C/C++使用openssl进行摘要和加密解密（md5, sha256, des, rsa）

openssl里面有很多用于摘要哈希、加密解密的算法，方便集成于工程项目，被广泛应用于网络报文中的安全传输和认证。下面以md5，sha256，des，rsa几个典型的api简单使用作为例子。

算法介绍

md5：https://en.wikipedia.org/wiki/MD5

sha256：https://en.wikipedia.org/wiki/SHA-2

des: https://en.wikipedia.org/wiki/Data_Encryption_Standard

rsa: https://en.wikipedia.org/wiki/RSA_(cryptosystem)

工程配置

以windows下为例

1. 编译openssl库，得到头文件include和链接库lib和dll
2. 配置包含头文件目录和库目录
3. 工程中设置链接指定的lib：fenbieshlibssl.lib，libcrypto.lib
4. 将对应的dll拷贝到exe执行目录：libcrypto-1_1.dll， libssl-1_1.dll

linux下同理

代码

#include <iostream>
#include <cassert>
#include <string>
#include <vector>
#include "openssl/md5.h"
#include "openssl/sha.h"
#include "openssl/des.h"
#include "openssl/rsa.h"
#include "openssl/pem.h"

// ---- md5摘要哈希 ---- //
void md5(const std::string &srcStr, std::string &encodedStr, std::string &encodedHexStr)
{
    // 调用md5哈希
    unsigned char mdStr[33] = {0};
    MD5((const unsigned char *)srcStr.c_str(), srcStr.length(), mdStr);

    // 哈希后的字符串
    encodedStr = std::string((const char *)mdStr);
    // 哈希后的十六进制串 32字节
    char buf[65] = {0};
    char tmp[3] = {0};
    for (int i = 0; i < 32; i++)
    {
        sprintf(tmp, "%02x", mdStr[i]);
        strcat(buf, tmp);
    }
    buf[32] = ''; // 后面都是0，从32字节截断
    encodedHexStr = std::string(buf);
}

// ---- sha256摘要哈希 ---- //
void sha256(const std::string &srcStr, std::string &encodedStr, std::string &encodedHexStr)
{
    // 调用sha256哈希
    unsigned char mdStr[33] = {0};
    SHA256((const unsigned char *)srcStr.c_str(), srcStr.length(), mdStr);

    // 哈希后的字符串
    encodedStr = std::string((const char *)mdStr);
    // 哈希后的十六进制串 32字节
    char buf[65] = {0};
    char tmp[3] = {0};
    for (int i = 0; i < 32; i++)
    {
        sprintf(tmp, "%02x", mdStr[i]);
        strcat(buf, tmp);
    }
    buf[32] = ''; // 后面都是0，从32字节截断
    encodedHexStr = std::string(buf);
}

// ---- des对称加解密 ---- //
// 加密 ecb模式
std::string des_encrypt(const std::string &clearText, const std::string &key)
{
    std::string cipherText; // 密文

    DES_cblock keyEncrypt;
    memset(keyEncrypt, 0, 8);

    // 构造补齐后的密钥
    if (key.length() <= 8)
        memcpy(keyEncrypt, key.c_str(), key.length());
    else
        memcpy(keyEncrypt, key.c_str(), 8);

    // 密钥置换
    DES_key_schedule keySchedule;
    DES_set_key_unchecked(&keyEncrypt, &keySchedule);

    // 循环加密，每8字节一次
    const_DES_cblock inputText;
    DES_cblock outputText;
    std::vector<unsigned char> vecCiphertext;
    unsigned char tmp[8];

    for (int i = 0; i < clearText.length() / 8; i++)
    {
        memcpy(inputText, clearText.c_str() + i * 8, 8);
        DES_ecb_encrypt(&inputText, &outputText, &keySchedule, DES_ENCRYPT);
        memcpy(tmp, outputText, 8);

        for (int j = 0; j < 8; j++)
            vecCiphertext.push_back(tmp[j]);
    }

    if (clearText.length() % 8 != 0)
    {
        int tmp1 = clearText.length() / 8 * 8;
        int tmp2 = clearText.length() - tmp1;
        memset(inputText, 0, 8);
        memcpy(inputText, clearText.c_str() + tmp1, tmp2);
        // 加密函数
        DES_ecb_encrypt(&inputText, &outputText, &keySchedule, DES_ENCRYPT);
        memcpy(tmp, outputText, 8);

        for (int j = 0; j < 8; j++)
            vecCiphertext.push_back(tmp[j]);
    }

    cipherText.clear();
    cipherText.assign(vecCiphertext.begin(), vecCiphertext.end());

    return cipherText;
}

// 解密 ecb模式
std::string des_decrypt(const std::string &cipherText, const std::string &key)
{
    std::string clearText; // 明文

    DES_cblock keyEncrypt;
    memset(keyEncrypt, 0, 8);

    if (key.length() <= 8)
        memcpy(keyEncrypt, key.c_str(), key.length());
    else
        memcpy(keyEncrypt, key.c_str(), 8);

    DES_key_schedule keySchedule;
    DES_set_key_unchecked(&keyEncrypt, &keySchedule);

    const_DES_cblock inputText;
    DES_cblock outputText;
    std::vector<unsigned char> vecCleartext;
    unsigned char tmp[8];

    for (int i = 0; i < cipherText.length() / 8; i++)
    {
        memcpy(inputText, cipherText.c_str() + i * 8, 8);
        DES_ecb_encrypt(&inputText, &outputText, &keySchedule, DES_DECRYPT);
        memcpy(tmp, outputText, 8);

        for (int j = 0; j < 8; j++)
            vecCleartext.push_back(tmp[j]);
    }

    if (cipherText.length() % 8 != 0)
    {
        int tmp1 = cipherText.length() / 8 * 8;
        int tmp2 = cipherText.length() - tmp1;
        memset(inputText, 0, 8);
        memcpy(inputText, cipherText.c_str() + tmp1, tmp2);
        // 解密函数
        DES_ecb_encrypt(&inputText, &outputText, &keySchedule, DES_DECRYPT);
        memcpy(tmp, outputText, 8);

        for (int j = 0; j < 8; j++)
            vecCleartext.push_back(tmp[j]);
    }

    clearText.clear();
    clearText.assign(vecCleartext.begin(), vecCleartext.end());

    return clearText;
}


// ---- rsa非对称加解密 ---- //
#define KEY_LENGTH  2048               // 密钥长度
#define PUB_KEY_FILE "pubkey.pem"    // 公钥路径
#define PRI_KEY_FILE "prikey.pem"    // 私钥路径

// 函数方法生成密钥对
void generateRSAKey(std::string strKey[2])
{
    // 公私密钥对
    size_t pri_len;
    size_t pub_len;
    char *pri_key = NULL;
    char *pub_key = NULL;

    // 生成密钥对
    RSA *keypair = RSA_generate_key(KEY_LENGTH, RSA_3, NULL, NULL);

    BIO *pri = BIO_new(BIO_s_mem());
    BIO *pub = BIO_new(BIO_s_mem());

    PEM_write_bio_RSAPrivateKey(pri, keypair, NULL, NULL, 0, NULL, NULL);
    PEM_write_bio_RSAPublicKey(pub, keypair);

    // 获取长度
    pri_len = BIO_pending(pri);
    pub_len = BIO_pending(pub);

    // 密钥对读取到字符串
    pri_key = (char *)malloc(pri_len + 1);
    pub_key = (char *)malloc(pub_len + 1);

    BIO_read(pri, pri_key, pri_len);
    BIO_read(pub, pub_key, pub_len);

    pri_key[pri_len] = '';
    pub_key[pub_len] = '';

    // 存储密钥对
    strKey[0] = pub_key;
    strKey[1] = pri_key;

    // 存储到磁盘（这种方式存储的是begin rsa public key/ begin rsa private key开头的）
    FILE *pubFile = fopen(PUB_KEY_FILE, "w");
    if (pubFile == NULL)
    {
        assert(false);
        return;
    }
    fputs(pub_key, pubFile);
    fclose(pubFile);

    FILE *priFile = fopen(PRI_KEY_FILE, "w");
    if (priFile == NULL)
    {
        assert(false);
        return;
    }
    fputs(pri_key, priFile);
    fclose(priFile);

    // 内存释放
    RSA_free(keypair);
    BIO_free_all(pub);
    BIO_free_all(pri);

    free(pri_key);
    free(pub_key);
}

// 命令行方法生成公私钥对（begin public key/ begin private key）
// 找到openssl命令行工具，运行以下
// openssl genrsa -out prikey.pem 1024
// openssl rsa - in privkey.pem - pubout - out pubkey.pem

// 公钥加密
std::string rsa_pub_encrypt(const std::string &clearText, const std::string &pubKey)
{
    std::string strRet;
    RSA *rsa = NULL;
    BIO *keybio = BIO_new_mem_buf((unsigned char *)pubKey.c_str(), -1);
    // 此处有三种方法
    // 1, 读取内存里生成的密钥对，再从内存生成rsa
    // 2, 读取磁盘里生成的密钥对文本文件，在从内存生成rsa
    // 3，直接从读取文件指针生成rsa
    RSA* pRSAPublicKey = RSA_new();
    rsa = PEM_read_bio_RSAPublicKey(keybio, &rsa, NULL, NULL);

    int len = RSA_size(rsa);
    char *encryptedText = (char *)malloc(len + 1);
    memset(encryptedText, 0, len + 1);

    // 加密函数
    int ret = RSA_public_encrypt(clearText.length(), (const unsigned char*)clearText.c_str(), (unsigned char*)encryptedText, rsa, RSA_PKCS1_PADDING);
    if (ret >= 0)
        strRet = std::string(encryptedText, ret);

    // 释放内存
    free(encryptedText);
    BIO_free_all(keybio);
    RSA_free(rsa);

    return strRet;
}

// 私钥解密
std::string rsa_pri_decrypt(const std::string &cipherText, const std::string &priKey)
{
    std::string strRet;
    RSA *rsa = RSA_new();
    BIO *keybio;
    keybio = BIO_new_mem_buf((unsigned char *)priKey.c_str(), -1);

    // 此处有三种方法
    // 1, 读取内存里生成的密钥对，再从内存生成rsa
    // 2, 读取磁盘里生成的密钥对文本文件，在从内存生成rsa
    // 3，直接从读取文件指针生成rsa
    rsa = PEM_read_bio_RSAPrivateKey(keybio, &rsa, NULL, NULL);

    int len = RSA_size(rsa);
    char *decryptedText = (char *)malloc(len + 1);
    memset(decryptedText, 0, len + 1);

    // 解密函数
    int ret = RSA_private_decrypt(cipherText.length(), (const unsigned char*)cipherText.c_str(), (unsigned char*)decryptedText, rsa, RSA_PKCS1_PADDING);
    if (ret >= 0)
        strRet = std::string(decryptedText, ret);

    // 释放内存
    free(decryptedText);
    BIO_free_all(keybio);
    RSA_free(rsa);

    return strRet;
}

int main(int argc, char **argv)
{
    // 原始明文
    std::string srcText = "this is an example";

    std::string encryptText;
    std::string encryptHexText;
    std::string decryptText;

    std::cout << "=== 原始明文 ===" << std::endl;
    std::cout << srcText << std::endl;

    // md5
    std::cout << "=== md5哈希 ===" << std::endl;
    md5(srcText, encryptText, encryptHexText);
    std::cout << "摘要字符： " << encryptText << std::endl;
    std::cout << "摘要串： " << encryptHexText << std::endl;

    // sha256
    std::cout << "=== sha256哈希 ===" << std::endl;
    sha256(srcText, encryptText, encryptHexText);
    std::cout << "摘要字符： " << encryptText << std::endl;
    std::cout << "摘要串： " << encryptHexText << std::endl;

    // des
    std::cout << "=== des加解密 ===" << std::endl;
    std::string desKey = "12345";
    encryptText = des_encrypt(srcText, desKey);
    std::cout << "加密字符： " << std::endl;
    std::cout << encryptText << std::endl;
    decryptText = des_decrypt(encryptText, desKey);
    std::cout << "解密字符： " << std::endl;
    std::cout << decryptText << std::endl;

    // rsa
    std::cout << "=== rsa加解密 ===" << std::endl;
    std::string key[2];
    generateRSAKey(key);
    std::cout << "公钥: " << std::endl;
    std::cout << key[0] << std::endl;
    std::cout << "私钥： " << std::endl;
    std::cout << key[1] << std::endl;
    encryptText = rsa_pub_encrypt(srcText, key[0]);
    std::cout << "加密字符： " << std::endl;
    std::cout << encryptText << std::endl;
    decryptText = rsa_pri_decrypt(encryptText, key[1]);
    std::cout << "解密字符： " << std::endl;
    std::cout << decryptText << std::endl;

    system("pause");
    return 0;
}

运行结果

=== 原始明文 ===
this is an example

=== md5哈希 ===
摘要字符： 乵�驥!範
摘要串： 9202816dabaaf34bb106a10421b9a0d0
=== sha256哈希 ===
摘要字符： 訪X5衽鄁媫j/醢?17?P?4膡zD
摘要串： d44c035835f1c5e0668b7d186a2ff5b0
=== des加解密 ===
加密字符：
?/灲�取鮋t8:夽U錺?说
解密字符：
this is an example

=== rsa加解密 ===
公钥:
-----BEGIN RSA PUBLIC KEY-----
MIIBCAKCAQEA59WESdYbPsD6cYATooC4ebClTpvbTsu3X29Ha0g31kW3AmLR2zLj
hMvdWjUhhVuM7xBoh3Ufoyj4jTGHVhunFfbzxNrt1Nb64N95bZH8e9u6LjJYqh4e
sNoFknG+McjoSLNqGW9Yd8ejKH1Ju6C9SBUcC43XbB3XdC2matgV1zTsKhqjuywm
gVN9DZdo2TlZkqsvOHC23rbQ+lP09rpQJ/RI4NQSnCUBqQxErCN85trcWRj1zyJA
WaBZSvKh7J5RJcrC2ByMDmL7jrDDZl7YEolyW93SSc4xTE9Dr20OXznXNDsfQc9r
RQHBri8Aqsu4WW3tHSBRmjW5kxFMxS4qxwIBAw==
-----END RSA PUBLIC KEY-----

私钥：
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

加密字符：
佷篒?z_�&欗霐嗪K赸;J╄[i9?S絑?て晄p?[hD∞51鱠,k|1裡郿     犓鈪鑒?饞w2?`vlu
L<萿囂?圖L潥?O0�佲y▃飕E堿^桮??�,e鉀煯A�CsJ挈R聡-鳊帔!eQC乥+1(齀
я盈Xj饮[o6覾羂≯傁澓
解密字符：
this is an example

注：

（1）在读取公钥文件时，PEM_read_RSA_PUBKEY()函数和PEM_read_RSAPublicKEY()的疑惑。有时候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。

          RSA PUBLIC KEY和PUBLIC KEY的两种公钥文件其存储方式是不一样的，PEM_read_RSAPublicKEY()只能读取RSA PUBLIC KEY开头形式的公钥文件（用函数生成的）；而PEM_read_RSA_PUBKEY()只能读取PUBLIC KEY开头格式的公钥文件（用命令行生成），所以公钥私钥读取函数一定要跟生成的密钥对的格式对应起来。

（2）公钥加密和私钥解密， 私钥加密公钥解密 这两种都可以使用

（3）一般加密之后的字符串因为编码跟中文对应不上所以是乱码，在很多场合选择用十六进制串输出

（4）实际的工程应用中读取密钥对需要加安全验证

（5）用纯代码不依赖openssl库也是可以自己实现这些加解密算法的，搞清楚原理就行

http://blog.csdn.net/u012234115/article/details/72762045