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CRYPTOLOGY (study of hidden writing)

SEMINAR ON. CRYPTOLOGY (study of hidden writing). BY PRIYA DAS GIRINDRA CHANDRA NATH. Contents. Introduction Cryptology Cryptography Secret key cryptography Public key cryptography Differences between 2 keys Application of cryptography Cryptanalysis Conclusion

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CRYPTOLOGY (study of hidden writing)

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  1. SEMINAR ON CRYPTOLOGY(study of hidden writing) BY PRIYA DAS GIRINDRA CHANDRA NATH

  2. Contents • Introduction • Cryptology • Cryptography • Secret key cryptography • Public key cryptography • Differences between 2 keys • Application of cryptography • Cryptanalysis • Conclusion • Bibliography

  3. Introduction • The science of cryptology is the science of secure communications, formed from the Greek words kryptós, "hidden", and logos, "word". • Need for cryptology.

  4. Cryptology • Cryptology is the science which incorporates both cryptography and cryptanalysis. • Cryptography and Cryptanalysis are the two sides of cryptology. encryption decryption Plaintext CiphertextPlaintext

  5. Cryptology • Useful terminology: • PLAINTEXT • CIPHERTEXT • CODE • CRYPTOGRAPHY • CRYPTANALYSIS • CRYPTOSYSTEM • ENCRYPTION • DECRYPTION • KEY

  6. Cryptography • Cryptography is the art or science of mathematical techniques related to such aspects of data security as • confidentiality • data integrity • non-repudiation • Authentication • Types of cryptographic functions: There are 2 kinds of cryptographic functions: • Secret Key or Single-key or Symmetric cryptography- uses only one key. • Public Key or Asymmetric cryptography- uses two keys.

  7. Secret key cryptography • Secret key cryptography involves the use of a single key. Simplified model of symmetric encryption: secret key shared secret key shared by sender and recipient by sender and recipient Transmitted cipher Encryption algorithm plaintext Decryption algorithm plaintext

  8. Secret key cryptography • Encryption Techniques in secret key cryptography: • Substitution cipher techniques: • Caesar Cipher • Polyalphabetic Cipher • Transposition cipher techniques • Product cipher technique

  9. Substitution cipher techniques Ceasar cipher: • The Caesar cipher involves replacing each letter of the alphabet with the letter standing three places further down the alphabet. we can define transformation by listing all possibilities, as fallows: PL: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z CI: D E F G H I J K L M N O P Q R S T U V W X Y Z A B C Example : we encrypt the phase “merchant taylors school” as: Plaintext : m e r c h a n t t a y l o r s s c h o o l Ciphertext : P H U F K D Q W W D B O R U V V F K R R O

  10. Polyalphabetic cipher In a polyalphabetic cipher, each occurrence of a character can have a different substitute.The relation between a character in the plaintext to a character in the ciphertext is a one to many relationship. Example: Plaintext : H E L L O Ciphertext: A B N Z F

  11. Transposition cipher Techniques: • Transposition ciphers rearrange the letters of the plaintext without changing the letters themselves. Example :In a two row rail fence the message MERCHANT TAYLORS’ SCHOOL becomes: Which is read out as: MRHNTYOSCOLECATALRSHO

  12. Product cipher • Product cipher is a keyword-based matrices. • There was also some use of a particular class of product ciphers called fractionation systems. In a fractionation system a substitution is first made from symbols in the plaintext to multiple symbols in the ciphertext, which is then super encrypted by a transposition. • One of the most famous field ciphers ever was a fractionation system - the ADFGVX cipher .This system was so named because it used a 6 ´ 6 matrix to substitution-encrypt the 26 letters of the alphabet and 10 digits into pairs of the symbols A, D, F, G, V and X.

  13. Product cipher Example :enciphering the phrase "Merchant Taylors" with this cipher using the key word "Subject". The final cipher is therefore: FAFDFGDDFAVXAAFGXVDXADDVGFDAFA

  14. Bob,s public key ring joy Ted Alice,s private key Alice mike Alice public key Transmitted ciphertext Decryption algorithm Encryption algrithm plaintext plaintext Public key cryptography • Public Key cryptography is based on the idea that a user can possess two keys - one public and one private key. • The public key can only be used to encrypt the data to be sent and the private key can only be used to decrypt it.

  15. Difference between single key and public key cryptography Single-key cryptographyPublic-key cryptography Need for work: Need for work: 1.The same algorithm with the 1. one algorithm is used for same key is used for encryption encryption & decryption & decryption. with a pair of keys. 2. The sender & the receiver must 2. The sender & receiver share the algorithm & the key. must each have one of the matched pair of the key. Need for securityNeed for security 1. The key must be kept secret. 1. One of the 2 keys must be kept secret.

  16. RSA Algorithm • The RSA algorithm is a block cipher in which the plaintext and ciphertext are integers between 0 and n-1 for some n. A typical size for n is 1024 bits, or 309 decimal digits. Algorithm: key generation: 1.Select p,q where p and q both prime numbers,p≠q. 2.Calculate n=p Χ q. 3. Calculate ϕ( n ) = (p-1)(q-1). 4.Select integer e gcd(ϕ( n ),e) = 1; 1<e<ϕ(n) 5.Calculate d de=1 mod ϕ(n) 6.Public key KU = {e,n} 7.Private key KR = {d, ϕ(n)} Encryption : Plaintext : M<n Ciphertext: C = M^e (mod n). Decryption: Ciphertext : C Plaintext : M = C^d(mod n).

  17. Applications of cryptography • It is used in military and diplomatic services. • Protecting confidential company information. • Protecting a telephone call. • Allowing someone to order a product on the Internet without the fear of their credit card number being intercepted and used against them. • Cryptography is all about increasing the level of privacy of individuals and groups.

  18. Cryptanalysis • Cryptanalysis is the study of mathematical methods which are used in attempting to defeat cryptographic techniques. • Types of cryptanalytic attacks: • A brute force attack • A ciphertext only attack • A chosen plaintext attack • A chosen ciphertext attack • Adaptive chosen plaintext attack

  19. Conclusion Without adequate security controls, the potential of electronic commerce will never be realized. Today, there are protocols that can ensure the integrity, authenticity, and non-repudiability of business transactions on the internet. It is the responsibility of every internet merchant to develop sites and invest in software products that will protect the consumer, as well as the merchant.

  20. THANK YOU

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