Method and apparatus for securely handling a personal identification number or cryptographic key using biometric techniques

Claims

We claim:

1. A method for securely storing at least a personal identification number (PIN), comprising the following steps:

obtaining a biometric information signal bearing information from a body part;

generating a sequence of random characters to obtain a PIN;

obtaining a generating function such that said random characters of said PIN are parameters of said generating function;

obtaining a transform of said generating function;

encrypting said transform of said generating function with said biometric information signal to obtain an encrypted PIN; and

writing said encrypted PIN into a store.

2. A method for recovering a personal identification number (PIN) for use in a device requiring a PIN for operation comprising the following steps:

obtaining a biometric information signal bearing information from a body part;

retrieving from storage an encrypted transform of a generating function, said generating function having characters of a PIN as parameters, said transform of said generating function previously encrypted with said biometric information signal;

decrypting said previously encrypted transform of said generating function utilising said biometric information signal as a key for decryption to obtain a decrypted transformed generating function;

undertaking an inverse transform operation on said decrypted transformed generating function to obtain an inverse transformed decrypted generating function; and

obtaining parameters from said inverse transformed decrypted generating function to obtain a PIN.

3. The method of claim 1 including the steps of:

encrypting information with a key which is a function of said PIN; and

storing said encrypted information on said storage means.

4. The method of claim 2 including the steps of:

retrieving encrypted information from said storage means; and

decrypting said information with a key which is a function of said PIN.

5. The method of claim 1 wherein said step of

obtaining a biometric information signal comprises obtaining a Fourier transform of a signal bearing information from a body part, said step of obtaining a transform of said generating function comprises obtaining a transform such that the transform has an inverse transform which exists and can be obtained optically and spatial frequencies which overlap with spatial frequencies of said Fourier transform of said signal bearing information from a body part and said step of encrypting said transform comprises dividing said transform of said generating function by said Fourier transform of said signal bearing information from a body part.

6. The method of claim 2 wherein said step of obtaining a biometric information signal comprises:

obtaining a coherent optical beam modulated with a biometric image of a body part; and

obtaining a beam carrying an optical Fourier transform of said biometric image.

7. The method of claim 6 wherein said step of decrypting said previously encrypted transform further comprises the steps of:

addressing a full-complex spatial light modulator (SLM) with said encrypted transform; and

illuminating said SLM with said beam carrying the Fourier transform of the biometric image to obtain an output beam;

wherein the step of undertaking an inverse transform operation on said decrypted transformed generating function comprises obtaining an optical transform of said output beam; and wherein the step of obtaining parameters from said inverse transformed decrypted generating function to obtain a PIN comprises the steps of:

registering an intensity distribution of said transformed output beam; and

retrieving said PIN from said intensity distribution.

8. The method of claim 5 wherein said step of writing the encrypted PIN into storage means further comprises:

recording a hologram, a complex amplitude of a spatial grating of said hologram being proportional to said encrypted PIN; and

attaching said hologram to storage means.

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

determining a complex conjugate of said encrypted PIN;

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

addressing a full-complex 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 reflective hologram by means of interference of said object beam with a reference beam which is coherent with said object beam.

10. The method of claim 6 wherein said step of decrypting said transform of said generating function further comprises the step of

illuminating a prerecorded hologram with said beam carrying the Fourier transform of the biometric image;

wherein the step of undertaking an inverse transform operation on said decrypted transformed generating function comprises

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

and wherein the step of obtaining parameters from said inverse transformed decrypted generating function to obtain a PIN comprises:

registering an intensity distribution of said transformed diffracted beam; and

calculating scalar products of said intensity distribution and each of a plurality of basis functions to obtain a PIN, said basis functions being the same as they were during encryption.

11. The method of claim 1 wherein said step of obtaining a biometric information signal comprises:

obtaining a coherent optical beam modulated with a biometric image of a body part; and

registering an intensity distribution of a Fourier spectrum of said biometric image.

12. The method of claim 11 including the steps of:

(a) processing said intensity distribution of the Fourier spectrum of the biometric image; and

(b) deriving a cipher function from said processed intensity distribution;

wherein the step of obtaining a generating function comprises obtaining a generating function such that said random characters are coefficients in an expansion of square of said generating function over basis functions;

wherein said step of obtaining a transform of said generating function comprises obtaining a first transform of said generating function such that the first transform has an inverse transform which exists and can be obtained optically and spatial frequencies which overlap with spatial frequencies of said Fourier spectrum of said biometric image;

and wherein the step of encrypting said transform of said generating function comprises the steps of:

(i) obtaining a product of said first transform of the generating function and a complex exponent of said cipher function; and

(ii) obtaining a second transform of said product such that said second transform has an inverse transform which exists and can be performed optically.

13. The method of claim 12 wherein step (a) comprises:

mapping said intensity distribution of the Fourier spectrum of the biometric image with a saturation function;

further processing said intensity distribution with a randomizing operator; and

obtaining a Gabor transform of said processed intensity distribution.

14. The method of claim 12 wherein step (b) comprises binarization or quantization of said processed intensity distribution to derive a cipher function.

15. The method of claim 4 wherein said step of obtaining a biometric information signal comprises:

obtaining a coherent optical beam modulated with a biometric image of a body part; and

registering an intensity distribution of Fourier spectrum of said biometric image.

16. The method of claim 15 including the steps of:

(a) processing said intensity distribution of the Fourier spectrum of the biometric image;

(b) deriving a cipher function from said processed intensity distribution;

wherein the step of decrypting said previously encrypted transform of said generating function comprises the steps of:

(c) addressing a first full-complex SLM with said encrypted transform;

(d) addressing a second phase-only SLM with the sign-inversed cipher function;

(e) illuminating said first SLM with a coherent light beam to obtain a beam modulated with said encrypted transform;

(f) obtaining an optical transform of said modulation beam such that said transform is inverse to a second transform which was performed during encryption;

(g) illuminating said second SLM with said optically transformed beam to obtain an output beam;

wherein the step of undertaking an inverse transform operation comprises;

(h) obtaining an optical transform of said output beam such that said transform is inverse to a first transform which was performed during encryption;

and wherein the step of obtaining parameters from said inverse transformed decrypted generating function to obtain a PIN comprises the steps of:

(i) registering an intensity distribution of said transformed output beam; and

(j) calculating scalar products of said intensity distribution and each of a plurality of basis functions to obtain a PIN, said basis functions being the same as basis functions used during encryption.

17. The method of claim 16 wherein step (a) comprises:

mapping said intensity distribution of the Fourier spectrum of the biometric image with a saturation function;

further processing said intensity distribution with a randomizing operator; and

obtaining a Gabor transform of said processed intensity distribution.

18. The method of claim 16 wherein step (b) comprises binarization or quantization of said processed intensity distribution to derive a cipher function.

19. The method of claim 12 wherein said step of writing the encrypted PIN into storage means further comprises:

recording a hologram, a complex amplitude of a spatial grating of said hologram being proportional to said encrypted PIN; and

attaching said hologram to storage means.

20. The method of claim 19 wherein said recording a hologram comprises the steps of:

addressing a first amplitude-only SLM with said generating function;

addressing a second phase-only SLM with said cipher function;

illuminating said first SLM with a coherent light beam to obtain a beam modulated with said generating function;

obtaining a first optical transform of said modulated beam;

illuminating said second SLM with said optically transformed beam to obtain an object beam;

obtaining a second optical transform of said beam; and

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

21. The method of claim 15 wherein said step of decrypting said transform of said generating function further comprises the steps of:

addressing a phase-only SLM with the sign-inversed cipher function;

illuminating a pre-recorded hologram with a coherent light beam;

obtaining an optical transform of a beam diffracted from said hologram such that said transform is inverse to a second complex-conjugated transform which was performed during encryption;

illuminating said SLM with said transformed diffracted beam to obtain an output beam;

wherein the step of undertaking an inverse transform operation on said decrypted transformed generating function comprising

obtaining an optical transform of said output beam such that said transform is inverse to the first complex conjugated transform which was performed during encryption;

and wherein the step of obtaining parameters from said inverse transformed decrypted generating function to obtain a PIN comprises:

registering an intensity distribution of said transformed output beam; and

calculating scalar products of said intensity distribution and each of a plurality of basis functions to obtain a PIN, said basis functions being the same as they were during encryption.

22. The method of claim 11 including the steps of:

encrypting information with a key which is a function of said PIN; and

storing said encrypted information on said storage means; and

wherein said encrypting a transform of said generating function step further comprises the steps of:

(a) processing said intensity distribution of the Fourier spectrum of the biometric image;

(b) deriving a unique vector from said processed intensity distribution; and

(c) encrypting said transform of said generating function with a symmetric algorithm, said unique vector being a key to said algorithm.

23. The method of claim 22 wherein step (a) comprises mapping said intensity distribution of the Fourier spectrum of the biometric image with a saturation function.

24. The method of claim 23 wherein step (a) further comprises obtaining Gabor transform of said processed intensity distribution.

25. The method of claim 22 wherein step (b) comprises the steps of:

selecting a pre-determined number of highest peaks in said processed intensity distribution to generate a selected peaks array;

transforming said selected peaks array to a polar co-ordinate system, the centre of which corresponds to the zeroth spatial frequency of said Fourier spectrum, to generate a polar co-ordinates array, each element in said polar co-ordinates array being represented by a vector comprising polar co-ordinates and a peak amplitude; and

deriving said unique vector from said polar co-ordinates array such that the number of elements in said unique vector are equal to a dimension of a key required by said symmetric algorithm.

26. The method of claim 22 wherein step (b) comprises the steps of:

transforming said processed intensity distribution to a polar co-ordinates system, the centre of which corresponds to the zeroth spatial frequency of said Fourier spectrum, to generate a polar co-ordinates distribution;

calculating a pre-determined number of first coefficients in an expansion of said polar co-ordinates distribution over spherical harmonics;

calculating a square of absolute value of each said coefficient, and normalizing said squares to obtain a normalized array; and

deriving said unique vector from said normalized array such that the number of elements in said unique vector are equal to a dimension of a key required by said symmetric algorithm.

27. Apparatus for encrypting a PIN, comprising:

means for obtaining a biometric information signal bearing characteristics of a body part;

means for generating a sequence of random characters to obtain a PIN;

means for obtaining a generating function comprising said random characters as parameters;

means for obtaining a transform of said generating function;

means for encrypting said transform of said generating function with said biometric information signal to obtain an encrypted PIN; and

means for writing said encrypted PIN into a store.

28. Apparatus for decrypting a PIN, comprising:

means for obtaining a biometric information signal bearing characteristics of a body part;

means for reviewing from storage a transform of a generating function, said generating function having characters of a PIN as parameters, said transform of said generating function previously encrypted with said biometric information signal;

means for decrypting said previously encrypted transform of said generating function, said biometric information signal being a key to said encrypted transform;

means for undertaking an inverse transform operation on said decrypted transform to obtain an inverse transformed decrypted generating function; and

means for obtaining parameters from said inverse transformed decrypted generating function to obtain a PIN.

29. The method of claim 5 wherein the step of obtaining a generating function comprises obtaining a plurality of orthogonal basis functions, said characters being parameters of said basis functions.

30. The method of claim 5 wherein the step of obtaining a generating function comprises obtaining a generating function such that said random characters are coefficients in an expansion of square of said generating function over basis functions.

31. The method of claim 7 wherein the step of retrieving said PIN from said intensity distribution comprises calculating scalar products of said intensity distribution and each of a plurality of basis function to obtain a PIN, said basis functions being the same as basis functions used during encryption of said encrypted PIN.