Ashish Gehani

DNA-based Cryptography

Recent research has considered DNA as a medium for ultra-scale computation and for ultra-compact information storage. One potential key application is DNA-based, molecular cryptography systems. We present some procedures for DNA-based cryptography based on one-time-pads that are in principle unbreakable. Practical applications of cryptographic systems based on one-time-pads are limited in conventional electronic media by the size of the one-time-pad; however DNA provides a much more compact storage medium, and an extremely small amount of DNA suffices even for huge one-time-pads. We detail procedures for two DNA one-time-pad encryption schemes: (i) a substitution method using libraries of distinct pads, each of which defines a specific, randomly generated, pair-wise mapping; and (ii) an XOR scheme utilizing molecular computation and indexed, random key strings. These methods can be applied either for the encryption of natural DNA or for artificial DNA encoding binary data. In the latter case, we also present a novel use of chip-based DNA micro-array technology for 2D data input and output. Finally, we examine a class of DNA steganography systems, which secretly tag the input DNA and then hide it within collections of other DNA. We consider potential limitations of these steganographic techniques, proving that in theory the message hidden with such a method can be recovered by an adversary. We also discuss various modified DNA steganography methods which appear to have improved security.

Transcoding characteristics of Web images

Transcoding is a technique employed by network proxies to dynamically customize multimedia objects for prevailing network conditions and individual client characteristics. Transcoding can be performed along a number of different axes and the specific transcoding technique used depends on the type of multimedia object. Our goal in this paper is to understand the nature of typical Internet images and their transcoding characteristics. We focus our attention on transcodings intended to customize an image for file size savings. Our results allow the developers of a transcoding proxy server to choose the appropriate transcoding techniques for the important classes of Internet images. We analyze the characteristics of images available on the Web through a representative trace. We show that most GIF images accessed on the Internet are small; about 80% of the GIF images are smaller than 6 KBs. JPEG images are larger than GIF images; about 40% of the JPEG images are larger than 6 KBs. We also establish the characteristics of popular image transcoding operations. We show that for JPEG images, the JPEG compression metric and a transcoding that reduces the spatial geometry are productive transcoding operations (saves at least 50% of the file size for 50% of the images). Our systematic study of image characteristics leads to some surprising results. For example, a naive spatial geometry reduction of GIF images by a factor of 2 along each axis actually causes an increase in the file size compared to the original image for 40% of the images. Thus it is important to understand the characteristics of individual images before choosing the proper transcoding operation.

Micro flow bio-molecular computation.

In this paper we provide a model for micro-flow based bio-molecular computation (MF-BMC). It provides an abstraction for the design of algorithms which account for the constraints of the model. Our MF-BMC model uses abstractions of both the recombinant DNA (RDNA) technology as well as of the micro-flow technology and takes into account both of their limitations. For example, when considering the efficiency of the recombinant DNA operation of annealing, we take into account the limitation imposed by the concentration of the reactants. The fabrication technology used to construct MEMS is limited to constructing relatively thin 3D structures. We abstract this by limiting the model to a small constant number of layers (as is done with VLSI models). Besides our contribution of the MF-BMC model, the paper contains two other classes of results. The main result is the volume and time efficient algorithm for message routing in the MF-BMC model, specifically useful for PA-Match. We will show that routing of strands between chambers will occur in time O(N x D/ m x n), where N is the number of strands in the MF-BMC, n is the number of chambers where RDNA operations are occurring, D is the diameter of the topology of the layout of the chambers, and m is proportional to the channel width. Operations that need annealing, such as PA-Match, are shown feasible in O(N2logN/n/n) volume instead of the previous use of omega(N2) volume, with reasonable time constraints. Applications of the volume efficient algorithm include the use of the Join operation for databases, logarithmic depth solutions to SAT (Boolean formula satisfiability) problems and parallel algorithms that execute on a PRAM. Existent algorithms can be mapped to ones that work efficiently in the MF-BMC model, whereas previous methods for applications such as PRAM simulation in BMC were not both time and volume efficient. Our other class of results are theoretical lower bounds on the quantities of DNA and the time needed to solve a problem in the MF-BMC model, analogous to lower bounds in VLSI. We bound the product BT from below, and further show that BT2 has a stronger lower bound of I2. Here B is the maximum amount of information encoded in the MF-BMC system at a time. T is the time for an algorithm to complete, and I is the information content of a problem.

Super-Resolution Video Analysis for Forensic Investigations

Super-resolution algorithms typically improve the resolution of a video frame by mapping and performing signal processing operations on data from frames immediately preceding and immediately following the frame of interest. However, these algorithms ignore forensic considerations. In particular, the high-resolution video evidence they produce could be challenged on the grounds that it incorporates data or artifacts that were not present in the original recording.

Parameterizing access control for heterogeneous peer-to-peer applications

Peer-to-peer overlays are being used for domain name resolution, massive multiplayer games, cooperative spam filtering, content sales and distribution, digital libraries, and data storage. As a result, applications often have conflicting access control needs. For example, an interactive game that needs fast response times for permission requests may prefer a capability-based access control subsystem (since the capabilities could be replicated). On the other hand, a digital library would choose an access control list approach (since it needs the ability to revoke permissions efficiently). Overlay designers are forced to either make an a priori choice for all applications, or to provide no access control functionality. We introduce DAAL (Decentralized Authentication and Authorization Layer) to allow application designers and users to select differing access control characteristics for each object. This allows a developer to use capability-like characteristics for objects whose access requests must complete quickly, while employing access control list-like functionality for other objects whose access needs to be efficiently revocable. Further, users can trade the efficiency of permission request and revoke operations for each object by adjusting its access control parameters. We empirically identify a simple criterion for parameter selection that guarantees good performance in the face of any predefined fraction of malicious peers in the overlay.

System Support for Forensic Inference

Digital evidence is playing an increasingly important role in prosecuting crimes. The reasons are manifold: financially lucrative targets are now connected online, systems are so complex that vulnerabilities abound and strong digital identities are being adopted, making audit trails more useful. If the discoveries of forensic analysts are to hold up to scrutiny in court, they must meet the standard for scientific evidence. Software systems are currently developed without consideration of this fact. This paper argues for the development of a formal framework for constructing “digital artifacts” that can serve as proxies for physical evidence; a system so imbued would facilitate sound digital forensic inference. A case study involving a filesystem augmentation that provides transparent support for forensic inference is described.