A Rose by Any Other Name...

by coatta 2/25/2012 10:22:00 AM
 
Actually, in coding names do matter. A few months back we moved our application from one hosting provider to another and everything worked except OpenID authentication. In fact, we had both applications running simultaneously and talking to the same OpenID provider, and one worked and the other didn't.
 
We were actually getting an error message that indicated a packet had been rejected due to a problem with a "nonce". Here's a definition from Wikipedia: nonce is an arbitrary number used only once to sign a cryptographic communication. That pretty much matches my notion of what a nonce is as well.
 
I figured this must be due to some peculiar packet duplication that was causing a nonce to be used twice. Seemed like it should be easy to sort out with a network trace, so we slapped one on and collected the traces. They were isomorphic until they weren't. When OpenId failed, it appeared to be because they simply just stopped talking.
 
OK, so time to dive into the code.
We trace through the code looking for where the nonce was processed. I kept expecting to run into a table that preserved nonce values so the code could check if a nonce had been seen more than once. I couldn't find one. Eventually we got to exact place in the code where the error originated. The "nonce" was actually a timestamp, and the error was because of clock drift between the OpenID provider and the new server we were running on.
 
Needless to say, this would have all been a lot more straightforward if they had used the right word! An error message along the lines of "the timestamp on message X is out of date" would have made this a lot easier to figure out. Having the field called "timestamp" rather than "nonce" would have made the code a lot easier to understand.

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