## 02ps-04 Decrpytion In Parallel Solution

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And the solution is that all of these modes can be decrypted in parallel.
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Let's look at each one of these modes one at a time.
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ECB can be decrypted in parallel
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because for each C-naught that we have
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we can decrypt it in reverse
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to end up with our original message.
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This can be run on one processor,
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and you do the same thing on this one and for all the other chunks
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of the message that we have, and all those can be run in parallel.
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Counter mode is also decryptable in parallel.
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For counter mode, the important part that we need to calculate
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is this bit into the XOR, and we know our nonce,
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and we know our counter advance,
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so this whole chunk can be calculated at one processor.
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This whole chunk can be calculated on another processor,
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and so on, and once we calculate those, we can calculate our XORs
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to reverse the C1 into the message, and this can also all be done in parallel.
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For cipher block chaining mode, similar to counter mode,
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the important part, this input into the xor again,
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which for the first block we know the initialization vector,
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so that can be calculated.
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Independently, we are already given C-naught,
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which can be processed in parallel to this part.
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In C-1 we know, and this could be processed in parallel, and again,
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we can process--calculate this, calculate this,
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and CBC can be decrypted in parallel.
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Similar to cipher block chaining mode, the cipher feedback mode
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is decryptable in parallel.
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The idea is very similar to the 2 modes we just discussed.
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We need to calculate the input into the XOR.
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This entire chain is known in advance.
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From C-naught we have this entire chain, which is also known in advance,
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and we can calculate all these inputs into the XOR in parallel and decrypt our message.
タイトル：
02ps-04 Decrpytion In Parallel Solution

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Team:
Udacity
プロジェクト：
CS387 - Applied Cryptography
Duration:
01:48