openssl 的RSA 非对称加密算法

原文地址：http://blog.sina.com.cn/s/blog_4f51dac40100u3co.html

程序将加密密钥和解密密钥写入文件 运行！
 
#include <openssl/rsa.h>
#include <openssl/pem.h>
//#include <unistd.h>
#include <iostream>
#include <io.h>
const char *g_pPubFile = "public.pem";
const char *g_pPriFile = "private.pem";
//maxCodeByte = g_nBits/8-11
 const int g_nBits = 1024;
 
  using namespace std;
 
  int MakeKey()
  {
      if (access(g_pPubFile,0) != 0 || access(g_pPriFile,0) != 0)
      {
          return 0;
      }
      //生成key,这里设置了1024，意味着最多可以编解码1024/8-11=117个字节，
      //RSA_F4为公钥指数，一般情况下使用RSA_F4即可，
      //其它两个参数可以设置为NULL
      RSA *pRsa = RSA_generate_key(g_nBits,RSA_F4,NULL,NULL);
      if (pRsa == NULL)
      {
          cout << "rsa_generate_key error" << endl;
          return -1;
      }
     BIO *pBio = BIO_new_file(g_pPubFile,"w");
     if (pBio == NULL)
      {
          cout << "BIO_new_file " << g_pPubFile << " error" << endl;
         return -2;
      }
      if(PEM_write_bio_RSAPublicKey(pBio,pRsa) == 0)
      {
          cout << "write public key error" << endl;
          return -3;
      }
      BIO_free_all(pBio);
      pBio = BIO_new_file(g_pPriFile,"w");
      if (pBio == NULL)
      {
          cout << "BIO_new_file " << g_pPriFile << " error" << endl;
          return -4;
      }
      if(PEM_write_bio_RSAPrivateKey(pBio,pRsa,NULL,NULL,0,NULL,NULL) == 0)
      {
          cout << "write private key error" << endl;
          return -5;
      }
      BIO_free_all(pBio);
      RSA_free(pRsa);
      return 0;
  }
 
  int Enc(char *in, int inLen, char *out, int &outLen)
  {
      BIO *pBio = BIO_new_file(g_pPubFile,"r");
      RSA *pRsa = PEM_read_bio_RSAPublicKey(pBio,NULL,NULL,NULL);
      BIO_free_all(pBio);
      outLen = RSA_public_encrypt(
              (RSA_size(pRsa)-11)>inLen?inLen:RSA_size(pRsa)-11,
              reinterpret_cast<unsigned char*>(in),
              reinterpret_cast<unsigned char*>(out),
              pRsa,
              RSA_PKCS1_PADDING);
      //RSA_free(pRsa);
      if(outLen >= 0)
          return 0;
     return -1;
 }
 
  int Dec(char *in, int inLen, char *out, int &outLen)
  {
      BIO *pBio = BIO_new_file(g_pPriFile,"r");
      RSA *pRsa = PEM_read_bio_RSAPrivateKey(pBio,NULL,NULL,NULL);
      BIO_free_all(pBio);
     outLen = RSA_private_decrypt(
             inLen,
              reinterpret_cast<unsigned char*>(in),
              reinterpret_cast<unsigned char*>(out),
              pRsa,
              RSA_PKCS1_PADDING);
      //RSA_free(pRsa);
      if(outLen >= 0)
          return 0;
      return -1;
  }
 
  int main()
  {
      MakeKey();
      char pOld[100]="for test";
      char szEnc[1024] = {0};
      int nEncLen = 0;
      char szDec[1024] = {0};
      int nDecLen = 0;
      Enc(pOld,strlen(pOld),szEnc,nEncLen);
     Dec(szEnc,nEncLen,szDec,nDecLen);
     cout << "decode: " << szDec << endl;
  cin.get();
 }