?題目提供了一個(gè)加解密的算法XECryption algorithm?

首先找規(guī)律，text輸入1，password不輸入，發(fā)現(xiàn)加密結(jié)果是.19.31.-1，再點(diǎn)一下發(fā)現(xiàn)結(jié)果變了.43.11.-5，經(jīng)過(guò)幾次實(shí)驗(yàn)之后發(fā)現(xiàn)每次結(jié)果都不一樣，但是加起來(lái)都等于49,也就是字符1的ascii的十進(jìn)制的值。

輸入其他字符驗(yàn)證一下，發(fā)現(xiàn)三個(gè)數(shù)相加都是對(duì)應(yīng)字符的十進(jìn)制的值。

text輸入1,password中輸入1， 結(jié)果.14.49.35，再點(diǎn)一下.43.49.6， 發(fā)現(xiàn)三個(gè)數(shù)之和是49+49

text輸入1,password中輸入12,結(jié)果.75.58.15，發(fā)現(xiàn)三個(gè)數(shù)之和是49+49+50

通過(guò)別的字符進(jìn)行進(jìn)一步驗(yàn)證，可以發(fā)現(xiàn)規(guī)律如下：

res[0]+res[1]+res[2] = dec(text) + dec(password[0]) + dec(password[1]) + ... +dec(password[len_pass - 1])

解題思路：

提供的加密的encrypt text首先三個(gè)數(shù)一組計(jì)算出和，由于是mail message，我們可以肯定是可以打印的肉眼能看到的字符，所以字符范圍為20-176,也就是說(shuō)password的取值必須保證解密出來(lái)的ascii字符在20-176之間，所以我們需要知道計(jì)算出來(lái)的和的最大值和最小值，password也得是可見(jiàn)字符，也必須落在20-176之間。

我們可以看到前面幾個(gè)的和為845, 859, 871, 879, 863，我們有理由懷疑前面幾個(gè)字符跟人名或者是dear之類的單詞有關(guān)

I have done some packet sniffing on my network and I have recovered this email that was sent from the CEO of the company to Chief Ecological Inspector Samuel Smith. However, it is encrypted and I cannot seem to decode it using any of my basic decryption tools.?

我們發(fā)現(xiàn)前面幾個(gè)的和之間的差正好等于Samuel幾個(gè)字母之間的差，所以我們可以得到下面的結(jié)論

?dec(password[0]) + dec(password[1]) + ... +dec(password[len_pass - 1]) = 845 - 83 = 762

這是一個(gè)多元一次方程 x+y+...+z = 762

有無(wú)窮多個(gè)解。

但是限制在所有的字符都在20-176之間，這個(gè)就需要猜了。我們需要首先知道password的長(zhǎng)度，我們先算一個(gè)平均值。試探得知762/6=127發(fā)現(xiàn)是DEL字符，不可見(jiàn)。

762/7 = 108，是字符l, 762%7 = 6, 108+6 = 114,字母r,所以我們的密碼可以為llllllr

python源碼如下：

from?__future__?import?print_function
str?=?"""296.294.255.268.313.278.311.270.290.305.322.252.276.286.301.305.264.301.251.269.274.311.304.
230.280.264.327.301.301.265.287.285.306.265.282.319.235.262.278.249.239.284.237.249.289.250.
282.240.256.287.303.310.314.242.302.289.268.315.264.293.261.298.310.242.253.299.278.272.333.
272.295.306.276.317.286.250.272.272.274.282.308.262.285.326.321.285.270.270.241.283.305.319.
246.263.311.299.295.315.263.304.279.286.286.299.282.285.289.298.277.292.296.282.267.245.304.
322.252.265.313.288.310.281.272.266.243.285.309.295.269.295.308.275.316.267.283.311.300.252.
270.318.288.266.276.252.313.280.288.258.272.329.321.291.271.279.250.265.261.293.319.309.303.
260.266.291.237.299.286.293.279.267.320.290.265.308.278.239.277.314.300.253.274.309.289.280.
279.302.307.317.252.261.291.311.268.262.329.312.271.294.291.291.281.282.292.288.240.248.306.
277.298.295.267.312.284.265.294.321.260.293.310.300.307.263.304.297.276.262.291.241.284.312.
277.276.265.323.280.257.257.303.320.255.291.292.290.270.267.345.264.291.312.295.269.297.280.
290.224.308.313.240.308.311.247.284.311.268.289.266.316.299.269.299.298.265.298.262.260.337.
320.285.265.273.307.297.282.287.225.302.277.288.284.310.278.255.263.276.283.322.273.300.264.
302.312.289.262.236.278.280.286.292.298.296.313.258.300.280.300.260.274.329.288.272.316.256.
259.279.297.296.283.273.286.320.287.313.272.301.311.260.302.261.304.280.264.328.259.259.347.
245.291.258.289.270.300.301.318.251.305.278.290.311.280.281.293.313.259.300.262.315.263.319.
285.282.297.283.290.293.280.237.234.323.289.305.279.314.274.291.309.273.294.249.283.262.271.
286.310.305.306.261.298.282.282.307.287.285.305.297.275.306.280.292.291.284.301.278.293.296.
277.301.281.274.315.281.254.251.289.313.307.244.256.302.301.317.305.239.316.274.277.296.269.
305.301.279.287.317.284.277.305.298.264.304.286.273.275.293.309.286.282.240.287.239.268.269.
267.315.311.292.270.271.272.336.282.237.275.316.306.239.305.314.240.296.306.270.247.245.302.
317.316.241.291.310.266.274.274.313.288.262.319.280.276.238.297.295.287.285.288.301.272.275.
247.305.292.286.272.310.291.301.322.256.315.298.263.281.276.237.294.284.296.284.302.273.298.
287.298.301.265.305.270.315.278.283.302.287.263.270.345.258.270.266.302.309.262.260.277.327.
263.277.254.283.276.239.272.264.276.279.264.267.298.264.244.245.273.292.289.273.248.259.263.
288.290.294.210.288.268.311.318.312.242.285.293.216.262.276.340.292.299.275.259.293.311.234.
266.294.278.307.286.267.307.285.269.310.288.274.270.326.273.276.311.304.267.302.318.265.299.
263.283.248.257.314.288.321.321.236.284.283.227.320.312.246.261.289.316.288.263.312.241.265.
288.298.286.287.274.306.279.276.289.307.303.293.281.298.317.252.312.283.278.263.304.305.258.
266.270.294.286.293.290.291.291.258.254.282.282.283.313.268.282.316.310.299.254.264.234.296.
270.265.326.288.292.293.321.305.250.320.299.253.270.296.297.298.266.312.234.273.287.309.286.
278.269.279.316.284.276.234.293.255.267.242.253.318.270.246.278.292.285.282.314.266.292.286.
263.313.249.290.255.289.264.292.301.299.278.291.292.225.250.261.283.303.262.264.264.303.299.
297.274.288.267.293.316.320.317.233.303.258.302.271.283.323.247.279.268.312.269.297.313.280.
280.273.266.332.276.313.284.281.316.279.290.273.313.308.305.260.302.306.273.234.279.281.284.
298.278.259.290.314.275.264.339.293.322.266.261.296.306.277.275.311.284.270.318.259.249.286.
292.301.285.280.303.283.287.299.277.273.293.228.311.283.272.304.292.277.271.306.302.278.298.
300.287.281.309.243.272.279.282.300.291.295.284.285.252.291.251.285.283.245.250.252.318.298.
277.235.288.259.263.278.274.307.261.260.350.250.288.256.282.316.261.285.295.292.300.298.264.
245.241.308.301.261.253.289.264.267.300.262.248.287.257.266.275.287.297.320.287.264.279.297.
232.231.256.288.243.252.277.274.245.256.253.229.290.263.305.278.260.294.312.283.301.275.276.
299.297.312.275.282.294.272.228.302.324.257.261.286.326.280.283.316.294.254.258.275.264.236.
240.277.255.231.258.286.242.277.253.296.290.250.314.320.239.292.313.261.294.261.317.273.285.
236.292.282.271.264.297.300.272.308.299.300.269.301.269.317.284.286.262.315.276.279.328.269.
254.252.232.272.268.309.273.264.296.305.272.267.291.324.302.297.268.268.263.298.300.261.312.
241.254.299.280.263.292.260.301.311.317.297.248.314.272.293.298.281.298.276.311.291.297.318.
261.274.300.293.297.267.295.261.275.334.289.238.267.289.283.257.300.262.304.311.278.274.265.
261.345.301.296.270.273.299.289.274.272.313.282.268.320.287.320.270"""
text?=?str.split('.')

acc_list?=?[]
for?i?in?range(0,?len(text)-2,?3):
????x?=?int(text[i])+int(text[i+1])+int(text[i+2])
????acc_list.append(x)
print(len(acc_list))
print(acc_list)
print(max(acc_list))
print(min(acc_list))

passwd?=?"llllllr"
pass_acc?=?0
for?j?in?range(0,?len(passwd)):
????pass_acc?+=?ord(passwd[j])
#the?first?word?is?"Samuel",?so?pass_acc?=?845?-?83?=?762
for?i?in?range(0,?len(acc_list)):
????print?(chr(acc_list[i]-pass_acc),?end='')

運(yùn)行可以發(fā)現(xiàn)打印出來(lái)的解密email如下：

Samuel Smith


Thank you for looking the other way on the increased levels of toxic chemicals in the river running alongside our industrial facilities. You can pick up your payment of $20,000 in the mailbox at the mansion on the corner of 53 and St. Charles tomorrow between the hours of 3:00am and 5:00am.


Thank you,


John Sculley
ToxiCo Industrial Chemicals

現(xiàn)在就可以發(fā)送message給ToxiCo_Watch了。

點(diǎn)擊網(wǎng)站用戶名下面的HTS Messages Center，然后點(diǎn)擊右面的Compose鏈接，會(huì)看到send message，然后就可以發(fā)送message了。