使用Openssl的AES加密算法

来源：互联网发布：电视盒子无法安软件编辑：程序博客网时间：2024/05/21 18:32

http://blog.gpjtag.com/?p=18

在网络应用的信息安全是基于密码学的，所以如果想做安全方面的邻域需要有一定的密码学基础。当然最好的学习方法就是边看书边尝试。

我的学习过程有三个阶段：

看书、通过使用一些软件了解基本的流程。
深入算法，自己实现部分加密算法。
了解常用的库的用法。

有人说“不要重复造轮子，有现成的要拿来用。”我赞同，但是这个的前提是你造过轮子，知道装配轮子的时候会有什么注意事项:)

所以在学习的过程中一定要“自己造轮子”，在工作的时候一定要“找轮子，用现成的”:)

Openssl是很常见的C接口的库，个人觉得易用。以下是AES加密的使用备忘。如果你有一定的密码学基础，那么就很好理解。代码是从网上弄下来的（原始地址已经忘记了），然后在尝试的过程中改了一点东西。其它的cbc、cfb、ecb加密方式的用法都是类似的，只是函数名有点区别，就不一一列举了。

一、接口简介

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//设置加密密钥，使用字符缓冲区
intAES_set_encrypt_key(
        constunsigned char*userKey,
        constint bits,
        AES_KEY *key);
 
//设置解密密钥，同样适用字符缓冲区
intAES_set_decrypt_key(
        constunsigned char*userKey,
        constint bits,
        AES_KEY *key);
 
//加解密的接口，通过最后的enc来区分是加密还是解密操作
//每次执行AES_cbc_encrypt后，iv（向量）会被更新，
//所以需要自己保存它。
voidAES_cbc_encrypt(
        constunsigned char*in,
        unsignedchar*out,
        constunsigned longlength,
        constAES_KEY *key,
        unsignedchar*ivec,
        constint enc);

二、一个简单的Makefile

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CFLAGS = /nologo /I .. /c /Fo./objs/
LFLAGS = /nologo
LLIBS  = ../lib/ssleay32MD.lib ../lib/libeay32MD.lib
all:./release/testaes.exe
 
./release/testaes.exe:./objs/testaes.obj
        link $(LFLAGS) ./objs/testaes.obj $(LLIBS) \
                /out:./release/testaes.exe
 
{.}.cpp{./objs}.obj:
        cl $(CFLAGS) $<
 
clean:
        rm -rf *.obj

三、示例代码

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#include <stdio.h>
#include <string.h>
#include <openssl/aes.h>
#include <openssl/rand.h>
 
/* file testaes.cpp */
 
staticvoid hexdump(
                FILE*f,
                constchar *title,
                constunsigned char*s,
                intl)
{
    intn = 0;
 
    fprintf(f,"%s", title);
    for(; n < l; ++n) {
        if((n % 16) == 0) {
                fprintf(f,"\n%04x", n);
        }
        fprintf(f," %02x", s[n]);
    }
 
    fprintf(f,"\n");
}
 
intmain(intargc, char**argv)
{
        //256bits key.
        unsignedchar  rkey[16];
        //Internal key.
        AES_KEY         key;
 
        //Testdata.
        unsignedchar  plaintext[AES_BLOCK_SIZE * 4];
        unsignedchar  ciphertext[AES_BLOCK_SIZE * 4];
        unsignedchar  checktext[AES_BLOCK_SIZE * 4];
 
        //Init vector.
        unsignedchar  iv[AES_BLOCK_SIZE * 4];
        //Save vector.
        unsignedchar  saved_iv[AES_BLOCK_SIZE * 4];
 
        intnr_of_bits = 0;
        intnr_of_bytes = 0;
 
        //Zeror buffer.
        memset(plaintext, 0, sizeofplaintext);
        memset(ciphertext, 0, sizeofciphertext);
        memset(checktext, 0, sizeofchecktext);
 
        //Generate random
        RAND_pseudo_bytes(rkey,sizeofrkey);
        RAND_pseudo_bytes(plaintext,sizeofplaintext);
        RAND_pseudo_bytes(saved_iv,sizeofsaved_iv);
 
        hexdump(stdout,"== rkey ==",
                        rkey,
                        sizeof(rkey));
        hexdump(stdout,"== iv ==",
                        saved_iv,
                        sizeof(saved_iv));
        printf("\n");
 
        hexdump(stdout,"== plaintext ==",
                        plaintext,
                        sizeof(plaintext));
        printf("\n");
 
        //Entrypt
        memcpy(iv, saved_iv, sizeof(iv));
        nr_of_bits = 8 * sizeof(rkey);
        AES_set_encrypt_key(rkey, nr_of_bits, &key);
        nr_of_bytes = sizeof(plaintext);
        AES_cbc_encrypt(plaintext,
                        ciphertext,
                        nr_of_bytes,
                        &key,
                        iv,
                        AES_ENCRYPT);
 
        hexdump(stdout,"== ciphertext ==",
                        ciphertext,
                        sizeof(ciphertext));
        printf("\n");
 
        //Decrypt
        memcpy(iv, saved_iv, sizeof(iv));
        nr_of_bytes = 8 * sizeof(rkey);
        AES_set_decrypt_key(rkey, nr_of_bits, &key);
        nr_of_bytes = sizeof(ciphertext) / 2;
        //Decrypt in two step:)
        AES_cbc_encrypt(ciphertext,
                        checktext,
                        nr_of_bytes,
                        &key, iv,
                        AES_DECRYPT);
        AES_cbc_encrypt(
                        ciphertext + nr_of_bytes,
                        checktext + nr_of_bytes,
                        nr_of_bytes,
                        &key,
                        iv,
                        AES_DECRYPT);
        hexdump(stdout,"== checktext ==",
                        checktext,
                        sizeof(checktext));
        printf("\n");
 
        return0;
}

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