Lossless Medical Image Security Shrikhande Rohini 1, Vinayak Bairagi 2 1 Researcher, Electronics & Telecommunication Department, Sinhgad Academy Of Engg. 2 Assistant Professor, Electronics & Telecommunication Dept. Sinhgad Academy Of Engg. 14dece@gmail.com ABSTRACT Security is the most important issue during transmission of medical images. As the medical images are sensitive so, it is necessary to protect them. Watermarking, digital fingerprint/signature, encryption, time of coding and encoding are the existing techniques for protecting images. But, all this methods have some drawbacks. Medical image security is an important issue when digital images and their pertinent patient information are transmitted across public networks. Picture archiving and communications system (PACS) is an integrated management system for archiving and distributing medical image data. Communication of medical images in a PACS environment is usually over the internal hospital network that is protected by a firewall from outside intruders. The paper outlines that the present methods, previous work, need for security and requirements for new system and presets an approach to further research for lossless medical image security. Keywords: Medical imaging, data security, data embedding, lossless, distortionless. 1. Introduction Today all business, government, organizations are connected through internet but it is both fascinating & complex because of the requirements for security services. Mechanisms to meet those services are quite complex. So the network security is the most important. Security is the protection from attack (Asim Banerjee, 2009). Data embedding is the most commonly used mechanism for medical images. Data embedding is classified into 2 categories 1] Lossy or irreversible data embedding where original image is modified in an irreversible manner to incorporate the underlying message and 2] Lossless or reversible data embedding this is relatively new development, where both image and the message (embedded data) can be recovered in a lossless fashion. This has applications in steganography, military applications, covert communications and especially medical imaging applications where any loss in the original image is not tolerated (Nithin Nagaraj and Rakesh Mullick, 2004). Data embedding applications could be divided into two groups depending on the relationship between the embedded message and the cover image (Jessica Fridrich, Miroslav Goljan, Rui Du). The first group is formed by steganographic applications in which the message has no relationship to the cover image and the cover image plays the role of a decoy to mask the very presence of communication. The content of the cover image has no value to the sender or the decoder. The second group of applications is frequently addressed as digital watermarking. In a typical watermarking application, the message has a close relationship to the cover image. The message supplies additional information about the image, such as image caption, ancillary data about the image origin, author signature, image authentication code, etc. Models of the human visual system are frequently used to make sure that the distortion due to embedding is imperceptible to the human eye. There are, however, some applications 536
for which any distortion introduced to the image is not acceptable. A good example is medical imagery, where even small modifications are not allowed for obvious legal reasons. In lossless watermarking, it is possible to completely remove the embedding distortion from the watermarked image and recover an exact copy of the original unwatermarked image. Lossless watermarks found applications in fragile authentication, integrity protection, and metadata embedding. It is especially important for medical and military images. Lossless embedding is a term for a class of data hiding techniques that are capable of restoring the embedded image to its original state without accessing any side information. Communication of medical images in a PACS environment is usually over the internal hospital network that is protected by a firewall from outside intruders. Three major organizations related to medical image/data security have issued guidelines, mandates, and standards for image/data security. Conventional Internet Security methods are not sufficient to guarantee that medical image had not been compromised during data transmission. 2. Aspects of security (William Stallings, 2010) Security is the protection of an organization or property from the attack. There are 3 aspects of security. 1) Security attack 2) Security mechanism 3) Security service 1) Security attack: It is any action that compromises the security of information owned by an organization. There are 2 types of attack. a) Passive attack Passive attacks are difficult to detect because they do not involve any alternation of the data. Typically, the message is sent and received in normal fashion and neither sender nor receiver is aware that the third party has read the message. The goal of the opponent is to obtain the information that is being transmitted. Figure 1: Image showing Passive attack b) Active attack It involves some modification of data stream or the creation of false stream. It is quite difficult to prevent active attack. 537
Figure 2: Image showing active attack 2) Security mechanism: A security mechanism is any process that is designed to detect, prevent or recover from a security attack. 3) Security service: a) Authentication There is assurance that the communicating entity is the one claimed b) Access control prevention of the unauthorized use of a resource c) Data confidentiality protection of the data from unauthorized disclosure d) Data integrity assurance that data received is exactly sent by an authorized entity e) Non repudiation protection against denial by one of the parties in a communication 4) Security properties There are three security properties a) Confidentiality Information about system or its users cannot be learned by an attacker. b) Integrity The system continues to operate properly, only reaching states that would occur if there were no attacker. c) Availability Actions by an attacker do not prevent users from having access to use of the system. Figure 3: Image showing security Properties 538
3. Existing method (Sarah Summers Sarah Wahl, 2006) There are four techniques to protect an image. 1) Watermarking 2) Digital Fingerprinting/Signatures 3) Encryption 1) Watermarking: Watermark is a secret message that is embedded into a cover (original or host) message. Digital watermarking is a technique which allows an individual to add hidden copyright notices or other verification message to digital audio, video or image signals and documents. a) Visible watermarks Visible watermarks change the signal altogether such that the watermarked signal is totally different from actual signal. b) Invisible watermarks: Invisible watermarks change the signal to a perceptually great extent i.e. there are only minor variations in output signal. 2) Digital fingerprints/signatures: It is based on the concept of public key encryption. A public key known to everyone and a private or secret key known only to the recipient of the message. When John wants to send a secure message to Jane, he uses Jane's public key to encrypt the message. Jane then uses her private key to decrypt it. It is mainly used in transmission of images. 3) Encryption: Plaintext is known as original message and cipher text is known as coded message. Encryption is the process of converting plaintext to cipher text to make it unreadable to anyone except those possessing key. Key specifies the particular transformation. Decryption is the process of restoring the plaintext from cipher text. 4. Drawbacks of Existing systems a) Major problem with watermarking schemas is that they are not very robust against different types of image manipulations or attacks. These techniques are quite complicated to implement in real time. b) Digital fingerprints: Technological Compatibility, Security Concerns, Legal Issues are the prime concerns with respect to finger print. c) Encryption: Criminals can use encryption to secure communications, or to store incriminating material on electronic devices. 5. Requirements for new system a) Lossless: It is the way of compressing the data which is fully reversible. The obtained image is exact replica of the original image. Therefore it is fully reversible. The word lossless is used to denote a form of compression that does not degrade the quality of the image being compressed. The decompressed image is exactly the same as the original image. In other words, the lossless method is a method of decompression in which no data is discarded. The image is stored in a non compressed format. 539
b) Progressive image: Here first low resolution version of the image is transmitted, and then, upon the reviwer s request, the low resolution can be progressively improved by further transmission. People don't optimize their images properly, which results in extremely slow loading time. When you intend to publish your images online, you have to comprimise the quality, just face the fact you cannot use a 10MB image on a website layout. It's not fair to visitors. A progressive image transmission allows visualization of a full sized image even when only a small piece of information has reached the receiver; this full sized image is an approximate version of the original image. The greater the amount of data received, the more similar the decompressed image is to the original one. In a progressive image transmission, every element of the transmitted data contains information for refining the image globally, instead of locally as a non progressive transmitter does. c) Embedding: The distortion due to embedding can be completely removed from the watermarked image without accessing any side channel. The lossless data embedding enables hash insertion while retaining the information content of the image in its entirety. Lossless embedding is a term for a class of data hiding techniques that are capable of restoring the embedded image to its original state without accessing any side information. d) Time of coding and decoding : Code in communications is set of symbols and rules for their manipulation by which the symbols can be made to carry information. Entropy coding is a special form of lossless data compression. It involves arranging the image components in a " zigzag " order employing run length encoding (RLE) algorithm that groups similar frequencies together, inserting length coding zeros, and then using Huffman coding on what is left. 6. Lossless Data Embedding with file size preservation (Jessica Fridrich, Miroslav Goljan, Qing Chen, Vivek Pathak) Lossless embedding is a term for a class of data hiding techniques that are capable of restoring the embedded image to its original state without accessing any side information. The formats addressed are RLE encoded bitmaps and sequentially encoded JPEG images. In this method, one first selects a subset X of image features that is losslessly compressible and that can be randomized without causing visible degradation to the image. In lossless embedding schemes designed for image formats that use some form of lossless compression, the increase in the file size could be many times larger than the actual number of embedded bits L. This inefficiency partially outweighs the advantage of embedding the data as opposed to appending it to the cover image. This paper is the first step to developing lossless embedding techniques that preserve the file size. The increase in the file size is, however, quite often disproportional to the length of the embedded data. 7. Medical image security in a PACS environment (F. Caoa, H.K. Huanga, X.Q. Zhoub, 2002) Medical image security is an important issue when digital images and their pertinent patient information are transmitted across public networks. Here it is proposed that a dedicated PACS security server that will act as an image authority to check and certify the image origin and integrity upon request by a user. The public key (asymmetric) cryptography technology 540
is an effective tool for a secure data communication. The method has been utilized recently in DICOM Security Profiles for secure communication of DICOM images. Medical image security in a PACS environment has become a pressing issue as communications of images increasingly extends over open networks, and hospitals are hard pushed by government mandates, and security guidelines to ensure health data security. However, there has not been an infrastructure or systematic method to implement and deploy these standards in a PACS environment. 8. Conclusions Embedded image is a bit by bit match with the original host data, hence it is proved that Zero distortion in the embedded domain. Medical images are sensitive so it is necessary to protect them. We have seen the limitations of different techniques. From all above points it is seen that there is a need of special technique for medical image communication which will takes care of security aspects. 9. References 1. Asim Banerjee, (2009), Introduction to Digital Image Processing, IEEE Workshop on Image Processing, pp 1 20. 2. Sarah Summers Sarah Wahl, (2006) Multimedia Security And Forensics, CS525 Semester Project Spring, pp 7 12. 3. William stallings, (2010) Cryptography & Network Security. 4. F. Caoa, H.K. Huanga, X.Q. Zhoub, (2002) Medical image security in a HIPAA mandated PACS environment, adepartment of Radiology, Childrens Hospital of Los Angeles, University of Southern California, 4650 Sunset Boulevard Mailstop 81, Los Angeles, CA 90027, USA. 5. Jessica Fridrich, Miroslav Goljan, Qing Chen, Vivek Pathak Lossless Data Embedding with File Size Preservation, Department of Electrical and Computer Engineering, SUNY Binghamton, Binghamton, NY 13902 6000, USA. 6. Jessica Fridrich, Miroslav Goljan, Rui Du, Lossless Data Embedding For All Image Formats, Department of Electrical Engineering, SUNY Binghamton, Binghamton, NY 13902. 7. Nithin Nagaraj and Rakesh Mullick, (2004) Zero distortion lossless data embedding, Imaging Technologies Lab GE Global Research Bangalore, India. 8. V.K.Bairagi, A.M.Sapkal, (2009) Selection of wavelets for medical image compression, proceedings of IEEE Int. Conf. Act 09, Kerala, pp 678 680. 541