[kwlug-disc] Hash functions.

[Joe Wennechuk]

Security is not a concern right now really I just want to be able to make coupons that can be sent by sms that can be uniquely identified so at they can be tracked upon redemption, and timed for destruction, etc.. I haven't fully examined the security implications I don't think at this point it is any problem that they could be reverse engineered or such. I think if they are activated on send and deactivated upon redemption; at the server ,it would be Okay(??).. Also because they are SMS the number of characters is of primary concern. I Guess I could use serial numbers and just increment in a base 127 system or something, but illusionary security by obscurity is kind of what I'm going for.

Joseph Wennechuk

________________




> Date: Sun, 2 Jan 2011 11:08:39 -0500
> From: 3lucid at gmail.com
> To: kwlug-disc at kwlug.org
> Subject: Re: [kwlug-disc] Hash functions.
> 
> On Sun, Jan 2, 2011 at 10:59 AM, Khalid Baheyeldin <kb at 2bits.com> wrote:
> > On Sun, Jan 2, 2011 at 5:46 PM, Joe Wennechuk
> > <youcanreachmehere at hotmail.com> wrote:
> >>
> >> I want to use a hash type function to generate a unique id for sms
> >> messages. I want the smallest possible number of bytes returned as the
> >> identifier, I can use all alnum, and even symbols maybe only ASCII up to
> >> 127, instead of 256. The input is going to be only 120 chrs+DateTime()+maybe
> >> some 10 digit identifier or something, so maybe 200-250 chrs max. for the
> >> input, and hopefully like 4-5 chrs for the output with collisions less than
> >> 1 in 500,000,000 or so (127^5 is like 33,000,000,000 so that seems
> >> ok???).... Is there a function to do this? All the ones I seem to see output
> >> in binary or hex only I think I could really reduce the size by using 127
> >> chars instaed of 16, and bites are critical to the app. I suppose I could do
> >> some parsing on the binary number and come up with something, but I rater
> >> just be done with it.
> >
> > It is unclear to me if you say hex is acceptable or not.
> >
> > If all you need is a unique hash from a string (however you generate it is
> > irrelevant), then a 32 character hash with hex values can be done using
> > md5().
> >
> > $your_hash = md5($your_string);
> >
> > http://php.net/manual/en/function.md5.php
> 
> Yes, it sounds to me like you just want a cryptographic hash, then
> run the hash value through a base-64 encoder to get an alphanumeric
> value rather than a hexadecimal value.
> 
> Alternatively, if security isn't your goal, you could use a CRC, which
> should give a smaller output value than MD5 or SHA1.
> 
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