这是一个有趣的问题

public function randomStr($length = 16) {
    $string = '';
        
    while (($len = strlen($string)) < $length) {
        $size = $length - $len;
            
        $bytes = random_bytes($size);
            
        $string .= substr(str_replace(['/', '+', '='], '', base64_encode($bytes)), 0, $size);
    }
        
        return $string;
}

从laravel偷来的

PHP 7标准库提供了random_bytes($length)函数，该函数生成加密安全的伪随机字节。

例子:

$bytes = random_bytes(20);
var_dump(bin2hex($bytes));

上面的例子将输出类似于:

string(40) "5fe69c95ed70a9869d9f9af7d8400a6673bb9ce9"

更多信息:http://php.net/manual/en/function.random-bytes.php

PHP 5(过时)

我只是在寻找如何解决这个相同的问题，但我也希望我的函数创建一个令牌，可以用于密码检索以及。这意味着我需要限制令牌的猜测能力。因为uniqid是基于时间的，而根据php.net“返回值与microtime()相差不大”，uniqid不符合条件。PHP建议使用openssl_random_pseudo_bytes()来生成加密安全的令牌。

一个快速、简短、直截了当的答案是:

bin2hex(openssl_random_pseudo_bytes($bytes))

它将生成一个长度= $bytes * 2的字母数字字符的随机字符串。不幸的是，这只有一个字母[a-f][0-9]，但它是有效的。

---

Below is the strongest function I could make that satisfies the criteria (This is an implemented version of Erik's answer).

function crypto_rand_secure($min, $max)
{
    $range = $max - $min;
    if ($range < 1) return $min; // not so random...
    $log = ceil(log($range, 2));
    $bytes = (int) ($log / 8) + 1; // length in bytes
    $bits = (int) $log + 1; // length in bits
    $filter = (int) (1 << $bits) - 1; // set all lower bits to 1
    do {
        $rnd = hexdec(bin2hex(openssl_random_pseudo_bytes($bytes)));
        $rnd = $rnd & $filter; // discard irrelevant bits
    } while ($rnd > $range);
    return $min + $rnd;
}

function getToken($length)
{
    $token = "";
    $codeAlphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    $codeAlphabet.= "abcdefghijklmnopqrstuvwxyz";
    $codeAlphabet.= "0123456789";
    $max = strlen($codeAlphabet); // edited

    for ($i=0; $i < $length; $i++) {
        $token .= $codeAlphabet[crypto_rand_secure(0, $max-1)];
    }

    return $token;
}

Crypto_rand_secure ($min， $max)作为rand()或mt_rand的替换。它使用openssl_random_pseudo_bytes来帮助创建一个介于$min和$max之间的随机数。

getToken($length)创建一个要在令牌中使用的字母表，然后创建一个长度为$length的字符串。

来源:http://us1.php.net/manual/en/function.openssl-random-pseudo-bytes.php # 104322

生成一个随机数使用 你最喜欢的随机数 发电机 乘除 得到一个与数字匹配的数字 你的代码字母表中的字符 将该索引处的项插入 你的代码字母。 重复1)，直到你有你想要的长度 想要

例如(伪代码)

int myInt = random(0, numcharacters)
char[] codealphabet = 'ABCDEF12345'
char random = codealphabet[i]
repeat until long enough

斯科特，是的，你写得很好，解决得很好!谢谢。

我还需要为我的每个用户生成唯一的API令牌。以下是我的方法，我使用用户信息(Userid和Username):

public function generateUniqueToken($userid, $username){

        $rand = mt_rand(100,999);
    $md5 = md5($userid.'!(&^ 532567_465 ///'.$username);

    $md53 = substr($md5,0,3);
    $md5_remaining = substr($md5,3);

    $md5 = $md53. $rand. $userid. $md5_remaining;

    return $md5;
}

请看看，如果我能做什么改进，请告诉我。谢谢

一个简单的解决方案是通过丢弃非字母数字字符将64进制转换为字母数字。

它使用random_bytes()来获得加密安全的结果。

function random_alphanumeric(int $length): string
{
    $result='';
    do
    {
        //Base 64 produces 4 characters for each 3 bytes, so most times this will give enough bytes in a single pass
        $bytes=random_bytes(($length+3-strlen($result))*2);
        //Discard non-alhpanumeric characters
        $result.=str_replace(['/','+','='],['','',''],base64_encode($bytes));
        //Keep adding characters until the string is long enough
        //Add a few extra because the last 2 or 3 characters of a base 64 string tend to be less diverse
    }while(strlen($result)<$length+3);
    return substr($result,0,$length);
}

编辑:我只是重新审视了一下，因为我需要一些更灵活的东西。这里有一个解决方案，执行得比上面的好一点，并提供了指定ASCII字符集的任何子集的选项:

<?php
class RandomText
{
    protected
        $allowedChars,
        //Maximum index to use
        $allowedCount,
        //Index values will be taken from a pool of this size
        //It is a power of 2 to keep the distribution of values even
        $distributionSize,
        //This many characters will be generated for each output character
        $ratio;
    /**
     * @param string $allowedChars characters to choose from
     */
    public function __construct(string $allowedChars)
    {
        $this->allowedCount = strlen($allowedChars);
        if($this->allowedCount < 1 || $this->allowedCount > 256) throw new \Exception('At least 1 and no more than 256 allowed character(s) must be specified.');
        $this->allowedChars = $allowedChars;
        //Find the power of 2 equal or greater than the number of allowed characters
        $this->distributionSize = pow(2,ceil(log($this->allowedCount, 2)));
        //Generating random bytes is the expensive part of this algorithm
        //In most cases some will be wasted so it is helpful to produce some extras, but not too many
        //On average, this is how many characters needed to produce 1 character in the allowed set
        //50% of the time, more characters will be needed. My tests have shown this to perform well.
        $this->ratio = $this->distributionSize / $this->allowedCount;
    }

    /**
     * @param int $length string length of required result
     * @return string random text
     */
    public function get(int $length) : string
    {
        if($length < 1) throw new \Exception('$length must be >= 1.');
        $result = '';
        //Keep track of result length to prevent having to compute strlen()
        $l = 0;
        $indices = null;
        $i = null;
        do
        {
            //Bytes will be used to index the character set. Convert to integers.
            $indices = unpack('C*', random_bytes(ceil(($length - $l) * $this->ratio)));
            foreach($indices as $i)
            {
                //Reduce to the smallest range that gives an even distribution
                $i %= $this->distributionSize;
                //If the index is within the range of characters, add one char to the string
                if($i < $this->allowedCount)
                {
                    $l++;
                    $result .= $this->allowedChars[$i];
                }
                if($l >= $length) break;
            }
        }while($l < $length);
        return $result;
    }
}

我用了这样一句话:

base64_encode(openssl_random_pseudo_bytes(3 * ($length >> 2)));

其中length是所需字符串的长度(能被4整除，否则它会四舍五入到最接近的能被4整除的数字)