> Provided the hash is cryptographic or at least well distributed wrt > clustering, repeating substrings, etc, you're right: entropic security driven > by the DoS heat death of my server as someone tries in vain to create a hash > collision! I could probably write a fail2ban rule for that. But I'm now > thinking again about using an on-the-fly hash with a TTL in the database to > discourage guessing and make it obvious that these are not meant to be > permalinks. > > Thanks for the good discussion! > One problem with entropic security is there is no security once someone gets the link. For example, a user has access but later has that access revoked, etc, or someone emails the link to an unauthorized person by accident, etc.
> On Feb 18, 2012 10:43 AM, "Bruno Jouhier" <[email protected]> wrote: > Idea 1: if your file is identified by a UUID (type 4, 128 bits, > randomly generated), there is simply no way any brute force algorithm > will be able to guess it (*). Why isn't this good enough? > > (*) even if entropy is only 90 bits out of 122, this gives 2^90 ~ > 10^27 combinations. If you can test one combination per nanosecond > (rather fast), this gives you 10^18 seconds ~ 10^13 days ~ 3 10^10 > years to enumerate all the combinations. So, to get 1% chance of > hitting a match, you'd have to wait on average 300 million year (or 1 > year with 300 million computers). > > This is not security by obscurity, this is entropic security. > > On Feb 18, 2:45 am, "C. Mundi" <[email protected]> wrote: > > This is obviously a solved problem. I don't want to reinvent the wheel. > > > > Imagine a digital music store. I have a set of static files which I need > > to serve only to authenticated users. So the set of accessible files > > depends on the user. How do I let each user get the files she is entitled > > to and no other files? > > > > Bad Idea 1: security by obscurity: hide the files behind query strings > > generated on the fly for session.user in the form of nasty looking hard to > > guess hashes. Ugly hack and vulnerable to brute force hash collision. > > Yuck! > > > > Bad Idea 2: set up an instance of node-static.Server() for each > > authenticated session, specifically serving a directory created on the fly > > for that session and containing symlinks to all (and only) files for which > > session.user has privileges. The main server would redirect requests for > > files to the ad hoc static server. Kludgus maximus! > > > > Good Idea: what you tell me. :) > > -- > Job Board: http://jobs.nodejs.org/ > Posting guidelines: > https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines > You received this message because you are subscribed to the Google > Groups "nodejs" group. > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/nodejs?hl=en?hl=en > > -- > Job Board: http://jobs.nodejs.org/ > Posting guidelines: > https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines > You received this message because you are subscribed to the Google > Groups "nodejs" group. > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/nodejs?hl=en?hl=en -- Job Board: http://jobs.nodejs.org/ Posting guidelines: https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines You received this message because you are subscribed to the Google Groups "nodejs" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/nodejs?hl=en?hl=en
