This code is a large-scale RSA encryption and decryption. The selection of q and p uses pseudo-randomly generated large numbers and performs primality testing; the three characters in the plaintext are divided into blocks, and the characters in the block are not satisfied. Three are filled, and the filling scheme used is PKCS#7 filling.
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <stdlib.h>
#include <time.h>
#include <math.h>
using namespace std;
long long int N;
long long int D;
// Generate pseudo prime numbers
const int MAX_ROW = 50;
size_t Pseudoprime()
{
bool ifprime = false;
size_t a = 0;
int arr[MAX_ROW]; //The array arr is {3, 4, 5, 6...52}
for (int i = 0; i < MAX_ROW; + + i)
{
arr[i] = i + 3;
}
while (!ifprime)
{
srand((unsigned)time(0));
ifprime = true;
a = (rand() % 10000) * 3 + 10000; //Generate an odd number in the range of 10000 to 40000
for (int j = 0; j < MAX_ROW; + + j)
{
if (a % arr[j] == 0)
{
ifprime = false;
break;
}
}
}
return a;
}
size_t repeatMod(size_t base, size_t n, size_t mod)//modular repeat square algorithm to find (b^n)%m
{
size_t a = 1;
while(n)
{
if (n & 1)
{
a = (a * base) % mod;
}
base = (base * base) % mod;
n = n >> 1;
}
return a;
}
//Miller-Rabin prime number detection
bool rabinmiller(size_t n, size_t k)
{
int s = 0;
int temp = n - 1;
while ((temp & amp; 0x1) == 0 & amp; & amp; temp)
{
temp = temp >> 1;
s++;
} //Represent n-1 as (2^s)*t
size_t t = temp;
while (k--) //Judge that the probability of misjudgment in round k is not greater than (1/4)^k
{
srand((unsigned)time(0));
size_t b = rand() % (n - 2) + 2; //Generate a b(2≤a ≤n-2)
size_t y = repeatMod(b, t, n);
if (y == 1 || y == (n - 1))
return true;
for (int j = 1; j <= (s - 1) & amp; & amp; y != (n - 1); + + j)
{
y = repeatMod(y, 2, n);
if(y==1)
return false;
}
if (y != (n - 1))
return false;
}
return true;
}
/*
//Simple prime number detection method
bool isprime(size_t n)
{
if(n==2)
return true;
for (int i = 2; i <= (int)sqrt((float)n); + + i)
{
if (n % i == 0)
return false;
}
return true;
}*/
// Calculate the greatest common divisor
unsigned long long gcd(unsigned long long a, unsigned long long b) {
if(b==0)
return a;
return gcd(b, a % b);
}
// Calculate modular inverse elements
unsigned long long modInverse(unsigned long long a, unsigned long long m) {
long long m0 = m;
long long y = 0, x = 1;
if(m==1)
return 0;
while (a > 1) {
long long q = a / m;
long long t = m;
m = a % m;
a = t;
t = y;
y = x - q * y;
x = t;
}
if (x < 0)
x + = m0;
return x;
}
// Fast modular exponentiation
unsigned long long modExp(unsigned long long base, unsigned long long exponent, unsigned long long modulus) {
unsigned long long result = 1;
base = base % modulus;
while (exponent > 0) {
if (exponent & 1) {
result = (result * base) % modulus;
}
exponent = exponent >> 1;
base = (base * base) % modulus;
}
return result;
}
// RSA segmented encryption function (including padding)
unsigned long long* encryptString(const char* plaintext, unsigned long long n, unsigned long long e, int blockSize, int* numBlocks) {
int plaintextLength = strlen(plaintext);
int paddingLength = blockSize - (plaintextLength % blockSize);
*numBlocks = (int)ceil((double)(plaintextLength + paddingLength) / blockSize);
unsigned long long* ciphertext = new unsigned long long[*numBlocks];
for (int i = 0; i < *numBlocks; i + + ) {
int startIndex = i * blockSize;
int endIndex = (i + 1) * blockSize;
if (endIndex > plaintextLength) {
endIndex = plaintextLength;
}
unsigned long long blockValue = 0;
for (int j = startIndex; j < endIndex; j + + ) {
blockValue = blockValue * 256 + (unsigned long long)plaintext[j];
}
if (i == (*numBlocks - 1)) {
//The last block is filled
for (int j = 0; j < paddingLength; j + + ) {
blockValue = blockValue * 256 + paddingLength;
}
}
ciphertext[i] = modExp(blockValue, e, n);
}
return ciphertext;
}
// RSA segmented decryption function (including depadding)
char* decryptString(unsigned long long* ciphertext, unsigned long long n, unsigned long long d, int blockSize, int numBlocks) {
char* plaintext = new char[numBlocks * blockSize + 1]; // Add 1 to store the null terminator
for (int i = 0; i < numBlocks; i + + ) {
unsigned long long decryptedBlock = modExp(ciphertext[i], d, n);
for (int j = blockSize - 1; j >= 0; j--) {
plaintext[i * blockSize + j] = (char)(decryptedBlock % 256);
decryptedBlock = decryptedBlock / 256;
}
}
//Remove padding bytes
int padding = (int)plaintext[numBlocks * blockSize - 1]; //The last byte indicates the padding length
int plaintextLength = numBlocks * blockSize - padding;
plaintext[plaintextLength] = '\0';
return plaintext;
}
void encryptNumber(long M, unsigned long long n, unsigned long long e) {
int r = 1;
e = e + 1;
while (e != 1)
{
r = r * M;
r = r % n;
e--;
}
printf("Original message: %ld\
", M);
printf("Encrypted message:");
cout << r << endl;
}
// Various parameters of RSA encryption and decryption
void rsa(int mode) {
cout << "Generating RSA encrypted public and private keys, please wait..." << endl;
unsigned long long int p = 0;
unsigned long long int q = 0;
for (int i = 0; i <= 1; i + + ) {
size_t ret = Pseudoprime();
if (i == 0 & amp; & amp; p == 0) {
if (rabinmiller(ret, 10)) {
cout << "generated" << ret << "is a prime number" << endl;
cout << "p is:" << ret << endl;
p = ret;
cout << "---------------------------------------------" << endl ;
}
else {
i--;
}
}
else if (i == 1 & amp; & amp; q == 0 & amp; & amp; p != 0) {
if (rabinmiller(ret, 10) & amp; & amp; ret != p) {
cout << "generated" << ret << "is a prime number" << endl;
cout << "q is:" << ret << endl;
q = ret;
cout << "---------------------------------------------" << endl ;
}
else {
i--;
}
}
}
unsigned long long int n = p * q; // Calculate n
unsigned long long int phi = (p - 1) * (q - 1); // Calculate Euler function phi(n)
unsigned long long int e = 0;
while (1) {
e = rand() % phi; // Randomly select an encryption index e
if (gcd(e, phi) == 1) // Ensure that e and phi are mutually prime
break;
}
cout << "n is:" << n << endl;
N = n;
cout << "Randomly generate e:" << e << endl;
cout << "The phi value is:" << phi << endl;
// Calculate the decryption index d
unsigned long long d = modInverse(e, phi);
printf("Private key (d): %llu\
", d);
D = d;
cout << "---------------------------------------------" << endl ;
if (mode == 10) {
char filename[256];
printf("Please enter the local file name containing plain text:");
scanf("%5s", filename);
FILE* file = fopen(filename, "r");
if (file == NULL) {
printf("Cannot open file %s\
", filename);
return;
}
fseek(file, 0, SEEK_END);
long fileSize = ftell(file);
fseek(file, 0, SEEK_SET);
char* plaintext = (char*)malloc((fileSize + 1) * sizeof(char));
fread(plaintext, sizeof(char), fileSize, file);
plaintext[fileSize] = '\0';
fclose(file);
int blockSize = 3;
int numBlocks;
unsigned long long* encrypted = encryptString(plaintext, n, e, blockSize, & amp;numBlocks);
printf("Original message: %s\
", plaintext);
printf("Encrypted message:");
for (int i = 0; i < numBlocks; i + + ) {
printf("%llu ", encrypted[i]);
}
printf("\
");
//Write to txt local file
printf("Please enter the file name to save the ciphertext:");
char filename1[256];
scanf("%5s", filename1);
FILE* file1 = fopen(filename1, "w");
if (file == NULL) {
printf("Cannot open file %s\
", filename1);
return;
}
for (int i = 0; i < numBlocks; i + + ) {
fprintf(file1, "%llu ", encrypted[i]);
}
fclose(file1);
printf("The ciphertext has been saved to file %s\
", filename1);
free(plaintext);
free(encrypted);
}
if (mode == 21) {
char plaintext[256];
printf("Please enter the plain text to be encrypted:");
scanf("%5s", plaintext);
int numBlocks;
unsigned long long* encrypted = encryptString(plaintext, n, e, 3, & amp;numBlocks);
printf("Original message: %s\
", plaintext);
printf("Encrypted message:");
for (int i = 0; i < numBlocks; i + + ) {
printf("%llu ", encrypted[i]);
}
cout << endl;
//Write to txt local file
printf("Please enter the file name to save the ciphertext:");
char filename[256];
scanf("%5s", filename);
FILE* file = fopen(filename, "w");
if (file == NULL) {
printf("Cannot open file %s\
", filename);
return;
}
for (int i = 0; i < numBlocks; i + + ) {
fprintf(file, "%llu ", encrypted[i]);
}
fclose(file);
printf("The ciphertext has been saved to file %s\
", filename);
free(encrypted);
}
if (mode == 22) {
long M;
cout << "Please enter a number:";
scanf("%ld", & amp;M);
encryptNumber(M, n, e);
}
}
//Main function
int main(void)
{
int choice = 0;
while (choice != 3) {
printf("Welcome to RSA encryption and decryption system\
");
cout << "------------------------------------------------- -------------------------------------------------- --------------------" << endl;
printf("Please select function:\
");
printf(" 1. Encryption\
");
printf(" 2. Decrypt\
");
printf(" 3. Exit\
");
printf("Select:");
scanf("%d", & amp;choice);
switch (choice) {
case 1: {
int option = 0;
printf("Please select input method:\
");
printf("1. Read plain text from local file\
");
printf("2. Directly output plain text\
");
printf("Select:");
scanf("%d", & amp;option);
if (option == 1) {
//Read plain text from file
// char* plainText = readPlainTextFromFile(filename);
// if (plainText == NULL) {
// break;
// }
// free(plainText);
rsa(10); break;
}
else if (option == 2) {
int op = 0;
bool flag = false;
printf("Please select input method:\
");
printf(" 1. Encrypted string\
");
printf(" 2. Encrypted number\
");
printf("Select:");
int modeNumber = 22; //Encrypted number
int modeString = 21; //Encrypted string
while (op > -1 & amp; & amp; flag == false) {
scanf("%d", & amp;op);
if (op == 1) {
rsa(modeString); flag = 1; break;
}
else if (op == 2)
break;
else {
printf("Invalid selection, please re-enter:\
");
}
}
while (op > -1 & amp; & amp; flag == false) {
scanf("%d", & amp;op);
if (op == 2) {
rsa(modeNumber); flag = 1; break;
}
else {
printf("Invalid selection, please re-enter:\
");
}
}
break;
}
}
//Decrypt the ciphertext
case 2: {
printf("Please select input method:\
");
printf(" 1. Read ciphertext from local file\
");
printf(" 2. Directly output the ciphertext\
");
printf("Select:");
int option = 0;
scanf("%d", & amp;option);
if (option == 2) {
unsigned long long ciphertext[256];
int numBlocks = 0;
printf("Please enter the ciphertext to be decrypted (separated by spaces, stopped by newlines):");
while (scanf("%llu", & ciphertext[numBlocks]) == 1) {
numBlocks + + ;
// Read and discard newlines
if (getchar() == '\
') {
break;
}
}
getchar(); // Clear newline characters in the input buffer
// Get private keys d and n
unsigned long long d, n;
cout << "Please enter private keys d and n" << endl;
cout << "d is: ";
cin >> d;
cout << "n is: ";
cin >> n;
//Perform decryption operation
char* decrypted = decryptString(ciphertext, n, d, 3, numBlocks);
printf("Decrypted message: %s\
", decrypted);
free(decrypted);
break;
}
else if (option == 1) {
cout <<
"Private key PR={" << D << "," << N << "}" << endl;
printf("Please enter the name of the ciphertext file to be read:");
char filename[256];
scanf("%5s", filename);
FILE* file = fopen(filename, "r");
if (file == NULL) {
printf("Cannot open file %s\
", filename);
return 1;
}
unsigned long long* ciphertext = NULL;
int numBlocks = 0;
int c;
//Read ciphertext data
unsigned long long block;
while ((c = fgetc(file)) != EOF) {
if (isdigit(c) || c == '-') {
ungetc(c, file);
if (fscanf(file, "%llu", & block) == 1) {
numBlocks + + ;
ciphertext = (unsigned long long*)realloc(ciphertext, numBlocks * sizeof(unsigned long long));
ciphertext[numBlocks - 1] = block;
}
}
else if (c == ' ') {
continue; // ignore space characters
}
}
fclose(file);
char* decrypted = decryptString(ciphertext, N, D, 3, numBlocks);
printf("Decrypted plain text: %s\
", decrypted);
free(ciphertext);
free(decrypted);
break;
}
}
case 3: {
printf("Exit the program.\
");
break;
}
default: {
printf("Invalid selection.\
");
break;
}
}
cout << endl;
}
return 0;
}
Any similarity is purely coincidental.