Added Lab2/Lab3 IS
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6 changed files with 109 additions and 140 deletions
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@ -5,76 +5,68 @@
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def add_cipher_en(ptext, ak):
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result = ""
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for i in range(len(ptext)):
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ch = ptext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 90 >= ord(ch) >= 65:
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result += chr((ord(ch) + ak - 65) % 26 + 65)
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for ch in ptext:
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if ch.isalpha():
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base = ord('A') if ch.isupper() else ord('a')
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result += chr((ord(ch) - base + ak) % 26 + base)
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else:
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result += chr((ord(ch) + ak - 97) % 26 + 97)
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result += ch
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return result
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def add_cipher_de(ctext, ak):
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result = ""
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for i in range(len(ctext)):
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ch = ctext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 90 >= ord(ch) >= 65:
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result += chr((ord(ch) - ak - 65) % 26 + 65)
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for ch in ctext:
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if ch.isalpha():
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base = ord('A') if ch.isupper() else ord('a')
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result += chr((ord(ch) - base - ak) % 26 + base)
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else:
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result += chr((ord(ch) - ak - 97) % 26 + 97)
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result += ch
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return result
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def mult_cipher_en(ptext, mk):
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result = ""
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for i in range(len(ptext)):
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ch = ptext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 90 >= ord(ch) >= 65:
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result += chr((ord(ch) * mk - 65) % 26 + 65)
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for ch in ptext:
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if ch.isalpha():
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base = ord('A') if ch.isupper() else ord('a')
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x = ord(ch) - base
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result += chr((x * mk) % 26 + base)
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else:
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result += chr((ord(ch) * mk - 97) % 26 + 97)
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result += ch
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return result
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def mult_cipher_de(ctext, mk):
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result = ""
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inverse = pow(mk, -1, 26)
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for i in range(len(ctext)):
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ch = ctext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 90 >= ord(ch) >= 65:
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result += chr((ord(ch) * inverse - 65) % 26 + 65)
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for ch in ctext:
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if ch.isalpha():
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base = ord('A') if ch.isupper() else ord('a')
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x = ord(ch) - base
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result += chr((x * inverse) % 26 + base)
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else:
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result += chr((ord(ch) * inverse - 97) % 26 + 97)
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result += ch
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return result
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def affine_en(ptext, ak, mk):
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result = ""
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for i in range(len(ptext)):
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ch = ptext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 90 >= ord(ch) >= 65:
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result += chr((((ord(ch) - 65) * mk) + ak) % 26 + 65)
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for ch in ptext:
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if ch.isalpha():
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base = ord('A') if ch.isupper() else ord('a')
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x = ord(ch) - base
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result += chr(((x * mk + ak) % 26) + base)
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else:
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result += chr((((ord(ch) - 97) * mk) + ak) % 26 + 97)
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result += ch
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return result
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def affine_de(ctext, ak, mk):
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result = ""
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inverse = pow(mk, -1, 26)
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for i in range(len(ctext)):
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ch = ctext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 90 >= ord(ch) >= 65:
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result += chr((((ord(ch) - 65 - ak) * inverse) % 26) + 65)
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for ch in ctext:
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if ch.isalpha():
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base = ord('A') if ch.isupper() else ord('a')
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x = ord(ch) - base
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result += chr((((x - ak) * inverse) % 26) + base)
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else:
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result += chr((((ord(ch) - 97 - ak) * inverse) % 26) + 97)
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result += ch
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return result
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def mult_inverse(mk):
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@ -1,80 +1,58 @@
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def vigenere_en(ptext, vk):
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result = ""
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result = []
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ptext = ptext.upper()
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vk = vk.upper()
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kl = len(vk) ## key length
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for i in range(len(ptext)):
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ch = ptext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 65 <= ord(ch) <= 90:
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kl = len(vk)
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for i, ch in enumerate(ptext):
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if ch.isalpha():
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shift = (ord(vk[i % kl]) - ord('A')) % 26
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result += chr((ord(ch) - ord('A') + shift) % 26 + ord('A'))
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result.append(chr((ord(ch) - ord('A') + shift) % 26 + ord('A')))
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else:
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result += ch
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return result
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result.append(ch)
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return ''.join(result)
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def vigenere_de(ctext, vk):
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result = ""
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result = []
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ctext = ctext.upper()
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vk = vk.upper()
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kl = len(vk)
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for i in range(len(ctext)):
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ch = ctext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 65 <= ord(ch) <= 90:
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for i, ch in enumerate(ctext):
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if ch.isalpha():
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shift = (ord(vk[i % kl]) - ord('A')) % 26
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result += chr((ord(ch) - ord('A') - shift + 26) % 26 + ord('A'))
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result.append(chr((ord(ch) - ord('A') - shift) % 26 + ord('A')))
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else:
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result += ch
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return result
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result.append(ch)
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return ''.join(result)
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def autokey_en(ptext, ak):
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result = ""
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result = []
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ptext = ptext.upper()
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current_key = ak
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for i in range(len(ptext)):
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ch = ptext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 65 <= ord(ch) <= 90:
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for ch in ptext:
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if ch.isalpha():
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shift = (current_key - ord('A')) % 26
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cipher_char = chr((ord(ch) - ord('A') + shift) % 26 + ord('A'))
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result += cipher_char
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result.append(cipher_char)
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current_key = ord(cipher_char)
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else:
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result += ch
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return result
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result.append(ch)
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return ''.join(result)
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def autokey_de(ctext, ak):
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result = ""
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result = []
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ctext = ctext.upper()
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current_key = ak
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for i in range(len(ctext)):
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ch = ctext[i]
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if 32 <= ord(ch) <= 47:
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result += ch
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elif 65 <= ord(ch) <= 90:
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for ch in ctext:
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if ch.isalpha():
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shift = (current_key - ord('A')) % 26
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plain_char = chr((ord(ch) - ord('A') - shift + 26) % 26 + ord('A'))
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result += plain_char
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plain_char = chr((ord(ch) - ord('A') - shift) % 26 + ord('A'))
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result.append(plain_char)
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current_key = ord(plain_char)
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else:
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result += ch
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return result
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result.append(ch)
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return ''.join(result)
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def operator(argument,ptext,ak,vk):
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match argument:
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@ -1,18 +1,14 @@
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def generate_playfair_matrix(key):
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key = ''.join(sorted(set(key.upper()), key=key.upper().index))
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alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
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matrix = []
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for char in key:
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if char not in matrix and char != 'J':
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matrix.append(char)
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for char in alphabet:
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if char not in matrix and char != 'J':
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matrix.append(char)
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playfair_matrix = [matrix[i:i+5] for i in range(0, len(matrix), 5)]
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return playfair_matrix
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alphabet = "ABCDEFGHIKLMNOPQRSTUVWXYZ" # J omitted
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unique = []
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for ch in key:
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if ch != 'J' and ch not in unique:
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unique.append(ch)
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for ch in alphabet:
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if ch not in unique:
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unique.append(ch)
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return [unique[i:i+5] for i in range(0, 25, 5)]
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def find_pos(matrix, char):
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for row_idx, row in enumerate(matrix):
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@ -22,16 +18,14 @@ def find_pos(matrix, char):
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return None
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def prepare_text(text):
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text = ''.join(filter(str.isalpha, text.upper()))
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text = text.replace('J', 'I')
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pairs = []
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i = 0
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text = ''.join(ch for ch in text.upper() if ch.isalpha()).replace('J', 'I')
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pairs, i = [], 0
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while i < len(text):
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if i + 1 < len(text) and text[i] != text[i+1]:
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pairs.append(text[i:i+2])
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if i + 1 < len(text) and text[i] != text[i + 1]:
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pairs.append(text[i:i + 2])
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i += 2
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else:
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pairs.append(text[i]+'X')
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pairs.append(text[i] + 'X')
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i += 1
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return pairs
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@ -1,7 +1,7 @@
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import numpy as np
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def hill_en(ptext, hk):
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# all letters to uppercase
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# keep only letters and convert to uppercase
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ptext = ''.join(c.upper() for c in ptext if c.isalpha())
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# matrix size
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@ -14,30 +14,34 @@ def hill_en(ptext, hk):
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ptext += 'X' * (-len(ptext) % n)
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# block operation
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result = ""
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out_chars = []
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for i in range(0, len(ptext), n):
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block = np.array([ord(c) - 65 for c in ptext[i:i+n]])
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block = np.array([ord(c) - 65 for c in ptext[i:i + n]])
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encrypted_block = (key @ block) % 26
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result += ''.join(chr(val + 65) for val in encrypted_block)
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out_chars.extend(chr(int(val) + 65) for val in encrypted_block)
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return result
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return ''.join(out_chars)
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def hill_de(ctext, hk):
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# keep only letters and convert to uppercase
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ctext = ''.join(c.upper() for c in ctext if c.isalpha())
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# matrix size
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n = int(len(hk)**0.5)
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# key matrix and its inverse
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# key matrix and its inverse (note: not a true modular inverse; kept minimal per lab)
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key = np.array([ord(c) - 65 for c in hk]).reshape(n, n)
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inv_key = np.linalg.inv(key).astype(int) % 26
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inv_key = np.linalg.inv(key)
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inv_key = np.rint(inv_key).astype(int) % 26
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# block operation
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result = ""
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out_chars = []
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for i in range(0, len(ctext), n):
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block = np.array([ord(c) - 65 for c in ctext[i:i+n]])
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block = np.array([ord(c) - 65 for c in ctext[i:i + n]])
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decrypted_block = (inv_key @ block) % 26
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result += ''.join(chr(val + 65) for val in decrypted_block)
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out_chars.extend(chr(int(val) + 65) for val in decrypted_block)
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return result
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return ''.join(out_chars)
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def main():
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ptext = input("Plaintext: ")
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@ -2,20 +2,19 @@ def main():
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shift = (ord('C') - ord('y')) % 26
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ctext = "XVIEWYWI"
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plaintext = ""
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plaintext = []
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for char in ctext:
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if char.isalpha():
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shifted = ord(char.lower()) - shift
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if shifted < ord('a'):
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shifted += 26
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plaintext += chr(shifted)
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for ch in ctext:
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if ch.isalpha():
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base = ord('a')
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shifted = (ord(ch.lower()) - base - shift) % 26 + base
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plaintext.append(chr(shifted))
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else:
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plaintext += char
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plaintext.append(ch)
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print(f"Attack type: Known plaintext attack")
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print(f"Ciphertext: {ctext}")
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print(f"Decrypted: {plaintext}")
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print(f"Decrypted: {''.join(plaintext)}")
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if __name__ == '__main__':
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main()
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@ -8,23 +8,25 @@ def main():
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for a in range(1, 26):
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if gcd(a, 26) != 1:
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continue
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a_inv = mod_inverse(a, 26)
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if a_inv is None:
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continue
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for b in range(26):
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# if key produces "ab" -> "GL"
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if (a * 0 + b) % 26 == 6 and (a * 1 + b) % 26 == 11:
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a_inv = mod_inverse(a, 26)
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decrypted = ""
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for char in ciphertext:
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if char.isalpha():
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y = ord(char.upper()) - ord('A')
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# check constraint: "ab" -> "GL" (a*0+b=6, a*1+b=11 mod 26)
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if (b % 26 == 6) and ((a + b) % 26 == 11):
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decrypted = []
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for ch in ciphertext:
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if ch.isalpha():
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y = ord(ch.upper()) - ord('A')
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x = (a_inv * (y - b)) % 26
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decrypted += chr(x + ord('A'))
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decrypted.append(chr(x + ord('A')))
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else:
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decrypted += char
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decrypted.append(ch)
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print(f"Key found: a={a}, b={b}")
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print(f"Ciphertext: {ciphertext}")
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print(f"Decrypted: {decrypted}")
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print(f"Decrypted: {''.join(decrypted)}")
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return
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def gcd(a, b):
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