# Symetrical encryption algo's? **URL:** \ **Category:** Ruby\ **Created:** [October 29, 2006, 2:56pm UTC](https://www.ruby-forum.com/t/symetrical-encryption-algos/74050 "2006-10-29T14:56:50Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [October 29, 2006, 2:56pm UTC](https://www.ruby-forum.com/t/symetrical-encryption-algos/74050/1 "2006-10-29T14:56:50Z")
hi - > I have a feeling I’m missing something, but if all you want to do is > generate obfuscated URLs, why not just the the SHA1-hash of a string > consisting of the “real” url and the user’s name? You can store the > generated urls in the server-side user-session so you don’t have to do any > decrypting. 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? 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. this is also for a mobile phone service where we reliably can get a uniqueID per user. we need to prevent people forwarding URLs which is why we need to key off the uniqueID but I need to be able to go both ways, given the key. eg: [ruby.site.com/uri=1b2347ghjhsdgf](http://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. other suggestions are to put all the URLs in a DB + then check against the userID/urlID key etc but i want to avoid DB access. tx! ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [October 29, 2006, 3:22pm UTC](https://www.ruby-forum.com/t/symetrical-encryption-algos/74050/2 "2006-10-29T15:22:49Z")
On 10/29/06, dc [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ``` > res = Digest::SHA1.hexdigest(str) > > ``` > > whats the reverse of this, > and where is the key from? SHA1 is, to my knowledge, not reversable. J`ey [http://www.eachmapinject.com](http://www.eachmapinject.com) ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [October 29, 2006, 4:01pm UTC](https://www.ruby-forum.com/t/symetrical-encryption-algos/74050/3 "2006-10-29T16:01:06Z")
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/](http://rubyforge.org/projects/crypt/) > but I need to be able to go both ways, given the key. eg: > > [ruby.site.com/uri=1b2347ghjhsdgf](http://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’) =\> #\ encrypted\_uri = CGI.escape(Base64::encode64(crypto.encrypt\_string(uri))) =\> “Ai32bnCHRKW1xVEfjtNt63dSQRzRq8SPCSiS6gs9b9fgteBEBSFB%2BLRYdUD2%0AijDQ%0A” irb(main):008:0\> url = “[ruby.site.com/#{encrypted\_uri}](http://ruby.site.com/#%7Bencrypted_uri%7D)” =\> "[ruby.site.com/Ai32bnCHRKW1xVEfjtNt63dSQRzRq8SPCSiS6gs9b9fgteBEBSFB%2BLRYdUD2 ijDQ](http://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 H.