1. CRYPTOGRAPHY PRESENTED BY : NILAY JAYSWAL BRANCH : COMPUTER SCIENCE & ENGINEERING ENTRY NO. : 14BCS033 1

2. OVERVIEW  Cryptography  Vocabulary  Encryption and Decryption  Transmission Technique  Symmetric Cryptography  Asymmetric Cryptography  Conclusion 2

3. What is Cryptography ?  Cryptography is the science of using mathematics to encrypt and decrypt data. Benefit ? Cryptography enables you to store sensitive information or transmit it across insecure networks so that it cannot be read by anyone except the intended recipient. 3

4. VOCABULARY  Plaintext: Data that can be read and understood without any special measures.  Encryption: The method of disguising plaintext in such a way as to hide its substance is called encryption.  Cipher text: Encrypting plaintext results in unreadable gibberish called cipher text.  Decryption: The process of reverting cipher text to its original plaintext is called decryption.  Key: some secret piece of information that customizes how the cipher text is 4

5. …continued  Cryptanalysis: The art of breaking ciphers, i.e. retrieving the plaintext without knowing the proper key.  Cryptographers: People who do cryptography  Cryptanalysts: Practitioners of cryptanalysis.  Cryptology: The branch of mathematics that studies the mathematical foundations of cryptographic methods.  Cipher: The Encoder 5

6. ENCRYPTION & DECRYPTION encryption plaintext decryption ciphertext plaintext 6

7. Why Cryptography ?  For “secret writing”  To establish a shared secret when other people (eavesdroppers) are listening.  Types of Cryptography 1. Symmetric key cryptography 2. Asymmetric key cryptography 7

8. Transmission Technique Sender Plaintext in Encoder Ciphertext out Eavesdropper Ciphertext in Decoder Plaintext in Receiver 8

9. CLASSIFICATION Cryptography Symmetric Key Cryptography Asymmetric Key Cryptograph 9

10. Symmetric Key Cryptography Classical Approach Modern Approach Classical Approach Transposition Cipher Substitution Cipher Modern Approach Stream CipherBlock Cipher 10

11. SYMMETRIC KEY CRYPTOGRPHY Symmetric Key Cryptography are algorithms for that use the same key for both encryption of plaintext and decryption of ciphertext. They may be identical or there may be a simple transformation to go between the two. Plaintext Encryption Key “ X “ Ciphertext Decryption Key “ X ” Plaintext 11

12. TRANSPOSITION CIPHER In classical cryptography, a transposition cipher changes one character from the plaintext to another i.e. the order of the characters is changed e.g. 1 2 3 4 5 6 7 8 9 Plaintext : T O P S E C R E T Ciphertext : 2 1 4 3 5 7 6 8 9 O T S P E R C T E 12

13. SUBSTITUTION CIPHER Substitution cipher is a method of encryption by which units of plaintext are substituted with ciphertext according to a regular system. e.g. Plaintext : A B C D X Y Z Ciphertext : A B C D E F X Y Z 13

14. STREAM CIPHER A Stream Cipher is a symmetric or secret-key encryption algorithm that encrypts a single bit at a time. With a Stream Cipher, the same plaintext bit or byte will encrypt to a different bit or byte every time it is encrypted. e.g. : Plain text: Pay 100 Binary of plain text : 010111101(hypothetical) Key : 100101011 Perform XOR Cipher text : 110010110 14

15. BLOCK CIPHER Block cipher technique involves encryption of one block of text at a time. Decryption also takes one block of encrypted text at a time. Length of the block is usually 64 or 128 bits. e.g. : Plain text : four and five Four and five Key Key Key wvfa ast wvfe Ciphertext : wvfa ast wvfe 15

16. ASYMMETRIC KEY CRYPTOGRAPHY Asymmetric Key Cryptography is an asymmetric scheme that uses a Pair of keys for encryption: a Public key, which encrypts data, and a corresponding Private key (secret key). Plaintext Encryption : Public Key Ciphertext Decryption : Private key Plaintext 16

17. CRYPTANALYSIS  Cryptanalysis refers to the study of ciphers, cipher text, or cryptosystems (that is, to secret code systems) with a view to finding weaknesses in them that will permit retrieval of the plain text from the cipher text, without necessarily knowing the key or the algorithm. This is known as breaking the cipher, cipher text, or cryptosystem.  Unlike cryptography which is a clearly defined science, Cryptanalysis is as much an art as it is a science. 17

18. Cryptanalysis Techniques  Known - plain text analysis  Chosen – plain text analysis (Differential cryptanalysis)  Cipher text - only analysis  Man – in – the - middle attack 18

19. ACOUSTIC CRYPTANALYSIS  It is a side channel attack which exploits sounds emitted by computers or machines.  Modern acoustic cryptanalysis mostly focuses on sounds emitted by computer keyboards and internal computer components  Historically it has also been applied to impact printers and electromechanical cipher machines. 19

20. CONCLUSION  Cryptography, being an art of encrypting and decrypting confidential information and private messages, should be implemented in the network security to prevent any leakage and threat.  It can be done by using any of these techniques discussed above for fortifying the personal data transmission as well as for secure transaction.  Acoustic cryptanalysis, being an art of decrypting or leaking confidential information from the sound generated from the CPU, Keyboard, printers, etc may be used in both constructive as well as destructive 20

21. REFERENCE  Yang, Sarah (14 September 2005), "Researchers recover typed text using audio recording of keystrokes", UC Berkeley News.  Adi Shamir & Eran Tromer. "Acoustic cryptanalysis". Blavatnik School of Computer Science, Tel Aviv University. Retrieved 1 November 2011.  http://en.wikipedia.org/wiki/Cryptography  https://www.coursera.org/course/crypto 21

22. THANK YOU… 22

23. Q & A 23