A tutorial on Creating Certificates for iOS developers.
1 ) Open Keychain Access (Applications / Utilities / Keychain Access)
2 ) Click on Keychain Access in the top menu bar and choose Certificate Assistant – Request a Certificate From a Certificate Authority…
3 ) Enter the name and email address used on your Apple iOS developer account and choose “Saved to disk”. (The “CA Email” field is left blank.)
4 ) Sign in to the iOS Provisioning Portal and select “Certificates” from the left side bar.
5 ) Upload the file you just saved under BOTH the “Development” and “Distribution” tabs. (You can create two different certificates using steps 1-3 if you wish, however unless you are working with a group and need control over who can do store builds this is unnecessary.)
6 ) Download your certificates under BOTH the “Development” and “Distribution” tabs, as well as the WWDR intermediate certificate.
7 ) With Keychain Access still open, drag and drop all three of the certificates you just downloaded onto the Keychain Access icon in the dock, one by one. (Some people have reported encountering issues trying to add multiple certificates at once, which is why I suggest adding them one at a time.)
These steps may seem simple and ultimately, they are – however it’s easy to mess them up and get all sorts of signing issues, so even if you have done this before it is worth being vigilant to avoid headaches come build time.