unique_id function

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Discussion of general topics related to the new release and its place in the world. Don't discuss new features, report bugs, ask for support, et cetera. Don't use this to spam for other boards or attack those boards!
medick
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unique_id function

Post by medick » Thu Jan 31, 2008 5:40 pm

Why unique_id function so overdone? It requires to few SQL queries just to get random md5. Why not replace it with more simple combination that doesn't need any DB or I/O resources?

Also it's possible to optimize set_config function - using one REPLACE query instead of few UPDATE and/or INSERT queries.

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Kellanved
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Re: unique_id function

Post by Kellanved » Fri Feb 01, 2008 1:17 pm

a) Because anything else wouldn't be as secure.
b) Doesn't optimize much and would be MySQL-only.

;)
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medick
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Re: unique_id function

Post by medick » Fri Feb 01, 2008 2:01 pm

a) Can you please explain for me why combination like

Code: Select all

return substr(md5(rand().'_'.microtime().'_'.rand()),rand(0,15),16)
is less secure?

b) MySQL is most popular and for big forums there is no words like "Doesn't optimize much". Just a thought.

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Kellanved
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Re: unique_id function

Post by Kellanved » Fri Feb 01, 2008 2:56 pm

a) Because it's just based on the current time. An attacker could have an excellent guess on what the generated value was (about one in 20, according to our experiments).

b) As stated before, it isn't faster and would break compatibility with the other DBMS. We don't support MySQL's weird quirks.
Config values are added only very seldomly; never in normal operation. A REPLACE is more expensive than an UPDATE. Why use a more expensive operation frequently to avoid an extremely unlikely situation that can only happen in not-performance critical situations.
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medick
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Re: unique_id function

Post by medick » Fri Feb 01, 2008 3:20 pm

a) Ok let's forget about time

Code: Select all

return substr(
    md5(
        rand().
        '_'.
        round(
            rand()*rand()/rand(),
            rand(1,4)
        ).
        '_'.
        rand()
    ),
    rand(0,15),
    16
);
There are a lot of deffierent combinations with md5, substr, rand, round that can be implemented and it's based only on random values every time.

2) I think I should agree with you.

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Kellanved
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Re: unique_id function

Post by Kellanved » Fri Feb 01, 2008 3:26 pm

It's still just the time that goes in the function. An attacker using the same seed will get the same result.
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medick
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Re: unique_id function

Post by medick » Fri Feb 01, 2008 3:31 pm

^ There are only rand(), md5(), and substr() functions now. The result doesn't depend on time.

Also you can get hash of getallheaders() or something like this.

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Kellanved
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Re: unique_id function

Post by Kellanved » Fri Feb 01, 2008 3:48 pm

rand depends on the time.
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Re: unique_id function

Post by ElbertF » Fri Feb 01, 2008 5:18 pm

And you can easily fake headers.

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Nicholas the Italian
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Re: unique_id function

Post by Nicholas the Italian » Sat Feb 02, 2008 9:23 pm

Not sure what we are exactly talking about, so I might be saying something stupid. But what about using user's IP as part of the seed? The attacker must (should) have a different one.

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