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74 lines
3.1 KiB
74 lines
3.1 KiB
/**
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*--------------------------------------------------------------------\n
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* HSLU T&A Hochschule Luzern Technik+Architektur \n
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*--------------------------------------------------------------------\n
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*
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* \brief model solution for ASYD assignment crypto 02
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* \file
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* \author Stefano Nicora, stefano.nicora@hslu.ch
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* \date 20.10.22
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*
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*--------------------------------------------------------------------
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*/
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#include <stdint.h>
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#include <stdio.h>
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#include "DHKE.h"
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#include "encryptionArithmetic.h"
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/* based on the square and multiply algorithm */
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/* https://www.biancahoegel.de/mathe/zahl/primitivwurzel.html */
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/* https://www.practicalnetworking.net/stand-alone/square-and-multiply/ */
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/* https://math.stackexchange.com/questions/1472480/learning-square-and-multiply-algorithm */
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/* https://www.dcode.fr/diffie-hellman-key-exchange */
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void moduloOperation(t_encryptionArithmetic* result, t_encryptionArithmetic* modulo, uint32_t keyLength);
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void squareAndMultiply(t_encryptionArithmetic *base, t_encryptionArithmetic *exponent, t_encryptionArithmetic* modulo, t_encryptionArithmetic* result, uint32_t keyLength) {
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/* assign base to result as the first step defined in the square & multply algorithm */
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for (uint8_t i = 0; i < (keyLength / 32); i++) {
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*(result->number + i) = *(base->number + i);
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}
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/* get amount of bits representing the exponent */
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uint16_t numberOfBits = encryptionArithmetic_numberSize(exponent->number, keyLength);
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/* execute square and multiply algorithm */
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for (int i = 0; i < numberOfBits - 1; i++) {
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/* -2 as we already did store the base inside our number and therefore skip the MSB */
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if (*(exponent->number) >> (numberOfBits - i - 2) & 1) /* if bit is 1 => multiply number with itself as well as with base */
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{
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encryptionArithmetic(result->number, result->number, result, keyLength, MUL); /* square */
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encryptionArithmetic(result->number, base->number, result, keyLength, MUL); /* multiply */
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}
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else /* if bit is 0 => multiply number with itself */
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{
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encryptionArithmetic(result->number, result->number, result, keyLength, MUL); /* square */
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}
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moduloOperation(result, modulo, keyLength);
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}
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printf("Square and Multiply result: %u\n", *result->number);
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}
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/* calculate modulo w/o the built in modulo operator */
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void moduloOperation(t_encryptionArithmetic* number, t_encryptionArithmetic* moduloValue, uint32_t keyLength) {
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/* number % moduloValue */
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/* https://www.geeksforgeeks.org/program-to-find-remainder-without-using-modulo-or-operator/ */
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/* allocate memory */
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t_encryptionArithmetic* mulRes, * divRes, mulRes_2, divRes_2;
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mulRes = &mulRes_2;
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divRes = &divRes_2;
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encryptionArithmetic_Init(mulRes, keyLength);
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encryptionArithmetic_Init(divRes, keyLength);
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/* perform modulo operation */
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encryptionArithmetic(number->number, moduloValue->number, divRes, keyLength, DIV);
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encryptionArithmetic(moduloValue->number, divRes->number, mulRes, keyLength, MUL);
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encryptionArithmetic(number->number, mulRes->number, number, keyLength, SUB);
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/* free memory */
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encryptionArithmetic_DeInit(mulRes);
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encryptionArithmetic_DeInit(divRes);
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} |