Linux libcrypto AES-128 CBC加密/解密只能在Ubuntu上使用，而不能在Raspberry Pi上使用 [英] Linux libcrypto AES-128 CBC Encryption/Decryption works on Ubuntu but not Raspberry Pi

问题描述

以下示例在64位桌面Ubuntu 16.04上正确地加密和解密为相同的原始字符串，但是当在Raspberry Pi(ARM)(以及另一个自定义Linux ARM板)上编译并运行相同的代码时，它将失败解密为原始字符串. Raspberry Pi和另一块ARM板都解密为相同但不正确的值.

The following example encrypts and decrypts to the same original string properly on a 64-bit Desktop Ubuntu 16.04, but when the same code is compiled and run on Raspberry Pi ( ARM ) ( and also another custom Linux ARM board ) it fails to decrypt to the original string. Both the Raspberry Pi and the other ARM board decrypt to the same, but incorrect, value.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/aes.h>
#include <openssl/crypto.h>

/* AES key for Encryption and Decryption */
const static unsigned char aes_key[]={0x00,0x11,0x22,0x33,0x44,0x55,0x66,0x77,0x88,0x99,0xAA,0xBB,0xCC,0xDD,0xEE,0xFF};

/* Print Encrypted and Decrypted data packets */
void print_data(const char *tittle, const void* data, int len);

int main( )
{
    /* Input data to encrypt */
    unsigned char aes_input[]={0x0,0x1,0x2,0x3,0x4,0x5};

    fprintf(stderr,"%s\n",SSLeay_version(SSLEAY_VERSION));

    /* Init vector */
    unsigned char iv[AES_BLOCK_SIZE];
    memset(iv, 0x00, AES_BLOCK_SIZE);

    /* Buffers for Encryption and Decryption */
    unsigned char enc_out[sizeof(aes_input)];
    unsigned char dec_out[sizeof(aes_input)];

    /* AES-128 bit CBC Encryption */
    AES_KEY enc_key, dec_key;
    AES_set_encrypt_key(aes_key, sizeof(aes_key)*8, &enc_key);
    AES_cbc_encrypt(aes_input, enc_out, sizeof(aes_input), &enc_key, iv,         AES_ENCRYPT);
    /* AES-128 bit CBC Decryption */
    memset(iv, 0x00, AES_BLOCK_SIZE); // don't forget to set iv vector again, else you can't decrypt data properly
    AES_set_decrypt_key(aes_key, sizeof(aes_key)*8, &dec_key); // Size of key is in bits
    AES_cbc_encrypt(enc_out, dec_out, sizeof(aes_input), &dec_key, iv, AES_DECRYPT);

    /* Printing and Verifying */
    print_data("\n Original ",aes_input, sizeof(aes_input)); // you can not print data as a string, because after Encryption its not ASCII

    print_data("\n Encrypted",enc_out, sizeof(enc_out));

    print_data("\n Decrypted",dec_out, sizeof(dec_out));

    return 0;
}

void print_data(const char *tittle, const void* data, int len)
{
    printf("%s : ",tittle);
    const unsigned char * p = (const unsigned char*)data;
    int i = 0;

    for (; i<len; ++i)
        printf("%02X ", *p++);

    printf("\n");
}

Ubuntu结果:

 OpenSSL 1.0.1f 6 Jan 2014

 Original  : 00 01 02 03 04 05 

 Encrypted : D5 40 D0 BB 16 1D 

 Decrypted : 00 01 02 03 04 05 

Raspberry Pi结果:

Raspberry Pi result:

OpenSSL 1.0.2l  25 May 2017

Original  : 00 01 02 03 04 05 

Encrypted : D5 40 D0 BB 16 1D 

Decrypted : D3 87 81 20 2B B9

自定义论坛结果:

OpenSSL 1.1.0f  25 May 2017

Original  : 00 01 02 03 04 05 

Encrypted : D5 40 D0 BB 16 1D 

Decrypted : D3 87 81 20 2B B9 

自定义面板(已更新OpenSSL以与Ubuntu匹配):

Custom Board ( Updated OpenSSL to match Ubuntu ):

 OpenSSL 1.0.1f 6 Jan 2014

 Original  : 00 01 02 03 04 05 

 Encrypted : D5 40 D0 BB 16 1D 

 Decrypted : D3 87 81 20 2B B9

为什么开源libcrypto在Ubuntu和2台不同的ARM机器上的行为不同?

Why does open source libcrypto not behave the same on Ubuntu and 2 different ARM machines?

推荐答案

通常在CBC模式下，您使用的缓冲区大小是密码的块大小的倍数.这是CBC的本质，在CBC类型例程的每个openssl手册页中都提到了这一点(不幸的是，我在AES_cbc_encrypt上找不到手册页或任何文档).

Normally with the CBC mode, you use a buffer of size which is a multiple of the block size of your cipher. This is the nature of CBC and it is mentioned in every openssl man page on CBC type routines (unfortunately I couldn't find a man page or any documentation on AES_cbc_encrypt).

运气不好，似乎在某些平台上可以使用错误的缓冲区大小.若要查看实际情况，请为enc_out多分配一个字节，并在加密后将该多余的字节清零.解密将失败.

The wrong buffer size appears to work on some platforms by sheer luck. To see what really happens, allocate one byte more for enc_out and zero out that extra byte after encryption. Decryption will fail.

unsigned char enc_out[sizeof(aes_input) + 1];
...
AES_cbc_encrypt(aes_input, enc_out, sizeof(aes_input), &enc_key, iv, AES_ENCRYPT);
enc_out[sizeof(aes_input)] = 0;

在我的机器上输出修改后的代码:

Output of the modified code on my machine:

Original  : 00 01 02 03 04 05 

Encrypted : D5 40 D0 BB 16 1D 00 

Decrypted : 89 FB 06 F4 CD 6A 

未经修改的代码将产生正确的"输出.

Unmodified code produces the "correct" output.

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