Abstract
We propose an optical cryptosystem for encrypting images of multi-depth objects based on the combination of optical heterodyne technique and fingerprint keys. Optical heterodyning requires two optical beams to be mixed. For encryption, each optical beam is modulated by an optical mask containing either the fingerprint of the person who is sending, or receiving the image. The pair of optical masks are taken as the encryption keys. Subsequently, the two beams are used to scan over a multi-depth 3-D object to obtain an encrypted hologram. During the decryption process, each sectional image of the 3-D object is recovered by convolving its encrypted hologram (through numerical computation) with the encrypted hologram of a pinhole image that is positioned at the same depth as the sectional image. Our proposed method has three major advantages. First, the lost-key situation can be avoided with the use of fingerprints as the encryption keys. Second, the method can be applied to encrypt 3-D images for subsequent decrypted sectional images. Third, since optical heterodyning scanning is employed to encrypt a 3-D object, the optical system is incoherent, resulting in negligible amount of speckle noise upon decryption. To the best of our knowledge, this is the first time optical cryptography of 3-D object images has been demonstrated in an incoherent optical system with biometric keys.
Highlights
Information security has become a practical and serious issue with the increasing growth of internet and telecommunications
Poon et al.25 have proposed optical scanning cryptography (OSC) to encrypt information incoherently based on optical scanning holography (OSH)26
We have proposed a cryptosystem for 3-D object images based on the optical heterodyne technique and biometric fingerprint keys
Summary
The overall effect is that we have an encrypted complex hologram, HCen(x, y; zc), of object |T(x, y; zc)|2 according to equations [11] and [12]. The decryption process for recovering the object image |T(x, y; zc)|2 from the encrypted hologram HCen(x, y; zc) is outline as follows. We have assumed the unity condition given by OTF*(kx, ky; zd) OTF(kx, ky; zd) = 1, where zd is the decoding distance and zc ∈ zd, i.e., zc belongs to zd As such, it can be inferred from equation [11] that the original object |T(x, y; zc)|2 can be recovered by multiplying the Fourier transform of the encrypted data HCen(x, y; zc) with the conjugate of the optical transfer function evaluated at decoding distance zd = zc, i.e., I−1{I{Hcen(x, y; zc)}OTF⁎(kx, ky; zd)|zd = zc}.
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