PHP使用密码和盐来获得C＃Rfc2898DeriveBytes（AES256）的IV和Key替代方案

Question

I want to regenerate my IV and Key from the password and salt I have stored. In my C# program I do It in the following way :

//passwordBytes = SHA256.Create().ComputeHash(passwordBytes);
var key = new Rfc2898DeriveBytes(passwordBytes, saltBytes, 1000);
AES.Key = key.GetBytes(AES.KeySize / 8);
AES.IV = key.GetBytes(AES.BlockSize / 8);

The code for this is PHP returning is return a different IV and Key :

<?php
include("enctest_inc.php");

$password = "mypassword";
$salt = "mysalthereitis";

$hasher = "SHA256";
$iterations = 1000;
$keysize = 256;
$ivsize = 128;

$out = pbkdf2($hasher, $password, base64_decode($salt), $iterations, ($keysize+$ivsize)/8, true);

// split key and IV
$key = substr($out, 0, $keysize/8);
$iv = substr($out, $ivsize/8);

// print for demonstration purposes
echo base64_encode($key);
echo "<br>";
echo base64_encode($iv);
echo '<br>';
echo '<br>';

echo 'KEY : LNY893Wa00onNQh4ignFdjaVkg6GdxomMZoR/axB+Mw='; //KEY FROM SSH PROGRAM WHICH IS THE RIGHT RETURN;
echo '<br>';
echo 'IV : //QxQj7PDMRE1YUVo+mJvQ==' //IV FROM SSH PROGRAM WHICH IS THE RIGHT RETURN;

I really wonder where the problem lays or how to debug this ?

The settings are in both PHP and C# the same :

PHP CODE :

$hasher = "SHA256";
$iterations = 1000;
$keysize = 256;
$ivsize = 128;

C# CODE :

string random_string_pwd = "mypassword";
byte[] passwordBytes = Encoding.UTF8.GetBytes(random_string_pwd);

//var random_salt = new ClientTools();
//string random_string_salt = random_pwd.RndStrings(15);
string random_string_salt = "mysalthereitis";
byte[] Salt = Encoding.UTF8.GetBytes(random_string_salt);

// Hash the password with SHA256
passwordBytes = SHA256.Create().ComputeHash(passwordBytes);
AES.KeySize = 256;
AES.BlockSize = 128;

var key = new Rfc2898DeriveBytes(passwordBytes, saltBytes, 1000);
AES.Key = key.GetBytes(AES.KeySize / 8);
AES.IV = key.GetBytes(AES.BlockSize / 8);

Answer 1

In PHP you Base64 decode the salt but it is not base64 encoded:
base64_decode($salt)

In C# you just get the bytes of the salt:
byte[] Salt = Encoding.UTF8.GetBytes(random_string_salt);

In PHP you are using SHA256
In C# you are using MSN Rfc2898DeriveBytes which uses SHA1:
Rfc2898DeriveBytes Class specifies: using a pseudo-random number generator based on HMACSHA1.
Using SHA256 on password bytes does not fix the MSN rfc2898derivebytes. This is an MSN issue since it does not allow the HAMC to be specified.

The solution is to change the PHP to just get the string bytes as data, not to try and Base64 decode something that is not Base64 encoded.

1. At a minimum do the same thing in each language
2. If you need to use the MSN Rfc2898DeriveBytes then change the PHP HMAC to SHA1.
3. Do not Base64 decode a string that is not Base64 encoded, this will often fail. In fact Base64 decoding mysalthereitis"