Integer to code and back

[Tom]

I need to convert an integer to a unique code string consisting only of
capital letters and numbers.
I also need to be able to convert it back to an integer again.

Example:

10 =DFG56JKG4 =10

How do I accomplish that?
Googling has not helped.

Regards

[Dan M]

On Wed, 03 Jan 2007 19:05:14 +0100, Tom wrote:

I need to convert an integer to a unique code string consisting only of
capital letters and numbers.
I also need to be able to convert it back to an integer again.

Example:

10 =DFG56JKG4 =10

How do I accomplish that?
Googling has not helped.

Regards

What is the logic used to map from integer to string?

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Dan M wrote:

On Wed, 03 Jan 2007 19:05:14 +0100, Tom wrote:

>10 =DFG56JKG4 =10

How do I accomplish that?

What is the logic used to map from integer to string?

I guess that Tom has absolutely no idea on how to do that.

Viable possibilities:
- - A hash table.
- - A simetric encryption function.

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Iván Sánchez Ortega -ivansanchez-algarroba-escomposlinux-punto-org-

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[Tom]

>>

>What is the logic used to map from integer to string?

I guess that Tom has absolutely no idea on how to do that.

Exactly!

I have triede base64_decode / encode but it fails as it uses non
alphanumerics.
So does base32

Viable possibilities:
- - A hash table.

Hmm doesn't ring a bell, and google gives me oodles of stuff that is not
directly related.
Could you please provide me with an example in pseudo code or something?

- - A simetric encryption function.

Well, same result when googling. The concept exists but apparently everybody
knows it so well they don't explain it but just refer to it :-D
An example please?

Thanks for answering!

Tom

[Michael Fesser]

..oO(Tom)

>I need to convert an integer to a unique code string consisting only of
capital letters and numbers.
I also need to be able to convert it back to an integer again.

Example:

10 =DFG56JKG4 =10

Just curious: Why do you need that? The integer itself is unique and
consists only of numbers ... so what's the purpose of the "encoding"?

Micha

[=?UTF-8?B?SXbDoW4gU8OhbmNoZXogT3J0ZWdh?=]

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Hash: SHA1

Tom wrote:

>- - A hash table.

Hmm doesn't ring a bell, and google gives me oodles of stuff that is not
directly related.
Could you please provide me with an example in pseudo code or something?

Basically, you generate a table that you store somewhere, and relates every
integer you can think of with its hash.

Got a new integer? Calculate the hash and store it in the table. Got a hash?
Check if it exists in the table.

How you exactly hash the integers is your problem, tough.

>- - A simetric encryption function.

Well, same result when googling. The concept exists but apparently
everybody knows it so well they don't explain it but just refer to it :-D
An example please?

RTFM. php.net/mcrypt

- --
- ----------------------------------
Iván Sánchez Ortega -ivansanchez-algarroba-escomposlinux-punto-org-

Un ordenador no es un televisor ni un microondas, es una herramienta
compleja.
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[Michael Fesser]

..oO(Iván Sánchez Ortega)

>Basically, you generate a table that you store somewhere, and relates every
integer you can think of with its hash.

A hash is not unique.

Micha

[Tom]

Got a new integer? Calculate the hash and store it in the table. Got a

hash?
Check if it exists in the table.

Ah, good idea. Thanks.

>>- - A simetric encryption function.

Well, same result when googling. The concept exists but apparently
everybody knows it so well they don't explain it but just refer to it :-D
An example please?

RTFM. php.net/mcrypt

1) How was I supposed to link "simetric encryption" to "mcrypt" ??? :-D :-D
2) Are you sure you it shouldn't be spelled "symmetric" ?

Tom

[Tom]

"Michael Fesser" <ne*****@gmx.dewrote in message
news:rn********************************@4ax.com...

.oO(Tom)

>>I need to convert an integer to a unique code string consisting only of
capital letters and numbers.
I also need to be able to convert it back to an integer again.

Example:

10 =DFG56JKG4 =10

Just curious: Why do you need that? The integer itself is unique and
consists only of numbers ... so what's the purpose of the "encoding"?

The purpose is to use it in links.
Each code will link to a given row in a database and then show an image.
But I don't want script kiddies to fetch all images iteratively :-)

Tom

[Moot]

Michael Fesser wrote:

.oO(Tom)

I need to convert an integer to a unique code string consisting only of
capital letters and numbers.
I also need to be able to convert it back to an integer again.

Example:

10 =DFG56JKG4 =10

Just curious: Why do you need that? The integer itself is unique and
consists only of numbers ... so what's the purpose of the "encoding"?

Micha

I'm curious as well...a number is already unique, what benefit are you
looking to get from the encoding?

Heck, if all you want is a way to convert a number to an alphanumeric
string and back reliably without any kind of obfuscation, then you
could just convert the int to hex and voila, you've got an alphanumeric
string that contains 0-9 and A-F which can easily be converted back to
decimal notation.

- Moot

[Kimmo Laine]

"Tom" <[e-mail] in message
news:45***********************@news.sunsite.dk...

2) Are you sure you it shouldn't be spelled "symmetric" ?

I'm pretty sure it's "symmetric", but let's find out, shall we...
http://www.googlefight.com/index.php...word2=simetric

"symmetric" 28,000,000 results vs. "simetric" 104,000 results...

--
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http://outolempi.net/ahdistus/ - Satunnaisesti päivittyvä nettisarjis
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[Toby Inkster]

Michael Fesser wrote:

A hash is not unique.

For small[1] integers $i, md5($i) should be unique.

____
1. Say, lower than 1,000,000,000

--
Toby A Inkster BSc (Hons) ARCS
Contact Me ~ http://tobyinkster.co.uk/contact

[Toby Inkster]

Tom wrote:

10 =DFG56JKG4 =10

How do I accomplish that?

How about this...

define('MYSECRET','Some unguessable string');

function int2code ($i)
{
$md5 = strtoupper(md5(MYSECRET.$i));
$mdStart = substr($md5, 0, 4);
$mdEnd = substr($md5, 28, 4);
return $mdStart.$i.$mdEnd;
}

function code2int ($code)
{
preg_match('/^([A-F0-9]{4})([0-9]+)([A-F0-9]{4})$/', $code, $matches);
$i = $matches[2];

$md5 = strtoupper(md5(MYSECRET.$i));
$mdStart = substr($md5, 0, 4);
$mdEnd = substr($md5, 28, 4);
if ($mdStart.$i.$mdEnd==$code)
return $i;

return FALSE; // Invalid code!
}

--
Toby A Inkster BSc (Hons) ARCS
Contact Me ~ http://tobyinkster.co.uk/contact

[Toby Inkster]

Iván Sánchez Ortega wrote:

Viable possibilities:
- - A hash table.
- - A simetric encryption function.

Possibility three:
- including the unencrypted integer in the query string, but signing it.

I've posted example code for this in my reply to Tom's post.

--
Toby A Inkster BSc (Hons) ARCS
Contact Me ~ http://tobyinkster.co.uk/contact

[Kimmo Laine]

"Toby Inkster" <us**********@tobyinkster.co.ukwrote in message
news:j2************@ophelia.g5n.co.uk...

Michael Fesser wrote:

>A hash is not unique.

For small[1] integers $i, md5($i) should be unique.

Unique yes, but md5 is one-way, and the op wanted a way to convert integers
to strings and back to integers. How do you convert an md5 digest to
integer?

--
"Ohjelmoija on organismi joka muuttaa kofeiinia koodiksi" - lpk
http://outolempi.net/ahdistus/ - Satunnaisesti päivittyvä nettisarjis
sp**@outolempi.net | rot13(xv***@bhgbyrzcv.arg)

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Tom wrote:

The purpose is to use it in links.
Each code will link to a given row in a database and then show an image.
But I don't want script kiddies to fetch all images iteratively :-)

Use "wget -r" and say good-bye to your "security".

--
----------------------------------
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Now listening to: Culture Beat - Metamorphosis0 - [3] Metamorphosis (9:33)
(95%)

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Kimmo Laine wrote:

Unique yes, but md5 is one-way, and the op wanted a way to convert
integers to strings and back to integers. How do you convert an md5 digest
to integer?

Using a rainbow table :-)

- --
- ----------------------------------
Iván Sánchez Ortega -ivansanchez-algarroba-escomposlinux-punto-org-

Un ordenador no es un televisor ni un microondas, es una herramienta
compleja.
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[Tom]

Hey

Wow!

Nice, exactly what I needed.

Thanks a lot!

Tom
"Toby Inkster" <us**********@tobyinkster.co.ukwrote in message
news:2r************@ophelia.g5n.co.uk...

Tom wrote:

>10 =DFG56JKG4 =10

How do I accomplish that?

How about this...

define('MYSECRET','Some unguessable string');

function int2code ($i)
{
$md5 = strtoupper(md5(MYSECRET.$i));
$mdStart = substr($md5, 0, 4);
$mdEnd = substr($md5, 28, 4);
return $mdStart.$i.$mdEnd;
}

function code2int ($code)
{
preg_match('/^([A-F0-9]{4})([0-9]+)([A-F0-9]{4})$/', $code, $matches);
$i = $matches[2];

$md5 = strtoupper(md5(MYSECRET.$i));
$mdStart = substr($md5, 0, 4);
$mdEnd = substr($md5, 28, 4);
if ($mdStart.$i.$mdEnd==$code)
return $i;

return FALSE; // Invalid code!
}

--
Toby A Inkster BSc (Hons) ARCS
Contact Me ~ http://tobyinkster.co.uk/contact

[Tom]

"Tom" <[e-mail] in message
news:45***********************@news.sunsite.dk...

Hey

Wow!

Nice, exactly what I needed.

Well, maybe I rushed to conclusions there :-D

I'm not too fond of having the unencrypted integer sitting right there in
all hashes :-D

But, it should be fairly straightforward to convert it to something else and
back.

Thanks :-)

[Jerry Stuckle]

Tom wrote:

"Michael Fesser" <ne*****@gmx.dewrote in message
news:rn********************************@4ax.com...

>>.oO(Tom)

>>>I need to convert an integer to a unique code string consisting only of
capital letters and numbers.
I also need to be able to convert it back to an integer again.

Example:

10 =DFG56JKG4 =10

Just curious: Why do you need that? The integer itself is unique and
consists only of numbers ... so what's the purpose of the "encoding"?

The purpose is to use it in links.
Each code will link to a given row in a database and then show an image.
But I don't want script kiddies to fetch all images iteratively :-)

Tom

So why only numbers and capital letters? Why not lower case, also?

Or, a better question - why not just store a hash in the table itself
and forget about converting back?

Personally I think I'd just mcrypt_enc() the auto increment field with a
key and store it in the row. Then use this value in the requests.

P.S. I would use mcrypt() because it does create unique values, unlike
hashing algorithms like md5().

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JDS Computer Training Corp.
js*******@attglobal.net
==================

[Toby Inkster]

Tom wrote:

I'm not too fond of having the unencrypted integer sitting right there in
all hashes :-D

What's wrong with having the unencrypted integer there? As long as you
make sure you *check* the hashes (which code2int does!), then you're safe.

<?php
// listing.php
require 'coding_stuff.php';
print "<ul>\n";
for ($i=1; $i<=10; $i++)
{
$c = int2code($i);
print "<li><a href=\"view.php?number={$c}\">view {$i}</a>\n";
}
print "</ul>\n";
?>

<?php
// view.php
require 'coding_stuff.php';
$c = $_GET['number'];
$i = code2int($c);
if ($i!==FALSE)
{
// show the image here.
}
?>

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[Toby Inkster]

Kimmo Laine wrote:

Unique yes, but md5 is one-way, and the op wanted a way to convert integers
to strings and back to integers. How do you convert an md5 digest to
integer?

Brute force; or saved lookup table.

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Contact Me ~ http://tobyinkster.co.uk/contact

[Tom]

"Toby Inkster" <us**********@tobyinkster.co.ukwrote in message
news:b9************@ophelia.g5n.co.uk...

Tom wrote:

>I'm not too fond of having the unencrypted integer sitting right there in
all hashes :-D

What's wrong with having the unencrypted integer there?

Well, remember I wanted the integer ENCRYPTED :-D

I said the integer came from an autonumber column, så fetch three hashes in
a row and you can easily spot the pattern.

But thanks for the attempt :-)

Tom

[Toby Inkster]

Tom wrote:

I said the integer came from an autonumber column, så fetch three
hashes in a row and you can easily spot the pattern.

Who cares that you can spot a pattern though? I don't see who that helps
the script kiddies, given that they can't generate the pattern themselves.

--
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Contact Me ~ http://tobyinkster.co.uk/contact

[Tom]

"Toby Inkster" <us**********@tobyinkster.co.ukwrote in message
news:1l************@ophelia.g5n.co.uk...

Tom wrote:

>I said the integer came from an autonumber column, så fetch three
hashes in a row and you can easily spot the pattern.

Who cares that you can spot a pattern though? I don't see who that helps
the script kiddies, given that they can't generate the pattern themselves.

Sorry, you're right.
Of course this won't help! DOH!

Note to self, don't write on usenet on low bllod sugar :-D

Task solved ;-)

Have a nice weekend,
Tom

[Mladen Gogala]

On Wed, 03 Jan 2007 10:27:55 -0800, Dan M wrote:

What is the logic used to map from integer to string?

It's called "hex representation". There is a little known
function called "sprintf" which can accomplish that.

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