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The bitcoin protocol relied on using proofs of work to provide scarcity in producing new blocks.
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For this question you are asked to order a list of tasks by how much expected work they require.
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Assume that H is a strong cryptographic hash function that produces 128 output bits
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from any length input.
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Comuting H(x) takes 1 unit of time.
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E indicates RSA encryption. K sub U is a known public key.
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But the corresponding private key is not known.
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Computing E(x) takes takes 1000 units of time.
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There are no memory limits, but the task has no access to precomputed values.
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Using those assumptions, order these by how much work they prove
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from the least expected work to the most expected work.
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For example, enter cebad if you think c requires the least amount of work
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and d the most amount of expected work.