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Shipping and Updating Your Product

The only thing that matters to the code signing system is that the signed code installed on the user’s system identical to the code that you signed. It does not matter how you package, deliver, or install your product as long as you don’t introduce any changes into the product. Compression, encoding, encrypting, and even binary patching the code are all right as long as you end up with exactly what you started with. You can use any installer you like, as long as it doesn't write anything into the product as it installs it. Drag-installs are fine as well.

When you have qualified a new version of your product, sign it just as you signed the previous version, with the same identifier and the same designated requirement. The user’s system will consider the new version of your product to be the same program as the previous version. In particular, the keychain will not distinguish older and newer versions of your program as long as both were signed and the unique Identifier hasn't changed.

You can take a partial-update approach to revising your code on the user’s system. To do so, sign the new version as usual, then calculate the differences between the new and the old signed versions, and transmit the differences. Because the differences include the new signature data, the result of installing the changes on the end-user's system will be the newly signed version. You cannot patch a signed application in the field. If you do so, the system will notice that the application has changed and will invalidate the signature, and there is no way to re-validate or resign the application in the field.

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