[Error] CSR algorithm/size incorrect. Expected: RSA(2048) - 인증서 오류

Since you made an install of a new OS you probably don't have any more your private and public key that you used to sign your app in XCode before. You need to regenerate those keys on your machine by revoking your previous certificate and ask for a new one the iOS development portal. As part of the process you will be ask to generate a Certificate Signing Request which is where you seem to have problem.

You will find all u need there which consist of (from the official doc):

1.Open Keychain Access on your Mac (located in Applications/Utilities).

2.Open Preferences and click Certificates. Make sure both Online Certificate Status Protocol and Certificate Revocation List are set to Off.

3.Choose Keychain Access > Certificate Assistant > Request a Certificate From a Certificate Authority.

Note: If you have a private key selected when you do this, the CSR won’t be accepted. Make sure no private key is selected. Enter your user email address and common name. Use the same address and name as you used to register in the iOS Developer Program. No CA Email Address is required.

4.Select the options “Saved to disk” and “Let me specify key pair information” and click Continue.

5.Specify a filename and click Save.

For the Key Size choose 2048 bits and for Algorithm choose RSA. Click Continue and the Certificate Assistant creates a CSR and saves the file to your specified location.

출처: https://stackoverflow.com/questions/12126496/how-to-obtain-certificate-signing-request