Find decryption function and decrypted-recovered plaintext

Question

1) Using the English alphabet (i.e., mod 26 arithmetic) let plaintext = {p₁, p₂,... , p_n} and corresponding ciphertext = {c₁, c₂,... , c_n}.

Suppose the encryption function is c_i = p_i + 10 (mod 26). You receive the ciphertext message EWEM SC K QBOKD CMRYYV

What is the decryption function, and the decrypted/recovered plaintext? What type of cipher is this? Show your calcs.

2) Bob believes that he has come up with a nifty hash function. He assigns a numeric value V_Char to each letter in the alphabet equal to the letter's position in the alphabet, i.e., V_A = 1, V_B = 2, ..., V_Z = 26. For a message, he calculates the hash value H = (V_{Char 1} x V_{Char 2} x V_{Char 3 ...}x V_{Char N}) mod(26).

Bob uses this function to send a one-word message, REGAL, to his banker Bill, along with his calculated hash value for the message. Alice is able to intercept the message, and generates an alternative message that has a hash value that collides with Bob's original hash value.

Give definition and properties of the hash function.

Show a message that Alice may have used to spoof Bob's message, and demonstrate that its hash value collides with Bob's original hash.