Question

Using RSA cipher, public key e=3, private key d=7 Encrypt the following message “Hello there” Decrypt the previous message

Answer 1

ANSWER:

From the question:

key e=3, private key d=7

ed 1%z where z = (p-1)(q-1)

3*7 1%z

21 1%z

z = 20

z = (p-1)(q-1)

z = (2)(10)

p-1=2 =>p=3

q-1=10 =>q=11

Calculate n = pq

n = 3 * 11

n = 33

Encrypt the string Hello there.

Characters   H   e   l   l   o   t   h   e   r   e
ASCII Value   72   101   108   108   111   20   116   104   101   114   101
Formula of encryption c = me mod n

H -> c = 723 mod 33 = 18

e -> c = 1013 mod 33 = 8

l -> c = 1083 mod 33 = 3

o -> c = 1113 mod 33 = 12

space c = 203 mod 33 =14

t -> c = 1163 mod 33 = 29

h -> c = 1043 mod 33 = 26

r -> c = 1143 mod 33 = 9

Therefore the encrypted string is 18 8 3 3 12 14 29 26 8 9 8

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