/************************************************* * Utility Functions Source File * * (C) 1999-2007 Jack Lloyd * *************************************************/ #include #include #include #include namespace Botan { /************************************************* * Round up n to multiple of align_to * *************************************************/ u32bit round_up(u32bit n, u32bit align_to) { if(n % align_to || n == 0) n += align_to - (n % align_to); return n; } /************************************************* * Round down n to multiple of align_to * *************************************************/ u32bit round_down(u32bit n, u32bit align_to) { return (n - (n % align_to)); } /************************************************* * Return the work required for solving DL * *************************************************/ u32bit dl_work_factor(u32bit n_bits) { const u32bit MIN_ESTIMATE = 64; if(n_bits < 32) return 0; const double log_x = n_bits / 1.44; const double strength = 2.76 * std::pow(log_x, 1.0/3.0) * std::pow(std::log(log_x), 2.0/3.0); if(strength > MIN_ESTIMATE) return static_cast(strength); return MIN_ESTIMATE; } /************************************************* * Estimate the entropy of the buffer * *************************************************/ u32bit entropy_estimate(const byte buffer[], u32bit length) { if(length <= 4) return 0; u32bit estimate = 0; byte last = 0, last_delta = 0, last_delta2 = 0; for(u32bit j = 0; j != length; ++j) { byte delta = last ^ buffer[j]; last = buffer[j]; byte delta2 = delta ^ last_delta; last_delta = delta; byte delta3 = delta2 ^ last_delta2; last_delta2 = delta2; byte min_delta = delta; if(min_delta > delta2) min_delta = delta2; if(min_delta > delta3) min_delta = delta3; estimate += hamming_weight(min_delta); } return (estimate / 2); } }