我正在尝试编译以下程序：
#include <openssl/conf.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#include <openssl/crypto.h>
#include <string.h>
int main (void)
{
/* Set up the key and iv. Do I need to say to not hard code these in a
* real application? :-)
*/
/* A 256 bit key */
unsigned char *key = (unsigned char *)"01234567890123456789012345678901";
/* A 128 bit IV */
unsigned char *iv = (unsigned char *)"01234567890123456";
/* Message to be encrypted */
unsigned char *plaintext =
(unsigned char *)"The quick brown fox jumps over the lazy dog";
/* 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];
int decryptedtext_len, ciphertext_len;
/* Initialise the library */
ERR_load_crypto_strings();
OpenSSL_add_all_algorithms();
OPENSSL_config(NULL);
/* Encrypt the plaintext */
ciphertext_len = encrypt (plaintext, strlen ((char *)plaintext), key, iv,
ciphertext);
/* Do something useful with the ciphertext here */
printf("Ciphertext is:\n");
BIO_dump_fp (stdout, (const char *)ciphertext, ciphertext_len);
/* Decrypt the ciphertext */
decryptedtext_len = decrypt(ciphertext, ciphertext_len, key, iv,
decryptedtext);
/* 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);
/* Clean up */
EVP_cleanup();
ERR_free_strings();
return 0;
}
int encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key,
unsigned char *iv, unsigned char *ciphertext)
{
EVP_CIPHER_CTX *ctx;
int len;
int ciphertext_len;
/* Create and initialise the context */
if(!(ctx = EVP_CIPHER_CTX_new())) handleErrors();
/* Initialise the encryption operation. IMPORTANT - ensure you use a key
* and IV size appropriate for your cipher
* In this example we are using 256 bit AES (i.e. a 256 bit key). The
* IV size for *most* modes is the same as the block size. For AES this
* is 128 bits */
if(1 != EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, key, iv))
handleErrors();
/* Provide the message to be encrypted, and obtain the encrypted output.
* EVP_EncryptUpdate can be called multiple times if necessary
*/
if(1 != EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len))
handleErrors();
ciphertext_len = len;
/* Finalise the encryption. Further ciphertext bytes may be written at
* this stage.
*/
if(1 != EVP_EncryptFinal_ex(ctx, ciphertext + len, &len)) handleErrors();
ciphertext_len += len;
/* Clean up */
EVP_CIPHER_CTX_free(ctx);
return ciphertext_len;
}
int decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
unsigned char *iv, unsigned char *plaintext)
{
EVP_CIPHER_CTX *ctx;
int len;
int plaintext_len;
/* Create and initialise the context */
if(!(ctx = EVP_CIPHER_CTX_new())) handleErrors();
/* Initialise the decryption operation. IMPORTANT - ensure you use a key
* and IV size appropriate for your cipher
* In this example we are using 256 bit AES (i.e. a 256 bit key). The
* IV size for *most* modes is the same as the block size. For AES this
* is 128 bits */
if(1 != EVP_DecryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, key, iv))
handleErrors();
/* Provide the message to be decrypted, and obtain the plaintext output.
* EVP_DecryptUpdate can be called multiple times if necessary
*/
if(1 != EVP_DecryptUpdate(ctx, plaintext, &len, ciphertext, ciphertext_len))
handleErrors();
plaintext_len = len;
/* Finalise the decryption. Further plaintext bytes may be written at
* this stage.
*/
if(1 != EVP_DecryptFinal_ex(ctx, plaintext + len, &len)) handleErrors();
plaintext_len += len;
/* Clean up */
EVP_CIPHER_CTX_free(ctx);
return plaintext_len;
}
void handleErrors(void)
{
ERR_print_errors_fp(stderr);
abort();
}
此计划来自https://wiki.openssl.org/index.php/EVP_Symmetric_Encryption_and_Decryption
无论如何，当我尝试编译它时，我得到以下错误：
test.c: In function âmainâ:
test.c:39:3: warning: âOPENSSL_configâ is deprecated [-Wdeprecated-declarations]
OPENSSL_config(NULL);
^
In file included from /usr/local/include/openssl/crypto.h:32:0,
from /usr/local/include/openssl/bio.h:20,
from /usr/local/include/openssl/conf.h:13,
from test.c:1:
/usr/local/include/openssl/conf.h:92:1: note: declared here
DEPRECATEDIN_1_1_0(void OPENSSL_config(const char *config_name))
^
test.c:42:20: warning: implicit declaration of function âencryptâ [-Wimplicit-function-declaration]
ciphertext_len = encrypt (plaintext, strlen ((char *)plaintext), key, iv,
^
test.c:50:23: warning: implicit declaration of function âdecryptâ [-Wimplicit-function-declaration]
decryptedtext_len = decrypt(ciphertext, ciphertext_len, key, iv,
^
test.c: In function âencryptâ:
test.c:78:37: warning: implicit declaration of function âhandleErrorsâ [-Wimplicit-function-declaration]
if(!(ctx = EVP_CIPHER_CTX_new())) handleErrors();
^
test.c: At top level:
test.c:150:6: warning: conflicting types for âhandleErrorsâ
void handleErrors(void)
^
test.c:78:37: note: previous implicit declaration of âhandleErrorsâ was here
if(!(ctx = EVP_CIPHER_CTX_new())) handleErrors();
^
/tmp/ccmG8aWM.o: In function `main':
test.c:(.text+0x47): undefined reference to `OPENSSL_init_crypto'
test.c:(.text+0x58): undefined reference to `OPENSSL_init_crypto'
test.c:(.text+0x65): undefined reference to `OPENSSL_config'
test.c:(.text+0xd1): undefined reference to `BIO_dump_fp'
/tmp/ccmG8aWM.o: In function `encrypt':
test.c:(.text+0x186): undefined reference to `EVP_CIPHER_CTX_new'
test.c:(.text+0x199): undefined reference to `EVP_aes_256_cbc'
test.c:(.text+0x1ad): undefined reference to `EVP_EncryptInit_ex'
test.c:(.text+0x1d2): undefined reference to `EVP_EncryptUpdate'
test.c:(.text+0x1ff): undefined reference to `EVP_EncryptFinal_ex'
test.c:(.text+0x21d): undefined reference to `EVP_CIPHER_CTX_free'
/tmp/ccmG8aWM.o: In function `decrypt':
test.c:(.text+0x264): undefined reference to `EVP_CIPHER_CTX_new'
test.c:(.text+0x277): undefined reference to `EVP_aes_256_cbc'
test.c:(.text+0x28b): undefined reference to `EVP_DecryptInit_ex'
test.c:(.text+0x2b0): undefined reference to `EVP_DecryptUpdate'
test.c:(.text+0x2dd): undefined reference to `EVP_DecryptFinal_ex'
test.c:(.text+0x2fb): undefined reference to `EVP_CIPHER_CTX_free'
/tmp/ccmG8aWM.o: In function `handleErrors':
test.c:(.text+0x328): undefined reference to `ERR_print_errors_fp'
collect2: error: ld returned 1 exit status
我在源代码中添加了#include <openssl/crypto.h>，因为https://www.openssl.org/docs/man1.1.0/crypto/OPENSSL_init_crypto.html暗示它存在，我仍然会收到“未定义的引用”错误。
有什么想法吗？
答案 0 :(得分：3)
您包含的头文件为您提供了OpenSSL函数的声明。但是，实际的库仍然需要链接。
编译时，需要将-lcrypto添加到gcc命令行的末尾，以便在OpenSSL加密库中进行链接。
此外，在定义它们之前，您在自己的代码中使用了函数。因此，编译器隐式声明它们接受任意数量的参数并返回int。因为这与实际声明匹配，所以会导致未定义的行为。
您应该为文件顶部的每个函数创建声明。这样，其他功能就知道如何调用它们。
#include <openssl/conf.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#include <openssl/crypto.h>
#include <string.h>
int encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key,
unsigned char *iv, unsigned char *ciphertext);
int decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
unsigned char *iv, unsigned char *plaintext);
void handleErrors(void);
int main(void)
{
...