Internet Security - Dang Thanh Binh's Page

PUBLIC-KEY INFRASTRUCTURE 207
Let us break the hash code into two decimal numbers as follows:
h = 1 41 10 03 03 22 39 12 90 71
43 18 37 47 76 01 18 20 35 10
Using dA = 13 and n = 851, compute the RSA signature:
1 13 (mod 851) ≡ 1
41 13 (mod 851) ≡ 545
.
10 13 (mod 851) ≡ 333
c = h d A = 001 669 084 400 400 091 348 719 157 303
Send c to B.
A → B
635 439 333 047 089 001 439 520 466 084
Send (ciphertext Y , encrypted value of K and signed hash code c) toB.
Server B
1. Decryption of secret session key K:
Received encryption key K:
K = 0270 2524 1479 0285 1773 3139 2753 3669 3198
Choose dB = 1019 (B’s private key) and decrypt K block by block:
270 1019 (mod 3337) ≡ 5
2524 1019 (mod 3337) ≡ 23
.
.
3198 1019 (mod 3337) ≡ 81
K = 05 23 67 72 55 02 68 10 81
or
K = 52367725502681081 (decimal)
= ba0c2b3c484ff9 (hexadecimal)
2. Decryption of m using DES:
Ciphertext Y = a78791c0c8f0b444
Restored DES key K = ba0c2b3c484ff9