Using functions to obfuscate the hash generation does not increase security. This is security by obscurity. The algorithm used to hash the data needs to be secure by itself.
I would not suggest to use other data as salt. For example if you use the username, you won't be able to change the values without rehashing the password.
I would use a dedicated salt value stored in the same database table.
Why? Because a lot of users use the same login credentials on different web services. And in case another service also uses the username as salt, the resulting hashed password might be the same!
Also an attacker may prepare a rainbow table with prehashed passwords using the username and other known data as salt. Using random data would easily prevent this with little programming effort.
ストレージの暗号化
SSL/SSHによってクライアント/サーバー間で通信されるデータは保護されますが、 データベースに保存されたデータは保護されません。SSLはあくまで通信上の プロトコルなのです。
一旦アタッカーがデータベースへ(ウェブサーバーを通さずに)アクセスできてしまうと、 そこに格納されているデータ自体が暗号化されていない限り、自由に閲覧され、 使用されてしまいます。データを暗号化することによって、この脅威を減らすことが できますが、この機能をサポートしているデータベースは僅かです。
この問題への最も簡単な対応策は、まず自分専用の暗号化パッケージを作成し、 それをあなたのPHPスクリプトから使用することです。PHPのOpenSSL, Sodium といった幾つかの拡張モジュールは、様々な暗号化アルゴリズムをサポート しているので役に立つでしょう。データ格納時に暗号化を行い、取得時に 復号化します。この方法についてはリファレンスを参照ください。
ハッシュ
もし完全にデータを隠したい場合や、元のデータ自体は必要ない場合(つまり 表示されない場合)は、ハッシュも考慮に入れたほうが良いでしょう。 ハッシュの良く知られた使用方法は、パスワードをそのまま格納せずに、 その暗号学的ハッシュ値を格納する方法です。
PHP は password 関数を提供しており、 機密データをハッシュしたりそのハッシュを扱ったりする便利な仕組みが用意されています。
password_hash() は、その時点で最も強力なアルゴリズムを使って、 与えられた文字列をハッシュします。また password_verify() は、与えられたパスワードのハッシュがデータベース内のハッシュと一致するかどうかを調べます。
例1 ハッシュされたパスワードフィールド
<?php
// ハッシュされたパスワードを格納する
$query = sprintf("INSERT INTO users(name,pwd) VALUES('%s','%s');",
pg_escape_string($username),
password_hash($password, PASSWORD_DEFAULT));
$result = pg_query($connection, $query);
// パスワードが正しいかどうか問い合わせる
$query = sprintf("SELECT pwd FROM users WHERE name='%s';",
pg_escape_string($username));
$row = pg_fetch_assoc(pg_query($connection, $query));
if ($row && password_verify($password, $row['pwd'])) {
echo 'Welcome, ' . htmlspecialchars($username) . '!';
} else {
echo 'Authentication failed for ' . htmlspecialchars($username) . '.';
}
?>
add a note
User Contributed Notes 5 notes
Reiner ¶
13 years ago
seigoryu at hotmail dot de ¶
12 years ago
I would strongly recommend using SHA-2 or better the new SHA-3 hash algorithm. MD5 is practically unusable, since there are very well working rainbow tables around the whole web. Almost the same for SHA-1. Of course you should never do a hash without salting!
somebody ¶
17 years ago
A better way to hash would be to use a separate salt for each user. Changing the salt upon each password update will ensure the hashes do not become stale.
about2mount at gmail dot com ¶
9 years ago
It's difficult to post scripts here for all to view on the subject of best security practices. But i would wish to point out that using a salt with a randomized and odd numbered long length salt value is do_able with two Php functions while retrieving and separating the salt when it comes out using simple math functions. But with everything we add we also have to think of the constant standardized login systems we stay behind with.
For one,,, adding and validating two to four passwords is not a bad idea. Also having no username or email going in. They can be stored after the user logs in after the validation process. It is possible to store the email on the first signup and only at that time. And if the user loses his passwords then validate by email only upon request within a contact form by a validated phone number stored in the database,, and then via their email account.
Fairydave at the location of dodo.com.au ¶
18 years ago
I think the best way to have a salt is not to randomly generate one or store a fixed one. Often more than just a password is saved, so use the extra data. Use things like the username, signup date, user ID, anything which is saved in the same table. That way you save on space used by not storing the salt for each user.
Although your method can always be broken if the hacker gets access to your database AND your file, you can make it more difficult. Use different user data depending on random things, the code doesn't need to make sense, just produce the same result each time. For example:
if ((asc(username character 5) > asc(username character 2))
{
if (month the account created > 6)
salt = ddmmyyyy of account created date
else
salt = yyyyddmm of account created date
}
else
{
if (day of account created > 15)
salt = user id * asc(username character 3)
else
salt = user id + asc(username character 1) + asc(username character 4)
}
This wont prevent them from reading passwords when they have both database and file access, but it will confuse them and slow them up without much more processing power required to create a random salt
