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I am learning cryptography at school and I was wondering:

  1. How are the blocks/streams after decryption synchronized at the receiver to form one long meaningful message?
  2. Am I right by saying that stream cipher will incur a LOT more overhead while synchronizing?
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You may want to reword this to be more detailed, or give an example situation –  Richie Frame Sep 11 '13 at 5:05
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I am not sure what you mean by synchronization. The ciphertext produced by basically every encryption scheme out there is, in some sense, "in the same order as" the plaintext. You might be confusing with the network stack and packets etc.. –  Thomas Sep 11 '13 at 7:07
    
Despite not fully understanding your question I'm pretty sure the answer to 2 is no. Other than that this question seems to be about data exchange protocol efficiency, and not cryptography and thus offtopic. –  orlp Sep 11 '13 at 7:51
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better explain with an example –  T.B Sep 11 '13 at 9:06

1 Answer 1

up vote 2 down vote accepted

The answer to your question will very much depend on implementation details, but you might not be versed enough in cryptographic protocol development to know exactly what to ask, so I'll take a stab at answering this and hopefully my attempt will help you refine the question as needed.

  1. How are the blocks/streams after decryption synchronized at the receiver to form one long meaningful message?

Sychronization is often done before decryption. Wrap the ciphertext with a protocol header, throw a sequence number into the protocol header, authenticate the entire thing (header and ciphertext). The receiver, after checking authentication, can order the ciphertexts using the sequence number and then decrypt.

  1. Am I right by saying that stream cipher will incur a LOT more overhead while synchronizing?

If you look at my description of how synchronization could be done, you'll notice that it is symmetric-key cipher agnostic. Thus the synchronization will be the same whether we are using a block cipher or a stream cipher.

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