我正在使用OpenSSL EVP例程来使用AES 128 cbc模式进行解密。
我使用NIST网站上指定的测试向量来测试我的程序。
程序似乎在EVP_DecryptFinal_ex例程中失败。
有人可以告诉我这是什么问题吗?
此外,我如何在此处进行错误检查以找出此例程失败的原因?
更新:
请检查以下代码。我添加了加密和解密部分。加密有效。但是在解密过程中,虽然两者的匹配结果,但密码的十六进制值似乎是80字节而不是预期的64字节(在NIST中提到),尽管解密有效并且解密的文本与明文匹配! 有人可以澄清一下吗?
预期的密文值应为:
cipher: 0000 76 49 ab ac 81 19 b2 46 ce e9 8e 9b 12 e9 19 7d
0010 50 86 cb 9b 50 72 19 ee 95 db 11 3a 91 76 78 b2
0020 73 be d6 b8 e3 c1 74 3b 71 16 e6 9e 22 22 95 16
0030 3f f1 ca a1 68 1f ac 09 12 0e ca 30 75 86 e1 a7
这是代码:
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <openssl/evp.h>
int AES_BLOCK_SIZE;
int main(int argc, char **argv)
{
EVP_CIPHER_CTX en;
EVP_CIPHER_CTX de;
EVP_CIPHER_CTX_init(&en);
EVP_CIPHER_CTX_init(&de);
const EVP_CIPHER *cipher_type;
unsigned char *mode;
unsigned char *passkey, *passiv, *plaintxt;
int vector_len = 0;
char *plain;
char *plaintext;
unsigned char *ciphertext;
int olen, len;
int i =0;
//NIST VALUES TO CHECK
unsigned char iv[] =
{ 0x00, 0x01, 0x02, 0x03,
0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x0a, 0x0b,
0x0c, 0x0d, 0x0e, 0x0f, 0 };
unsigned char key[] =
{ 0x2b, 0x7e, 0x15, 0x16,
0x28, 0xae, 0xd2, 0xa6,
0xab, 0xf7, 0x15, 0x88,
0x09, 0xcf, 0x4f, 0x3c , 0 };
unsigned char input[] =
{ 0x6b, 0xc1, 0xbe, 0xe2,
0x2e, 0x40, 0x9f, 0x96,
0xe9, 0x3d, 0x7e, 0x11,
0x73, 0x93, 0x17, 0x2a,
0xae, 0x2d, 0x8a, 0x57,
0x1e, 0x03, 0xac, 0x9c,
0x9e, 0xb7, 0x6f, 0xac,
0x45, 0xaf, 0x8e, 0x51,
0x30, 0xc8, 0x1c, 0x46,
0xa3, 0x5c, 0xe4, 0x11,
0xe5, 0xfb, 0xc1, 0x19,
0x1a, 0x0a, 0x52, 0xef,
0xf6, 0x9f, 0x24, 0x45,
0xdf, 0x4f, 0x9b, 0x17,
0xad, 0x2b, 0x41, 0x7b,
0xe6, 0x6c, 0x37, 0x10, 0 };
printf("AES ALGORITHM FOR 128 bit CBC MODE\n");
cipher_type = EVP_aes_128_cbc();
AES_BLOCK_SIZE = 128;
passkey = key;
passiv = iv;
plain = input;
printf("iv=");
for(i = 0; i < sizeof iv; i++){
printf("%02x", iv[i]);
}
printf("\n");
printf("key=");
for(i = 0; i < sizeof key; i++){
printf("%02x", key[i]);
}
printf("\n");
printf("Initializing AES ALGORITHM FOR CBC MODE..\n");
EVP_EncryptInit_ex(&en, cipher_type, NULL, passkey, passiv);
EVP_DecryptInit_ex(&de, cipher_type, NULL, passkey, passiv);
olen = len = strlen(input)+1;
printf("len value before aes_encrypt \"%d\"\n", len);
int c_len = len + AES_BLOCK_SIZE - 1;
int f_len = 0;
ciphertext = (unsigned char *)malloc(c_len);
if(!EVP_EncryptInit_ex(&en, NULL, NULL, NULL, NULL)){
printf("ERROR in EVP_EncryptInit_ex \n");
return NULL;
}
if(!EVP_EncryptUpdate(&en, ciphertext, &c_len, plain, len)){
printf("ERROR in EVP_EncryptUpdate \n");
return NULL;
}
printf("strlen value of ciphertext after update \"%d\"\n", strlen(ciphertext));
if(!EVP_EncryptFinal_ex(&en, ciphertext+c_len, &f_len)){
printf("ERROR in EVP_EncryptFinal_ex \n");
return NULL;
}
printf("strlen value of ciphertext after final \"%d\"\n", strlen(ciphertext));
EVP_CIPHER_CTX_cleanup(&en);
len = c_len + f_len;
printf("len value after aes_encrypt \"%d\"\n", len);
len = strlen(ciphertext);
printf("strlen value of ciphertext after aes_encrypt \"%d\"\n", len);
int p_len = len;
f_len = 0;
plaintext = (unsigned char *)malloc(p_len);
//memset(plaintext,0,sizeof(plaintext));
if(!EVP_DecryptInit_ex(&de, NULL, NULL, NULL, NULL)){
printf("ERROR in EVP_DecryptInit_ex \n");
return NULL;
}
EVP_CIPHER_CTX_set_padding(&de, 0);
if(!EVP_DecryptUpdate(&de, plaintext, &p_len, ciphertext, len)){
printf("ERROR in EVP_DecryptUpdate\n");
return NULL;
}
if(!EVP_DecryptFinal_ex(&de, plaintext+p_len, &f_len)){
printf("ERROR in EVP_DecryptFinal_ex\n");
return NULL;
}
EVP_CIPHER_CTX_cleanup(&de);
len = p_len + f_len;
printf("Decrypted value = %s\n", plaintext);
printf("len value after aes_decrypt \"%d\"\n", len);
if (strncmp(plaintext, input, olen))
printf("FAIL: enc/dec failed for \"%s\"\n", input);
else
printf("OK: enc/dec ok for \"%s\"\n", plaintext); // \"%s\"\n
printf("OK: ciphertext is \"%s\"\n", ciphertext); // \"%s\"\n
printf("\n");
unsigned char *s3 = ciphertext;
printf("s3 =\n");
int nc = 0;
while(*s3 != '\0'){
printf("%02x", *s3);
s3++;
nc ++;
if(nc == 16){
printf("\n");
nc = 0;
}
}
printf("\n");
//printf("nc = %d\n", nc);
free(ciphertext);
free(plaintext);
return 0;
}
答案 0 :(得分:9)
就像你需要在加密和解密时匹配密钥和IV一样,你还需要匹配填充设置。 NIST测试没有填充。以下是OpenSSL documentation的摘录:
EVP_DecryptInit_ex(), EVP_DecryptUpdate()和 EVP_DecryptFinal_ex()是 相应的解密操作。 EVP_DecryptFinal()将返回一个 如果填充已启用,则为错误代码 最后一个块不正确 格式化即可。参数和 限制与 加密操作除了if padding启用解密数据 缓冲区传递给 EVP_DecryptUpdate()应该有 足够的空间(inl + cipher_block_size)字节除非 在这种情况下,密码块大小为1 inl字节就足够了。
搜索同一页面的“填充”,您会看到函数EVP_CIPHER_CTX_set_padding
:
EVP_CIPHER_CTX_set_padding()启用 或禁用填充。默认情况下 加密操作使用填充 标准块填充和填充 检查并删除时 解密。如果pad参数是 零然后没有执行填充, 加密的数据总量或 然后解密必须是倍数 将出现块大小或错误。
因此,在您致电EVP_CIPHER_CTX_init
并开始解密之前的某个时刻,您需要这样做:
EVP_CIPHER_CTX_set_padding(&de, 0);
答案 1 :(得分:3)
要在OpenSSL功能失败后显示错误,您可以使用:
ERR_print_errors_fp(stderr);
答案 2 :(得分:0)
我在EVP_DecryptFinal_ex例程中遇到了同样的问题。我发现你不会通过strlen(ciphertext)
获得密文的长度,因为函数strlen()
返回C字符串的长度。
加密后的密文可以包含被认为是C字符串结尾的'\ 0'字符,因此您将无法获得具有函数strlen()
的正确长度的密文。
相反,您应该记住加密后密文的长度。在您的计划中,您可以使用c_len
和f_len
:
if(!EVP_EncryptUpdate(&en, ciphertext, &c_len, plain, len)){
printf("ERROR in EVP_EncryptUpdate \n");
return NULL;
}//Here you get length of ciphertext in c_len
printf("strlen value of ciphertext after update \"%d\"\n", strlen(ciphertext));
if(!EVP_EncryptFinal_ex(&en, ciphertext+c_len, &f_len)){
printf("ERROR in EVP_EncryptFinal_ex \n");
return NULL;
}//Here you get the rest of padded ciphertext in f_len
//This printf won't print out the real lengt of ciphertext you should put in (c_len+f_len)
printf("strlen value of ciphertext after final \"%d\"\n", strlen(ciphertext));
EVP_CIPHER_CTX_cleanup(&en);
len = c_len + f_len;//This is the real length of ciphertext
printf("len value after aes_encrypt \"%d\"\n", len);
len = strlen(ciphertext);//And here you rewrite it, delete this line and you should get it right
另一件事,当您打印出密文时,不要使用:
printf("OK: ciphertext is \"%s\"\n", ciphertext);
“%s”也被视为C字符串,只能打印出整个密文的一部分。改为使用:
int i = 0;
printf("\nCiphertext:");
for(i = 0; i < len; i++)//variable len is length of ciphertext memorized after encryption.
{printf("%c",ciphertext[i]);}