c语言 通过openssl进行rsa的加密和解密

参考资料

https://blog.csdn.net/enjoyinwind/article/details/23530303

https://blog.csdn.net/stormbjm/article/details/46898757

摘自：https://blog.csdn.net/u011983700/article/details/108240200

 

最近项目中需要用到RSA加密，网上这方面的资料很多，研究了一番，发现直接用openssl的rsa接口非常方便，可以直接通过别人提供的公钥私钥进行加密解密，也可以通过openssl生成密钥对将公钥提供给别人使用。

具体的RSA加密原理就不在这里赘述，直接上代码，代码参考上面两个链接。

其中的重点记录一下哈：

问题1，openssl提供了bio接口以支持各种形式的秘钥读取。在使用bio接口从内存中读取pem格式的公钥时，总是读取公钥失败，经不断查找资料，发现在我们得到base64编码的RSA公钥后，从内存中读取这个公钥时要注意以下几点：（1）公钥字符串开头要加上“-----BEGIN PUBLIC KEY-----\n”，结尾加上“\n-----END PUBLIC KEY-----\n”。否则会出现error:0906D06C:PEM routines:PEM_read_bio:no start line（2）公钥字符串每隔64个字符要加一个换行，否则会报秘钥格式错误。

问题2，PEM_read_RSA_PUBKEY()函数和PEM_read_RSAPublicKEY()的疑惑。为什么读取私钥文件用的PEM_read_RSAPrivateKey()，针对上述openssl命令生成的公钥文件，在读取其内容时用对称的PEM_read_RSAPublicKEY()接口却会报错，必须要用PEM_read_RSA_PUBKEY()才可以。 原因是生成公钥时要把-pubout参数改成-RSAPublicKey_out

 

目前支持两种模式获取公钥和私钥。第一种方式比较常用，直接通过文件获取公私钥。第二种方式通过内存获取，这种方式比较灵活，可以将密钥保存在数据库，文件，甚至直接写在代码里，只要使用的时候将其转成对应格式的字符串即可。

另外，由于通过rsa加密以后的二进制密文有时候不太方便传输，所以一般会将其通过base64进行编码然后再进行传输。

在进行代码开发前，首先需要安装openssl库，ubuntu下直接执行一下命令即可。

sudo apt-get install libssl-dev

// rsa.h

#ifndef _RSA_H
#define _RSA_H
 
#define PRIVATEKEY "key.pem"
#define PUBLICKEY "key_pub.pem"
 
int rsa_pub_encrypt(char *str,char *path_key,char** outstr);
int rsa_prv_decrypt(char *str,char *path_key,int inlen,char** outstr);
 
#endif

// rsa.c
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<openssl/rsa.h>
#include<openssl/pem.h>
#include<openssl/err.h>
#include "rsa.h"
 
#define RSAPUBKEY
#define KEYFORMFILE 1
#define KEYFORMMEM    2
#define KEYFORM    KEYFORMMEM
 
 
static int do_operation(RSA* rsa_ctx,char *instr,char* path_key,int inlen,char** outstr,int type)
{
    if(rsa_ctx == NULL || instr == NULL || path_key == NULL)
    {
        perror("input elems error,please check them!");
        return -1;
    }
 
    int rsa_len,num;
    rsa_len=RSA_size(rsa_ctx);
    *outstr=(unsigned char *)malloc(rsa_len+1);
    memset(*outstr,0,rsa_len+1);
    switch(type){
        case 1: //pub enc
        if(inlen == 0){
            perror("input str len is zero!");
            goto err;
        }
 
        num = RSA_public_encrypt(inlen,(unsigned char *)instr,(unsigned char*)*outstr,rsa_ctx,RSA_PKCS1_PADDING);
 
        break;
        case 2: //prv dec
        num = RSA_private_decrypt(inlen,(unsigned char *)instr,(unsigned char*)*outstr,rsa_ctx,RSA_PKCS1_PADDING);
        break;
        default:
        break;
    }
 
    if(num == -1)
    {
        printf("Got error on enc/dec!\n");
err:
        free(*outstr);
        *outstr = NULL;
        num = -1;
    }
 
    return num;
}
char* pubkey="-----BEGIN PUBLIC KEY-----\n\
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAv1Gt1Q3FCo9rgwR1+bsR\
qaInU+2OFnoYdhp2189doeAwP+XH3LLBnxeDRfH1PZKrvEFtKBWaB2112lN4dL/T\
/dSOezszKHPTSg0PaxW4F+ooAY0gTQWGSuSMcY8H4RpkI7sNFFfOYQZYT0albs+e\
RepaHtfQCfM/cFTmpHVDXqdK4uCRNZbhff2+5oEN/j0eW5t4aq+G+Qu1gz9poH5B\
uqea69foG4LRcnwVKCXz+5ZrzE2YWYayvCEgpojXmkLcemvWkJD+K0SUsKoZ/7Wn\
vMBg1mfkSlNTFzpDgKjYESnnUgUobwDtBT9Wdq0RHVVTyZLh4CvZMeS1NcHBqDxp\
PQIDAQAB\
\n-----END PUBLIC KEY-----\n";
 
int rsa_pub_encrypt(char *str,char *path_key,char** outstr)
{
    RSA *p_rsa;
    BIO *bio = NULL;
    FILE *file;
    int flen,rsa_len,num;
#if KEYFORM==KEYFORMFILE
    if((file=fopen(path_key,"r"))==NULL){
        perror("open key file error");
        return -1;
    }
#else
    if ((bio = BIO_new_mem_buf(pubkey, -1)) == NULL)       //从字符串读取RSA公钥
    {
        perror("BIO_new_mem_buf failed!");
    }
#endif
 
#ifdef RSAPUBKEY
#if KEYFORM==KEYFORMFILE
    if((p_rsa=PEM_read_RSA_PUBKEY(file,NULL,NULL,NULL))==NULL){
#else
    if((p_rsa=PEM_read_bio_RSA_PUBKEY(bio,NULL,NULL,NULL))==NULL){
#endif
#else
    if((p_rsa=PEM_read_RSAPublicKey(file,NULL,NULL,NULL))==NULL){
#endif
        ERR_print_errors_fp(stdout);
        return -1;
    }
 
    num = do_operation(p_rsa,str,path_key,strlen(str),outstr,1);
 
    RSA_free(p_rsa);
#if KEYFORM==KEYFORMFILE
    fclose(file);
#else
    BIO_free_all(bio);
#endif
 
    return num;
}
 
char* prikey="-----BEGIN RSA PRIVATE KEY-----\n\
MIIEogIBAAKCAQEAv1Gt1Q3FCo9rgwR1+bsRqaInU+2OFnoYdhp2189doeAwP+XH\
3LLBnxeDRfH1PZKrvEFtKBWaB2112lN4dL/T/dSOezszKHPTSg0PaxW4F+ooAY0g\
TQWGSuSMcY8H4RpkI7sNFFfOYQZYT0albs+eRepaHtfQCfM/cFTmpHVDXqdK4uCR\
NZbhff2+5oEN/j0eW5t4aq+G+Qu1gz9poH5Buqea69foG4LRcnwVKCXz+5ZrzE2Y\
WYayvCEgpojXmkLcemvWkJD+K0SUsKoZ/7WnvMBg1mfkSlNTFzpDgKjYESnnUgUo\
bwDtBT9Wdq0RHVVTyZLh4CvZMeS1NcHBqDxpPQIDAQABAoIBAGleFLzoLoMYZf/s\
bwUxEBM66SoCBWU/rUUuYhGNdWX30NsANEjKcnSqQHQ/Q++7XbX62qFe9Evu7x9l\
JUw3cgu0Cxy3h/9Zex6nfrxdY9xX69ye2xFQX5vTr73DJnXFUS2UkSmJCnLJSc2v\
fOFAm0yqOyQNe9hfDatSNwyQQKBZ0iiBP4DMfZyW0L0uREDb1Zex4PL5EMt9dlNh\
m6rObetXBXU9Fu1UFSbH2BFzjbsgCJ/kr2ty3hwTv8ygFrNrFJtDfEGdln6vmIiE\
Lbq12UElXtKi2Ko+uulzILFNSSHzi7aJt0y+szBnXkF0XVirvBgIEGCQvL2ynf5O\
Vr96N0kCgYEA7ixwmmjevu4zvcW2nVrXbV+0H0088OKKJMrs92daECL1H/lRCAxI\
MOK6nXEgPy6siMPbErPt3j2bj63HAZVXMfkv4xhn5kCbbhqxS6EsBwoy3hH8Mg9a\
EIbIurdtIZPaElC/nMbD8EoLZpruNhuezQJpsJOm9zIswpj5SYLmEIsCgYEAzaN5\
2eAyEWPTf8Jd+EwhHfGYRnvdNCnlO1G4mbY5w6UU0grko1uuE7XzCfDYAeRgqUHc\
FDFcj3K/wTofj/KqcUBATy7WolkQOc5TF9P6z8HBPpCaxIHgIT3xMzCLSeSlZkK5\
5MBEl0kCGYdTOhGFlQkmNfYb9b3Y3AmJ3NVlnlcCgYA2w3ccufJFmoXBI93qboHM\
P04uSFcz2BMFhLdZ56S4wyDzuiLco95Rh0B7hRByFqxLQiV0NnUCPc4wCjgQ8CK9\
dduB7xGsyrwyY+bSSfvSnpC1qRMA+7CsziEHdbedGd7xiSmVxco1zQC0Ffmh7VXl\
M6HTnQ+uFRZfpEbllTiLIwKBgGW2lm7OFfXECrkGyrQl87t75HX4jlFe56OPqF9f\
YvMClGnQOYcTsebN+IjSOAW3kJgnm1PhlobdmztYJIRu4x9hSG3iHQfwRbZR94ex\
sj1Q+OSZYfQQyWun18YaHMtP7P/HwWsELuklk4RNCz2NrSUqgVvvf6TtYnZzwV0Z\
sEnBAoGAF7be2xB6tDoGic/oKahwbR9rviur7zKA+LPapeRwxXElWYCE2ON1NUlF\
+Z+5ajqGjUtQWXDCPqaLO5gSPipPHxX6tYIeolk1C5veZBkeHgG4TLMuIxtpGayw\
6/P3Pru8xzm8gZZTYqpmnFoXS6gQ2sNtrbyLJNNzH9bUNH7diVU=\
\n-----END RSA PRIVATE KEY-----\n";
 
int rsa_prv_decrypt(char *str,char *path_key,int inlen,char** outstr)
{
    RSA *p_rsa;
    BIO *bio = NULL;
    FILE *file;
    int rsa_len,num;
 
#if KEYFORM==KEYFORMFILE
    if((file=fopen(path_key,"r"))==NULL){
        perror("open key file error");
        return -1;
    }
#else
    if ((bio = BIO_new_mem_buf(prikey, -1)) == NULL)       //从字符串读取RSA公钥
    {
        perror("BIO_new_mem_buf failed!");
    }
#endif
 
#if KEYFORM==KEYFORMFILE
    if((p_rsa=PEM_read_RSAPrivateKey(file,NULL,NULL,NULL))==NULL){
#else
    if((p_rsa=PEM_read_bio_RSAPrivateKey(bio,NULL,NULL,NULL))==NULL){
#endif
        ERR_print_errors_fp(stdout);
        return -1;
    }
 
    num = do_operation(p_rsa,str,path_key,inlen,outstr,2);
    RSA_free(p_rsa);
#if KEYFORM==KEYFORMFILE
    fclose(file);
#else
    BIO_free_all(bio);
#endif
 
    return num;
}

/*base64.h*/
#ifndef _BASE64_H
#define _BASE64_H
 
#include <stdlib.h>
#include <string.h>
 
unsigned char *base64_encode(unsigned char *str,int strlen);
 
unsigned char *base64_decode(unsigned char *code,int *codelen);
 
#endif

/*base64.c*/
#include "base64.h"
 
unsigned char *base64_encode(unsigned char *str,int strlen)
{
    long len;
    long str_len;
    unsigned char *res;
    int i,j;
//定义base64编码表
    unsigned char *base64_table="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
//计算经过base64编码后的字符串长度
    str_len=strlen;
    if(str_len % 3 == 0)
        len=str_len/3*4;
    else
        len=(str_len/3+1)*4;
 
    res=malloc(sizeof(unsigned char)*len+1);
    res[len]='\0';
 
//以3个8位字符为一组进行编码
    for(i=0,j=0;i<len-2;j+=3,i+=4)
    {
        res[i]=base64_table[str[j]>>2]; //取出第一个字符的前6位并找出对应的结果字符
        res[i+1]=base64_table[(str[j]&0x3)<<4 | (str[j+1]>>4)]; //将第一个字符的后位与第二个字符的前4位进行组合并找到对应的结果字符
        res[i+2]=base64_table[(str[j+1]&0xf)<<2 | (str[j+2]>>6)]; //将第二个字符的后4位与第三个字符的前2位组合并找出对应的结果字符
        res[i+3]=base64_table[str[j+2]&0x3f]; //取出第三个字符的后6位并找出结果字符
    }
 
    switch(str_len % 3)
    {
        case 1:
            res[i-2]='=';
            res[i-1]='=';
            break;
        case 2:
            res[i-1]='=';
            break;
    }
 
    return res;
}
 
unsigned char *base64_decode(unsigned char *code,int *codelen)
{
//根据base64表，以字符找到对应的十进制数据
    int table[]={0,0,0,0,0,0,0,0,0,0,0,0,
             0,0,0,0,0,0,0,0,0,0,0,0,
             0,0,0,0,0,0,0,0,0,0,0,0,
             0,0,0,0,0,0,0,62,0,0,0,
             63,52,53,54,55,56,57,58,
             59,60,61,0,0,0,0,0,0,0,0,
             1,2,3,4,5,6,7,8,9,10,11,12,
             13,14,15,16,17,18,19,20,21,
             22,23,24,25,0,0,0,0,0,0,26,
             27,28,29,30,31,32,33,34,35,
             36,37,38,39,40,41,42,43,44,
             45,46,47,48,49,50,51
               };
    long len;
    long str_len;
    unsigned char *res;
    int i,j;
 
//计算解码后的字符串长度
    len=strlen(code);
//判断编码后的字符串后是否有=
    if(strstr(code,"=="))
        str_len=len/4*3-2;
    else if(strstr(code,"="))
        str_len=len/4*3-1;
    else
        str_len=len/4*3;
 
    res=malloc(sizeof(unsigned char)*str_len+1);
    res[str_len]='\0';
    *codelen=str_len;
//以4个字符为一位进行解码
    for(i=0,j=0;i < len-2;j+=3,i+=4)
    {
        res[j]=((unsigned char)table[code[i]])<<2 | (((unsigned char)table[code[i+1]])>>4); //取出第一个字符对应base64表的十进制数的前6位与第二个字符对应base64表的十进制数的后2位进行组合
        res[j+1]=(((unsigned char)table[code[i+1]])<<4) | (((unsigned char)table[code[i+2]])>>2); //取出第二个字符对应base64表的十进制数的后4位与第三个字符对应bas464表的十进制数的后4位进行组合
        res[j+2]=(((unsigned char)table[code[i+2]])<<6) | ((unsigned char)table[code[i+3]]); //取出第三个字符对应base64表的十进制数的后2位与第4个字符进行组合
    }
 
    return res;
 
}

// main.c
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include "base64.h"
#include "rsa.h"
//#include "aes.h"
 
void ras_test()
{
    char *ptr_en=NULL,*ptr_de=NULL;
    char *ptr_enbase=NULL,*ptr_debase=NULL;
    int len;
 
    len=rsa_pub_encrypt("abcd1234",PUBLICKEY,&ptr_en);
    printf("pubkey encrypt=%d:\n",len);
 
    ptr_enbase=base64_encode(ptr_en,len);
    printf("base64_encode len=%d\n",strlen(ptr_enbase));
    printf("%s\n",ptr_enbase);
 
    int decode_len;
    ptr_debase=base64_decode("JqdnYAhiZbXNV+h7t3jSj6DcYRwQevRjyz9qg4H7m"
            "JizgXnUAZ0saWIwrVf+5p+TTTlLzadfSVgM4NtMsqO1kRD/M15u3j/"
            "009KoKXPa3PZQI3o+r8tkaVloG+LMGt4IndI2jZdZ5gFv8gFQUdkoZ"
            "jiuXa3NWnX99909dN/l0c8LTyNVF+mKt8EP8nEo6ICq/9sMl0qI8v5"
            "DiXHRurtJVewH/2+iofAACidXlvihvQsWgt+KDntCwl2+lo+F+Fmcx"
            "dlntnsPZVibgIYS+Mjoged4782Agp6srMyNsCmarE+mSeyhA3ywK0T"
            "srUEQoKm3qJVD6XPXVbAO5B6MCVFd0Q==",&decode_len);
    printf("decode_len=%d\n",decode_len);
 
    rsa_prv_decrypt(ptr_debase,PRIVATEKEY,len,&ptr_de);
    printf("prvkey decrypt:%s\n",ptr_de==NULL?"NULL":ptr_de);
 
    if(ptr_enbase!=NULL){
        free(ptr_enbase);
    }
    if(ptr_debase!=NULL){
        free(ptr_debase);
    }
 
    if(ptr_en!=NULL){
        free(ptr_en);
    }
    if(ptr_de!=NULL){
        free(ptr_de);
    }
}
 
int main(int argc,char** argv)
{
    ras_test();
 
    return 0;
}