AES 128 CBC：如何計算正確的IV？

Question

<?php 

$data = ' 
    -What is the answer to the Ultimate Question of Life, the Universe, and Everything ? 
    -42 
'; 
$method = 'AES-128-CBC'; 
$password = 'secret password'; 
$raw_output = $raw_input = true; 

$iv_len = openssl_cipher_iv_length($method); 
$iv = openssl_random_pseudo_bytes($iv_len); 

$encrypted = openssl_encrypt($data, $method, $password, $raw_output, $iv); 
var_dump($encrypted); 


echo 'Decryption with known IV: OK'; 
$decrypted = openssl_decrypt($encrypted, $method, $password, $raw_input, $iv); 
var_dump($decrypted); 

echo 'Decryption with calculated IV: Fail<br><br>'; 
$iv = substr($encrypted, 0, $iv_len); 
echo 'Without substring'; 
$decrypted = openssl_decrypt($encrypted, $method, $password, $raw_input, $iv); 
var_dump($decrypted); 
echo 'With substring'; 
$encrypted = substr($encrypted, $iv_len); 
$decrypted = openssl_decrypt($encrypted, $method, $password, $raw_input, $iv); 
var_dump($decrypted); 

我在做什麼錯？

Answer 1

看來你似乎假設你的IV是在加密輸出的開始，但你並沒有明確地把它放在那裏。

嘗試：

$encrypted = $iv . openssl_encrypt($data, $method, $password, $raw_output, $iv); 

，並嘗試與解密：

$iv = substr($encrypted, 0, $iv_len); 
$encrypted = substr($encrypted, $iv_len); 
$decrypted = openssl_decrypt($encrypted, $method, $password, $raw_input, $iv); 
var_dump($decrypted);