本文供給的代碼中 slowequals 函數(shù)是如何工作的
上一答復(fù)講到了我們需要比較時(shí)候固定的函數(shù)，這部門具體講一下代碼的實(shí)現(xiàn)。
1. private static boolean slowEquals(byte[] a, byte[] b)
2. {
3. int diff = a.length ^ b.length;
4. for(int i = 0; i
5. diff |= a[i] ^ b[i];
6. return diff == 0;
7. }
這段代碼利用了異或(XOR)把持符”^”來比較整數(shù)是不是相等，而沒有益用”==”把持符。啟事在于假定兩個(gè)數(shù)完全一致，異或以后的值為零。因?yàn)?0 XOR 0 = 0, 1 XOR 1 = 0, 0 XOR 1 = 1, 1 XOR 0 = 1。
所以，第一行代碼假定a.length便是b.length，變量diff便是0,不然的話diff就是一個(gè)非零的值。然后，讓a，b的每個(gè)字節(jié)XOR以后再跟diff OR。如許，只有diff一開端是0,并且，a，b的每個(gè)字節(jié)XOR的成果也是零，最后輪回完成后diff的值才是0,這類環(huán)境是a，b完全一樣。不然最后diff是一個(gè)非零的值。
我們利用XOR而不合用”==”的啟事是”==”凡是編譯成分支的情勢(shì)。好比C代碼”diff &= a == b” 可能編譯成下面的X86匯編。
MOV EAX, [A]
CMP [B], EAX
JZ equal
JMP done
equal:
AND [VALID], 1
done:
AND [VALID], 0
分支會(huì)導(dǎo)致代碼履行的時(shí)候呈現(xiàn)差別。
C代碼的”diff |= a ^ b”編譯以后近似于，
MOV EAX, [A]
XOR EAX, [B]
OR [DIFF], EAX
履行時(shí)候跟兩個(gè)變量是不是相等沒有關(guān)系。
為甚么要會(huì)商這么多關(guān)于hash的東西
用戶在你的網(wǎng)站上輸進(jìn)暗碼，是相信你的安然性。假定你的數(shù)據(jù)庫被黑了。而用戶暗碼又沒有得當(dāng)?shù)暮亲o(hù)，那么歹意的報(bào)復(fù)打擊者便可以操縱這些暗碼測(cè)驗(yàn)測(cè)驗(yàn)登岸其他的網(wǎng)站和辦事。進(jìn)行撞庫報(bào)復(fù)打擊。(良多用戶在所有的處所都是利用不異的暗碼)這不但僅是你的網(wǎng)站安然，是你的所有效戶的安然。你要對(duì)你用戶的安然負(fù)責(zé)。
大年夜大都的web開辟者城市碰著設(shè)計(jì)用戶賬號(hào)系統(tǒng)的需求。賬號(hào)系統(tǒng)最首要的一個(gè)方面就是若何呵護(hù)用戶的暗碼。一些大公司的用戶數(shù)據(jù)庫泄漏事務(wù)也時(shí)有產(chǎn)生，所以我們必需采納一些辦法來呵護(hù)用戶的暗碼，即便網(wǎng)站被攻破的環(huán)境下也不會(huì)造成較大年夜的風(fēng)險(xiǎn)。
PHP PBKDF2 暗碼hash代碼
代碼下載
/*
* Password Hashing With PBKDF2 (http://crackstation.net/hashing-security.htm).
* Copyright (c) 2013, Taylor Hornby
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
// These constants may be changed without breaking existing hashes.
define("PBKDF2_HASH_ALGORITHM", "sha256");
define("PBKDF2_ITERATIONS", 1000);
define("PBKDF2_SALT_BYTE_SIZE", 24);
define("PBKDF2_HASH_BYTE_SIZE", 24);
define("HASH_SECTIONS", 4);
define("HASH_ALGORITHM_INDEX", 0);
define("HASH_ITERATION_INDEX", 1);
define("HASH_SALT_INDEX", 2);
define("HASH_PBKDF2_INDEX", 3);
function create_hash($password)
{
// format: algorithm:iterations:salt:hash
$salt = base64_encode(mcrypt_create_iv(PBKDF2_SALT_BYTE_SIZE, MCRYPT_DEV_URANDOM));
return PBKDF2_HASH_ALGORITHM . ":" . PBKDF2_ITERATIONS . ":" . $salt . ":" .
base64_encode(pbkdf2(
PBKDF2_HASH_ALGORITHM,
$password,
$salt,
PBKDF2_ITERATIONS,
PBKDF2_HASH_BYTE_SIZE,
true
));
}
function validate_password($password, $correct_hash)
{
$params = explode(":", $correct_hash);
if(count($params) < /*
* Password Hashing With PBKDF2 (http://crackstation.net/hashing-security.htm).
* Copyright (c) 2013, Taylor Hornby
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
// These constants may be changed without breaking existing hashes.
define("PBKDF2_HASH_ALGORITHM", "sha256");
define("PBKDF2_ITERATIONS", 1000);
define("PBKDF2_SALT_BYTE_SIZE", 24);
define("PBKDF2_HASH_BYTE_SIZE", 24);
define("HASH_SECTIONS", 4);
define("HASH_ALGORITHM_INDEX", 0);
define("HASH_ITERATION_INDEX", 1);
define("HASH_SALT_INDEX", 2);
define("HASH_PBKDF2_INDEX", 3);
function create_hash($password)
{
// format: algorithm:iterations:salt:hash
$salt = base64_encode(mcrypt_create_iv(PBKDF2_SALT_BYTE_SIZE, MCRYPT_DEV_URANDOM));
return PBKDF2_HASH_ALGORITHM . ":" . PBKDF2_ITERATIONS . ":" . $salt . ":" .
base64_encode(pbkdf2(
PBKDF2_HASH_ALGORITHM,
$password,
$salt,
PBKDF2_ITERATIONS,
PBKDF2_HASH_BYTE_SIZE,
true
));
}
function validate_password($password, $correct_hash)
{
$params = explode(":", $correct_hash);
if(count($params) < /*
* Password Hashing With PBKDF2 (http://crackstation.net/hashing-security.htm).
* Copyright (c) 2013, Taylor Hornby
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
// These constants may be changed without breaking existing hashes.
define("PBKDF2_HASH_ALGORITHM", "sha256");
define("PBKDF2_ITERATIONS", 1000);
define("PBKDF2_SALT_BYTE_SIZE", 24);
define("PBKDF2_HASH_BYTE_SIZE", 24);
define("HASH_SECTIONS", 4);
define("HASH_ALGORITHM_INDEX", 0);
define("HASH_ITERATION_INDEX", 1);
define("HASH_SALT_INDEX", 2);
define("HASH_PBKDF2_INDEX", 3);
function create_hash($password)
{
// format: algorithm:iterations:salt:hash
$salt = base64_encode(mcrypt_create_iv(PBKDF2_SALT_BYTE_SIZE, MCRYPT_DEV_URANDOM));
return PBKDF2_HASH_ALGORITHM . ":" . PBKDF2_ITERATIONS . ":" . $salt . ":" .
base64_encode(pbkdf2(
PBKDF2_HASH_ALGORITHM,
$password,
$salt,
PBKDF2_ITERATIONS,
PBKDF2_HASH_BYTE_SIZE,
true
));
}
function validate_password($password, $correct_hash)
{
$params = explode(":", $correct_hash);
if(count($params) < HASH_SECTIONS)
return false;
$pbkdf2 = base64_decode($params[HASH_PBKDF2_INDEX]);
return slow_equals(
$pbkdf2,
pbkdf2(
$params[HASH_ALGORITHM_INDEX],
$password,
$params[HASH_SALT_INDEX],
(int)$params[HASH_ITERATION_INDEX],
strlen($pbkdf2),
true
)
);
}
// Compares two strings $a and $b in length-constant time.
function slow_equals($a, $b)
{
$diff = strlen($a) ^ strlen($b);
for($i = 0; $i < strlen($a) && $i < strlen($b); $i++)
{
$diff |= ord($a[$i]) ^ ord($b[$i]);
}
return $diff === 0;
}
/*
* PBKDF2 key derivation function as defined by RSA's PKCS #5: https://www.ietf.org/rfc/rfc2898.txt
* $algorithm - The hash algorithm to use. Recommended: SHA256
* $password - The password.
* $salt - A salt that is unique to the password.
* $count - Iteration count. Higher is better, but slower. Recommended: At least 1000.
* $key_length - The length of the derived key in bytes.
* $raw_output - If true, the key is returned in raw binary format. Hex encoded otherwise.
* Returns: A $key_length-byte key derived from the password and salt.
*
* Test vectors can be found here: https://www.ietf.org/rfc/rfc6070.txt
*
* This implementation of PBKDF2 was originally created by https://defuse.ca
* With improvements by http://www.variations-of-shadow.com
*/
function pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output = false)
{
$algorithm = strtolower($algorithm);
if(!in_array($algorithm, hash_algos(), true))
trigger_error('PBKDF2 ERROR: Invalid hash algorithm.', E_USER_ERROR);
if($count <= 0 || $key_length <= 0)
trigger_error('PBKDF2 ERROR: Invalid parameters.', E_USER_ERROR);
if (function_exists("hash_pbkdf2")) {
// The output length is in NIBBLES (4-bits) if $raw_output is false!
if (!$raw_output) {
$key_length = $key_length * 2;
}
return hash_pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output);
}
$hash_length = strlen(hash($algorithm, "", true));
$block_count = ceil($key_length / $hash_length);
$output = "";
for($i = 1; $i <= $block_count; $i++) {
// $i encoded as 4 bytes, big endian.
$last = $salt . pack("N", $i);
// first iteration
$last = $xorsum = hash_hmac($algorithm, $last, $password, true);
// perform the other $count - 1 iterations
for ($j = 1; $j < $count; $j++) {
$xorsum ^= ($last = hash_hmac($algorithm, $last, $password, true));
}
$output .= $xorsum;
}
if($raw_output)
return substr($output, 0, $key_length);
else
return bin2hex(substr($output, 0, $key_length));
}
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