ON

ON

Cryptography

WHY DO WE NEED TO SECURE NETWORK ???

Information needs to be hidden from unauthorized access (confidentiality)

protected from unauthorized change (integrity)

available to an authorized entity when it is needed (availability).

Symmetry key Encryption

What observation is done here????????(w.r.t locking)

TRADITIONAL CIPHERS

-> Confidentiality is achieved using ciphers

-> Traditional ciphers are called symmetric-key ciphers (or secret-key ciphers) because the same key is used for encryption and decryption

General Idea of Traditional ciphers

Traditional Ciphers

Substitution ciphers Transposition ciphers

A substitution

cipher replaces one symbol with

another.

A transposition

cipher reorders symbols.

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E HT T M TAO Y ZCNE IAK N GT S

Write row by row

e ht tm ta oy zc ne ia kn gt s

Plaintext

Ciphertext

Read column by column

e

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Read row by row

Ciphertext

Write column by column

Plaintext

e ht tm ta oy zc ne ia kn gt s

Transmission

Till now we were aware of only “Text” form of the data

What if we want to send audio/ video??????

Modern CiphersTraditional ciphers• only text

Modern ciphers• numbers• graphics• audio, and video data

Character oriented ciphers

Bit oriented ciphers

How actually modern ciphers works?Data will be converted to stream of bit

And send the encrypted stream

Encrypt the stream

Modern block ciphers