How to create a 8-character hash to be sure this can be unique in several million cases? I don’t want it for password, for example how bitly is generating this kind of hash for url and it is unique in millions of urls?
Any php coding suggestion?
That makes no sense, as any hash depends on the input value, so you have to define WHICH million cases you mean. By random i may get a collision just within two tries. And hashes are never unique, as they are just a reduction of the input, so you get an infinite amount of collisions when exeeding the hash size.
Pretty sure OP is just misusing the word hash. He is asking about a Unique Id.
Yes, unique id, thanks for random_bytes, but what if we have certain value and we want to create a unique id base on the value?
For example how stripe is generating a unique id for a CC data? May be it is storing cc data in db and map it with a unique id and when it uses this id to search cc data? Or what?
What is the point? A unique id is a unique id no matter how it was generated.
Try searching the online PHP manual for the time () and microtime() functions, both return numerics unlikely ever to repeat 
The same topic i want to know into better way. Is there any one to help me?
What’s wrong with the answers that have already been given???
I guess it depends on how you define “several” in the first post. A simple incrementing number will give you up to 99 million unique IDs.
if you specify what you want it for then we might give you better answers
I suppose they are simply generating a random string and uniqueness can be checked by a unique key in the database.
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