FreeBSD下使用OpenSSL实现TLS加密通信

本示例代码演示了如何在FreeBSD平台下使用OpenSSL库实现TLS加密通信，通过使用SSL_CTX结构体设置TLS版本及加密算法等参数，使用SSL_accept和SSL_connect函数实现服务器与客户端的套接字安全连接。

#include <openssl/ssl.h>
#include <openssl/err.h>

SSL_CTX *ssl_ctx;

int init_openssl()
{
    SSL_library_init();
    SSL_load_error_strings();
    ssl_ctx = SSL_CTX_new(TLSv1_2_method());
    if (!ssl_ctx) {
        ERR_print_errors_fp(stderr);
        return 1;
    }
    SSL_CTX_set_cipher_list(ssl_ctx, "COMPLEMENTOFALL");
    SSL_CTX_set_verify(ssl_ctx, SSL_VERIFY_PEER, NULL);
    if (!SSL_CTX_use_certificate_file(ssl_ctx, "/path/to/cert.pem", SSL_FILETYPE_PEM) ||
        !SSL_CTX_use_PrivateKey_file(ssl_ctx, "/path/to/key.pem", SSL_FILETYPE_PEM)) {
        ERR_print_errors_fp(stderr);
        return 1;
    }
    return 0;
}

void cleanup_openssl()
{
    SSL_CTX_free(ssl_ctx);
    EVP_cleanup();
}

int do_server_loop(SSL *ssl)
{
    char buf[1024];
    int len;
    len = SSL_read(ssl, buf, sizeof(buf) - 1);
    if (len <= 0) {
        printf("Error: SSL_read returned len=%d\n", len);
        return -1;
    }
    buf[len] = '\0';
    printf("Received message: %s\n", buf);
    len = SSL_write(ssl, "Reply from server", strlen("Reply from server"));
    if (len <= 0) {
        printf("Error: SSL_write returned len=%d\n", len);
        return -1;
    }
    return 0;
}

int ssl_server(int sockfd)
{
    SSL *ssl;
    int ret;
    ssl = SSL_new(ssl_ctx);
    SSL_set_fd(ssl, sockfd);
    ret = SSL_accept(ssl);
    if (ret < 0) {
        ERR_print_errors_fp(stderr);
    } else {
        ret = do_server_loop(ssl);
    }
    SSL_shutdown(ssl);
    SSL_free(ssl);
    return ret;
}

int ssl_client(int sockfd)
{
    SSL *ssl;
    int ret;
    ssl = SSL_new(ssl_ctx);
    SSL_set_fd(ssl, sockfd);
    ret = SSL_connect(ssl);
    if (ret < 0) {
        ERR_print_errors_fp(stderr);
    } else {
        ret = SSL_write(ssl, "Hello from client", strlen("Hello from client"));
        if (ret > 0) {
            char buf[1024];
            ret = SSL_read(ssl, buf, 1024);
            if (ret > 0) {
                buf[ret] = '\0';
                printf("Received message: %s\n", buf);
            }
        }
    }
    SSL_shutdown(ssl);
    SSL_free(ssl);
    return ret;
}

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