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Also, because code that you sign with a distribution certificate bears your stamp of approval, avoid handing out signed code that is not final.In practice, Xcode applies your signature when you export your app for distribution.The digital certificate has a usage extension that enables it to be used for signing, and it contains the public key that complements your private key.The certificate is not secret, and is itself generally signed by a certificate authority, which effectively vouches for your identity.Making changes after you sign invalidates the signature.Consider a signed application bundle as a read-only entity.
This is generally the option of last resort, but may be helpful in certain special cases, especially when trying to debug an issue.
Alternatively, you can run Xcode normally signs on your behalf.
You simply choose a signing identity in the General tab of a given target, and Xcode takes care of the details.
Read this chapter to gain a better understanding of what Xcode does on your behalf, or to handle special cases where you need to intervene in the code signing process., which consists of a private key plus a digital certificate.
The private key is an encryption key that only you have, making it impossible for anyone to forge your signature, as long as you keep the key secure.