## Description

Crypto Question 3 400 pts

After entring the luxurious condomium,you get the feel that you are in home of a yester Star. the extravagant flooring and furnishings shows the richness of this star. But where is she? There she is, lying peacefuly on her couch. See what Envy has done to her…with a perfectly well maintained attractive body she still looks sex diva, except for her face beyond recogniton. Her identity is crucial to know who killed her and why? In absence of any personal data around there is only a file. with a cryptic text in it. Preity sure she has used her own name to XOR encrypt the file. And challenge is to know her name.

## Resolution

This challenge were maybe the most complicated of the crypto category.

It’s a XOR with an unknown key with an unknown length.

This little handmade program solve this kind of XOR task using frequency analysis.

with open('cipher','rb') as f: message = f.read() T = [] cur = -1 for i in range(len(message)): if i%12==0: T.append('') cur = cur+1 T[cur] = T[cur]+("%02x" % message[i]) for i in range(len(T[cur])//2,12): T[cur] = T[cur]+'00' englishLetterFreq = {' ': 15,'E': 12.70, 'T': 9.06, 'A': 8.17, 'O': 7.51, 'I': 6.97, 'N': 6.75, 'S': 6.33, 'H': 6.09, 'R': 5.99, 'D': 4.25, 'L': 4.03, 'C': 2.78, 'U': 2.76, 'M': 2.41, 'W': 2.36, 'F': 2.23, 'G': 2.02, 'Y': 1.97, 'P': 1.93, 'B': 1.29, 'V': 0.98, 'K': 0.77, 'J': 0.15, 'X': 0.15, 'Q': 0.10, 'Z': 0.07} for i in range(10): englishLetterFreq.update({str(i):1.5}) for i in range(ord('a'),ord('z')): englishLetterFreq.update({chr(i):englishLetterFreq[chr(i-ord('a')+ord('A'))]}) print(englishLetterFreq) key = '' ar = ['']*len(T) for letter in range(0,len(T[10]),2): goodLetter = 0 doIt = input("Do it with hands ?") max = 0 for letterValue in range(256): score = 0 score2 = 0 temp = '' for i in range(len(T)): a = letterValue^int(T[i][letter:letter+2],16) temp = temp+' '+chr(a) if (a>=ord('A') and a<=ord('Z')) or (a>=ord('a') and a<=ord('z')) or (a>=ord('0') and a<=ord('9')) or a==ord(' '): score = score+1 score2 = score2+englishLetterFreq.get(chr(a),0) if score>9 and doIt == '1': print("We had a good letter to xor with : "+str(letterValue)) print("We obtained "+temp) replace = input("Replace current ?") if replace=='1': goodLetter = letterValue if score2>max and doIt != '1': print("We had a good letter to xor with : "+str(letterValue)) print("We obtained "+temp) goodLetter = letterValue max = score2 key = key+format(goodLetter,'02x') for i in range(len(T)): ar[i] = ar[i]+chr(goodLetter^int(T[i][letter:letter+2],16)) print("Current state :") print("Key = "+key) for i in ar: print(i) print()

We obtain :

julie And St eve's Sex li fE doeSn't g oing tHe way they Want t o be, They w ant to know how thEy can add mOre an d pure pleas ure on their sex lIfe. S o they go to the lIbrary where they rEAd A book about AnciEn t secrEts of the KAma Su trA, dUrINg rEAdinG thEy uniNtEntion ally vIsIt a ncieNt India where they mEet A mIstr ess. THe mis tress GuIdEs Julie and S tEve ANd tEa ches tHem Ka ma SutRa sEc rEts ANd lEa ds theM to m any plAces w hEre tHey me et manY peop lE who pract icAlly teach them Many m ore KAMa Sut ra secRets.* - WritTen by JeaNnA Fine anna

Now we know her name as asked 🙂

Flag was “**Jeanna Fine**“