RSA (初階版)

花了兩個星期多左右從重新複習c/c++到終於寫出一個可以跑的程式作業,真是太感動了~~如果有路過的高手參觀歡迎指教~ (特別感謝一位好朋友的指導）

	/*SecureTool is abbreviated to "st" as a prefix of function name.*/
	#include<stdio.h>
	#include<stdint.h>
	uint64_t st_power(uint64_t base, uint64_t exponent, uint64_t devider)
	{
	uint64_t temp = base;
	for (int i = 1; i < exponent; i++)
	{
	uint64_t remainder = temp%devider;
	temp = remainder * base;
	}
	return temp % devider;
	}
	int st_encrypt(uint64_t* code, uint64_t public_key, uint64_t n,size_t length, uint64_t* output)
	{
	for (int i = 0; i < length; i++)
	{
	output[i] = st_power(code[i], public_key, n);
	}
	return 0;
	}
	int st_decrypt(uint64_t* code, uint64_t private_key, uint64_t n, size_t length, uint64_t* output)
	{
	for (int i = 0; i < length; i++)
	{
	uint64_t remainder = st_power(code[i],private_key,n);
	if (remainder > 26 && remainder < 100)
	{
	remainder += n;
	}
	output[i] = remainder;
	}
	return 0;
	}
	uint64_t st_key_inverse (uint64_t public_key, uint64_t devider)
	{
	uint64_t remainder = 1;
	while(1)
	{
	remainder += devider;
	if(remainder % public_key == 0)
	{
	return (remainder / public_key);
	}
	}
	}
	int st_encode(const char* string, char* output)
	{
	unsigned int i = 0;
	for(const char* s = string; *s; s++)
	{
	if (*s >= 'A' && *s <= 'Z') // Upper case roman character
	{
	output[i++] = *s - 'A';
	}
	else if (*s == ' ')
	{
	output[i++] = 26;
	}
	else
	{
	return 1; // ERROR invalid char
	}
	}
	if (i%2)
	{
	output[i++] = 26;
	} // pad if needed
	return 0;
	}
	int st_decode(uint64_t* code,char* output,size_t length)
	{
	char w = ' ',x = ' ';
	for(int i = 0; i < length; i++)
	{
	uint64_t v = code[i] / 100;
	if (v != 26)
	{
	w = v + 'A';
	output[i*2] = w;
	}
	else
	{
	output[i*2] = ' ';
	}
	uint64_t u = code[i] % 100;
	if(u != 26)
	{
	x = u + 'A';
	output[i*2+1] = x;
	}
	else
	{
	output[i*2+1] = ' ';
	}
	}
	return 0;
	}
	int main()
	{
	const char string[] = "STOP";
	printf("plain text:%s\n", string);
	const size_t string_length = sizeof(string);
	//printf("text size: %lu\n", string_length);
	const size_t blocks_length = (string_length) / 2;
	char blocks[string_length];
	uint64_t m[blocks_length], c[blocks_length], m2[blocks_length];
	uint64_t e = 13;
	uint64_t p = 43;
	uint64_t q = 59;
	uint64_t n = p * q;
	uint64_t t = (p - 1) * (q - 1);
	uint64_t d = st_key_inverse(e, t);
	printf("p = %lu\nq = %lu\nn = %lu\ne = %lu\n", p, q, n, e);
	printf("d = %lu\n", d);
	st_encode(string, (char*)blocks);
	printf("M = ");
	for (size_t i = 0; i < blocks_length; i++)
	{
	m[i] = blocks[i*2]*100 + blocks[i*2+1];
	printf("%lu ", m[i]);
	}
	st_encrypt(m, e, n, blocks_length, c);
	st_decrypt(c, d, n, blocks_length, m2);
	printf("\nC = ");
	for (int i = 0; i < blocks_length; i++){
	printf("%lu ", c[i]);
	}
	printf("\nafter decoding:");
	char text[string_length];
	st_decode(m2, text, blocks_length);
	for (int i = 0; i < blocks_length; i++)
	{
	printf("%lu ",m2[i]);
	}
	printf("\ndecoded text:");
	for (int i = 0; i < string_length - 1; i++)
	{
	printf("%c", text[i]);
	}
	printf("\n");
	return 0;
	}

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