Detailed explanation of password security in PHP Password Hashing

<?php

//require &#39;password.php&#39;;
/**
 * 正确的密码是secret-password
 * $passwordHash 是hash 后存储的密码
 * password_verify()用于将用户输入的密码和数据库存储的密码比对。成功返回true，否则false
 */
$passwordHash = password_hash(&#39;secret-password&#39;, PASSWORD_DEFAULT);
echo $passwordHash;
if (password_verify(&#39;bad-password&#39;, $passwordHash)) {
  // Correct Password
  echo &#39;Correct Password&#39;;
} else {
  echo &#39;Wrong password&#39;;
  // Wrong password
}

<?php
class User
{
  // Store password options so that rehash & hash can share them:
  const HASH = PASSWORD_DEFAULT;
  const COST = 14;//可以确定该算法应多复杂，进而确定生成哈希值将花费多长时间。（将此值视为更改算法本身重新运行的次数，以减缓计算。）

  // Internal data storage about the user:
  public $data;

  // Mock constructor:
  public function __construct() {
    // Read data from the database, storing it into $data such as:
    // $data->passwordHash and $data->username
    $this->data = new stdClass();
    $this->data->passwordHash = &#39;dbd014125a4bad51db85f27279f1040a&#39;;
  }

  // Mock save functionality
  public function save() {
    // Store the data from $data back into the database
  }

  // Allow for changing a new password:
  public function setPassword($password) {
    $this->data->passwordHash = password_hash($password, self::HASH, [&#39;cost&#39; => self::COST]);
  }

  // Logic for logging a user in:
  public function login($password) {
    // First see if they gave the right password:
    echo "Login: ", $this->data->passwordHash, "\n";
    if (password_verify($password, $this->data->passwordHash)) {
      // Success - Now see if their password needs rehashed
      if (password_needs_rehash($this->data->passwordHash, self::HASH, [&#39;cost&#39; => self::COST])) {
        // We need to rehash the password, and save it. Just call setPassword
        $this->setPassword($password);
        $this->save();
      }
      return true; // Or do what you need to mark the user as logged in.
    }
    return false;
  }
}