Question: 1 . A bank uses ( K , E , D ) , a one - time pad symmetric encryption scheme with key space K

1. A bank uses (K,E,D), a one-time pad symmetric encryption scheme with key space K={0,1} for their cryptographic needs. Observe that the encryption and decryption keys are identical as it is a symmetric OTP crypto system. The bank wishes to split the decryption key k in {0,1} into two pieces p1 and p2 so that both are needed for decryption. The idea is that piece p1 can be given to one executive and p2 to another so that both must contribute their pieces for decryption to proceed. Following this idea, the bank generates a random k1 in {0,1} and sets k1 k k1. Note that k1 k1= k. The bank can give k1 to one executive and k1 to another executive. Both must be present for decryption to proceed since, by itself, each piece contains no information about the secret key k (note that each piece is a one-time pad encryption of k, interesting!).
Now, suppose the bank wants to split k into three pieces p1, p2, and p3 so that any two of the pieces enable decryption using k. This ensures that even if one executive is out sick, decryption can still succeed. To do so the bank generates two random pairs (k1,k1) and (k2,k2) as in the previous paragraph so that k1k1=k2k2=k. How should the bank assign pieces so that any two pieces enable decryption using k, but no single piece can decrypt?

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