Comparison of biometric data in the encrypted domain

A method comprising steps of:

• computing a cipher of a masked score, the masked score representing the result of applying a primary mask r to a score representing a distance between a test biometric datum (x) relating to an individual and a reference biometric datum (yu), the computation comprising:
• for any j ranging from 1 to k and for any i ranging from 1 to d, with k≥1 and d≥2, determining, in a precomputed look-up table, a term equal to (Ti,j+ri,j)mod 2n matching a pair consisting of a portion of the test biometric datum (x) and a portion of a cipher (cyu) of the reference biometric datum, where:
• the cipher of the reference biometric datum (cyu) results from an encryption of the reference biometric datum (yu) using a primary encryption key (pk),
• n is a predefined integer,
• a sum
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• mod 2n of the tables Ti,j constitutes an estimate of a cipher of the score in unmasked form,
• the primary mask r is connected to secondary masks ri,j by the following relationship:
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• performing the following summation in order to obtain the cipher of the masked score:
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• for any i ranging from 1 to d, performing the following steps by way of a decryption device of index i:
• decrypting the cipher of the masked score using a secondary decryption key (ski) of index i, the decryption producing a datum (ŝ) representing the masked score modulo 2n,
• generating a partial result (oi) of index i from the datum (ŝ) and an unmasking datum (ki) of index i,
• wherein:
• the secondary decryption keys (sk1, . . . , skd) of respective indices ranging from 1 to d stem from a primary decryption key (sk) associated with the encryption key (pk),
• the partial results (o1, . . . , od) of respective indices ranging from 1 to d make it possible to compute a check result (o) indicating whether or not the test biometric datum (x) matches the reference biometric datum.