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I just stumbled upon this SO question. I was wondering if it would be still secure to split the encrypted packet into multiple packets, which are then transferred over the wire separately.

  • Could someone tamper with the MAC or contents of the packet if it was split and sent separately?
  • Is splitting information into packets a common way to transfer large amounts of data? What security implication does it have?

2 Answers 2

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If you encrypt the blob all together, compute the HMAC, and then you split the packets up for sending, your data will be just as secure as if you'd sent it all at once anyway. The network stack will likely split the data up into different TCP packets anyway.

You can also use a stream cipher (e.g. AES-CTR) and encrypt on the fly.

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Intuïtively: If sending the data as a whole is secure, then splitting it must be secure too, because the attacker can split any data themselves however they want.

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