Play Nice

play_nice/alphabet

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+lsi28c14ot0vbf7nagh3mpjuxy5kwz6edqr9

play_nice/enc

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+1x5hqlod8x7oa88h0de1b5r6xja5sd

play_nice/flag_enc

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+f391b621282ef5063ab2de93ab9e4bff

play_nice/playfair.py

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+#!/usr/bin/python3 -u
+import signal
+
+SQUARE_SIZE = 6
+
+def generate_square(alphabet):
+	assert len(alphabet) == pow(SQUARE_SIZE, 2)
+	matrix = []
+	for i, letter in enumerate(alphabet):
+		if i % SQUARE_SIZE == 0:
+			row = []
+		row.append(letter)
+		if i % SQUARE_SIZE == (SQUARE_SIZE - 1):
+			matrix.append(row)
+	return matrix
+
+def get_index(letter, matrix):
+	for row in range(SQUARE_SIZE):
+		for col in range(SQUARE_SIZE):
+			if matrix[row][col] == letter:
+				return (row, col)
+	print("letter not found in matrix.")
+	exit()
+
+def encrypt_pair(pair, matrix):
+	p1 = get_index(pair[0], matrix)
+	p2 = get_index(pair[1], matrix)
+
+	if p1[0] == p2[0]:
+		return matrix[p1[0]][(p1[1] + 1)  % SQUARE_SIZE] + matrix[p2[0]][(p2[1] + 1)  % SQUARE_SIZE]
+	elif p1[1] == p2[1]:
+		return matrix[(p1[0] + 1)  % SQUARE_SIZE][p1[1]] + matrix[(p2[0] + 1)  % SQUARE_SIZE][p2[1]]
+	else:
+		return matrix[p1[0]][p2[1]] + matrix[p2[0]][p1[1]]
+
+def encrypt_string(s, matrix):
+	result = ""
+	if len(s) % 2 == 0:
+		plain = s
+	else:
+		plain = s + "lsi28c14ot0vbf7nagh3mpjuxy5kwz6edqr9"[0]
+	for i in range(0, len(plain), 2):
+		result += encrypt_pair(plain[i:i + 2], matrix)
+	return result
+
+alphabet = open("key").read().rstrip()
+m = generate_square(alphabet)
+msg = open("msg").read().rstrip()
+enc_msg = encrypt_string(msg, m)
+print("Here is the alphabet: {}\nHere is the encrypted message: {}".format(alphabet, enc_msg))
+signal.alarm(18)
+resp = input("What is the plaintext message? ").rstrip()
+if resp and resp == msg:
+	print("Congratulations! Here's the flag: {}".format(open("flag").read()))
+
+# https://en.wikipedia.org/wiki/Playfair_cipher

play_nice/sol.py

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+#!/home/maxime/.pyvenv/bin/python3
+
+SQUARE_SIZE = 6
+
+def generate_square(alphabet):
+    assert len(alphabet) == pow(SQUARE_SIZE, 2)
+    m = []
+    for i, letter in enumerate(alphabet):
+	    if i % SQUARE_SIZE == 0:
+		    row = []
+	    row.append(letter)
+	    if i % SQUARE_SIZE == (SQUARE_SIZE - 1):
+		    m.append(row)
+    return m
+
+def get_index(letter, m):
+	for row in range(SQUARE_SIZE):
+		for col in range(SQUARE_SIZE):
+			if m[row][col] == letter:
+				return (row, col)
+	print("letter not found in m.")
+	exit()
+
+def decode_pair(m, pair):
+    p1 = get_index(pair[0], m)
+    p2 = get_index(pair[1], m)
+
+    if p1[0] == p2[0]:
+	    return m[p1[0]][(p1[1] - 1)  % SQUARE_SIZE] + m[p2[0]][(p2[1] - 1)  % SQUARE_SIZE]
+    elif p1[1] == p2[1]:
+	    return m[(p1[0] - 1)  % SQUARE_SIZE][p1[1]] + m[(p2[0] - 1)  % SQUARE_SIZE][p2[1]]
+    else:
+	    return m[p1[0]][p2[1]] + m[p2[0]][p1[1]]
+
+
+with open("alphabet", 'r') as a, open("flag_enc", 'r') as e:
+    m = generate_square(a.read().strip())
+    enc = e.read().strip()
+    assert len(enc) % 2 == 0
+
+    msg = ""
+    for i in range(0, len(enc), 2):
+        msg += decode_pair(m, enc[i:i+2])
+
+    print(msg)
+