What is Cryptography? What is its Scope? How can we use this for our security purposes? etc..

1. Cryptography
Encryption & Decryption process applied with
documents and emails

2. Define four aspects of security in a network: privacy,
authentication, integrity, and nonrepudiation.
Understand how these aspects can be achieved using
encryption and decryption.
Understand the difference between secret-key and
public-key encryption.
OBJECTIVES
Realize how a digital signature can provide privacy,
integrity, and nonrepudiation.

3. Aspects of security
 Privacy :only the sender and the receiver of the message are
able to understand the contents of the messages.
 Authentication : the receiver needs to be sure of the sender’s
identity.(vice versa)
 Integrity : the contents of the message should not be changed
during transmission.
 Non-repudiation: a secure system needs to prove that the
sender actually sent the message.

4. Privacy/Confidentiality/Secrecy
 The privacy can be achieved using encryption / decryption
methods.
 Two categories of encryption/decryption:
Secret key(Symmetric key)
Public key(Asymmetric key)

5. Secret key encryption
 Ciphertext : data are encrypted
 Plaintext : the data are not encrypted
 Note that the secret key encryption algorithms are often
referred to as symmetric encryption algorithms.

6. Symmetric encryption
A Single key, a shared key
Encrypt with the key
Decrypt with the same key
 Secret key
 Keep it secret!
 If it gets out, you’ll need another key
Does not scale very well
Give the key to a lot of people
Watch them lose the key
Very fast to use
Not a lot of overhead
Often combined with asymmetric encryption

7. An example
ORIGINAL MESSAGE: GO HOME
ENCRYPTION KEY: shift by 2
ENCODE MESSEGE: IQ JQOG

8. Public key encryption
 The whole idea of this method is that the encryption
and decryption algorithms are not the inverse of each
other.

9. Combination
 The public key is used to encrypt the secret key.
 The secret key is used to encrypt the message.

10. An example

11. Digital Signature

12. Digital signature
 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(piece) of the document
 A digital signature is basically a way to answer that
an electronic document (email, spreadsheet, text
file etc.) is authentic.

13. Digital Signature Algorithm
Digital Signature can be used to identify the message source
and the integrity of the message by using specialised Digital
Signature Algorithm(DSA).
Slightest modification in then message would discard the
message and report back to its sender…

14. Hashing
M(P1)=H
M = Hash function
P1= Plain Text
H1= Hash Value
For Example
Input number: 191089
Hashing algorithm: Input number x 243
Hash value: 46434627

15. Signing the document
Step-1: The original text/document goes through the hash
algorithm to generate a hash value, say H1
Step-2: This hash value H1 is encrypted by using the
signer’s(sender’s) Private key to generate the digital
signature, say D1
Step-3: This digital signature combined with the original text
becomes the ‘Digitally signed document’ and send over the
public/ private network.

16. Verifying the document
Step-1: The document part is hashed to generate a value, say
H2.
Step-2: The digital signature D1 is decrypted by using the
Public key of the sender to generate another value, say H3.
Step-3: If H2 and H3 matches then the authenticity of the
document is verified otherwise the document generated may
not be exact!

17. Overall how it Works

18. Other ways of authentication
Password
Digital certificate

19. Thank you