1
00:00:00,210 --> 00:00:06,750
Now that letters that are encrypted with the same subcu we can now use to get and circulate those to

2
00:00:06,750 --> 00:00:13,380
try decrypting with some potential killens, not the next, we will move on to attempting the decryption

3
00:00:13,380 --> 00:00:20,160
with unlikely KMD now recalled Kosofsky examination function isn't guaranteed to return the actual length

4
00:00:20,160 --> 00:00:26,550
of the Virginia key, but rather a list of several possible lenth sorted in order of most likely.

5
00:00:26,550 --> 00:00:27,610
To least likely.

6
00:00:28,380 --> 00:00:35,400
And if the code has determined Long Island, it will try again using a different Kēlen attempt hack

7
00:00:35,400 --> 00:00:38,820
with the Keelen function, which is the next that we have to find here.

8
00:00:39,300 --> 00:00:40,250
It does.

9
00:00:40,290 --> 00:00:43,870
This went past the ciphertext and determined the killing.

10
00:00:44,190 --> 00:00:47,870
If successful, this function returns a string of hacked message.

11
00:00:48,180 --> 00:00:51,260
If the hacking feels function returns none.

12
00:00:51,270 --> 00:00:54,210
The hacking code works only on uppercase letters.

13
00:00:54,480 --> 00:00:58,980
But we want to run or return any decrypted string with its original disk.

14
00:00:59,220 --> 00:01:05,200
So we need to preserve the original string and to do this with the uppercase form of the ciphertext

15
00:01:05,200 --> 00:01:09,110
string in a separate variable that is your ciphertext up.

16
00:01:09,530 --> 00:01:16,980
We if we assume the value is the most likely guyland is correct guillén the hacking algorithm then calls

17
00:01:17,250 --> 00:01:25,440
your get and Sukie letters for each subject and brute force through all the twenty six possible letters

18
00:01:25,440 --> 00:01:32,850
to find the one that produces decrypted text whose letter frequency most closely matches the frequency

19
00:01:32,850 --> 00:01:34,610
of English for that subject.

20
00:01:35,070 --> 00:01:42,660
And the first attempt on an empty list is stored in all frequency schools, which was stored the frequency

21
00:01:42,660 --> 00:01:48,360
Matsuko written by the frequency analysis dot your English frequency.

22
00:01:48,360 --> 00:01:55,130
Matsuko, which we have already created, and the same function we are trying to call it here.

23
00:01:55,650 --> 00:01:56,750
So over here.

24
00:01:57,300 --> 00:02:04,980
So the for loop, which is over here in this line, it's at the end of variable to each integer from

25
00:02:04,980 --> 00:02:06,780
one to the most likely guyland.

26
00:02:06,990 --> 00:02:13,020
And recall that when the range is passed as to argument, the range goes up to but not including the

27
00:02:13,020 --> 00:02:13,900
second argument.

28
00:02:13,920 --> 00:02:18,870
Hence we have put a plus one into the code so that the integer value is most likely.

29
00:02:18,870 --> 00:02:26,320
Gillanders included in the range, the letter of the end, the subject written from your get and subcu

30
00:02:26,340 --> 00:02:26,850
letters.

31
00:02:27,090 --> 00:02:30,450
And next, we need to decrypt the letters of the end.

32
00:02:30,750 --> 00:02:31,620
Give it all this.

33
00:02:31,620 --> 00:02:36,630
Twenty is possible Sakis to see which one produces the English like letter frequencies.

34
00:02:36,810 --> 00:02:43,320
So a list of English frequency match score is stored in a list in a variable named frequency schools

35
00:02:43,320 --> 00:02:49,830
here and this variable starts on an empty list and then for loop on it, loop through each of the twenty

36
00:02:49,830 --> 00:02:52,160
six uppercase letters from the letters.

37
00:02:52,250 --> 00:02:59,280
Still, the possible values or the possible key values decrypt the ciphertext by calling your vagina's

38
00:02:59,400 --> 00:03:04,150
for the Modot decrypt messages and the subject is impossible.

39
00:03:04,150 --> 00:03:06,390
The key is only one letter, but the string.

40
00:03:06,390 --> 00:03:11,310
In the end, the letter is made up of only the letters from message that would have been encrypted.

41
00:03:11,310 --> 00:03:12,210
Would that give?

42
00:03:12,210 --> 00:03:14,700
The code has determined the key length correctly.

43
00:03:15,240 --> 00:03:21,870
So next, the decrypted text is then passed onto frequency analysis dot English frequency Matsuko function

44
00:03:21,870 --> 00:03:27,750
to see how closely the frequency of letters in the decrypted text matches the little frequency of regular

45
00:03:27,750 --> 00:03:30,660
English, which we have already learned in the earlier session.

46
00:03:31,200 --> 00:03:37,370
Then we put this frequency match code and the keys used to decrypt and what tuple and stored in key

47
00:03:37,380 --> 00:03:42,450
and frequency matched tuple, which is this particular variable on this line.

48
00:03:42,660 --> 00:03:50,280
And then the Stupples opponent to the end of frequency schools by saying frequencies kosdaq up pentimento

49
00:03:50,670 --> 00:03:57,650
after the for loop completes the frequency score list should contain the six keys and frequency might

50
00:03:57,690 --> 00:04:02,150
score tuple one for each of the twenty six subcu.

51
00:04:02,400 --> 00:04:07,830
Then we need to sort this list so that you build with the largest English frequency map score comes

52
00:04:07,830 --> 00:04:08,330
first.

53
00:04:08,640 --> 00:04:14,130
This means that we want to solve the tuple and frequency scores by adding value at index one and in

54
00:04:14,130 --> 00:04:14,930
the reverse order.

55
00:04:15,300 --> 00:04:21,720
Hence we have done this sort method over here on frequency score list, passing the function value that

56
00:04:21,720 --> 00:04:27,600
is good item at index one from the key argument node that we are not calling the function.

57
00:04:27,600 --> 00:04:34,170
As you can tell from the lack of parentheses and the value true is pastoralist's function call the keyword

58
00:04:34,170 --> 00:04:40,190
arguments sorted in descending order, hence the distal parameters apostrophe the function over here

59
00:04:40,650 --> 00:04:42,510
now if we move on further.

60
00:04:42,720 --> 00:04:49,170
So initially the num most frequency letters constant was said to integer value for in the above line

61
00:04:49,170 --> 00:04:50,940
if you have seen over here.

62
00:04:52,500 --> 00:04:54,160
This one had to settle for here.

63
00:04:55,050 --> 00:05:01,980
Now, if we go back to over my thought here, if we see the next thing that after sorting the tubas

64
00:05:01,980 --> 00:05:06,990
and the frequencies scoring intervals out of the offender list containing only the first three Dupas,

65
00:05:07,230 --> 00:05:13,790
all the tubas with the three highest English frequency, Matsuko to our all frequency schools.

66
00:05:14,010 --> 00:05:16,290
So as a result are all frequencies schools.

67
00:05:16,290 --> 00:05:22,380
And Exito contains frequencies, codes for the fourth subject and one contains the frequencies code

68
00:05:22,380 --> 00:05:23,440
for the second subject.

69
00:05:23,970 --> 00:05:30,330
So after the loop completes here, the all frequencies code should contain a number of list values equal

70
00:05:30,330 --> 00:05:33,020
to the integer values and most likely Kēlen.

71
00:05:33,510 --> 00:05:36,540
Now, for example, of the most likely length was three.

72
00:05:36,540 --> 00:05:43,410
All frequencies score would be a list of Thrillist for list would hold the pupil for the top three highest

73
00:05:43,410 --> 00:05:51,000
matching Saki's for the four subcu of the second list would hold of the pupil for the top three highest

74
00:05:51,000 --> 00:05:54,880
margins of for second UPU of the full beginner and so on.

75
00:05:55,380 --> 00:06:01,560
So originally if we wanted to brute force through the full beginner number of possible keys would be

76
00:06:01,560 --> 00:06:04,470
twenty six raised to the power of the chelate.

77
00:06:04,980 --> 00:06:10,820
But checking the English frequency matching helped determine the four most likely letters for each.

78
00:06:11,730 --> 00:06:21,280
So this is a huge improvement over how many more possible he's so now the end giver argument for print

79
00:06:21,690 --> 00:06:21,940
now.

80
00:06:21,960 --> 00:06:24,750
Next, we want to bring the output to the user after this.

81
00:06:24,750 --> 00:06:29,340
To do this, we use the print, but as an argument to an optional parameter.

82
00:06:29,790 --> 00:06:31,170
We haven't used it before.

83
00:06:31,380 --> 00:06:36,620
Now, whenever a print function is called, it brings to the screen the string Bastar it along with

84
00:06:36,630 --> 00:06:37,610
a new line character.

85
00:06:37,980 --> 00:06:43,020
So to print something else at the end of the string instead of a Newlon character, we can specify the

86
00:06:43,020 --> 00:06:46,500
string for different functions and the key argument.

87
00:06:47,100 --> 00:06:51,720
For example, we will enter something in the interactive shell to see how to use the print functions.

88
00:06:51,990 --> 00:07:01,290
And the keyword argument, if we go back over here and if we try to see the fine print stuff and in

89
00:07:01,290 --> 00:07:03,210
this we are defining, say, print.

90
00:07:04,390 --> 00:07:13,660
See, right now, we are giving here and is equal to say and in single court, then next we are defining

91
00:07:13,660 --> 00:07:24,760
print see single quotes again hacking and the end is equal to just open closed bracket.

92
00:07:25,450 --> 00:07:29,450
Now, next print we are giving here greetings.

93
00:07:29,530 --> 00:07:33,880
Great things and defining and is equal to, say, X, Y, Z.

94
00:07:34,660 --> 00:07:42,760
And next we are giving print just saying thank you all.

95
00:07:42,800 --> 00:07:43,280
Thanks.

96
00:07:43,440 --> 00:07:44,560
OK with no end.

97
00:07:45,010 --> 00:07:53,390
And then we say here call print stuff so we get Biton with a new line.

98
00:07:53,650 --> 00:07:56,380
Hacking is just having nothing at the end of it.

99
00:07:56,620 --> 00:08:00,900
So it continues gradings on the same line and we have X, Y, Z.

100
00:08:00,910 --> 00:08:04,870
So after X, Y, Z again, we have the next think tanks which is being printed.

101
00:08:05,080 --> 00:08:08,440
So passing in is equal to slash and preindustrial.

102
00:08:08,470 --> 00:08:14,740
Normally how we would passing in is equal to just open to a single course or some string replaces the

103
00:08:14,740 --> 00:08:16,230
usual newline character.

104
00:08:16,480 --> 00:08:20,320
So subsequent print calls are not displayed on the new line.

105
00:08:20,740 --> 00:08:22,240
That is what this difference is.

106
00:08:22,720 --> 00:08:23,960
That's it from the session.