Download a file in a File Provider Extension in iOS

Question

Created Nov ’23

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I am developing a cloud-based application and have integrated the FileProviderExtension. However, files larger than 20 MB are not downloading as it’s throwing a memory limit exception. In this process, I have downloaded the file data, but after downloading the data, I need to decrypt the data. I am getting a memory limit exception during decryption. I am using the below lines to decrypt the data.

      let symmetricKey = SymmetricKey(data: key)
      let sealedBox = try AES.GCM.SealedBox(combined: inputData)
      let decryptedData = try AES.GCM.open(sealedBox, using: symmetricKey)

I am getting memory limit exception at AES.GCM.open(sealedBox, using: symmetricKey)

Answer 1

DTS Engineer OP

Apple

Nov ’23

This is pretty much the same issue as your other thread. Normally I’d just link to that, but there is one extra wrinkle here: How do you do streaming encryption with AES.GCM?

It turns out that you can’t, at least not directly when using Apple CryptoKit. See this thread.

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Answer 2

Harish-osi OP

Nov ’23

We are downloading the file chunk by chunk. Even with a chunk size of 5MB, it still reaches the 20MB memory limit. Additionally, we decrypt every chunk using AES.GCM for seal/open API.

Answer 3

DTS Engineer OP

Apple

Nov ’23

5 MiB is a pretty big chunk size given your 20 MiB limit. Can you reduce that?

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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