My OAuth request signature differs from my service provider's one

I'm developing an app using OAuth1.0a for iPad.

My problem is that I can't get the right signature for my request_token request. The service I want to connect with has a debugging tool that allows to check the signature you should have depending on your OAuth parameters.

The result is :

i get the right signature base code
i get different signatures

According to my understanding of OAuth, this means that :

my signature algorithm is bugged (HMAC-SHA1) (but I get it from a 3rd-party : https://github.com/jdg/oauthconsumer/tree/master/Crytpo/)
the service provider is wrong

Is there any free tool, possibly online, that can build a signature from a signature base code and a key to check who's right and who's wrong ?

Thanks for your help

Solution

I've figured out what my problem was, my consumer key contains special characters ('+' and '=') and with these characters, the signature from my provider and from the OAuth iOS framework are different.

I've tried to take a look at the RFC to try to decide who was right but couldn't make a decision. So i'm just gonna try to hack the OAuth code to make it work with my provider. I'll share the trick on this page once I've found it.

So just be aware that special characters encoding might be tricky, and if you have an opinion about how special characters should be encoded to sign your signature base, feel free to share.