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39 lines
1.2 KiB
Python
39 lines
1.2 KiB
Python
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"""By analysing a user's login attempts, can you determine the secret numeric passcode?
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A common security method used for online banking is to ask the user for three random characters from a passcode. For example, if the passcode was 531278, they may ask for the 2nd, 3rd, and 5th characters; the expected reply would be: 317.
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The text file, keylog.txt, contains fifty successful login attempts.
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Given that the three characters are always asked for in order, analyse the file so as to determine the shortest possible secret passcode of unknown length.
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"""
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def main():
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key = []
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with open('p079/keylog.txt', 'r') as f:
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while True:
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line = f.readline()
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if not line:
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break
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prev = None
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for c in line.strip():
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c = int(c)
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if c not in key:
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if prev:
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# Place right of prev
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i = key.index(prev) + 1
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key.insert(i, c)
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pass
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else:
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key.insert(0, c)
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elif prev and key.index(c) < key.index(prev):
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# Move if not right of prev
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old = key.index(c)
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key.insert(key.index(prev) + 1, c)
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key.pop(old)
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pass
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prev = c
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print 'Key:', ''.join(str(c) for c in key)
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if __name__ == '__main__':
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main()
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