题目内容
A向B发送消息P，并使用公钥体制进行数字签名。设E表示公钥，D表示私钥，则B要保留的证据是(5)。基于数论原理的RSA算法的安全性建立在(6)的基础上。Kerberos是MIT为校园网设计的身份认证系统，该系统利用智能卡产生(7)密钥，可以防止窃听者捕获认证信息。为了防止会话劫持，Kerberos提供了(8)机制，另外报文中还加入了(9)，用于防止重发攻击(Replay Attack)。
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A．FIN=1，序号＝YB．序号=Y，ACKx+1C．ACKx+1D．FIN=1，序号=Y，ACKx+1=1
期货公司与客户签订《期货经纪合同》后，应当向客户出示《期货交易风险说明书》。()
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Albert Einstein was the first to suggest the existence of stimulated emission in a paper published in 1917. However, for many years physicists thought that atoms and molecules always were much more likely to emit light spontaneously and that stimulated emission thus always would be much weaker. It was not until after the Second World War that physicists began trying to make stimulated emission dominate. They sought ways by which one atom or molecule could stimulate many others to emit light, amplifying it to much higher powers.
The first to succeed was Charles H. Townes, then at Columbia University in New York. Instead of working with light, however, he worked with microwaves, which have a much longer wavelength, and built a device he called a "maser," for Microwave Amplification by the Stimulated Emission of Radiation. Although he thought of the key idea in 1951, the first maser was not completed until a couple of years later. Before long, many other physicists were building masers and trying to discover how to produce stimulated mission at even shorter wavelengths.
The key concepts emerged about 1957. Townes and Arthur Schawlow, then at Bell Telephone Laboratories, wrote a long paper outlining the conditions needed to amplify stimulated emission of visible light waves. At about the same time, similar ideas crystallized in the mind of Gordon Gould, then a 37-year-old graduate student at Columbia, who wrote them down in a series of notebooks. Townes and Schawlow published their ideas in a scientific journal, Physical Review Letters, but Gould filed a patent application. Three decades later, people still argue about who deserves the credit for the concept of the laser.
Which of the following statements best describes a laser？
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