January 22, 2002
Practical Aspects of Modern Cryptography
44
nAn unconditionally secure cipher
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nProblems:
nNumber of random bits needed = sum of lengths of all messages to be encrypted (not reusable)
nRandom bits must be known to both sender and recipient.
Background: The One-Time Pad
Key = random bits  = 1100010011100100011…
Message = bits         = 1110011001100110001…
Ciphertext = XOR
 of Key, Message = 0010001010000010010...