RSA Algorithm

RSA is a public key algorithm (Asymmetric key cryptography), named after its inventors Rivest, Shamir, and Adleman. It uses two keys e and d as the public and private keys. The key selection steps are as follow,

• Receiver (Bob) choose two large prime numbers p and q.
• Bob find out n as: n=p*q Note that the value of p must be less than n. otherwise we need to divide the plaintext into blocks in-order p less n.
• Bob calculate another number z as: z=(p-1)*(q-1)
• Bob choose a random integer e, and calculate d as: d*e= 1 mod z
• Bob keeps z and d as secret, announces e and n to public.

Any sender, who need to send data to Bob generate ciphertext as follow:

                        C=Pe mod n

Where p is the data to send and n and e are keys announced by Bob to public.

While receiving a ciphertext Bob convert it to plaintext as follow,

                        P=C d mod n

Advanced Encryption Standard (AES)

AES was designed to increase the key size than DES. AES is a round cipher with keys of three different sizes: 12-bits key (10 rounds), 192-bits key (12 rounds) an 256-bits key ( 14 rounds). All of the above operates on 128-bits length data block. AES is symmetric key cryptographic algorithm.

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