Bit level based secret sharing for image encryption

A new secret sharing scheme capable ofprotecting image data coded with B bits per pixel is introduced and analyzed in this paper. The proposed input-agnostic encryption solution generates B-bit shares by combining bit-level decomposition/stacking with a {k, n}-threshold sharing strategy. Perfect reconstruction is achieved by performing decryption through simple logical operations in the decomposed bit-levels without the need for any postprocessing operations. The framework allows for costeffective cryptographic image processing of B-bit images over the Internet. 2005 Pattern Recognition Society. Published by Elsevier Ltd. All rights reserved.

Secret sharing-based image encryption technologies can be utilized to secure data transmission in multimedia networks and mobile public networks which are used for exchange ofprivate images such as scanned (e.g. financial) documents and digital personal photographs. Visual cryptography is a secret sharing procedure for image data, which uses the properties ofthe human visual system to force the recognition ofa secret message from overlapping encrypted images (shares) without additional computations and any knowledge ofcryptography. In existing schemes a wellknown {k, n}-threshold procedure is used to encrypt the secret image into n shares, which are then distributed amongst n recipients . The shares contain seemingly random information, however, based on the transparent/frosted representation ofthe shares ifany k (or more) recipients stack their shares printed as transparencies together on an overhead projector the secret image is visually revealed. On the other hand, any (k − 1) or fewer shares cannot be used to decrypt the transmitted information. Unfortunately, visual sharing schemes cannot restore the transmitted information to its original quality when the original input is a natural image. This is due to the fact that the {k, n}-threshold scheme operates on binary or binarized inputs and uses optical frosted/transparent representation. A common procedure is to convert continuous-tone images into halftone images [5] with a binary representation. Then the half-tone version of the input image is used instead of the original information. The requirement for inputs of the binary or dithered nature only and the fact that the output is not recovered in digital form limits the applicability ofvisual cryptography. The secret sharing scheme proposed here offers a new approach to secret sharing encryption which differs signifi- cantly from traditional image sharing schemes in Refs. [2–4] or (color) input-specific {2, 2} (private-key) scheme in Ref. [1]. Unlike past image sharing schemes, the proposed {k, n}- technique operates directly on the bit planes ofthe digital

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