Vernam Cipher Group Members: Muhammad Awais Muhammad Hasnain khan

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Presentation transcript:

Vernam Cipher Group Members: Muhammad Awais Muhammad Hasnain khan Muhammad Shahid Rafiq Muhammad Shozib

Vernam Cipher Vernam Cipher, also known as the one-time-pad.Gilbert Vernam invented and patented his cipher in 1917 while working at AT&T. Vernam cipher Also known as One-time-pad.

What Is One-Time pad? In cryptography, the one-time pad is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as the message being sent. In this technique, a plaintext is paired with a random secret key (also referred to as a one-time pad)

Encryption Formula: plaintext + key = cipher text

Decryption Forumla: cipher text-key=plain-text

Some Rules for Encryption First We chose plain text which we want to convert into cipher text. We can chose random key. Key length is always equal to length of cipher text. After adding plain text and keys .If num is ≥26 then we subtract 26 from cipher text in Encryption. Keys have two copies One for sender and one for receiver. Keys is discarded after one time use.

Encryption Example

Decryption

Another Example “same message” but now this time key is different.

Encyption H E L L O 7 (H) 4 (E) 11 (L) 11 (L) 14 (O) message + 23 (X) 12 (M) 2 (C) 10 (K) 11 (L) key = 30 16 13 21 25 message + key = 4 (E) 16 (Q) 13 (N) 21 (V) 25 (Z) (message + key) E Q N V Z → ciphertext

Decryption: E Q N V Z cipher-text 4 (E) 16 (Q) 13 (N) 21 (V) 25 (Z) cipher-text - 23 (X) 12 (M) 2 (C) 10 (K) 11 (L) key = -19 4 11 11 14 For negative value we add 26 for make it positive 7 (H) 4 (E) 11 (L) 11 (L) 14 (O) cipher-text – key H E L L O → message

This cipher is unbreakable in a very strong sense This cipher is unbreakable in a very strong sense. The intuition is that any message can be transformed into any cipher (of the same length) by a pad, and all transformations are equally likely

Modern use of the Vernam Cipher The Vernam Cipher can also be implemented with modern computer technology.

Why OTP is secure? The security depends on the randomness of the key.

Drawback in OTP Key-stream should be as long as plain-text. Key distribution & Management difficult.

Solution Stream Ciphers in which key-stream is a solution Stream cipher generated in pseudo-random fashion from relatively short secret key.