Perhaps the simplest “serious” symmetric block encryption algorithm is the Tiny Encryption...

Perhaps the simplest “serious” symmetric block encryption algorithm is the Tiny Encryption Algorithm (TEA). TEA operates on 64-bit blocks of plaintext using a 128-bit key. The plaintext is divided into two 32-bit blocks (L0, R0), and the key is divided into four 32-bit blocks (K0, K1, K2, K3). Encryption involves repeated application of a pair of rounds, defined as follows for rounds i and i+ 1:

where F is defined as

and where the logical shift of x by y bits is denoted by x≪ y; the logical right shift of x by y bits is denoted by x≫ y; and δi is a sequence of predetermined constants.

a. Comment on the significance and benefit of using the sequence of constants.

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b. Illustrate the operation of TEA using a block diagram or flow chart type of depiction.

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c. If only one pair of rounds is used, then the ciphertext consists of the 64-bit block (L2, R2). For this case, express the decryption algorithm in terms of equations.

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d. Repeat part (c) using an illustration similar to that used for part (b).