I was just released from being mired in litany of predicaments due to code signing procedures and here's my story...

So I work on a new macbook, someone else's, and i fail to code sign my app before deploying it to my device.

After two days I finally figured it out. (or better put: people sharing their knowledge on internet got it figured out).

Basically, code signing process is following:

You need to have the following in your computer when code sign:
- public and private key pair.
- certificate issued by you (if you are administrator of your Apple developer program)
- Apple intermediate certificate.

You got to have public and private key for code signing. This pair is created on your computer when you created certificates and provisioning profile FOR THE FIRST TIME. If you move development to other machine, you will have to do something to move this pair to the new machine.... The easiest way would be to re-create everything from scratch: delete your certificate in developer.apple.com and recreate it by submitting new certificate request from keychain.

If you develop on a new machine, the private key is usually missing. You can tell by going to the keychain. Your certificate should have a little triangle next to it, that you can click and it will show you the public and private key pair. If you don't have that triangle, you have the certificate but not the key pair and your code signing won't work.

The intermediate certificate can be downloaded from the the usual place in developer site without having to submit certificate request first. If you don't install this, you'll get this error from XCode: /usr/bin/codesign fail or something similar.

Code signing is one part. Then there's this thing called provisioning profile which basically says which certificate to sign which app and which app can be deployed on which device...

Er... I'm unsure. But that's my impression of two days fixing code signing error.

One more thing, I deleted all passwords in keychain because I used my own apple credential in XCode automatic refresh and now I wanted to use someone else's. I couldn't find the right password for XCode in keychain so I deleted them all. .-))
It worked. I was asked to enter new credential when I clicked refresh in XCode organizer. But another problem arose: When I created certificate request it gave me errors like incorrect passphrase or something. I could not create certificate request because I deleted all of my passwords! Solution is simple: restart the computer!