From: khaines@...
Date: 2006-10-29T23:59:46+09:00
Subject: Re: symetrical encryption algo's ?

On Sun, 29 Oct 2006, dc wrote:

> is there a way to de-sha1 these hashed results to get the original data?
> and to do the shash with a specific key?
> all i could find was:
>
>          res = Digest::SHA1.hexdigest(str)
>
> whats the reverse of this,
> and where is the key from?

No.

A hashing algorithm is a one way algorithm.  You can't get your original 
data back from it.

> we need to pass URLs back and forth from a ruby site to a PHP site. so
> i was looking for a reasonably easy algorithm that would work for
> both. I've had problems with blowfish on PHP  giving different results
> on different OSs. So i dont really want to risk something more obscure
> given such different environments.

As I've mentioned, I'm doing this using a pure ruby crypto library found 
on Rubyforge: http://rubyforge.org/projects/crypt/

> but I need to be able to go both ways, given the key. eg:
>
> ruby.site.com/uri=1b2347ghjhsdgf
>
> I can then decode this + with the users ID/key + send them on their way,
> and also pack up URLs to send ppl back to the php page.

If Rijndael(AES), Gost, or IDEA can work reliably via PHP, then you do 
something like this:

irb(main):001:0> require 'rubygems'
=> true

irb(main):002:0> require 'crypt/rijndael'
=> true

irb(main):003:0> require 'base64'
=> true

irb(main):004:0> require 'cgi'
=> true

irb(main):005:0> uri = 'uri=1b2347ghjhsdgf'
=> "uri=1b2347ghjhsdgf
"
irb(main):006:0> crypto = Crypt::Rijndael.new('I am a key')
=> #<Crypt::Rijndael:0xb726dd9c @shiftIndex=0, @keyWords=8, @blockWords=4, 
...[snip]...

irb(main):007:0> encrypted_uri = CGI.escape(Base64::encode64(crypto.encrypt_string(uri)))
=> "Ai32bnCHRKW1xVEfjtNt63dSQRzRq8SPCSiS6gs9b9fgteBEBSFB%2BLRYdUD2%0AijDQ%0A"

irb(main):008:0>  url = "ruby.site.com/#{encrypted_uri}"
=> "ruby.site.com/Ai32bnCHRKW1xVEfjtNt63dSQRzRq8SPCSiS6gs9b9fgteBEBSFB%2BLRYdUD2%0AijDQ%0A"


Just reverse the steps to get the original data back:

irb(main):009:0> original = crypto.decrypt_string(Base64::decode64(CGI.unescape(encrypted_uri)))
=> "uri=1b2347ghjhsdgf"


Kirk Haines