I am trying Google Cloud Messaging sample app for iOS platform. https://developers.google.com/cloud-messaging/ios/start
To generate GoogleServices-Info.plist APNS development and production certificates are needed (PKCS#12 file format). I have created .p12 file in MAC KeyChain Access (bundling both APNS dev certificate and private key).
But when uploading the .p12 file, it says it is not in valid format (The certificate must be a valid PKCS12 file).
Here's my solution, without the terminal !
delete your actual certificate ( in Keychain ) : "Apple Development IOS Push Service" & "Apple Production IOS Push Service"
Go to Apple Developer, Identifiers, App IDs, Select "YourApp", Edit, Push Notification and download the 2 certificates (dev & prod)
import these 2 certificates in Keychain
in Keychain, go to "My Certificates", find the "Apple Development IOS Push Service" & "Apple Production IOS Push Service", click on the arrow to expand the Certificate + Key
Select both the the Certificate + Key, Right click "Export 2 items", you have your .p12 valid certificate ready for upload to GCM Services
This link helped me : http://faq.appaloosa-store.com/knowledgebase/articles/61785-how-to-generate-push-notification-p12-file
For anyone still having this issue, the solution for me was to not select both the key and the certificate for export - rather just export the certificate which ALREADY includes the key.
This problem comes when we use Firefox to upload the .p12 file. In Chrome I am able to upload the same file.
you can select only one also to export in .p12 format..
macApplication > Keychain Access > My Certificates > Export in .p12 format
来源：https://stackoverflow.com/questions/30602340/how-to-generate-valid-apns-certificate-p12-for-use-in-gcm-for-ios