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A Quantum Digital Signature (QDS) refers to the quantum mechanical equivalent of either a classical digital signature or, more generally, a handwritten signature on a paper document. Like a handwritten signature, a digital signature is used to protect a document, such as a digital contract, against forgery by another party or by one of the participating parties. As e-commerce has become more important in society, the need to certify the origin of exchanged information has arisen. Modern digital signatures enhance security based on the difficulty of solving a mathematical problem, such as finding the factors of large numbers (as used in the RSA algorithm). Unfortunately, the task of solving these problems becomes feasible when a quantum computer is available (see Shor's algorithm). To face this new problem, new quantum digital signature schemes are in development to provide protection against tampering, even from parties in possession of quantum computers and using powerful quantum cheating strategies. == Classical public-key method == The public-key method of cryptography allows a sender to sign a message (often only the cryptographic hash of the message) with a sign key in such a way that any recipient can, using the corresponding public key, check the authenticity of the message. To allow this, the public key is made broadly available to all potential recipients. To make sure only the legal author of the message can validly sign the message, the public key is created from a random, private sign key, using a one-way function. This is a function that is designed such that computing the result given the input is very easy, but computing the input given the result is very difficult. A classic example is the multiplication of two very large primes: The multiplication is easy, but factoring the product without knowing the primes is normally considered infeasible. : ''easy'' : ''very difficult'' 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「Quantum digital signature」の詳細全文を読む スポンサード リンク
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