This is Cryptography presentation. This explains fundamental concepts of cryptography.This starts from very basic topics and then moving to the important concepts used in today's cryptosystems. This can be used by college students as their project ppts.

1. CRYPTOGRAPHY
Mrinalini Sharma
M.Tech (ECE), 1st Sem.
00516414216

2. THREATS

3. SECURITY GOALS

4. CRYPTOGRAPHY
 CRYPTOGRAPHY plays major roles in fulfilling this demand.
 Greek word meaning “Secret Writing”.
 Science & art of transforming messages to make them secure &
immune to attacks.

5. COMPONENTS OF CRYPTOGRAPHY
• Plaintext – Original message (message in its natural format readable by an
attacker).
• Ciphertext – Message altered to be unreadable by anyone.
[ CIPHER refers to the encryption & decryption algorithms.]
• Key – Sequence that controls the operation and behavior of the
cryptographic algorithm.
• Keyspace – Total number of possible values of keys in a crypto algorithm.

7. CRYPTOGRAPHY TYPES

8. 1. SYMMETRIC-KEY
 Also known as SECRET-KEY Cryptography.
 Same key is used for encryption and decryption i.e. shared
key.
 Main types –

9. SYMMETRIC-KEY CRYPTOGRAPHY

10. SUBSTITUTION CIPHERS
• In this, letters/number/symbols of plaintext are replaced by
other letters/numbers/symbols.
e.g. A D, T Z
2 5, 3 6

11. TRANSPOSITION CIPHERS
• In the transposition technique the positions of
letters/numbers/symbols in plaintext is changed with one
another.
Plain text: MEET ME AFTER PARTY
Cipher text: TEMEEMEFAPTRYRAT
Key Usec: 421635

12. Data Encryption Standard (DES)
• Developed by IBM.
• Plaintext is processed in 64-bit blocks.
• The DES algorithm is a careful and complex combination of two fundamental
building blocks of encryption:
– Substitution
– Transposition
• DES uses only standard arithmetic and logical operations on numbers up to
64 bits long.
– Transforms 64-bit input in a series of steps into a 64-bit output
– The same steps are used to decrypt messages
– Sender and receiver share the same key (Symmetric)
• Now considered to be insecure
– Key size is 56 bits, considered to be too small

14. Data Encryption Standard (DES)
• 1st 64 bit plain text is handed over to initial permutation
function.
• IP is performed over the plain text.
• IP produces two halves of the permuted blocks left
plain text (LPT) & right plain text (RPT).
• Now LPT & RPT goes 16 rounds of encryption process,
each with its own key.
• Now LPT & RPT are rejoined and FINAL PERMUTATION
(FP) is performed on the combined block.
• The result is 64 bit cipher text.

16. ADVANTAGES
• DES is also an ANSI and ISO standard - anybody can
learn the details and implement it.
• Hard to crack.
DISADVANTAGES
• Software implementations of DES are slow.

17. TDES & AES
• TDES
– Triple DES – Use algorithm 3 times
– 3 different keys (56-bits each)
– 168 bits total (192 if parity bits are included)
– Superceded by AES
• AES
– Advanced Encryption Standard
– Fixed block size of 128 bits
– Key size can be 128, 192, or 256 bits

18. 2. ASYMMETRIC-KEY
 Also knowns as PUBLIC-KEY Cryptography.
 Sender & receiver use different keys for encryption &
decryption namely PUBLIC & PRIVATE respectively.
 Main algorithms –
 RSA (Rivest, Shamir & Adleman)
 Diffie - Hellman

19. ASYMMETRIC-KEY CRYPTOGRAPHY

20. THE RSA ALGORITHM
• Published by Ron Rivest, Adi Shamir, and Len Adleman in
1978.
• Best known and widely used public-key scheme.
• Block cipher in which plaintext and ciphertext are integers
between 0 and n – 1 for some n.

21. RSA KEY GENERATION
1) Select to prime numbers: p, q
– Private, chosen
2) Calculate n = pq
– Public, calculated
3) Calculate Φ(n) = (p-1)(q-1)
4) Select an integer e such that:
– gcd(Φ(n), e) = 1 and 1 < e < Φ(n)
– Public, chosen
5) Calculate d where d = e-1modΦ(n)
– ed = 1 mod Φ(n)
– Private, calculated

22. RSA ENCRYPTION/DECRYPTION
• To encrypt a message M the sender:
– Obtains public key of recipient KU={e,n}
– Computes: C = Me mod n
• Where 0≤M<n
• To decrypt the ciphertext C the owner:
– Uses their private key KR={d,n}
– Computes: M = Cd mod n

23. EXAMPLE
1) Let p = 7 and q = 17
2) n = pq = 7 x 17 = 119
3) Φ(n) = (p-1)(q-1) = 6 X 16 = 96
4) Let e = 5
– gcd(Φ(n), e) = gcd(96,5) = 1
– 1 < 5 < 96
5) d = e-1 mod Φ(n)
– Therefore, de = 1 mod 96
– d = 77
• 77 x 5 = 385 = 4 x 96 + 1
KEY GENERATION :
The two resulting keys are as follows:
– Public Key: KU = {e,n} = {5, 119}
– Private Key: KR = {d,n} = {77, 119}

24. ENCRYPTION
• To encrypt a message M, where M = 19:
– C = Me mod n
– 195 mod 119 = 2476099 mod 119
– 2476099 / 119 = 20807 with a remainder of 66
– Therefore, C = 66
DECRYPTION
• M = Cd mod n
• 6677mod 119 = (1.27 x 10140) mod 119
• (1.27 x 10140) / 119 = (1.06 x 10138) with a remainder of 19
• Therefore, M = 19

25. APPLICATIONS
• Defense services
• Secure data manipulation
• E–commerce
• Business transactions
• Internet payment systems
• User identification systems
• Access control
• Data security

26. CONCLUSION
By using of encryption techniques a fair unit of confidentiality,
authentication, integrity, access control and availability of
data is maintained.

27. THANK-YOU !!!