我正在尝试编写一个示例程序来使用 Openssl 进行 AES 加密。
这个答案有点受欢迎，所以我将提供一些更新的东西，因为 OpenSSL 添加了一些可能会对您有所帮助的操作模式。
首先，不要使用AES_encrypt 和AES_decrypt。它们级别低，更难使用。此外，它是一个纯软件例程，它从不使用硬件加速，如 AES-NI。最后，它在一些不知名的平台上会遇到字节序问题。
改为使用EVP_* 接口。 EVP_* 函数使用硬件加速，如 AES-NI（如果可用）。而且它不会在晦涩的平台上遇到字节序问题。
其次，您可以使用像CBC这样的模式，但密文将缺乏完整性和真实性保证。所以你通常需要像 EAX、CCM 或 GCM 这样的模式。 （或者您必须在使用单独的密钥加密后手动应用 HMAC。）
第三，OpenSSL 有一个您可能会感兴趣的 wiki 页面：EVP Authenticated Encryption and Decryption。它使用 GCM 模式。
最后，这是使用 AES/GCM 进行加密的程序。 OpenSSL wiki 示例就是基于它。
#include <openssl/evp.h>
#include <openssl/aes.h>
#include <openssl/err.h>
#include <string.h>
int main(int arc, char *argv[])
{
OpenSSL_add_all_algorithms();
ERR_load_crypto_strings();
/* Set up the key and iv. Do I need to say to not hard code these in a real application? :-) */
/* A 256 bit key */
static const unsigned char key[] = "01234567890123456789012345678901";
/* A 128 bit IV */
static const unsigned char iv[] = "0123456789012345";
/* Message to be encrypted */
unsigned char plaintext[] = "The quick brown fox jumps over the lazy dog";
/* Some additional data to be authenticated */
static const unsigned char aad[] = "Some AAD data";
/* Buffer for ciphertext. Ensure the buffer is long enough for the
* ciphertext which may be longer than the plaintext, dependant on the
* algorithm and mode
*/
unsigned char ciphertext[128];
/* Buffer for the decrypted text */
unsigned char decryptedtext[128];
/* Buffer for the tag */
unsigned char tag[16];
int decryptedtext_len = 0, ciphertext_len = 0;
/* Encrypt the plaintext */
ciphertext_len = encrypt(plaintext, strlen(plaintext), aad, strlen(aad), key, iv, ciphertext, tag);
/* Do something useful with the ciphertext here */
printf("Ciphertext is:\n");
BIO_dump_fp(stdout, ciphertext, ciphertext_len);
printf("Tag is:\n");
BIO_dump_fp(stdout, tag, 14);
/* Mess with stuff */
/* ciphertext[0] ^= 1; */
/* tag[0] ^= 1; */
/* Decrypt the ciphertext */
decryptedtext_len = decrypt(ciphertext, ciphertext_len, aad, strlen(aad), tag, key, iv, decryptedtext);
if(decryptedtext_len < 0)
{
/* Verify error */
printf("Decrypted text failed to verify\n");
}
else
{
/* Add a NULL terminator. We are expecting printable text */
decryptedtext[decryptedtext_len] = '\0';
/* Show the decrypted text */
printf("Decrypted text is:\n");
printf("%s\n", decryptedtext);
}
/* Remove error strings */
ERR_free_strings();
return 0;
}
void handleErrors(void)
{
unsigned long errCode;
printf("An error occurred\n");
while(errCode = ERR_get_error())
{
char *err = ERR_error_string(errCode, NULL);
printf("%s\n", err);
}
abort();
}
int encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *aad,
int aad_len, unsigned char *key, unsigned char *iv,
unsigned char *ciphertext, unsigned char *tag)
{
EVP_CIPHER_CTX *ctx = NULL;
int len = 0, ciphertext_len = 0;
/* Create and initialise the context */
if(!(ctx = EVP_CIPHER_CTX_new())) handleErrors();
/* Initialise the encryption operation. */
if(1 != EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL))
handleErrors();
/* Set IV length if default 12 bytes (96 bits) is not appropriate */
if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))
handleErrors();
/* Initialise key and IV */
if(1 != EVP_EncryptInit_ex(ctx, NULL, NULL, key, iv)) handleErrors();
/* Provide any AAD data. This can be called zero or more times as
* required
*/
if(aad && aad_len > 0)
{
if(1 != EVP_EncryptUpdate(ctx, NULL, &len, aad, aad_len))
handleErrors();
}
/* Provide the message to be encrypted, and obtain the encrypted output.
* EVP_EncryptUpdate can be called multiple times if necessary
*/
if(plaintext)
{
if(1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
handleErrors();
ciphertext_len = len;
}
/* Finalise the encryption. Normally ciphertext bytes may be written at
* this stage, but this does not occur in GCM mode
*/
if(1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len)) handleErrors();
ciphertext_len += len;
/* Get the tag */
if(1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, tag))
handleErrors();
/* Clean up */
EVP_CIPHER_CTX_free(ctx);
return ciphertext_len;
}
int decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *aad,
int aad_len, unsigned char *tag, unsigned char *key, unsigned char *iv,
unsigned char *plaintext)
{
EVP_CIPHER_CTX *ctx = NULL;
int len = 0, plaintext_len = 0, ret;
/* Create and initialise the context */
if(!(ctx = EVP_CIPHER_CTX_new())) handleErrors();
/* Initialise the decryption operation. */
if(!EVP_DecryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL))
handleErrors();
/* Set IV length. Not necessary if this is 12 bytes (96 bits) */
if(!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 16, NULL))
handleErrors();
/* Initialise key and IV */
if(!EVP_DecryptInit_ex(ctx, NULL, NULL, key, iv)) handleErrors();
/* Provide any AAD data. This can be called zero or more times as
* required
*/
if(aad && aad_len > 0)
{
if(!EVP_DecryptUpdate(ctx, NULL, &len, aad, aad_len))
handleErrors();
}
/* Provide the message to be decrypted, and obtain the plaintext output.
* EVP_DecryptUpdate can be called multiple times if necessary
*/
if(ciphertext)
{
if(!EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len))
handleErrors();
plaintext_len = len;
}
/* Set expected tag value. Works in OpenSSL 1.0.1d and later */
if(!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, 16, tag))
handleErrors();
/* Finalise the decryption. A positive return value indicates success,
* anything else is a failure - the plaintext is not trustworthy.
*/
ret = EVP_DecryptFinal_ex(ctx, plaintext + len, &len);
/* Clean up */
EVP_CIPHER_CTX_free(ctx);
if(ret > 0)
{
/* Success */
plaintext_len += len;
return plaintext_len;
}
else
{
/* Verify failed */
return -1;
}
}