Cryptography involves techniques for securing communication and information. It uses ciphers and encryption algorithms to convert plain text into encrypted ciphertext. There are two main types of encryption: symmetric key encryption which uses a shared secret key for encryption and decryption, and asymmetric (public key) encryption which uses separate public and private keys. Cryptography is used for secure communication over the internet, wireless networks, and to encrypt files and content. Common ciphers include the Caesar cipher which shifts each letter by a fixed number of positions. Ciphers can be attacked using statistical analysis of letter frequencies or brute force methods to decrypt the ciphertext without the key.

1. Fundamentals of
Cryptography
Workshop

2. What is Cryptography ?
“KRYPTO” “GRAPHENE”
KRYPTO GRAPHENE
SECRET WRITING

3. Why do we need Cryptography?
ORGANISATIONHITMAN
KILL BELICOFF
Channel

4. UTTER FAILURE

5. HISTORY
• 50 B.C. Julius Caesar uses cryptographic
technique
• 1250 British monk Roger Bacon
describes simple ciphers
• 1466 Leon Alberti develops a cipher
disk
• 1861 Union forces use a cipher during
Civil War

6. HISTORY
• 1914 World War I – British, French, and
German forces use encryption
technology
• 1917 William Friedman, Father of U.S.
encryption efforts starts a school
for teaching cryptanalysis in
Illinois
• 1917 AT&T employee Gilbert Vernam
invents polyalphabetic cipher
• 1919 Germans develop the Enigma machine
for encryption

7. HISTORY
• 1937 Japanese design the Purple
machine for encryption
• 1942 Navajo windtalkers help with secure
communication during World War II
• 1948 Claude Shannon develops statistical
methods for encryption/decryption
• 1976 IBM develops DES
• 1976 Diffie – Hellman develop public key /
private key cryptography
• 1977 Rivest – Shamir – Adleman develop the
RSA algorithm for public key / private key

8. Where do we use Cryptography ?
Secure communication:
• web traffic: HTTPS
• wireless traffic: 802.11i WPA2 (and WEP), GSM, Bluetooth
Encrypting files on disk: EFS, TrueCrypt
Content protection (e.g. DVD, Blu-ray): CSS, AACS
User authentication
… and much much more

9. SECURE COMMUNICATION
no eavesdropping
no tampering

10. PLAIN TEXT
 Plaintext is a text , in natural readable form. It is the message or data
before it gets encrypted. In simple words it is the original message.
 It is sometimes called clear text . Plaintext is denoted by M (message)
or P (plaintext).
 It can be a stream of bits , a text file , a bitmap image, a stream of
digitized voice etc.
E.g.: ”Mission is a Go !!!”

11. CIPHER TEXT
 An encrypted message is called cipher text . It is denoted by C (cipher
text).
 Sometime it has the same size as the plaintext, sometimes larger than
the plaintext.
 It is the results obtained from the plaintext by applying the encryption
algorithm on the plaintext.
 Cipher text is unreadable by anyone except the intended recipients.
E.g. :“jhbaiudcbew564kjb”

12. ENCRYPTION
 The process of disguising a message in such a way to hide its
substance is called encryption.
 It is the process of scrambling a message using a specialized
cryptographic algorithm to make it unreadable by anyone except the
intended recipients.
 The encryption function E, operates on M to produce C. In
mathematical notation E(M)=C

13. Types of Encryption
• SYMMETRIC KEY ENCRYPTION
• PUBLIC KEY ENCRYPTION

14. SYMMETRIC KEY ENCRYPTION
• Symmetric encryption is the oldest and best-
known technique. A secret key, which can be a
number, a word, or just a string of random letters,
is applied to the text of a message to change the
content in a particular way. This might be as
simple as shifting each letter by a number of
places in the alphabet

15. ASYMMETRIC KEY ENCRYPTION
• Public-key encryption, in which a message is
encrypted with a recipient's public key. The
message cannot be decrypted by anyone who does
not possess the matching private key, who is thus
presumed to be the owner of that key and the
person associated with the public key. This is used
in an attempt to ensure confidentiality.

16. ASYMMETRIC KEY ENCRYPTION

17. ASYMMETRIC KEY ENCRYPTION

18. ASYMMETRIC KEY ENCRYPTION

19. CONCEPTS
• A private key cipher is composed of two algorithms
• encryption algorithm E
• decryption algorithm D
• The same key K is used for encryption & decryption
• K has to be distributed beforehand

20. NOTATIONS
• Encrypt a plaintext P using a key K & an encryption algorithm E
C = E(K,P)
• Decrypt a cipher text C using the same key K and the matching
decryption algorithm D
P = D(K,C)
• Note: P = D(K,C) = D(K, E(K,P))

21. CAESAR CIPHER
• The Caesar cipher is a substitution cipher,
named after Julius Caesar.
• Operation principle:
each letter is translated into the letter a fixed
number of positions after it in the alphabet
table.
• The fixed number of positions is a key both for
encryption and decryption.

22. CAESAR CIPHER
The action of a Caesar cipher is to replace each plaintext letter with a different one a fixed
number of places down the alphabet. The cipher illustrated here uses a shift of 3

23. An Example
• For a key K=3,
plaintext letter: ABCDEF...UVWXYZ
cipher text letter: DEF...UVWXYZABC
• Hence
TREATY IMPOSSIBLE
is translated into
WUHDWB LPSRVVLEOH

24. ATTACKS
• With the help of fast computers, 99.99%
ciphers used before 1976 are breakable
by using one of the 4 types of attacks
(described later).
• Modern cluster computers and future
quantum computers can break several
existing ciphers due to the power of
such computers.

25. ATTACKS ON CAESAR CIPHER
• By using statistics on letters
• frequency distributions of letters
letter percent
A 7.49%
B 1.29%
C 3.54%
D 3.62%
E 14.00%
..................................
• By Brute Force attacks.

26. SUMMARY
• What is cryptography ?
• Why do we need Cryptography ?
• Types of Encryption ?
• Notations
• Fundamental Terms
• Caesar Cipher
• Attack on Caesar Cipher

27. THE END
ANY QUERIES ?
Manojit Ballav
Email: manojitballav@outlook.com
Phone: 9352957266