I accidentally deleted the private and public key pair of my certificate, but I can't find anything helpful to undo or add those to my certificate again.
Actually the developement certificate has expired, so i redownloaded the new one. Than I wanted to add the private/public key to my new certificate. And there it happend, i deleted it.
How can I get these and set them to my actual certificate again.
I had this issue two days ago.
Open Keychain Access
What you have to do is make backups of all your certificates and then go and delete all the private and public keys and certificates on your machine relevant to apple.
Then in Keychain Access click on Keychain Access(Menu Bar) and in the menu select Certificate Assistant -> Request a certificate from a certificate authority.
Enter your details and make sure Saved to disk and Let me specify key chain pair is selected.
Save it.
On the next screen: These values must be:
Key Size: 2048 bits
Algorithm: RSA
You then need to log into the Provisioning Portal on apple's website and revoke all certificates there.
Then click distribution and say Add Certificate and select the file you created earlier.
You can then request all certificates again. Re-download all certificates, once you start opening the downloaded certificates your new key pair and certificate will be in Keychain Access.
If you have any questions check out http://developer.apple.com/ios/manage/distribution/index.action
来源：https://stackoverflow.com/questions/6707865/apple-keychain-private-public-key-issue