What is a distribution certificate?
A distribution certificate is a digital certificate issued by Apple that identifies you as the trusted signer of an app you are distributing through TestFlight or the App Store. It works together with a private key stored on your Mac, and signing a build with it is how Apple confirms the build came from your account and has not been altered. It is one of the pieces that make up code signing.
How a distribution certificate fits into code signing
Code signing on Apple platforms relies on a public and private key pair. You generate a private key on your Mac and ask Apple to issue a matching certificate, which is the public half plus Apple's stamp of trust. When you build for release, the tools use your private key to sign the app and embed the distribution certificate. A provisioning profile ties that certificate to a specific app identifier and set of entitlements. Apple's servers then verify the signature when you upload, and iOS verifies it again when the app is installed.
Distribution versus development certificates
Apple separates certificates by purpose. A development certificate lets you build and run an app on devices registered to your account while you are working on it. A distribution certificate is for builds that leave your hands: TestFlight betas and App Store releases. Trying to upload a release build signed with a development certificate will fail. Keeping them separate limits what a leaked development certificate could do, since it cannot sign App Store builds.
Managing certificates and how AppFlight helps
Distribution certificates are created and revoked from your Apple Developer account or through Xcode's automatic signing, which can generate and manage them for you. Because a single certificate can sign many apps, most accounts keep just one and protect the private key. AppFlight handles signing as part of its path to the App Store, so the distribution certificate, provisioning profile, and signed build are produced for you rather than configured by hand. A signed, uploaded build still goes through Apple's review before it can be released, so a submitted app is not the same as an approved one.
FAQ
What is the difference between a distribution and a development certificate?
A development certificate signs builds you run on your own test devices during development. A distribution certificate signs builds meant for TestFlight or the App Store. They serve different stages, and Apple keeps them as separate certificate types.
How many distribution certificates can I have?
An Apple Developer account is limited to a small number of distribution certificates at a time. A single certificate can sign many apps, so most accounts only need one, which the whole team can share securely.
What happens when a distribution certificate expires?
Distribution certificates are valid for a period set by Apple, typically one year. Apps already on the App Store keep working, but you must create or renew a certificate to sign and upload new builds after it expires.