MINI-HTTPS

1. Mentor sends you Public Parameters (p=15728303; g=5) of 24 bits length. Generate public and private keys PrKA=x and PuKA=a.

Send public key [a] to the Mentor.

2. Compute random secret number u of 24-bit length and compute session public parameter KA. Sign KA with Schnorr signature scheme by computing two components of signature SigA=(r,s).

Send [KA,r,s] to the Mentor.

3. Mentor sends you (PuKB=…, KB=…, R=…, S=…). Verify Mentor’s signature SigB=(R, S) on KB by assigning to the variable V verification value either 0 or 1.

If a signature is not valid then V=0 and send value [0] to the Mentor.

If a signature is valid then V=1 and compute secret session symmetric key KAB=K. Transform K to the hexadecimal form Kh.

Create the string of message variable m=’MMDD’ consisting of the month and day of your birth. Encrypt message m using 10 rounds of AES128 cipher with key Kh by computing ciphertext

>> C=AES128(m,Kh,10,'e').

Send [V, C] to the Mentor for decryption and for resending message m to your friend Bob2.

4. Ok, Bob2 informed me that all the sum of money he received from the Knowledge Bank he dedicates to buy the gift for your birthday. This sum I am sending you as a ciphertext (CM=…). Please decrypt and check it and then encrypt it again with the added string ‘ok’ right after the sum by computing ciphertext C1.

Send [C1] to the Mentor.