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# cryptography

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### cryptography

1. 1. What is cryptography?Cryptography is the practice and study of techniquesfor secure communication in the presence of third parties(called adversaries).More generally, it is about constructing and analyzing thatovercome the influence of adversaries and which arerelated to various aspects in information security such asdata confidentiality, data integrity, and authentication.
2. 2. HISTORY OF CRYPTOGRAPHYTHE ORIGIN OF CRYPTOGRAPHY TOOK PLCAE AROUND 2000 B.C. IN EGYPT.Before the modern era, cryptography was concerned solely withmessage confidentiality (i.e., Encryption)—conversion ofmessages from a comprehensible form into an incomprehensibleone and back again at the other end, rendering it unreadable byinterceptors or eavesdroppers without secret knowledge.Encryption was used to ensure secrecy in communications,such as those of spies, military leaders, and diplomats.
3. 3. CLASSIC CRYPTOGRAPHY The main classical cipher types are transpositionciphers, which rearrange the order of letters in a message andsubstitution ciphers, which symmetrically replace letters withother letters.EXAMPLE., ‘hello world’ becomes ehlol owrdl in a triviallysimple rearrangement scheme. A cipher (or cypher) is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure.
4. 4. An early substitution cipher was the Caesar cipher, in which each letter inthe plain text was replaced by a letter some fixed number of positions furtherdown the alphabet.Suetonius reports that Julius Caesar used it with a shift of three tocommunicate with his generals. Reconstructed ancient Greek scytale (rhymes with "Italy"), an early cipher device.
5. 5. THE COMPUTER ERA OR MODERN CRYPTOGRAPHY
6. 6. • The development of digital computers and electronics after WWII made possible much more complex ciphers. Furthermore, computers allowed for the encryption of any kind of data represent able in any binary format, unlike classical ciphers which only encrypted written language texts; this was new and significant. German Lorenz cipher machine, used in World War II to encrypt very-high-level general staff messages.
7. 7. •These days a fine example of cryptography isCredit card with smart-card capabilities. The 3-by-5-mm chipembedded in the card is shown, enlarged. Smart cards combine low costand portability with the power to compute cryptographic algorithms
8. 8. Padlock icon from the Firefox Webbrowser, meant to indicate a page has been sentin SSL or TLS-encrypted protected form.However, seeing an icon results when code isintended to render it. Malicious code can providethe icon even when the connection is not actuallybeing protected by SSL or TLS
9. 9. This is aCRYPTOGRAPHYPIECE
10. 10. The mod e r n f ie ld o f c rypt ogra phy c a n bed ivid e d in t o s e ve r a l a r e a s o f s t u d y : SYMMETRIC KEY CRYPTOGRAPHY : Symmetric-key cryptography refers to encryption methods in which both the sender and receiver share the same key PUBLIC KEY CRYTOGRAPHY : Public key cryptography refers to encryption methods in which both the sender and receiver share the different keys. The basic elements of cryptography are: 1. Encryption 2. Decryption 3. Key
11. 11. The above example was of symmetric key cryptography. Here we can see the difference between PUBLIC and PRIVATE key
12. 12. •The Data Encryption Standard (DES) and the Advanced Encryption Standard (AES) are block cipher designs which have been designated cryptography standards by the US government (though DESs designation was finally withdrawn after the AES was adopted).
13. 13. PUBLIC KEY ENCRYPTION(Asymmetric key)
14. 14. APPLICATIONS OFCRYPTOGRAPHY• ATM• e-mail• Secure remote access• ISDN• PEM• PGD• Smart Cards and many more