Method for protecting confidentiality of a file distributed and stored at a plurality of storage service providers

Abstract

This method comprises the steps of: —choosing () a security parameter n,—segmenting () the file in n chunks S, . . . , Sn, —randomly choosing () ncoefficients afor i=1, . . . , n and j=1, . . . , n,—verifying () that the vectors a, . . . , a, for i=1, . . . , n, are linearly independent, otherwise generating the coefficients again, —computing () n linear combinations Ci=aS+ . . . +aS+ . . . +a·S, for i=1, n,—choosing () n storage service providers O, . . . , Oamong said plurality of storage service provider, —generating () n file identifiers ID', . . . , ID′designating said file (F),—storing () the combination Ci at the storage service provider Oin association with the file identifier ID′, for i=1, . . . , n,—storing the file identifier ID′and the provider identifier O, for i=1, . . . , n, in a file descriptor corresponding to the file (F), this file descriptor being stored in a local memory (LM),—storing the set of coefficients a, . . . , aso that it can be re-associated with the combination C, for i=1, n;—randomly choosing n super-coefficients a′, . . . , a′, . . . , a′for j=1, . . . , n,—computing a linear over-combination OC′=a′-C+ . . . +a′·C+ . . . +a′·C,—and storing the over-combination OC′ and the coefficients a′, . . . , a′, . . . , a′for j=1, . . . , n.