Holographic method for encrypting and decrypting information using a fingerprint

• US 5,740,276 A
• Filed: 07/27/1995
• Issued: 04/14/1998
• Est. Priority Date: 07/27/1995
• Status: Expired due to Fees

• Current Assignee: Mytec Technologies Inc (Advent International Corporation)
• Original Assignee: Mytec Technologies Inc (Advent International Corporation)
• Inventors: Stoianov, Alexei, Tomko, George J.
• Primary Examiner(s): Couso, Jose L.
• Assistant Examiner(s): Do, Anh Hong
• Application Number:
  US08/508,297
• Time in Patent Office: 992 Days
• Field of Search: 382/210, 382/211, 382/124, 382/127, 382/280, 382/232, 359/561, 380/4, 380/19, 364/822, 902/2
• US Class Current: 382/210
• CPC Class Codes: G06V 40/12 Fingerprints or palmprints
• CPC Class Codes: G07C 9/37 using biometric data, e.g. fingerprints, iris scans or voice recognition

Abstract

A method using a fingerprint image as a cipher for optical encrypting and decrypting information which is presented in the form of an analogous signal. The method includes recording a Fourier hologram, the complex amplitude of the spatial grating of the hologram being a Fourier transform of the information image divided by a Fourier transform of the fingerprint image. To prepare the hologram, a full-complex spatial light modulator (SLM) may be used. The parameters of the Fourier transforms are chosen such that the optical spatial frequencies of the information image and the cipher lie in the same physical range. In another embodiment, the intensity distribution of the Fourier spectrum of the fingerprint image is captured. The cipher image is obtained by illuminating a phase-only SLM which is addressed with a function derived from this intensity distribution. The hologram may be amplitude or phase; thin, thick or volume; transparent or reflective; prepared optically or computer-generated. The hologram is attached to a substrate, such as a personal card. To decrypt the information, an individual places the same fingerprint has been used as the cipher onto an input device, and the hologram is illuminated by an optical beam modulated with characteristics of the fingerprint image.

Claims

1. A holographic method for encrypting an information image, comprising the following steps:

obtaining a fingerprint image signal;

obtaining a cipher signal based on a Fourier transform of said fingerprint image signal;

obtaining a transformed information image signal to be encrypted;

at least one of said cipher signal and said transformed information image signal chosen so that a spatial frequency content of said transformed information image signal overlaps with a spatial frequency content of said cipher signal;

recording a hologram based on said cipher signal and said transformed information image signal such that a complex amplitude of a spatial grating of said hologram comprises a spatial complex conjugate of said transformed information image signal divided by a spatial complex conjugate of said cipher signal.

2. The method of claim 1 wherein said cipher signal is obtained by taking a Fourier transform of said fingerprint image signal.

3. The method of claim 2 wherein said transformed information image signal is obtained by taking a Fourier transform of an information image signal modulated with said information image.

4. The method of claim 2 wherein said hologram is a thin hologram and wherein said transformed information image signal is obtained by taking a Fresnel transform of an information image signal.

5. The method of claim 1 wherein said step of obtaining a cipher signal based on a Fourier transform of said fingerprint image signal comprises obtaining a digital fingerprint image signal and deriving a Fourier transform of said fingerprint image signal from said digital fingerprint image signal.

6. The method of claim 3 wherein said hologram recording step comprises the steps of:

determining a complex conjugate of said Fourier transformed information image signal;

determining a complex conjugate of said Fourier transformed fingerprint image signal; and

dividing said complex conjugate of said Fourier transformed information image signal by a function of said complex conjugate of said Fourier transformed fingerprint image signal to obtain an addressing signal.

7. The method of claim 6 wherein said hologram recording step further comprises the steps of:

addressing an SLM with said addressing signal;

illuminating said SLM with coherent light to produce an object beam; and

recording a hologram by means of interference of said object beam with a reference beam which is coherent with said object beam.

8. The method of claim 6 wherein said hologram recording step further comprises the steps of:

determining an inverse Fourier transform of said addressing signal to obtain an inverse transformed addressing signal;

addressing an SLM with said inverse transformed addressing signal;

illuminating said SLM with coherent light to produce an object beam;

obtaining an optical Fourier transform of said object beam; and

recording a hologram by means of interference of said object beam with a reference beam which is coherent with said object beam.

9. The method of claim 3 wherein said step of obtaining a Fourier transformed information image signal comprises the steps of:

addressing a first SLM with an information image signal;

illuminating said first SLM with a source of coherent light to produce a first recording beam; and

optically Fourier transforming said first recording beam, and wherein said hologram recording step further comprises the steps of;

determining a complex conjugate of said Fourier transformed fingerprint image signal;

dividing a constant by a function of said complex conjugate of said Fourier transformed fingerprint image signal to obtain an addressing signal;

deriving an inverse Fourier transform of said addressing signal;

addressing a second SLM with said inverse Fourier transform of said addressing signal;

illuminating said second SLM with a source of coherent light to produce a second recording beam which is coherent with said first recording beam;

optically Fourier transforming said second recording beam; and

interfering said Fourier transformed first recording beam with said Fourier transformed second recording beam.

10. The method of claim 6 wherein said step of dividing comprises determining whether an absolute value of a frequency component of said Fourier transformed fingerprint image signal exceeds a pre-determined offset and, if so, dividing by said Fourier transformed fingerprint image signal at said frequency component and, if not, dividing by a function of said offset and said frequency component at said frequency component.

11. The method of claim 6 wherein said hologram recording step further comprises the steps of:

addressing a hologram generator with said addressing signal;

recording a computer-generated hologram, said addressing signal being a complex amplitude of the spatial grating of said hologram.

12. The method or claim 1 wherein said cipher signal is obtained by:

obtaining a function based on an intensity distribution of a Fourier transform of said fingerprint image; and

obtaining a complex exponential function of said intensity distribution based function.

13. The method of claim 12 wherein said step of obtaining a function based on an intensity distribution of a Fourier spectrum of said fingerprint image comprises performing an optical Fourier transform of said fingerprint image and capturing the intensity distribution of said Fourier transform.

14. The method of claim 12 wherein said step of obtaining a function based on an intensity distribution of a Fourier spectrum of said fingerprint image comprises obtaining said intensity distribution and seeding a random number generator with said intensity distribution to generate a randomized distribution.

15. The method of claim 12 wherein said step of obtaining a transformed information image signal to be encrypted and said hologram recording step comprise the steps of:

addressing a first phase-only SLM with said cipher signal;

illuminating said first SLM with a source of coherent light to produce a first recording beam;

addressing a second SLM with an information image signal;

illuminating said second SLM with a source of coherent light to produce a second recording beam which is coherent with said first recording beam;

passing said second recording beam through a Fourier transform lens to obtain a transformed second recording beam; and

recording a hologram by means of interference of said first recording beam with said transformed second recording beam.

16. A holographic method for decrypting information comprising the steps of:

obtaining a fingerprint image signal;

obtaining a cipher signal based on a Fourier transform of said fingerprint image signal such that a spatial frequency content of said cipher signal overlaps with a spatial frequency content of a transformed information image signal;

illuminating a pre-recorded hologram with said cipher signal, said pre-recorded hologram having a complex amplitude of a spatial grating comprising a spatial complex conjugate of said transformed information image signal divided by a spatial complex conjugate of said cipher signal;

obtaining an optical inverse transform of a beam diffracted from said hologram; and

registering an intensity distribution from said diffracted beam, said intensity distribution representing an information image in said transformed information image signal.

17. The method of claim 16 wherein the step of obtaining said cipher signal comprises obtaining a beam carrying an optical Fourier transform of said fingerprint image.

18. The method of claim 17 wherein said step of obtaining an optical inverse transform of a beam diffracted from said hologram comprises obtaining an inverse Fourier transform of a beam diffracted from said hologram.

19. The method of claim 17 wherein said hologram is a thin hologram and said step of obtaining an optical inverse transform of a beam diffracted from said hologram comprises obtaining an inverse Fresnel transform of a beam diffracted from said hologram.

20. The method of claim 16 wherein said cipher signal is obtained by:

obtaining a function based on an intensity distribution of a Fourier transform of said fingerprint image; and

obtaining a complex exponential function of said intensity distribution.

21. A holographic method for securely handling an information image, comprising the following steps:

(a) encrypting said information image with the following steps;

obtaining a fingerprint image signal;

obtaining a cipher signal based on a Fourier transform of said fingerprint image signal;

obtaining a transformed information image signal to be encrypted;

at least one of said cipher signal and said transformed information image signal chosen so that a spatial frequency content of said transformed information image signal overlaps with a spatial frequency content of said cipher signal;

recording a hologram based on said cipher signal and said transformed information image signal such that a complex amplitude of a spatial grating of said hologram comprises a spatial complex conjugate of said transformed information image signal divided by a spatial complex conjugate of said cipher signal; and

(b) decrypting said information image with the following steps;

illuminating said hologram with said cipher signal;

obtaining an optical inverse transform of a beam diffracted from said hologram; and

registering an intensity distribution from said diffracted beam, said intensity distribution representing said information image.

22. The method of claim 21 wherein said cipher signal is obtained by taking a Fourier transform of said fingerprint image signal.

23. The method of claim 22 wherein said transformed information image signal is obtained by taking a Fourier transform of an information image signal modulated with said information image and wherein said step of obtaining an optical inverse transform of a beam diffracted from said hologram comprises obtaining an inverse Fourier transform of a beam diffracted from said hologram.

24. The method of claim 22 wherein said hologram is a thin hologram and wherein said transformed information image signal is obtained by taking a Fresnel transform of an information image signal and wherein said step of obtaining an optical inverse transform of a beam diffracted from said hologram comprises obtaining an inverse Fresnel transform of a beam diffracted from said hologram.

25. The method of claim 21 wherein said cipher signal is obtained by:

obtaining a function based on an intensity distribution of a Fourier transform of said fingerprint image; and

obtaining a complex exponential function of said intensity distribution.

26. The method of claim 23 wherein said hologram recording step comprises the steps of:

determining a complex conjugate of said Fourier transformed information image signal;

determining a complex conjugate of said Fourier transformed fingerprint image signal; and

dividing said complex conjugate of said Fourier transformed information image signal by a function of said complex conjugate of said Fourier transformed fingerprint image signal to obtain an addressing signal.

27. The method of claim 23 wherein said step of obtaining a Fourier transformed information image signal comprises the steps of:

addressing a first SLM with an information image signal;

illuminating said first SLM with a source of coherent light to produce a first recording beam; and

optically Fourier transforming said first recording beam,

and wherein said hologram recording step further comprises the steps of;

determining a complex conjugate of said Fourier transformed fingerprint image signal;

dividing a constant by a function of said complex conjugate of said Fourier transformed fingerprint image signal to obtain an addressing signal;

deriving an inverse Fourier transform or said addressing signal;

addressing a second SLM with said inverse Fourier transform of said addressing signal;

illuminating said second SLM with a source or coherent light to produce a second recording beam which is coherent with said first recording beam;

optically Fourier transforming said second recording beam; and

interfering said Fourier transformed first recording beam with said Fourier transformed second recording beam.