生成较短的公共ID [英] Generate shorter public id

问题描述

我正在寻找一种方法来为我的对象生成公共id（例如facebook uid）。该id应该是唯一的，用户不应该猜测它（或下一个）。

现在我正在使用这个：

  sha1（'fixed a fixed string'。$ this-> getId（））
  

问题是sha1会生成很长的字符串（40个字符），我希望它更短。我想过使用MD5，但它已知不会保存，因为您可以创建冲突。这是真的在我的情况是一个问题吗？

我有什么替代方案？

解决方案我做了一些测试，看看id将使用不同的哈希函数多久。我还用 convBase 将0-9a -z到0-9a-zA-Z，建议使用 ：

  $ i = mt_rand（1，PHP_INT_MAX）; 
 sha1（$ i）：40 322c73c44958e4219fd6679aead094192cb672fe 
 convBase（sha1（$ i））：34 1JHrlXObHSVMcbn2bHRBCBIRD3RVKQHMQzg 
 md5（$ i）：32 7b09f8cd76be44403b90e971a5a61e6c 
 convBase（md5（$ i） ）：28 5bgdGpBZekbb3PQlILrSKMtHC24A 
 $ i：9 107300785 
 convBase（$ i）：5 7gdPP 
  

因此，即使转换为其他基数，sha1也是非常长的。另外我还不确定MD5是否安全。无论如何，有28个字符，如果你想在twitter上发布它，它仍然很长：
http://mydomainsux.com/invite/5bgdGpBZekbb3PQlILrSKMtHC24A

使用 convBase（$ i）存在不唯一的问题。你将不得不手动检查。不过，我认为这是要走到这里的方法，因为如果你使用散列，那么也可能会有一个自然的勾结，所以你必须检查。

我读到你可以预先在表格中生成ID，并在需要时选择一个。这样你不必每次都测试唯一性。

I am looking for a way to generate public ids for my objects (like a facebook uid). The id should be unique and the user should not be able to guess it (or the next one).

Right now I am using this:

sha1('a fixed random string' . $this->getId())

The problem is that sha1 generates very long strings (40 chars) and I would like it to be shorter. I thought about using MD5 but it's known to be not save because you can create collisions. Is this really a problem in my case?

What alternatives do I have?

解决方案

I made some tests to see how long the id will be using different hash functions. I also used convBase to convert from 0-9a-z to 0-9a-zA-Z as suggested:

$i = mt_rand(1, PHP_INT_MAX);
sha1($i):           40 322c73c44958e4219fd6679aead094192cb672fe
convBase(sha1($i)): 34 1JHrlXObHSVMcbn2bHRBCBIRD3RVKQHMQzg
md5($i):            32 7b09f8cd76be44403b90e971a5a61e6c
convBase(md5($i)):  28 5bgdGpBZekbb3PQlILrSKMtHC24A
$i:                  9 107300785
convBase($i):        5 7gdPP

So sha1 is very long even if converted to the other base. Also I am still not sure if MD5 is secure. Anyway, with 28 characters it is still kind of long if you want to post it in an URL on twitter: http://mydomainsux.com/invite/5bgdGpBZekbb3PQlILrSKMtHC24A

The shortest solution with convBase($i) has the problem of not being unique. You would have to check for that manually. Still, I think this is the way to go here because if you use a hash there could also be a natural collusion so you have to check anyway.

I read that you can pre generate the id's in a table and just pick one whenever you need one. This way you do not have to test for uniqueness every time.

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