Partial unrolling for software security

A non-transitory storage comprising:

• a computer program product protected against leakage of sensitive data wherein a plurality of N computation units are executed depending on a driving value (DV), the driving value (DV) being a sequence of condition values having a length of N units, each unit having V possible values, wherein V≥2, the driving value (DV) being dedicated to handle sensitive data, each of the plurality of N computation units comprising a code to perform computations using sensitive data and susceptible to let sensitive data leak, the computer program product protected by:
• instructions to:
• set parameters ki and Pi for each i=1, 2, . . . n, where
• n is the number of different lengths of parts,
• ki is the number of parts having Pi computation units,
• Pi≠Pi+1, Pi>1 and Pi<N, and
• N=k1×P1+ . . . +ki×Pi+ . . . +kn×Pn−;
• unroll (S1) k1+ . . . +ki+ . . . +kn parts of computation units of said computer program, by rewriting the computations into a sequence of computation units protecting the sensitive data, said unrolling step (S1) resulting in VP1+ . . . +VPi+ . . . VPn possible parts of computation units;
• instructions corresponding to the VP1+ . . . +VPi+ . . . VPn possible parts of computation units;
• instructions to partition the driving value into k1+ . . . +ki+ . . . +kn parts of units, and instructions to cause the computer program, during execution of the computer program, to select (S2) parts of computation units for execution among the VP1+ . . . +VPi+ . . . VPn possible parts of computation units is to be executed according to the parts of the partitioned driving value;
• and
• instructions to dynamically update the driving value (DV) by modifying its parts while respecting its initial unit order and keeping ki and Pi unchanged and selecting parts of computation units for execution among the VP1+ . . . +VPi+ . . . VPn possible parts of computation units is to be executed according to the dynamically updated driving value.

A method to protect a computer program stored in a computerized device against leakage of sensitive data by said computerized device wherein a plurality of N computation units are executed depending on a driving value (DV), the driving value (DV) being a sequence of condition values having N condition values, each condition value having V possible values, the driving value (DV) being dedicated to handle sensitive data, each of the plurality of N computation units comprising a code to perform computations using sensitive data and susceptible to let sensitive data leak, said method comprising:

• unrolling a loop-case construct having V computation units of said computer program stored in said computerized device by rewriting the loop-case construct into parts that are combinations of computation units, each part having a length greater than one and less than N and wherein each part is one of a set of possible sequences of computation units having the same length as the corresponding each part, respectively;
• executing by said computerized device, in a executable computer program, instructions corresponding to each possible combination of computation units of lengths corresponding to the lengths of the parts of the unrolled sequence;
• partitioning the driving value into sub-sequences of condition values having lengths corresponding to the lengths of said computation unit sequences;
• processing the partitioned driving value by, for each sub-sequence thereof, executing the corresponding computation unit combination in the executable computer program;
• and
• dynamically updating the driving value by modifying the partitioning of the driving value into sub-sequences while respecting the original condition value sequence and processing the dynamically updated driving value by, for each sub-sequence thereof, executing the corresponding computation unit combination in the executable computer program by said computerized device.