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Welcome to the first session in our python hacking advanced level course in this session, forced,

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we would write such a program to narrow down the list of potential decryption outputs to the right one

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for topics covered in this session would be over patterns.

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Candidates, potential decryption letters, letters, cipher mappings, regular expressions, subject

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matter.

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So now let's come to first using the word Partons to decrypt.

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Now, in brute force attack, we try each possible to check whether it can be krip the ciphertext.

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If the key is correct, decryption result in a readable English.

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But by analyzing the ciphertext first, we can reduce the number of possible keys to try and maybe even

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find a full or partial key.

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So let's assume the original plaintext consists mostly of vowels in an English dictionary file like

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one we use in the earlier sessions.

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Although a cipher text won't be made up of real English words, it will still contain a group of letters

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broken up by spaces just like votes in a regular sentence.

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So we'll call this as a cipher vote, for example.

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And in a substitution cipher, every letter of the alphabet has exactly one unique corresponding encryption.

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Let them now.

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We will call that letter in the ciphertext as a cipher letters not because each plaintext letters can

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encrypt to only one side four letter.

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We are not encrypting spaces in this version.

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The plaintext and ciphertext will share the same word, but does not.

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For example, say we have a plain text like C

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Mississippi and still now the corresponding ciphertext would look something like, say, R.G. B, B,

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G, BCBG X, x, g, b, x, space b, x, g, h, for example.

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Now the number of letters in the first vote of the plaintext and the forced cipher board are saying,

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look at this, it's one, two, three, four, five, six, seven, eight, nine, ten, eleven.

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Look at this.

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One, two, three, four, five, six, seven, eight, nine, ten, eleven.

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OK, so we have made here, I think, a mistake.

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This one, it's like this the one, two, three, four, five, six, seven, eight, nine, ten, eleven.

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Now, the same is true for the second plaintext also.

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So if you look at this, it's one, two, three, four, five.

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And this one also has five.

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So the plaintext and the ciphertext share the same pattern of letters and spaces.

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Also notice that letters that repeat in the plaintext repeat the same number of times in the same place

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in ciphertext.

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Also like here, if we are building here, beebees repeating here, if we are repeating BP here, X-axis

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repeating here we are repeating l so you're just repeating.

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So we would therefore assume that a cipher word corresponds to a word in the English dictionary file

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and that word patterns would match.

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Then we can find which word in the dictionary decipher what decrypts do we can figure out the description

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of each cipher letter in that war.

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And if we figure out enough cipher letter decryption using this technique, we may be able to give the

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entire message.

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So now let's come to understand the finding work patterns.

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Now let's examine the whole pattern of design for word.

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For example, the Etch A Sketch, you, for example, now you can see that decipher what has certain

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characteristics which the original plaintext word must share, what words must have the following things

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in common.

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One is they should be five letters long for third and fourth letters should be same because here we

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have h h h.

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Right.

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They should have exactly three different letters.

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That is, it should be replaced by one little G should be replaced by one letter.

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You should be replaced by one little.

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So now in this particular pattern, you may have votes, for example, like, say, a puppy or you may

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have your here you can see forced our repeating third and fourth.

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Then there are only three characters that be one.

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Right.

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And there are also in the same pattern.

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So be for the first, say third and fourth, and you for the second and for the first one.

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Similarly, you may have another word likes it, mommy, or for that case, Bobbit or C naanu with these

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all fits in the same pattern.

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So these words along with others in the English dictionary that matches the criteria, are all the possible

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descriptions for this particular word.

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Now, to represent a vocal proponent of that program can understand will make each partner into a set

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of numbers separated by if that is not, that indicates the pattern of the letters not creating what

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pattern is easy.

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False letter gets a number zero and the first occurrence of each different letter thereafter gets the

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next number.

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So, for example, the word patency over here, if you're I don't know what that would be says is zero,

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not one, but two.

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So over here and same we say if we have version, say, for example, classification, which is a lower

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level here, we may have something like Zettl.

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One, two, three, four, five.

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Then again, let's have your say four zero two six four seven eight.

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Now, in this case, in the simple substitution cipher, no matter which keys used to encrypt a plaintext,

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what an insightful would always have the same word pattern.

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So the word pattern for ciphertext over here that we have used will come to something like zero, then

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one, then again, zero zero.

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And next is two, which means the word pattern for a plain text corresponding to this will be equal

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to also zero one zero zero two.

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Now, moving to finding the potential decryption letters now to decrypt this, what we need to find

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all the words in an English dictionary whose work pattern is this, that we have this great civil call,

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the plain text word that have the same word pattern as a cipher Wolf.

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The candidates in this particular session just to understand.

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So here's a list of all the candidates available for this in which we have calculated this puppy, mommy

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will be our nanny.

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Now, using the word patterns, we can guess which plaintext little cipher letters might decrypt them,

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which will call as a potential decryption letters.

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Now to crack a message encrypted with a simple substitution cipher.

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We need to find all the potential decryption letters first of each word in the message and determine

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the actual decryption letter through the process of elimination.