1. Come up with as efficient an encoding as you can to specify a completely general one-to-one...
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1. | Come up with as efficient an encoding as you can to specify a completely general one-to-one mapping between 64 bit input values and 64-bit output values. |
2. | Token cards display a number that changes periodically, perhaps every minute. Each such device has a unique secret key. A human can prove possession of a particular such device by entering the displayed number into a computer system. The computer system knows the secret keys of each authorized device. How would you design such a device? |
3. | How many DES keys, on average, encrypt a particular plaintext block to a particular ciphertext block? |
4. | Make an argument as to why the initial permutation of the bits of the DES key cannot have any security value. |
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