Question

I’m writing a web app that points to external links. I’m looking to create a non-sequential, non-guessable id for each document that I can use in the URL. I did the obvious thing: treating the url as a string and str#crypt on it, but that seems to choke on any non-alphanumberic characters, like the slashes, dots and underscores.

Any suggestions on the best way to solve this problem?

Thanks!

Answer 1

Depending on how long a string you would like you can use a few alternatives:

require 'digest' Digest.hexencode('http://foo-bar.com/yay/?foo=bar&a=22') # '687474703a2f2f666f6f2d6261722e636f6d2f7961792f3f666f6f3d62617226613d3232'  require 'digest/md5' Digest::MD5.hexdigest('http://foo-bar.com/yay/?foo=bar&a=22') # '43facc5eb5ce09fd41a6b55dba3fe2fe'  require 'digest/sha1' Digest::SHA1.hexdigest('http://foo-bar.com/yay/?foo=bar&a=22') # '2aba83b05dc9c2d9db7e5d34e69787d0a5e28fc5'  require 'digest/sha2' Digest::SHA2.hexdigest('http://foo-bar.com/yay/?foo=bar&a=22') # 'e78f3d17c1c0f8d8c4f6bd91f175287516ecf78a4027d627ebcacfca822574b2' 

Note that this won’t be unguessable, you may have to combine it with some other (secret but static) data to salt the string:

salt = 'foobar' Digest::SHA1.hexdigest(salt + 'http://foo-bar.com/yay/?foo=bar&a=22') # 'dbf43aff5e808ae471aa1893c6ec992088219bbb' 

Now it becomes much harder to generate this hash for someone who doesn’t know the original content and has no access to your source.