1. CONTENTS
o Introduction
o Need of Cryptography
o Types of Attacks
o Techniques of Cryptography
o Encryption Algorithm
• Symmetric
• Asymmetric
o Digital Signature
o Conclusion
2. INTRODUCTION
What is Cryptography?
“Hidden Writing”
Mainly used to protect Information.
Goal of Cryptography
Ensure security of communication over insecure
medium
Communicate even with possibility of adversary
3. NEED OF ENCRYPTION
Confidentiality
Integrity
Authentication
Nonrepudiation
Access Control
Availability
4. TYPES OF ATTACKS
A General View
A Technical View
A Practical Side of Attacks
Programs that Attack
5. PLAIN PLAIN
TEXT TEXT
ENCRYPTION DECRYPTION
CIPHER
TEXT
SENDER RECEIVER
BASIC BLOCK DIAGRAM
6. BASIC TERMINOLOGIES
Encryption
Encryption is the process of encoding a message so that its
meaning is not obvious
Decryption
Decryption is the reverse process, transforming an encrypted
message back into its normal, original form
Cryptosystem
A system for encryption and decryption is called a
cryptosystem.
7. BASIC TERMINOLOGIES
Plaintext
Cipher text
Key –
key refers to a sequence of symbols or a numerical value used
by an algorithm to alter information & making that information
secure
Encryption algorithm
The cryptosystem involves a set of rules for how to encrypt the
plaintext and how to decrypt the cipher text.
Cryptanalysis
Cryptanalysis is an attempt to break the cipher text.
9. ENCRYPTION ALGORITHM
Symmetric
Same key for encryption and decryption
Key distribution problem
Asymmetric
Key pairs for encryption and decryption
Public and private keys
10. SYMMETRIC ALGORITHM
It is also called as Secret Key Cryptography
Single key used for both encrypt & decrypt
Key must be known to both the parties
Key
Original
Plaintext Ciphertext Plaintext
Encryption Decryption
Symmetric Cryptosystem
11. ASYMMETRIC ALGORITHM
Private keys are used for decrypting.
Public keys are used for encrypting
encryption
plaintext ciphertext
public key
decryption
ciphertext plaintext
private key
12. COMPARISON
Secret Key (Symmetric) Public Key (Asymmetric)
Number of Key 1 2
Protection of Key Must be kept secret One key must be kept secret
& other can be freely
exposed
Best Uses secrecy and integrity of Key exchange, authentication
data
Key Distribution Problematic Safer
Speed Fast Slow; typically, 10,000 times
slower than secret key
13. SYMMETRIC ALGORITHM
Data Encryption Standard (DES):
56 bits key
Advance Encryption Standard (AES):
128, 192 or 256 bits key
International
Data Encryption
Algorithm(IDEA):
128 bits key
14. DATA ENCRYPTION STANDARD
Developed by IBM and it is known as the Data Encryption
Standard
It is also known as Data Encryption Algorithm
The DES algorithm is a careful and complex combination of
two fundamental building blocks of encryption:
Substitution and
Transposition
DES uses only standard arithmetic and logical operations on
numbers up to 64 bits long
15. Plain text (64 bits)
Initial Permutation (IP)
LPT RPT
key 16 rounds 16 rounds key
Final Permutation
Cipher text (64 bits)
BROAD LEVEL STEPS IN DES
16. DATA ENCRYPTION STANDARD
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.
17. DETAILS OF ONE ROUND IN DES
Key Transformation
Expansion Permutation
S- box Substitution
P- box Permutation
XOR and Swap
18. ADVANTAGES OF DES:
o DES is also an ANSI and ISO standard - anybody
can learn the details and implement it.
o Since DES was designed to run on hardware, it is
fast in hardware.
o Hard to crack.
DISADVANTAGES OF DES:
o Hardware implementations of DES are very fast;
DES was not designed for software and hence runs
relatively slowly.
19. ASYMMETRIC ALGORITHM
Rivest Shamir Adleman (RSA) Encryption:
Based on factoring the product of large prime numbers.
Knapsack Algorithm:
If M1,M2…., Mn are given values & S is the sum,
S=b1M1+b2M2….+bnMn
where, bi can be 0 or 1
20. RSA
It is named after its three inventors Rivest
Shamir and Adleman
This algorithm was introduced in 1978 and to
date remains secure.
RSA has been the subject of extensive
cryptanalysis, and no serious flaws have yet been
found.
The encryption algorithm is based on the
underlying problem of factoring large numbers.
21. RSA
p and q are two large prime numbers
n=p.q
m = (p-1)(q-1)
a is such that 1 < a < m and gcd (m , a) = 1.
b is such that ( a. b) mod m = 1
22. RSA ENCRYPTION & DECRYPTION
Message M < n.
Encryption key = (a , n).
Decryption key = (b , n).
Encrypt => E = Ma mod n.
Decrypt => M = Eb mod n.
23. Advantage
Individuals can post their public key on their Web
site.
The number of the keys is only twice of the
number of user.
Disadvantage
It is slower than symmetric algorithms.
The cipher text may be larger than plain text.
24. DIGITAL SIGNATURE
When an author signs a document, it cannot
be changed.
When you send a document
electronically, you can also sign it.
Digital signature can be done in two ways:
You can sign the whole document
You can sign a digest of the document
25. Signing the whole document
You can not provide these aspects of security using the
secret key.
The method provides authentication & non-repudiation.
26. Signing the digest
The two most common hash functions are:
Message digest 5 (MD5)
Secure hash algorithm (SHA-1)
The properties of hash function
One-way: the digest can only be created from the
message, but not vice versa
One-to-one: be very difficult to find two messages that
create the same digest.
29. APPLICATIONS OF ENCRYPTION
Cryptographic Hash Function
Digital Signature
Certificate
Secure electronic transactions
Office equipment
30. CONCLUSION
RSA finds its strongest application when parties
who have no prior relationship want to share
sensitive data with each other.
Thus , even though slower as compared to
symmetric algorithms it is & will be widely used as it
can be used in digital signature for long haul
transmission.