RSA Principle 4

Encryption and decryption

Pub Key: (14363, 97)
Prv Key: (14363, 9553)

If A want send message m to B.
A need use B’s public key to encrypt M[Integer and M < n].

$$m^e \equiv c \quad(mod \quad n)$$

Suppose A want send “Hello B” to B, the first alphabet ‘H’ should be encrypt like this.

$$c = 72^{97} \quad mod \quad 14363$$

The ciphertext c is 5769

B received A’s message 5769, B use private key to decrypt it.

$$c^d \equiv m \quad(mod \quad n)$$

->

$$M = 5769^{9553} \quad mod \quad 14363$$

The text is 72[ ‘H’ in ASCII ]

Signatures and signed inspection certificate

It’s a opposite progress of above one.

Sender in order to show it’s identity, it need to use it’s private key to encrypt[autograph] abstract message like hash code or mac code.

Receiver got message, use public key to decrypt[certificate] the signature, than contract the clear text with message’s abstract.