英语翻译A stronger version of the substitution cipher is the general substitutioncipher,which allows the cipher alphabet to be any rearrangement of thealphabet.In this case,there are roughly 400,000,000,000,000,000,000,000,000possible keys,becaus

英语翻译A stronger version of the substitution cipher is the general substitutioncipher,which allows the cipher alphabet to be any rearrangement of thealphabet.In this case,there are roughly 400,000,000,000,000,000,000,000,000possible keys,becaus
英语翻译
A stronger version of the substitution cipher is the general substitution
cipher,which allows the cipher alphabet to be any rearrangement of the
alphabet.In this case,there are roughly 400,000,000,000,000,000,000,000,000
possible keys,because this is the number of ways to rearrange the alphabet.
Although a large number of keys is not the sole requirement for a secure
cipher,it certainly makes the codebreaker’s job harder,because checking
every single possible key would be impractical.
Typically,a communications network will use a single algorithm for several
months or years,but will employ a variety of keys.For example,a different
key can be used each day.This means that if a key is captured by the enemy,
then only one day’s communications are immediately jeopardised.It is
assumed that the enemy already knows the algorithm,because it is inevitable
that details of the system will have been leaked or stolen.The significance of
the key,as opposed to the algorithm,is an enduring principle of cryptography,
and it was definitively stated in 1883 by the Dutch linguist Auguste
Kerckhoffs von Nieuwenhof in his famous article ‘La Cryptographie Militaire’:
the security of a cryptosystem must not depend on keeping secret the
crypto algorithm; the security depends only on keeping secret the key.This is
Kerckhoffs’ Principle.
One method for cracking a ciphertext is to guess the true meaning of part of
the encrypted message,which is known as a crib.For example,the codebreaker
might know that a ciphertext that begins ‘XBKJ ...’ is a letter,so
XBKJ might stand for ‘dear ...’,which means that the true values for four
letters have been established,which in turn might be helpful in deciphering
the rest of the message.
Without a crib,and with so many keys,the general substitution cipher
seemed impregnable for centuries,but eventually a flaw was revealed.One of
the first scholars to exploit the weakness of the substitution cipher was
the ninth-century Arab philosopher al-Kindi,who recorded his codebreaking
technique,now known as frequency analysis,in ‘A Manuscript on
Deciphering Cryptographic Messages’.
Frequency analysis focuses on the fact that the letters in the Arabic,Roman,
or any other alphabet have a distinct variation in frequency.In English,for
example,e is the most common letter,accounting on average for roughly 13 per
cent of all letters in a piece of text.The next most common letters are t,a,and n,
whereas letters such as x,q,and z are very rare,as any scrabble player will testify.
Al-Kindi realised that if a letter was substituted for another letter (or symbol),
then the new letter would take on the frequency of the original letter.
Therefore,by studying the frequency of the letters in the ciphertext,it should
be possible to establish their true value.For example,if L is the most common
letter in the ciphertext,then L probably represents e.

英语翻译A stronger version of the substitution cipher is the general substitutioncipher,which allows the cipher alphabet to be any rearrangement of thealphabet.In this case,there are roughly 400,000,000,000,000,000,000,000,000possible keys,becaus
较强的版本的替代密码是普通的替代品
密码,从而允许密码字母表是任何重新排列
字母表.在这种情况下,大约有4亿个,200,000万200,000万800亿
可能的钥匙,因为这里有很多办法让重新排列字母.
尽管大量的钥匙并不是唯一要求的安全
密码,这当然使的工作非常困难,因为片中检查
每一个可能的键将是不切实际的.
通常情况下,一个通信网络将使用一个单一的算法数
在几个月或几年,但会雇用各式各样的钥匙.例如,一个不同的
关键可以用每一天.这意味着如果一个键被敌人俘虏,
只有一天的通讯是立即jeopardised.这是
假定,敌人已经知道该算法,因为它是不可避免的
系统的细节将被泄露或被盗.的意义
最关键的,相对于算法原理,是一种不朽的密码学,
最后声明,这是1883年由荷兰语言学家奥古斯特
在他Kerckhoffs·冯·Nieuwenhof啦Cryptographie Militaire著名的文章':'
必须有安全保障的密码体制的不依赖于保密
密码算法的安全性只取决于保密的关键.这是
Kerckhoffs '的原则.
一种方法就是猜测一密文开裂的一部分的真正含义
将加密后的信息,被称为床里.例如,片中
也许知道,一开始的XBKJ密文.”是信,所以
XBKJ可以站为“亲爱的.’,这意味着真正的价值,为四人
字母已经形成,这反过来会有助于破解
其余的讯息.
没有一个婴儿床,如此多的钥匙,通用的替代密码
几个世纪以来,看起来坚不可摧的,但最后一个漏洞被透露.人的
第一个学者利用的弱点是替代密码
在第九世纪阿拉伯

通常情况下,一个通信网络将使用一个单一的算法数
在几个月或几年,但会雇用各式各样的钥匙。例如,一个不同的
关键可以用每一天。这意味着如果一个键被敌人俘虏,
只有一天的通讯是立即jeopardised。这是
假定,敌人已经知道该算法,因为它是不可避免的
系统的细节将被泄露或被盗。的意义
最关键的,相对于算法原理,是一种不朽的密码学,
最后声明,...

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通常情况下,一个通信网络将使用一个单一的算法数
在几个月或几年,但会雇用各式各样的钥匙。例如,一个不同的
关键可以用每一天。这意味着如果一个键被敌人俘虏,
只有一天的通讯是立即jeopardised。这是
假定,敌人已经知道该算法,因为它是不可避免的
系统的细节将被泄露或被盗。的意义
最关键的,相对于算法原理,是一种不朽的密码学,
最后声明,这是1883年由荷兰语言学家奥古斯特
在他Kerckhoffs·冯·Nieuwenhof啦Cryptographie Militaire著名的文章':'
必须有安全保障的密码体制的不依赖于保密
密码算法的安全性只取决于保密的关键。这是
Kerckhoffs '的原则。
一种方法就是猜测一密文开裂的一部分的真正含义
将加密后的信息,被称为床里。例如,片中
也许知道,一开始的XBKJ密文。”是信,所以
XBKJ可以站为“亲爱的。。。’,这意味着真正的价值,为四人
字母已经形成,这反过来会有助于破解
其余的讯息。
没有一个婴儿床,如此多的钥匙,通用的替代密码
几个世纪以来,看起来坚不可摧的,但最后一个漏洞被透露。人的
第一个学者利用的弱点是替代密码
在第九世纪阿拉伯

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