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Welcome to the next session in Python Hacking, that is about decrypting with the transposition cipher,

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not unlike the seasonal cipher, the decryption process of a transposition cipher is also different

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from an encryption process.

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So in this session, we will create another program which will be for decrypting the transposition cipher

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to handle the decryption.

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Also with that, we would be covering the ground, might not see my daughter law functions also and

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then or boolean operators.

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And the truth will now come to how to decrypt with the transposition cipher manually, as we had done

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manually the encryption part in the Excel format.

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We would also do it in the decryption format also.

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So the text that we have supposed to decrypt is this that we had already encrypted now before step is

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to be for decrypting is the way to calculate the number of boxes that need to be drawn now for determining

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this number.

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They must be dividing the length of the cipher text message by Olcay and rounded up to the nearest whole

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number if it is not an unknown number already.

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OK, so the length of the ciphertext that we have is basically 30 and the key that we have used is also

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eight.

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So if we divide 30 by eight, we get three point seventy five.

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So rounding up three point seventy five will come before.

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So you'll have to draw the grid.

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That is four columns and each column will have eight.

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That is the key.

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So you also need to calculate the number of boxes which you have to shade, and that is using the total

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number of 32 boxes.

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So there is a track the length of the ciphertext.

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So that is 30 to minus 30.

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That is to follow the shade of the bottom two boxes in the rightmost column would be shaded.

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So you will have to then start filling up the boxes, placing one of the ciphertext in each box, starting

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at the top left the filling towards the right, as you did when you were encrypting it.

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So, for example, now let's say we are drawing here three, four, five, six, seven, eight.

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Now, let us just make this and also we will increase the length of it.

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But.

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And now what we do is we start adding up these characters one by one.

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So the first one that we have is.

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Also, we will just increase the font size here.

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Now let's go on adding it one by one.

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Does the first character first, then who?

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S then become below it is white.

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See you as.

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Now, let's just check this again.

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It being or as it is why I see you asked at stake are a so dusty OK then we have until for the next

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48 hours.

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It is agi s g i s g then you home and E E again and G now wherever you would be having their spaces.

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So here we would be filling up with this character.

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So you have your own space, then you have their dot, then you have M, A, C, E, then again you

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have there the character in all your.

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Also we have used three characters.

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Yes.

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Now, this is just a blank or the last pipeline symbol there.

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So what we'll do is we will.

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We have made some mistakes.

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You know, this is a single year.

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Also, we have used it here.

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We would also have, again, a space that this is also seen now here we would be having seen we are

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supposed to leave the next two blocks as blank.

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So let us have the edge or we would have a two edge then.

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See?

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And so these two, we would be insulting.

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It is like the last one.

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So now in this vein, this is correct, because after this, we have one space.

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So we have insulted the space character.

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We have a full stop after which we are having that again, full value for space, then M, x, c, e.

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So after this.

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Now, this is how we have basically used it for decrypting.

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And now if you notice over here, let us write down the first character that we have.

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Sipi via the h o n space H.

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Then in the next one, what do you have.

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It is a C and G space C then what do you have or you are s e space m e and then the last one ss a ge

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full stop.

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That is what if you combine that together.

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Suppose that's right down over here.

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Vitan H a c g c or you are a c ss eight G bottom.

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That's how we have again decrypted the message.

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So via encrypting it is in a horizontal way while decrypting it is in the vertical.

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We saw a quick recap to the step for decrypting.

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One is calculate the number of columns you need by dividing the length of the message by the key and

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then rounding it up.

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Second, this drop oxygen column and rolls use number of columns.

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You calculate that in the first step and the number of rules as the same as the E number three is calculate

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the number of boxes crocheted by picnicked open number of boxes.

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That is subtracting the length of the ciphertext with the length of the normal key that you have next

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is shaded the number of boxes you calculated in the earlier step at the bottom of the rightmost column,

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then start filling up the correct dose of the ciphertext starting at the top row and going from left

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to right.

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Skip any of the shaded boxes.

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You will get a plaintext by reading the leftmost column from the top to bottom and continuing to do

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so in each of the column.

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So note that if you have used a different key, you will draw the wrong number of rules even if you

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follow the other step and decryption process.

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Correcting the plaintext would be random garbage.

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Similarly, as you would use for a Ronke, we don't see the Saiful.

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Now let us write down.

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So score for this transposition decryption program.

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So for that, let's go back to our financial and.

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Create a new fight.

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Now, the first thing is we need to also import Matt Antiplatelet so we will see first import Matt Gunma,

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then we would define again mean here and we would have my.

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Message a star now that's equal to we will take down the encrypted text, which is there as it does

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so let's put it here.

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And after this, let's remove the pipeline symbol here.

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We will define my first year and that's equal to also it.

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Then we will take your plain text SDR, which is for our friend.

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Now, here we would be creating the decrypt message SDR method.

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Here we would pass Mixter and.

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My message is clear, and whatever the value is written, that is what we are storing in plain text,

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then we would be printing that again, plain text SDR.

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But concatenating on pipeline symbol.

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After which we also see people clip, don't use the copy metal and copy the plain text still.

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Now after this this method and all of your and we the next method that is decrypt message start, which

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takes the Gasteyer and the messages.

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And inside this particular function that we have now, the transposition decrypt function will basically

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simulate the columns and the rules of the grid that the plain text is written on by using a list of

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strings.

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So first we need to calculate a few values, the number of columns in our transposition grid.

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So for that, we will take a number of.

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Columns that's equal to be converted to integer using my God seal, and he'll be past the length of

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our message, a star divided by converting to float the value of KSTU.