AES加密和解密——使用openssl编程

AES是一套对称密钥的密码术，目前已广泛使用，用于替代已经不够安全的DES算法。所谓对称密钥，就是说加密和解密用的是同一个密钥，消息的发送方和接收方在消息传递前需要享有这个密钥。和非对称密钥体系不同，这里的密钥是双方保密的，不会让任何第三方知道。

对称密钥加密法主要基于块加密，选取固定长度的密钥，去加密明文中固定长度的块，生成的密文块与明文块长度一样。显然密钥长度十分重要，块的长度也很重要。如果太短，则很容易枚举出所有的明文-密文映射；如果太长，性能则会急剧下降。AES中规定块长度为128 bit，而密钥长度可以选择128, 192或256 bit 。暴力破解密钥需要万亿年，这保证了AES的安全性。

AES的算法较为复杂，在此不细加阐述。下面是使用openssl进行AES加密和解密的示例程序：

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<pre class="cpp" courier="" new",="" courier,="" "lucida="" console",="" monaco,="" "dejavu="" sans="" mono",="" "nimbus="" mono="" l",="" "bitstream="" vera="" "microsoft="" yahei";"="" style="margin-top: 0px; margin-bottom: 0px; padding: 0.8em; font-family: 'Courier New', Courier, 'Lucida Console', Monaco, 'DejaVu Sans Mono', 'Nimbus Mono L', 'Bitstream Vera Sans Mono'; overflow: visible; background-color: rgb(255, 255, 255); width: auto; border: 1px solid rgb(221, 221, 221); float: none; clear: none; line-height: 1.333; ">/** aes.cc* - Show the usage of AES encryption/decryption*/ #include <stdio.h>#include <string.h>#include <stdlib.h>#include <openssl/aes.h> int main(int argc, char** argv) { AES_KEY aes; unsigned char key[AES_BLOCK_SIZE]; // AES_BLOCK_SIZE = 16 unsigned char iv[AES_BLOCK_SIZE]; // init vector unsigned char* input_string; unsigned char* encrypt_string; unsigned char* decrypt_string; unsigned int len; // encrypt length (in multiple of AES_BLOCK_SIZE) unsigned int i; // check usage if (argc != 2) { fprintf(stderr, "%s <plain text>\n", argv[0]); exit(-1); } // set the encryption length len = 0; if ((strlen(argv[1]) + 1) % AES_BLOCK_SIZE == 0) { len = strlen(argv[1]) + 1; } else { len = ((strlen(argv[1]) + 1) / AES_BLOCK_SIZE + 1) * AES_BLOCK_SIZE; } // set the input string input_string = (unsigned char*)calloc(len, sizeof(unsigned char)); if (input_string == NULL) { fprintf(stderr, "Unable to allocate memory for input_string\n"); exit(-1); } strncpy((char*)input_string, argv[1], strlen(argv[1])); // Generate AES 128-bit key for (i=0; i<16; ++i) { key[i] = 32 + i; } // Set encryption key for (i=0; i<AES_BLOCK_SIZE; ++i) { iv[i] = 0; } if (AES_set_encrypt_key(key, 128, &aes) < 0) { fprintf(stderr, "Unable to set encryption key in AES\n"); exit(-1); } // alloc encrypt_string encrypt_string = (unsigned char*)calloc(len, sizeof(unsigned char)); if (encrypt_string == NULL) { fprintf(stderr, "Unable to allocate memory for encrypt_string\n"); exit(-1); } // encrypt (iv will change) AES_cbc_encrypt(input_string, encrypt_string, len, &aes, iv, AES_ENCRYPT); // alloc decrypt_string decrypt_string = (unsigned char*)calloc(len, sizeof(unsigned char)); if (decrypt_string == NULL) { fprintf(stderr, "Unable to allocate memory for decrypt_string\n"); exit(-1); } // Set decryption key for (i=0; i<AES_BLOCK_SIZE; ++i) { iv[i] = 0; } if (AES_set_decrypt_key(key, 128, &aes) < 0) { fprintf(stderr, "Unable to set decryption key in AES\n"); exit(-1); } // decrypt AES_cbc_encrypt(encrypt_string, decrypt_string, len, &aes, iv, AES_DECRYPT); // print printf("input_string = %s\n", input_string); printf("encrypted string = "); for (i=0; i<len; ++i) { printf("%x%x", (encrypt_string[i] >> 4) & 0xf, encrypt_string[i] & 0xf); } printf("\n"); printf("decrypted string = %s\n", decrypt_string); return 0;}

编译Makefile:

<pre class="cmake" courier="" new",="" courier,="" "lucida="" console",="" monaco,="" "dejavu="" sans="" mono",="" "nimbus="" mono="" l",="" "bitstream="" vera="" "microsoft="" yahei";"=""
style="margin-top: 0px; margin-bottom: 0px; padding: 0.8em; font-family: 'Courier New', Courier, 'Lucida Console', Monaco, 'DejaVu Sans Mono', 'Nimbus Mono L', 'Bitstream Vera Sans Mono'; overflow: visible; font-size: 12px; background-color: rgb(255, 255,
255); width: auto; border: 1px solid rgb(221, 221, 221); float: none; clear: none; line-height: 1.333; ">CC=g++CFLAGS=-Wall -g -O2LIBS=-lcrypto all: aes aes: aes.cc $(CC)
$(CFLAGS)
aes.cc -o $@ $(LIBS) clean:
@rm -f aes

转自 http://www.lovelucy.info/openssl-aes-encryption.html