object can contain data such as a block of text or an entire image. In order to get a better look at the inner structure of our document, we can open it in a text editor.
We can see two objects, one containing some configuration parameters, and another containing a stream of data. The stream of data is largely unreadable. In some cases, this can indicate regular binary data or encrypted data of some kind. In our case, we are looking at compressed data. Streams inside PDF documents can be compressed in a number of ways depending on the type of data the stream stores. In order to get a better view of the data within the streams in our file, we will first want to decompress the contents.
To do this we will use pdftk, a tool designed for ease of use in creating and modifying PDF documents. The command we will use is as follows: pdftk page1-wm.
Once this command finishes, we will have a new file on our filesystem: page1-wm-dec. This file contains the same data as our original file, but with all compressed streams now decompressed. The contents of the stream from the first code snippet above has been decompressed, as seen below: Decompressed representation of the first stream in our PDF document. Once a malicious user reaches this point, removal of the image watermark becomes a much more attainable goal.
Even if the image was decompressed, it is still binary data. Now that the streams of the file have been decompressed, locating the remaining binary data the data that is likely to be an image , becomes much easier. An attacker knows image data will be in a stream, so their first step might be to step through the file, examining each stream along the way. Depending on the size of the file, this could be difficult or even impractical.
Instead, an attacker can look for keywords that are likely to accompany image data.
In our case, it is contained in the last stream in the file, likely because its addition was the last modification made before sharing the document. For more complicated or lengthy documents, a malicious user could focus on one page of the document, locate the watermark data there, and then apply that knowledge to the rest of the document to locate all watermark data.
In some cases, the watermark data is only stored once at the beginning of the document and referenced throughout to keep file sizes low, making the process even more straightforward. Removal can be performed in a few ways. An attacker could remove just the stream data, leaving an empty object, or just delete the object entirely. Either way, next time the document is viewed, the watermark will not be present, but all other aspects of the document will remain intact.
We will remove the entire object simply by deleting everything between and including the obj field before the stream and the endobj field afterward. We will save the modified file as page1-wm-dec-EDIT. Our newly modified document opened in Adobe Reader can be seen below: Our final document with watermark removed.
From here, the user is free to print, copy, and redistribute the document with much lower risk of being identified as the source of a leak. Text-based Watermarking Flaws Text-based watermarking is typically implemented very similarly to image-based watermarking, but simply using plaintext strings instead of binary image data. The document we will be using for this exercise can be seen below: Our test PDF document with a text watermark.
The process here is similar to the more manual approach described above for for removing image watermarks. First we decompress our PDF document: pdftk page1-watermark. If any are found, the results will be printed to STDOUT, which is the terminal in which the command is run by default.
Running this command will result in the following output: Binary file page1-watermark-dec. From here, removal is trivial. Using a tool such as GNU sed , we can programmatically find and replace all instance of the watermark text with the empty string, removing all visual elements of the watermark.
We instead want to store the result in a file that can be easily opened with a PDF viewer.
Once this command finishes execution, we will have a file on our filesystem called page1-watermark-dec-EDIT.In an image authentication application the intent is to detect modifications to the data. First we decompress our PDF document: pdftk page1-watermark.
This may put an effect on the host signal. Spatial domain watermarking b. Digital documents can be copied and scattered easily to large numbers of people without any cost. In the case of proving the you are already selling large volumes of images, consider if ownership of the media, an even more simple attack which watermarking is worth the time it takes to add them to all of can apply is to pick some bits randomly from the your images. Disadvantages of digital watermarking 7.
This is done for a variety of a Effectiveness: One example of digital signature technology being used for image authentication is the trustworthy digital camera [2 24].