Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Protection at a particular protocol layer
Reexamination Certificate
1997-10-08
2001-04-17
Swann, Tod (Department: 2132)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Protection at a particular protocol layer
C713S186000
Reexamination Certificate
active
06219794
ABSTRACT:
BACKGROUND OF THE INVENTION
While many forms of encryption/decryption algorithms (cipher systems) exist today, a weak link of all systems is the secure management of the encryption/decryption key. There are basically two types of cipher systems: those based on a single symmetric key, and those based on two distinct public/private keys. A symmetric key algorithm uses a single key to both encrypt and decrypt the data. These algorithms are usually fast and their security lies entirely in maintaining secrecy of the symmetric key. Two problems with these systems are the transportation of the key from the sender to the intended recipient, and the secure storage of the symmetric key. A public/private key system uses a two key method. The public key is used for encryption and can be distributed over open channels. Because the public key can be sent over open channels, the inconvenience and security risk associated with key transportation is minimized. However, the private key is still used to decrypt the information, and thus must be kept secret.
In the age of electronic transactions, PIN's have become the dominant method by which these encryption keys are secured. The encryption keys are then only as secure as the length of the PIN, as the PIN recalls or decrypts the encryption key. The length of a PIN which can easily be remembered is limited; thus the security of the system is also limited. PIN's are now, of course, prevalent in many other areas of life, such as banking, access control, and as an identification means for social programs. As the number of PIN's that one needs to remember/store escalates, the potential for a security breach arises. This invention overcomes the need to carry, store, or remember private keys for encryption/decryption, or PIN's for any other application by deriving a digital key from a biometric, during a live verification process.
SUMMARY OF THE INVENTION
In the present invention, the digital key is linked to the biometric only through a secure block of data known as the protected filter. The correct key will only be derived via the interaction of this protected filter with the correct user biometric. For a biometric to be used conveniently and securely in a method to recover a digital key from a protected filter, the method should possess the following four features:
1) Preferably, the method should be capable of producing an arbitrary M-bit digital key in conjunction with the biometric.
2) The same M-bit digital key should be released each time the system is used by the authorized holder of the protected filter.
3) Preferably, no key should be released when an unauthorized user of the protected filter attempts to use the system.
4) The protected filter, as an independent data block, has to be resilient to “attack”.
In German patent DE 42 43 908 A1 to Bodo, a method was proposed for extracting a digital key directly from a biometric. While the invention of Bodo thus provides a method for producing a digital key from a biometric, the security of such a system is irrevocably lost if the digital key is ever compromised. For this reason, feature 1 above is preferred; i.e. for a system to remain secure, there should be the ability to change the digital key. The invention described herein proposes a method for linking a key to the biometric, rather than directly deriving the key from the biometric; thus the key can be changed at any time simply by re-enrolling the user and recreating the protected filter.
Methods have been described to re-generate signals using a biometric, based on the use of conventional matched filters in correlators. It is well known by those skilled in the art that a matched filter does not allow a trade-off between distortion tolerance and discrimination. Thus, in a system using a matched filter, it is impossible to optimally comply with both features 2 and 3 above. Also, it is known that the extraneous terms produced at the output of a system using a matched filter eliminate the possibility of exactly reproducing a block of pre-determined data. Thus, known methods using matched filters do not easily accommodate feature 1 above. Furthermore, the impulse response of a matched filter will usually reveal enough information about the biometric for an “attacker” to recreate the biometric, and thus the signals. Therefore, a matched filter approach does not possess feature 4.
According to the present invention, there is provided a method for securely recovering a digital key, comprising the steps of: capturing at least one biometric image; obtaining transformed image information comprising transforming said at least one biometric image to a transform domain; retrieving a protected filter from storage, said protected filter comprising a phase-only filter; applying said transformed image information to said phase-only filter to obtain verification information; and obtaining a digital key from said verification information.
According to another aspect of the invention there is provided a method of linking a binary one-dimensional key having M elements with a given two-dimensional complex valued array comprising the steps of:
(i) concatenating real and imaginary parts of said complex valued array to form a concatenated two-dimensional array;
(ii) ranking positive elements and negative elements of said concatenated array by magnitude;
(ii) storing row and column indices of said ranked positive elements in a positive locations vector and row and column indices of said ranked negative elements in a negative locations vector; and
(iv) for each one of the M elements of said key, extracting L elements from said negative location vector if said one key bit is a zero and extracting L elements from said positive location vector if said one bit is a one to generate a two-dimensional link array having L rows and M columns.
According to another aspect of the present invention, there is provided a method for generating a protected filter, comprising the steps of: capturing at least one biometric image; obtaining transformed image information comprising transforming said at least one biometric image to a transform domain; generating a random phase-only function; obtaining a complex conjugate of the phase component of said transformed image information; multiplying said phase-only function with said complex conjugate to generate a phase-only filter; and storing a protected filter, said protected filter comprising said phase-only filter.
According to yet another aspect of the present invention, there is provided a method for secure user verification, comprising the steps of: capturing at least one biometric image; obtaining transformed image information comprising transforming said at least one biometric image to a transform domain; obtaining magnitude information from said transformed image information; retrieving a phase-only filter from storage; applying at least said magnitude information to said phase-only filter to obtain a transitory filter with phase and magnitude information; multiplying said transformed image information with said transitory filter to obtain verification information; comparing said verification information with a retrieved reference pattern and, on obtaining a satisfactory match, providing a user verification signal.
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patent:
Bhagavatula Vijayakumar
Gilroy Rene M.
Roberge Danny B.
Soutar Colin
Stoianov Alexei
Marshall O'Toole Gerstein Murray & Borun
Mytec Technologies Inc.
Smithers Matthew
Swann Tod
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