| dc.description.abstract | In this research the process of watermarking and digital signatures are used in the same system. There are three steps to make digital signatures. First step is generating a 128-bit hash value of a digital image using MD5 hashing techniques from a cover image. Second step is modifying the 128-bit hash value using Gray code encoding so that adjacent numbers have a single digit differing by one. Third step is encrypting the modified 128-bit hash value to get a digital signature value using techniques of public key cryptography (asymmetric encryption). The digital signature is used for making a watermark image by transforming every single value of digital signature into binary numbers (two-bit color image). In the process of watermarking, watermark image is inserted into cover image using Cox method and it generates a watermarked image in a grayscale. The reversal process is used for getting back the value of digital signature from a watermarked image. There are two steps in reversal process. First step is watermark extraction. The watermark image is extracted from watermarked image using Cox method and filtered using one of two filtering methods to get the filtered watermark that free from distortion. Second step is verifying digital signatures. The filtered watermark image (two-bit color image) is transformed back into digital signatures value and decrypted using techniques of public key cryptography (asymmetric encryption) to get the modified 128-bit hash value. Gray code decoder is used for changing the modified 128-bit hash value into its original value of 128-bit hash. After that, verify the 128-bit hash value that is generated from reversal process with the 128-bit hash value that is generated from cover image. If the value is similar then the image is valid. This research successfully applied the techniques of digital signature generation, watermark insertion, watermark extraction, and digital signature verification, with note the experiments were performed under normal circumstances (without giving attacks). This application of digital signature and watermarking techniques with additional security service has resistance against JPEG compression attack, but it has no resistance against rotation, cropping, and resizing attacks. | en |
