A method for calculating a function as a sub-function fX of a datum of a client, a sub-function fY of a datum, and a product of n indexed sub-functions fi of both data by randomly generating, n indexed invertible data ri from the set with m being a prime number, generating, for each i from 1 to n, a set for which each element is formed by a product of a datum ri with a possible result of the sub-function of two variables fi evaluated in both data, applying an oblivious transfer protocol between the client and a server so that the client recovers, for each i an intermediate datum ti equal to: ti=ri×fi(xi,Y), obtaining, by the client a result T from intermediate data such that: T=fX(X′)×Πi=1nti, obtaining, by the server a result R from inverted data such that: R=fY(Y)×Πi=1nri−1 using the results in a cryptographic application.