The disclosure relates to
decomposition of masked values in a cryptographically secure digital signing
system. Example embodiments include a method of decomposing mod 44 an N bit Boolean share input (b'B,k), where N>12, the method comprising: i) reducing (302-305) a number of bits in the Boolean share input (b'B,k) by adding a lower 11:0 bits of the input (b'B,k) to an upper portion of the input left shifted by 2 bits to provide a first intermediate result ( t1B,13) having M bits; ii) reducing (306-309) a number of bits of the first intermediate result ( t1B,13) by adding a lower 6:0 portion of the intermediate result to an upper portion left shifted by 2 bits and subtracted from a multiple of 44 to provide a second intermediate result ( t3B,8); and iii) adjusting (310-316) the second intermediate result ( t3B,8) by adding and / or subtracting 44 to provide an output ( w1B,k′) having a value within an interval of 0:43, the output ( w1B,k′) being a mod 44 representation of the input (b'B,k).