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I was wondering whether there exists a symmetric encryption scheme such that

  1. there is 1 sender and n receivers. Each receiver has 1 random and independent symmetric key. The sender knows the symmetric keys of all receivers in advance.
  2. the sender can encrypt one message using the above n keys and produce a ciphertext. Each receiver can decrypt the ciphertext using his own symmetric key to recover the message.
  3. the above n keys are used only for encrypting/decrypting 1 message.
  4. the encryption is deterministic. This excludes some trivial constructions such that sampling one shared key that is used for encrypting the message, followed by respectively encrypting the shared key using n symmetric keys.
  5. the scheme achieves somewhat one-time-CPA security. Of course, compared to the standard notion, the difference is that we need to consider n keys instead of 1 key.

Motivation: Now I am facing one problem that a large file needs to be sent to multiple users (only once) under the condition that the randomness generator of the sender is broken (or unreliable).

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  • $\begingroup$ I'm not sure what all the requirement you list have to do with the problem you mention as motivation. Anyway, this kind of question is more on-topic at Cryptography. $\endgroup$ Apr 29 at 4:36

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Not sure there's anything out of the box.

A trivial construction might be to encrypt the file with a symmetric key and then encrypt the symmetric key n times with receiver symmetric keys and prepend that to the ciphertext. The downsides are obvious.

A broken randomness is going to be a major downside for any symmetric cipher that uses an IV (all the good ones).

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