This document summarizes a seminar on cryptography presented by Ashish. It defines cryptography as the science of encrypting messages to make them secure. It outlines the basic terms used in cryptography like plaintext, ciphertext, encryption, and decryption. It describes the different categories of cryptography including secret key cryptography, public key cryptography, and hash functions. Popular algorithms for encryption like DES, AES, RSA, and algorithms for hashing like MD5 and SHA are also mentioned. Finally, it discusses applications of cryptography in areas like defense, e-commerce, and data security and provides references used for the seminar.

1. A SEMINAR
ON
CRYPTOGRAPHY
By ;
Ashish Dhar
Roll No – 17
Semester – iv
Regd No. - 1625209002
Hii... I m
Ashish
1
Hii... I m
Ashish

2. CONTENTS
 What is Cryptography
 Basic terms
 Categories
 Algorithms used
 Applications
 Conclusion
 References
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3. WHAT IS CRYPTOGRAPHY ???
 Cryptography is the science and art of transforming
messages and make them immune to attack.
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4. BASIC TEARMS
 Plaintext : A message in its natural format readable
by attacker
 Cipher : The algorithm that does the encryption
 Ciphertext : The encrypted version of the message
that is unreadable to anyone except the intended
recipients
 Encryption : The process of scrambling the data
using a specialized cryptographic algorithm
 Decryption : The process of converting ciphertext
back to the original plaintext
 Key : A string of bits used to encrypt the plaintext or
decrypt the ciphertext
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5. ENCRIPTION BY CAESAR CIPHER
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
Plaintext : ASHISH
Ciphertext(Encrypted) : DVKLVK

6. DECRYPTION BY PIGPEN CIPHER
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Answer: WELCOME

7. Secret/Private key
Public key
Hash functions
TYPES OF CRYPTOGRAPHY
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8. SECRET KEY CRYPTOGRAPHY
 Also known as symmetric key cryptography.
 Sender & receiver uses same key & an
encryption/decryption algorithm to encrypt/decrypt
data. i.e. the key is shared.
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9. SECRET KEY CRYPTOGRAPHY CONTD…
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ENCRYPTION DECRYPTION
CIPHERTEXT
SENDER RECEIVER
SECRET
KEY

10. PUBLIC KEY CRYPTOGRAPHY
 Also known as asymmetric key cryptography.
 Sender & receiver uses different keys for
encryption & decryption namely PUBLIC &
PRIVATE respectively
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11. PUBLIC KEY CRYPTOGRAPHY CONTD…
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ENCRYPTION DECRYPTION
CIPHERTEXT
SENDER RECEIVER
PUBLIC
KEY
PRIVATE
KEY

12. HASH FUNCTION
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 Hashing:
 Mathematical process for converting inputs into fixed-length outputs
 Hash function:
 Algorithm that does the hashing. Uses an input + a shared secret or
password. Example: MD5, Secure Hash Algorithm.
 Hash:
 Fixed-length output of the hashing

13. ALGORITHMS USED
 DES
 Triple DES
 AES
 IDEA
 ElGamal
 Diffle-Hellman
 RSA
 SHA-1
 SHA-2
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14. 14
RSA PUBLIC KEY ALGORITHM
Security of RSA is due to the difficulty of factoring large numbers
Therefore, p and q must be very large: 100s of bits
Choose large primes p and q
Compute n = pq
Compute m = (p – 1)(q – 1)
Choose small e coprime to m
i.e. choose 1 < e < m, s.t
gcd(e, m) = 1
Find d, 1 <d <m s.t
de = 1(mod m)
Publish n and e as public key
Keep n and d as private key
Encryption example:
y = xe mod n
= 65 mod 133
= 7776 mod 133
= 62
p = 7, q = 19
n = 7  19 = 133
m = 6  18 = 108
e = 5
d = 65
Public key: 133, 5
Private key: 133, 65
Decryption example:
x = yd mod n
= 6265 mod 133
= 62(3844)32 mod 133
= 62(120)32 mod 133 =...= 6

15. APPLICATIONS
 Defense services
 Secure data manipulation
 E –commerce
 Business transactions
 Internet payment systems
 User identification systems
 Data security
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16. CONCLUSION
 We use different types of algorithms to establish
security services in different service mechanisms.
We use either private key cryptography or public
key cryptography according to requirement.
 If we want to send message quickly we use private
key algorithm and if we want to send messages
secretly we use public key algorithm
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17. REFERENCES
 “Cryptography and Network Security” by William
Stallings
 http://www.google.com
 http://www.wikipedia.org
 http://www.studymafia.org
 http://www.youtube.com
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18. GUIDANCE
 Mr. Ajay Kumar Tripathy
 Mr. Amarjeet Mohanty
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