椭圆曲线密码实现D-H密钥交换的代码c语言代码，不使用OpenSSL库；

以下是一个简单的椭圆曲线密码实现D-H密钥交换的C语言代码，不使用OpenSSL库：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

typedef struct point {
    int x;
    int y;
} point;

typedef struct curve {
    int a;
    int b;
    int p; //质数
    point g; //生成元
} curve;

int inv(int a, int m) {
    int m0 = m, t, q;
    int x0 = 0, x1 = 1;
    if (m == 1) {
        return 0;
    }
    while (a > 1) {
        q = a / m;
        t = m;
        m = a % m;
        a = t;
        t = x0;
        x0 = x1 - q * x0;
        x1 = t;
    }
    if (x1 < 0) {
        x1 += m0;
    }
    return x1;
}

int mod(int a, int m) {
    int r = a % m;
    return r < 0 ? r + m : r;
}

point point_add(point p1, point p2, curve c) {
    point res;
    int s;
    if (p1.x == p2.x && p1.y != p2.y) {
        res.x = -1;
        res.y = -1;
        return res;
    }
    if (p1.x == p2.x) {
        s = mod(3 * p1.x * p1.x + c.a, c.p) * inv(2 * p1.y, c.p) % c.p;
    } else {
        s = mod(p2.y - p1.y, c.p) * inv(p2.x - p1.x, c.p) % c.p;
    }
    res.x = mod(s * s - p1.x - p2.x, c.p);
    res.y = mod(s * (p1.x - res.x) - p1.y, c.p);
    return res;
}

point point_mul(point p, int k, curve c) {
    point res = { -1, -1 };
    while (k > 0) {
        if (k % 2 == 1) {
            res = res.x == -1 ? p : point_add(res, p, c);
        }
        p = point_add(p, p, c);
        k /= 2;
    }
    return res;
}

void generate_key(curve c, point g, int n, int *pub_key, int *pri_key) {
    srand(time(NULL));
    int d = rand() % n;
    *pri_key = d;
    *pub_key = point_mul(g, d, c).x;
}

int main() {
    curve c = { 1, 6, 11, { 2, 7 } };
    int n = 17;
    int alice_pub_key, alice_pri_key, bob_pub_key, bob_pri_key;
    generate_key(c, c.g, n, &alice_pub_key, &alice_pri_key);
    generate_key(c, c.g, n, &bob_pub_key, &bob_pri_key);
    printf("Alice's public key: %d\n", alice_pub_key);
    printf("Bob's public key: %d\n", bob_pub_key);
    int alice_shared_key = point_mul({ bob_pub_key, 0 }, alice_pri_key, c).x;
    int bob_shared_key = point_mul({ alice_pub_key, 0 }, bob_pri_key, c).x;
    printf("Alice's shared key: %d\n", alice_shared_key);
    printf("Bob's shared key: %d\n", bob_shared_key);
    return 0;
}

其中，curve结构体表示椭圆曲线的参数，point结构体表示椭圆曲线上的点。inv函数和mod函数分别实现了求逆元和模运算。point_add函数实现了椭圆曲线上点的加法，point_mul函数实现了椭圆曲线上点的倍乘。generate_key函数实现了密钥生成过程。在main函数中，我们使用curve结构体定义了一个椭圆曲线，使用generate_key函数生成了Alice和Bob的公私钥，并计算了他们的共享密钥。