Visual cryptography

Development of masks to let overlaying n transparencies A, B,... printed with black rectangles reveal a secret image — n = 4 requires 16 (24) sets of codes each with 8 (24-1) subpixels, which can be laid out as 3×3 with the extra bit always black

Visual cryptography is a cryptographic technique which allows visual information (pictures, text, etc.) to be encrypted in such a way that the decrypted information appears as a visual image.

One of the best-known techniques has been credited to Moni Naor and Adi Shamir, who developed it in 1994.[1] They demonstrated a visual secret sharing scheme, where a binary image was broken up into n shares so that only someone with all n shares could decrypt the image, while any n − 1 shares revealed no information about the original image. Each share was printed on a separate transparency, and decryption was performed by overlaying the shares. When all n shares were overlaid, the original image would appear. There are several generalizations of the basic scheme including k-out-of-n visual cryptography,[2][3] and using opaque sheets but illuminating them by multiple sets of identical illumination patterns under the recording of only one single-pixel detector.[4]

Using a similar idea, transparencies can be used to implement a one-time pad encryption, where one transparency is a shared random pad, and another transparency acts as the ciphertext. Normally, there is an expansion of space requirement in visual cryptography. But if one of the two shares is structured recursively, the efficiency of visual cryptography can be increased to 100%.[5]

Some antecedents of visual cryptography are in patents from the 1960s.[6][7] Other antecedents are in the work on perception and secure communication.[8][9]

Visual cryptography can be used to protect biometric templates in which decryption does not require any complex computations.[10]

  1. ^ Naor, Moni; Shamir, Adi (1995). "Visual cryptography". Advances in Cryptology – EUROCRYPT'94. Lecture Notes in Computer Science. Vol. 950. pp. 1–12. doi:10.1007/BFb0053419. ISBN 978-3-540-60176-0.
  2. ^ Verheul, Eric R.; Van Tilborg, Henk C. A. (1997). "Constructions and Properties of k out of n Visual Secret Sharing Schemes". Designs, Codes and Cryptography. 11 (2): 179–196. doi:10.1023/A:1008280705142. S2CID 479227.
  3. ^ Ateniese, Giuseppe; Blundo, Carlo; Santis, Alfredo De; Stinson, Douglas R. (2001). "Extended capabilities for visual cryptography". Theoretical Computer Science. 250 (1–2): 143–161. doi:10.1016/S0304-3975(99)00127-9.
  4. ^ Jiao, Shuming; Feng, Jun; Gao, Yang; Lei, Ting; Yuan, Xiaocong (2020). "Visual cryptography in single-pixel imaging". Optics Express. 28 (5): 7301–7313. arXiv:1911.05033. doi:10.1364/OE.383240. PMID 32225961. S2CID 207863416.
  5. ^ Gnanaguruparan, Meenakshi; Kak, Subhash (2002). "Recursive Hiding of Secrets in Visual Cryptography". Cryptologia. 26: 68–76. doi:10.1080/0161-110291890768. S2CID 7995141.
  6. ^ Cook, Richard C. (1960) Cryptographic process and enciphered product, United States patent 4,682,954.
  7. ^ Carlson, Carl O. (1961) Information encoding and decoding method, United States patent 3,279,095.
  8. ^ Kafri, O.; Keren, E. (1987). "Encryption of pictures and shapes by random grids". Optics Letters. 12 (6): 377–9. Bibcode:1987OptL...12..377K. doi:10.1364/OL.12.000377. PMID 19741737.
  9. ^ Arazi, B.; Dinstein, I.; Kafri, O. (1989). "Intuition, perception, and secure communication". IEEE Transactions on Systems, Man, and Cybernetics. 19 (5): 1016–1020. doi:10.1109/21.44016.
  10. ^ Askari, Nazanin; Moloney, Cecilia; Heys, Howard M. (November 2011). Application of Visual Cryptography to Biometric Authentication. NECEC 2011. Retrieved 12 February 2015.