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#1
April 15th, 2008, 11:03 AM
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One-time-pad question
I found this question on an exam past paper and couldn't think of a justified solution.
A message is double encrypted by using the one time pad twice with two keys k1 and k2. Show that this procedure is no more secure than using a single encryption and calculate the key k3 that this double encryption corresponds to. Any ideas??
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#2
April 15th, 2008, 09:13 PM
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A one-time pad is perfectly secure (entropy-wise, that is, which is what you're discussing). There will be no discernible pattern after the OTP has been applied, so applying anything else, including another OTP, will be useless.
Assuming you apply your OTP via XOR (which is the standard), the k3 you seek will be equal to k1 XOR k2.
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