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  1. 1. Cryptography By: Mohd. Asif Ansari
  2. 2. Contents  What is Cryptography...?  Security Requirements  Encryption & Decryption  Types of Cryptography  What is KEY…?  Advantages  Disadvantages  Conclusion
  3. 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. 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. 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. 6. Decryption It is the reverse of encryption. It is transformation of encrypted data back into some clear form.
  7. 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. 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. 9. The art of protecting information by transforming it into an unreadable format, called cipher text.
  10. 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. 11. Secret Key Cryptography
  12. 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. 13. Public-Key Cryptography
  14. 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. 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. 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. 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. 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. 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. 20. Thank you…!