Method of encrypting digital data, a method of masking a biometric print, and application to making a security document secure
The invention relates to a method of masking a plain datum b having n bits. The inventive method is characterised in that a masked datum m is produced using the following masking function: (I), wherein p is a prime number, b i is the bit at position i of plain datum b, and q i is the prime number at position i in a set of prime numbers (q 1 , . . . , q n ). The invention also relates to a method of masking a biometric print, consisting in: determining a set of s real minutiae which are characteristic of the print; mixing and arranging the real minutiae with t false minutiae; and forming a mixed biometric datum b having n=s+t bits, such that, for any i: b i =1 if position i corresponds to a real minutia, and b i =0 if position i corresponds to a false minutia. The invention can be used to secure a security document such as a bank cheque. m = ∏ i = 1 n q i b i mod p ( I )
1. A method of masking biometric information, comprising the steps of: Converting physical biometric information into biometric datum b having n bits; and
producing a masked datum m using the following hash function:
m
=
∏
i
=
1
n
q
i
b
i
mod
p
,
mod p, where p is a prime number, b i is the bit at position i of biometric datum b, and q i is the prime number at position i in a set of prime numbers (q i . . . q n );
wherein said method is applied to data of a biometric print, comprising the steps of determining a set of s real minutiae, which are characteristic of said print, mixing and arranging the real minutiae with t false minutiae, and forming a mixed biometric datum having n=s+t bits, such that, for any i:
b i =1 if position i corresponds to a real minutiae and
b i =0 if position i corresponds to a false minutiae
and applying the hash function to this mixed datum in order to produce a masked datum.
2. The masking method according to claim 1 , in which p is a large prime number and the components of the set of prime numbers are small.
3. The method according to claim 1 , in which the real minutiae and the false minutiae are mixed in a random fashion.
4. The method of claim 3 , further including the step of:
storing said masked datum on or in a security document.
5. A method of verifying a security document secured by a method according to claim 4 , comprising the following steps:
digitizing a physical biometric print of a person presenting the security document,
masking the digitised print using randomly mixed real material and false material, and said hash function, to produce a masked datum,
comparing the masked datum with a reference datum, and
verifying the security document if the masked datum and the reference datum are in concordance with a predefined rate of error, and refusing the document otherwise.
6. The method according to claim 5 , wherein, during the comparison step, if a barcode associated with the reference datum is stored on the security document, the following steps are performed:
reading the barcode;
searching a table storing the bar code and the reference datum to obtain the reference datum associated with the barcode; and
comparing the reference datum with the masked datum.
7. The method of claim 3 , further including the steps of:
associating a barcode with said masked datum;
storing said barcode on or in a security document; and
storing the barcode and the masked datum in a table.
8. A method of verifying a security document secured by a method according to claim 7 , comprising the following steps:
digitizing a physical biometric print of a person presenting the security document,
masking the digitized print using randomly mixed real material and false material, and said hash function, to produce a masked datum,
comparing the masked datum with a reference datum, and
verifying the security document if the masked datum and the reference datum are in concordance with a predefined rate of error, and refusing the document otherwise.