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Diffie–Hellman key exchange (D–H) 〔Synonyms of Diffie–Hellman key exchange include: *Diffie-Hellman-Merkle key exchange *Diffie–Hellman key agreement *Diffie–Hellman key establishment *Diffie–Hellman key negotiation *Exponential key exchange *Diffie–Hellman protocol *Diffie–Hellman handshake〕 is a specific method of securely exchanging cryptographic keys over a public channel and was one of the first public-key protocols as originally conceptualized by Ralph Merkle.〔 D–H is one of the earliest practical examples of public key exchange implemented within the field of cryptography. Traditionally, secure encrypted communication between two parties required that they first exchange keys by some secure physical channel, such as paper key lists transported by a trusted courier. The Diffie–Hellman key exchange method allows two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure channel. This key can then be used to encrypt subsequent communications using a symmetric key cipher. Diffie–Hellman is used to secure a variety of Internet services. However, research published in October 2015 suggests that the parameters in use for many D-H Internet applications at that time are not strong enough to prevent compromise by very well-funded attackers, such as the security services of large governments.〔 The scheme was first published by Whitfield Diffie and Martin Hellman in 1976. By 1975, James H. Ellis, Clifford Cocks and Malcolm J. Williamson within GCHQ, the British signals intelligence agency, had previously shown how public-key cryptography could be achieved; however, their work was kept secret until 1997. Although Diffie–Hellman key agreement itself is a non-authenticated key-agreement protocol, it provides the basis for a variety of authenticated protocols, and is used to provide forward secrecy in Transport Layer Security's ephemeral modes (referred to as EDH or DHE depending on the cipher suite). The method was followed shortly afterwards by RSA, an implementation of public-key cryptography using asymmetric algorithms. , from 1977, is now expired and describes the now public domain algorithm. It credits Hellman, Diffie, and Merkle as inventors. ==Name== In 2002, Hellman suggested the algorithm be called Diffie–Hellman–Merkle key exchange in recognition of Ralph Merkle's contribution to the invention of public-key cryptography (Hellman, 2002), writing: : The system...has since become known as Diffie–Hellman key exchange. While that system was first described in a paper by Diffie and me, it is a public key distribution system, a concept developed by Merkle, and hence should be called 'Diffie–Hellman–Merkle key exchange' if names are to be associated with it. I hope this small pulpit might help in that endeavor to recognize Merkle's equal contribution to the invention of public key cryptography. 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「Diffie–Hellman key exchange」の詳細全文を読む スポンサード リンク
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