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Added Lab2/Lab3 IS

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This commit is contained in:
sherlock 2025-08-12 09:43:39 +05:30
parent 011d5aded1
commit 0755dd4b76
6 changed files with 109 additions and 140 deletions
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22
IS/Lab/Lab1/q6_affine_bf.py
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@ -8,23 +8,25 @@ def main():
for a in range(1, 26):
if gcd(a, 26) != 1:
continue
a_inv = mod_inverse(a, 26)
if a_inv is None:
continue
for b in range(26):
# if key produces "ab" -> "GL"
if (a * 0 + b) % 26 == 6 and (a * 1 + b) % 26 == 11:
a_inv = mod_inverse(a, 26)
decrypted = ""
for char in ciphertext:
if char.isalpha():
y = ord(char.upper()) - ord('A')
# check constraint: "ab" -> "GL" (a*0+b=6, a*1+b=11 mod 26)
if (b % 26 == 6) and ((a + b) % 26 == 11):
decrypted = []
for ch in ciphertext:
if ch.isalpha():
y = ord(ch.upper()) - ord('A')
x = (a_inv * (y - b)) % 26
decrypted += chr(x + ord('A'))
decrypted.append(chr(x + ord('A')))
else:
decrypted += char
decrypted.append(ch)
print(f"Key found: a={a}, b={b}")
print(f"Ciphertext: {ciphertext}")
print(f"Decrypted: {decrypted}")
print(f"Decrypted: {''.join(decrypted)}")
return
def gcd(a, b):