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Detailed explanation of several ways PHP handles passwords

怪我咯

Jan 16, 2017 pm 03:26 PM

在我们的日常开发中，经常会对我们的密码进行加密，对于很多PHP开发者在最先接触PHP的时候，处理密码的首选加密函数可能就是MD5了，我当时就是这样的：

$password = md5($_POST["password"]);

MD5对密码加密的方式是最常见的加密方式，但是现在MD5的加密方式目前已经不太安全了，因为它的加密算法实在是显得有点简单了，而且很多破解密码的站点都存放了很多经过MD5

加密的密码字符串，所以这里我是非常不提倡还在单单使用MD5来加密用户的密码的。

那么除了我们的md5对密码加密，小编今天就给各位看官收集一些PHP中其他的几种加密方式

一. SHA256 和 SHA512

其实跟前面的MD5同期的还有一个SHA1加密方式的，不过也是算法比较简单，所以这里就不介绍了。而这里即将要说到的SHA256 和 SHA512都是来自于SHA2家族的加密函数，看名字

可能你就猜的出来了，这两个加密方式分别生成256和512比特长度的 hash字串。

他们的使用方法如下：

$password = hash("sha256", $password);

PHP内置了hash()函数，你只需要将加密方式传给hash()函数就好了。你可以直接指明sha256, sha512, md5, sha1等加密方式。

二. 盐值

在加密的过程，我们还有一个非常常见的东西：盐值。对，我们在加密的时候其实会给加密的字符串添加一个额外的字符串，以达到提高一定安全的目的，并且盐值要记录下来，方便以后

的比对：

function generateHashWithSalt($password) {
  $intermediateSalt = md5(uniqid(rand(), true));
  $salt = substr($intermediateSalt, 0, 6);
  return hash("sha256", $password . $salt);
}

三. Bcrypt

Bcrypt不失为一种比较不错的加密方式了，但是后面介绍的 Hashing API更好。

function generateHash($password) {
  if (defined("CRYPT_BLOWFISH") && CRYPT_BLOWFISH) {
    $salt = &#39;$2y$11$&#39; . substr(md5(uniqid(rand(), true)), 0, 22);
    return crypt($password, $salt);
  }
}

Bcrypt 其实就是Blowfish和crypt()函数的结合，我们这里通过CRYPT_BLOWFISH判断Blowfish是否可用，然后像上面一样生成一个盐值，不过这里需要注意的是，crypt()的盐值必须以 $2a$ 或者 $2y$ 开头。

四. Password Hashing API

这里才是我们的重头戏，Password Hashing API是PHP 5.5之后才有的新特性，它主要是提供下面几个函数供我们使用：

password_hash()     //对密码加密.
password_verify()    //验证已经加密的密码，检验其hash字串是否一致.
password_needs_rehash() //给密码重新加密.
password_get_info()   //返回加密算法的名称和一些相关信息.

使用这套 API不仅简单，而且更加安全，这也是 PHP官方推荐的加密方式。

$hash = password_hash($passwod, PASSWORD_DEFAULT);

PASSWORD_DEFAULT目前使用的就是Bcrypt加密算法，这里需要注意的是，如果你代码使用的都是PASSWORD_DEFAULT加密方式，那么在数据库的表中，password字段就得设置超

过60个字符长度，你也可以使用PASSWORD_BCRYPT算法，该算法加密后的字符串长度总为60。

这里使用 password_hash()你完全可以不提供盐值(salt)和消耗值 (cost)，你可以将后者理解为一种性能的消耗值，cost越大，加密算法越复杂，消耗的内存也就越大。当然，如果你需要

指定对应的盐值和消耗值，你可以这样写：

$options = [
  &#39;salt&#39; => custom_function_for_salt(), //自定义函数来获得盐值
  &#39;cost&#39; => 12 // the default cost is 10
];
$hash = password_hash($password, PASSWORD_DEFAULT, $options);

不过一般自定义 cost就好了， salt值则使用默认的。

加密好后，只需要简单的使用即可验证密码是否正确

<?php
if (password_verify($password, $hash)) {
  // Pass
}
else {
  // Invalid
}

直接使用password_verify就可以对我们之前加密过的字符串（存在数据库中）进行验证了。

如果要更换更改加密的方式，则必须使用以下代码来重新加密：

if (password_needs_rehash($hash, PASSWORD_DEFAULT, [&#39;cost&#39; => 12])) {
  // cost 变为 12
  $hash = password_hash($password, PASSWORD_DEFAULT, [&#39;cost&#39; => 12]);
 
  // 然后重新保存 hash值
}

只有这样，PHP的 Password Hashing API才会知道我们重现更换了加密方式，这样才能完成之后的密码验证。

password_get_info()，这个函数一般可以看到下面三个信息：

1、algo – 算法实例

2、algoName – 算法名字

3、options – 加密时候的可选参数

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持PHP中文网。

更多好文章，尽在PHP中文网......

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