C 语言如何利用 openssl 进行 rsa pkcs1 加密

char *rsa_encrypt(char *plain, char *to, char *key_path) {
    char *p_en;
    RSA *p_rsa;
    FILE *file;
    int f_len, rsa_len;
    if((file = fopen(key_path, "r")) == NULL){
        perror("open file error");
        return NULL;
    }

    if((p_rsa = PEM_read_RSAPublicKey(file, NULL, NULL, NULL)) ==  NULL){
        ERR_print_errors_fp(stdout);
        return NULL;
    }

    f_len = strlen(plain);
    rsa_len = RSA_size(p_rsa);
    p_en = (char *)malloc(rsa_len+1);
    memset(to, 0, rsa_len+1);
    if(RSA_public_encrypt(rsa_len, (unsigned char*)plain, (unsigned char*)p_en, p_rsa, RSA_PKCS1_PADDING) < 0){
        ERR_print_errors_fp(stdout);
        return NULL;
    }
    strcpy(to, (char *)p_en);
    RSA_free(p_rsa);
    fclose(file);
}