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1. A string over a finite set is a finite sequence of elements from 2. Show that the following procedure defines a cryptosystem. Let w be a string over {A, B, ...,Z}. Choose two shift cipher keys k and k2. Encrypt the elements of w in odd-numbered positions with ki and those in even-numbered positions with k2. Then reverse the order of the encrypted string. Determine the plaintext space, the ciphertext space, and the key space. 1. A string over a finite set is a finite sequence of elements from 2. Show that the following procedure defines a cryptosystem. Let w be a string over {A, B, ...,Z}. Choose two shift cipher keys k and k2. Encrypt the elements of w in odd-numbered positions with ki and those in even-numbered positions with k2. Then reverse the order of the encrypted string. Determine the plaintext space, the ciphertext space, and the key space