安裝完成後，產生RSA公鑰和私鑰
輸入openssl進入程式
OpenSSL> genrsa -out test.key 1024
產生了1024bit的私鑰，然後根據該私鑰產生公鑰
rsa -in test.key -pubout -out rsatest_pub.key

建立rsatest.c程式碼如下
vim rsatest.c

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<openssl/rsa.h>
#include<openssl/pem.h>
 

#include<openssl/err.h>



#define OPENSSLKEY "test.key"
#define PUBLICKEY "test_pub.key"
#define BUFFSIZE 1024
char* my_encrypt(char *str,char *path_key);//加密
char* my_decrypt(char *str,char *path_key);//解密
int main(void){
    char *source="i like dancing !";
    char *ptr_en,*ptr_de;
    printf("source is    :%s\n"
 
,source);
    ptr_en=my_encrypt(source,PUBLICKEY);
    printf("after encrypt:%s\n",ptr_en);
    ptr_de=my_decrypt(ptr_en,OPENSSLKEY);
    printf("after decrypt:%s\n",ptr_de);
    if(ptr_en!=NULL){
        free(ptr_en);
    }   
    if(ptr_de!=NULL){
        free(ptr_de);
    }   
    return 0;
}
char
 
 *my_encrypt(char *str,char *path_key){
    char *p_en;
    RSA *p_rsa;
    FILE *file;
    int flen,rsa_len;
    if((file=fopen(path_key,"r"))==NULL){
        perror("open key file error");
        return NULL;    
    }   
    if((p_rsa=PEM_read_RSA_PUBKEY(file,NULL,NULL,NULL))==NULL){
        ERR_print_errors_fp(stdout);
        return NULL;
    }   
    flen=strlen(str);
    rsa_len=RSA_size(p_rsa);
    p_en=(unsigned char *)malloc(rsa_len+1);
    memset(p_en,0,rsa_len+1);
    if(RSA_public_encrypt(rsa_len,(unsigned char *)str,(unsigned char*)p_en,p_rsa,RSA_NO_PADDING)<0){
        return NULL;
    }
    RSA_free(p_rsa);
    fclose(file);
    return p_en;
}
char *my_decrypt(char *str,char *path_key){
    char *p_de;
    RSA *p_rsa;
    FILE *file;
    int rsa_len;
    if((file=fopen(path_key,"r"))==NULL){
        perror("open key file error");
        return NULL;
    }
    if((p_rsa=PEM_read_RSAPrivateKey(file,NULL,NULL,NULL))==NULL){
        ERR_print_errors_fp(stdout);
        return NULL;
    }
    rsa_len=RSA_size(p_rsa);
    p_de=(unsigned char *)malloc(rsa_len+1);
    memset(p_de,0,rsa_len+1);
    if(RSA_private_decrypt(rsa_len,(unsigned char *)str,(unsigned char*)p_de,p_rsa,RSA_NO_PADDING)<0){
        return NULL;
    }
    RSA_free(p_rsa);
    fclose(file);
    return p_de;
}

檢驗結果,gcc rsatest.c -o hello -lssl
最後-lssl 是為了引入共享庫ssl