程序代码：

#include <iostream>
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
using namespace std;

int gcd(int a, int b) // 求最大公约数
{
    if (b == 0)
        return a;
    else
        return gcd(b, a % b);
}

int mod(int a, int b, int n) // 快速模运算
{
    int c = 0;
    for (int i = b - 1; i >= 0; i--)
    {
        c = 2 * c;
        if ((n >> i) & 1)
        {
            c++;
        }
        c = c % n;
        a = ((long long)a * a) % n;
    }
    return c;
}

char* utf8IntsToString(const int* ints, int len) // 将UTF-8编码的整数数组转换成字符串
{
    char* str = new char[len + 1];
    int j = 0;
    for (int i = 0; i < len; i++) {
        if (ints[i] < 0x80) { // ASCII字符
            str[j] = (char)ints[i];
            j++;
        }
        else { // 非ASCII字符，使用UTF-8编码
            if (ints[i] < 0x800) {
                str[j] = (char)((ints[i] >> 6) | 0xC0);
                str[j + 1] = (char)((ints[i] & 0x3F) | 0x80);
                j += 2;
            }
            else if (ints[i] < 0x10000) {
                str[j] = (char)((ints[i] >> 12) | 0xE0);
                str[j + 1] = (char)(((ints[i] >> 6) & 0x3F) | 0x80);
                str[j + 2] = (char)((ints[i] & 0x3F) | 0x80);
                j += 3;
            }
            else { // 不支持4字节编码
                str[j] = '?';
                j++;
            }
        }
    }
    str[j] = '\0';
    return str;
}

int* stringToUtf8Ints(const char* str, int& len); // 转换字符串为UTF-8编码的整数数组
char* utf8IntsToString(const int* ints, int len); // 转换UTF-8编码的整数数组为字符串

int main()
{
    srand((unsigned)time(NULL));

    // 生成公私钥对
    int p, q, n, fn, e, d;
    p = 61; // 随机选取两个素数p和q
    q = 53;
    n = p * q;
    fn = (p - 1) * (q - 1);
    do {
        e = rand() % (fn - 2) + 2;
    } while (gcd(e, fn) != 1);
    for (d = 1; d <= fn; d++) {
        if (((long long)e * d) % fn == 1)
            break;
    }
    cout << "公钥为 (" << e << ", " << n << ")" << endl; // 输出公私钥
    cout << "私钥为 (" << d << ", " << n << ")" << endl;

    // 加密消息
    string msg;
    cout << "请输入要加密的消息：";
    getline(cin, msg);
    int len;
    int* M = stringToUtf8Ints(msg.c_str(), len);
    int* C = new int[len];
    for (int i = 0; i < len; i++) {
        C[i] = mod(M[i], e, n);
    }
    cout << "加密结果：";
    for (int i = 0; i < len; i++)
        cout << C[i] << " ";
    cout << endl;

    // 解密消息
    char* D = utf8IntsToString(C, len);
    int* M2 = stringToUtf8Ints(D, len);
    for (int i = 0; i < len; i++) {
        M2[i] = mod(C[i], d, n);
    }
    char* str = utf8IntsToString(M2, len);
    cout << "解密结果：" << str << endl;

    delete[] M;
    delete[] C;
    delete[] D;
    delete[] M2;
    delete[] str;

    return 0;
}

RSA.cpp:(.text+0x49a): undefined reference to `stringToUtf8Ints(char const*, int&)'
RSA.cpp:(.text+0x5d2): undefined reference to `stringToUtf8Ints(char const*, int&)'
[Error] ld returned 1 exit status