??定義：設(shè)x=x1x2……xn是含有n個(gè)字母的串，則在x中隨機(jī)選擇兩個(gè)元素且這兩個(gè)元素相同的概率為：

??猜測(cè)密鑰長(zhǎng)度：假設(shè)密鑰長(zhǎng)度為d，提取相同密鑰字加密的密文，測(cè)試其重合指數(shù)：

???若果猜測(cè)正確，則重合指數(shù)接近0.065；

???否則，字符串表現(xiàn)得更加隨機(jī)，一般在0.038~0.065之間

Step2:確定密鑰字相對(duì)位移

重合互指數(shù)

??設(shè)X=x1x2……xn，Y=y1y2……ym，分別為長(zhǎng)度為n和m的串，其重合互指數(shù)為從X與Y中分別隨機(jī)選出一個(gè)元素且兩個(gè)元素相同的概率。

??考慮不同密鑰字加密后密鑰串的重合互指數(shù)：

其中s表示密文分組對(duì)應(yīng)的密鑰字母的相對(duì)位移。

經(jīng)過多位前輩的計(jì)算，當(dāng)s為正確相對(duì)位移值時(shí)，該重合互指數(shù)的值應(yīng)該趨向于0.065。

Step3：窮搜密鑰字

??確定密鑰字之間關(guān)系式基礎(chǔ)上，窮舉搜索26種可能。

例題

密文：krkpewxvftksopztecxvbuhfvycgxouflihoffptrcwffwhkcevxhiuzfposdvccyctpmjtbfymllctiwxtacsmjmoncwdnawjrwtjgjsuystvbxgvcmgczbqecllttfkjlacpfttjgeegtbvkfpmhjzqaxhvvpgxoeychrcwumchhyigixhqdciawunmjerefkekcozqttznfdjlopuyqhjgrjawcpfrgxhwiljgrgiycrqkiajfgvrlrxgkkghdbqnliaovzrltgafslacjvjexrwjrdzsvruprttfkwxfgrlstznnmjerdvjdlhkwwdngjfsawgjfunhitjcaykgrptzicibtwrcpycwbkxfibrqemivotvwdnotvldmvgicshbqkztmfqlzaxrqekntqefscmbqkfxguyzjaaorgccmcovrwxbckgdgonrqhxadcclbznjfdpzgegtgqawygxkgcjiasofqiecxvbdyageztjikvrxymqlapghcbcrtfgfdnhitjcaytqiknlsnwgrtbpfrlkwvvycraqicqnhpfrwbbizliasyfpawqqljslhqgktmccumgxmqlsemcvycsxovy

密鑰：crypto

明文：

I am alive here, my beloved, for the reason to adore you.Oh!How anxious I have been for you and how sorry I am about all you must have suffered in having no news from us.May heaven grant that this letter reaches you. Do not write to me, this would compromise all of us and above all,do not return underany circumstances. It is known that it was youwhohelped us to get away from here and all would belostif you should show yourself.We are guarded day and night. Ido not care you are not here. Do not be troubled on my account. Nothing will happen to me. The national assemble willshow leniency. Farewell the most loved of men. Be quiet if you can take care of yourself.For myself I cannot write any more, but nothing in the world could stop me to adore youp to the death.

文件鏈接

https://download.csdn.net/download/Qtuanqi/16634721

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