New Vignere

new_vignere/cypher

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+lejjlnjmjndkmjinkilbmlljjkmnakmmighhocmllojhjmaijpiohnlojmokjkja

new_vignere/new_vignere.py

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+import string
+
+LOWERCASE_OFFSET = ord("a")
+ALPHABET = string.ascii_lowercase[:16]
+
+def b16_encode(plain):
+	enc = ""
+	for c in plain:
+		binary = "{0:08b}".format(ord(c))
+		enc += ALPHABET[int(binary[:4], 2)]
+		enc += ALPHABET[int(binary[4:], 2)]
+	return enc
+
+def shift(c, k):
+	t1 = ord(c) - LOWERCASE_OFFSET
+	t2 = ord(k) - LOWERCASE_OFFSET
+	return ALPHABET[(t1 + t2) % len(ALPHABET)]
+
+flag = "redacted"
+assert all([c in "abcdef0123456789" for c in flag])
+
+key = "redacted"
+assert all([k in ALPHABET for k in key]) and len(key) < 15
+
+b16 = b16_encode(flag)
+enc = ""
+for i, c in enumerate(b16):
+	enc += shift(c, key[i % len(key)])
+print(enc)

new_vignere/sol.py

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+#!python3
+import re
+import string
+
+with open("cypher", "r") as f:
+    cypher = f.read().strip()
+assert len(cypher)%2==0
+
+LOWERCASE_OFFSET = ord("a")
+ALPHABET = string.ascii_lowercase[:16]
+FLAG_ALPHABET = "0123456789abcdef"
+FLAG_ALPHABET_B16 = []
+a = ord('a')
+
+def b16_encode(plain):
+	enc = ""
+	for c in plain:
+		binary = "{0:08b}".format(ord(c))
+		enc += ALPHABET[int(binary[:4], 2)]
+		enc += ALPHABET[int(binary[4:], 2)]
+	return enc
+
+def b16_decode(encoded):
+    dec = ""
+    assert len(encoded)%2 == 0
+    for i in range(len(encoded)//2):
+        e1 = ALPHABET.index(encoded[2*i])
+        e2 = ALPHABET.index(encoded[2*i+1])
+        dec += chr((e1<<4) + e2)
+    return dec
+
+for c in FLAG_ALPHABET:
+    FLAG_ALPHABET_B16.append(b16_encode(c))
+
+KEY_SETS = []
+for i in range(len(cypher)//2):
+    KEY_SET_0 = set()
+    KEY_SET_1 = set()
+    char_0 = ALPHABET.index(cypher[i*2])
+    char_1 = ALPHABET.index(cypher[i*2+1])
+    for flag_char in FLAG_ALPHABET_B16:
+        f0 = ord(flag_char[0]) - a
+        f1 = ord(flag_char[1]) - a
+        k0 = chr((char_0 - f0)%len(ALPHABET)+a)
+        k1 = chr((char_1 - f1)%len(ALPHABET)+a)
+        KEY_SET_0.add(k0)
+        KEY_SET_1.add(k1)
+    KEY_SETS.append(KEY_SET_0)
+    KEY_SETS.append(KEY_SET_1)
+
+possible_kls = []
+for kl in range(2, 16):
+    length_doable = True
+    key_options = [[]]*kl
+    for i in range(kl):
+        possible_cs = []
+        for c in KEY_SETS[i]:
+            c_possible = True
+            for j in range(i, len(KEY_SETS), kl):
+                if c not in KEY_SETS[j]:
+                    c_possible = False
+                    break
+            if c_possible:
+                possible_cs.append(c)
+        if len(possible_cs) == 0:
+            length_doable = False
+            break
+        else:
+            key_options[i] = possible_cs
+    if length_doable:
+        possible_kls.append(key_options)
+print(len(possible_kls))
+key = ""
+for kl in possible_kls:
+    print(kl)
+    for kc in kl:
+        key += kc[0]
+print(key)
+
+b16_flag = ""
+for i, c in enumerate(cypher):
+    c = ALPHABET.index(c)
+    k = ord(key[i%len(key)])-a
+    b16_flag += chr((c - k)%len(ALPHABET)+a)
+print(b16_flag)
+
+flag = b16_decode(b16_flag)
+print(flag)
+