Cryptography is the science of securing communication and information. It uses techniques like encryption and decryption to transform information into an unreadable format, called cipher text. There are different types of cryptography like secret key cryptography which uses a single key for encryption and decryption, and public key cryptography which uses different keys for encryption and decryption. Cryptography ensures security requirements like authentication, privacy, integrity and non-repudiation of digital information. It has advantages like privacy of communication but also disadvantages like the time needed for encryption and decryption.

1. Cryptography
By: Mohd. Asif Ansari

2. Contents
 What is Cryptography...?
 Security Requirements
 Encryption & Decryption
 Types of Cryptography
 What is KEY…?
 Advantages
 Disadvantages
 Conclusion

3. Definition
Cryptography is the science of information security.
Derived from the Greek word “KRYPTOS”.
Writing in secret code and is an ancient art.
In data and telecommunications, cryptography is necessary
when
communicating
over
any
untrusted
medium, particularly the Internet.

4. Some specific security requirements
 Authentication: The process of proving one's identity.
 Privacy: Ensuring that no one can read the message except
the intended receiver.
 Integrity: Assuring the receiver that the received message
has not been altered in any way from the original.
 Non-repudiation: A mechanism to prove that the sender
really sent this message.

5. Encryption
It is the transformation of data into some unreadable form.
Its purpose is to keep the information hidden from anyone for whom it
is not intended.

6. Decryption
It is the reverse of encryption.
It is transformation of encrypted data back into some clear
form.

7. Types of Cryptography
 Secret Key Cryptography: Uses a single key for both
encryption and decryption.
 Public Key Cryptography: Uses one key for encryption and
another for decryption.
 Hash Functions: Uses a mathematical transformation to
encrypt information.

8. What is Key….?
In cryptographic systems, the term key refers to a numerical
value used by an algorithm to alter information, making that
information secure and visible only to individuals who have
the corresponding key to recover the information.

9. The art of protecting information by transforming it
into an unreadable format, called cipher text.

10. Secret Key Cryptography
With secret key cryptography, a single key is
used for both encryption and decryption. As shown
in Figure 1A, the sender uses the key (or some set
of rules) to encrypt the plaintext and sends the
ciphertext to the receiver. The receiver applies the
same key (or ruleset) to decrypt the message and
recover the plaintext. Because a single key is used
for both functions, secret key cryptography is also
called symmetric encryption.

11. Secret Key Cryptography

12. Public-Key Cryptography
Generic PKC employs two keys that are mathematically
related although knowledge of one key does not allow
someone to easily determine the other key. One key is used to
encrypt the plaintext and the other key is used to decrypt the
ciphertext. The important point here is that it does not matter
which key is applied first, but that both keys are required for
the process to work (Figure 1B). Because a pair of keys are
required, this approach is also called asymmetric cryptography.

13. Public-Key Cryptography

14. Hash Functions
Also called message digests and one-way encryption, are algorithms
that use no key.
A fixed-length hash value is computed based upon the plaintext that
makes it impossible for either the contents or length of the plaintext to
be recovered.
Typically used to provide a digital fingerprint of a file's contents.
Provide a measure of the integrity of a file.

15. Different Hash Algorithms
Message Digest (MD) algorithms: Produce a 128-bit hash value.
 Secure Hash Algorithm (SHA): Produces a 160-bit hash value.
 RIPEMD: RACE Integrity Primitives Evaluation. 32-bit
 HAVAL: Hash of Variable Length hash values that are
128, 160, 192, 224, or 256 bits in length.
 Whirlpool: Operates on messages less than 2256 bits in
length, and produces a message digest of 512 bits.
Tiger: Designed to be secure, run efficiently on 64-bit processors.


16. Signed Messages
Message
Message
+
signature
Sent thru’ Internet
Calculated
Hash
Message
+
Signature
if
COMPARE
Hash
SIGN hash
With Sender’s
Private key
Sender
Hash
Receiver
Decrypt
Signature
With Sender’s
Public Key
OK
Signatures
verified

17. Advantages
 It hides the message and your privacy is safe.
 No one would be able to know what it says unless there's a key to
the code.
 You can write what ever you want and how ever you want (any
theme any symbol for the code) to keep your code a secret.
 You are able to use Cryptography during lessons without the teacher
knowing.

18. Disadvantages
 Takes a long time to figure out the code.
 It takes long to create the code.
 If you were to send a code to another person in the past, it will take
long to get to that person.
 Overall it’s a long process.

19. Conclusion
As the Internet and other forms of electronic communication
become more prevalent, electronic security is becoming
increasingly important.
Cryptography is used to protect e-mail messages, credit card
information, and corporate data.
One of the most popular cryptography systems used on the
Internet is Pretty Good Privacy because it's effective and
free.

20. Thank you…!