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The trunk protocol is a thought experiment involving a trunk or suitcase with two locks on it that can perform secure transactions using a public shipping service. It has the advantage of being concrete and without requiring a knowledge of mathematics or computer science.〔The concept is self evident, but it is not known who invented it.〕 ^ The Trunk Protocol *Alice wishes to send something to Bob. *Alice has a trunk with two hasps on it. *Alice places the item into the trunk and puts her lock on a hasp and locks it. *Alice sends the trunk via railway express to Bob. *Bob puts his lock onto the second hasp and locks it. *Bob sends the trunk back to Alice via railway express. *Alice removes her lock and returns the trunk to Bob. *Bob removes his lock and takes the item out of the trunk. The trunk protocol can be turned into a mathematical protocol by using any commutative encryption function EK(M), meaning that EK(EK *(M)) = EK *(EK(M)) for any two keys K, K * and message M. For example, EK(M) = MK (mod p), where p is a 500-bit prime. The commutativity is related to the fact that the locks on the trunk can be removed in any order, regardless of the order in which they were attached. The security of the function EK(M) = MK (mod p) is based on the well known difficulty of computing the Discrete logarithm when the prime p is large. The trunk protocol can be used to implement a commitment scheme. For example, we can use it to implement coin flipping over a telephone. ^ Protocol for coin flipping over a telephone *Alice flips a coin. *Alice writes the outcome, either "heads" or "tails" on a card. *Alice places the card into her trunk and locks one hasp. *She sends the trunk to Bob. *Bob receives the trunk, locks the second hasp, and sends the trunk back to Alice. *Bob flips a coin and tells Alice the outcome, either "heads" or "tails" over the telephone. *Alice removes her lock and returns the trunk to Bob. *Bob removes his lock, opens the trunk, and removes and reads Alice's card. *If Alice's coin flip, as revealed by her card, agrees with Bob's coin flip she wins. ==See also== Three-pass protocol 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Trunk protocol」の詳細全文を読む スポンサード リンク
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