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Cryptography basices


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computer security

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Cryptography basices

  1. 1. Cryptography
  2. 2. Introduction • Cryptography (or cryptology;  from Greek κρυπτός, "hidden, secret";  and γράφειν, graphein, "writing", or -λογία, logia, "study", respectively)[1] is the practice  and study of techniques for secure  communication in the presence of third parties. • Network security is mostly achieved through the use of cryptography. • A science based on abstract algebra.
  3. 3. Definitions • Computer Security - generic name for the collection  of tools designed to protect data from the hackers • Network Security - measures to protect data during  their transmission. • Internet Security - measures to protect data during  their transmission over a collection of interconnected  networks. • our focus is on Internet Security • which consists of measures to determine, prevent,  detect, and correct security violations that involve the  transmission & storage of information.
  4. 4. Security Trends
  5. 5. Security Attack • any action that compromises the security of information owned by an organization • information security is about how to prevent attacks, or failing that, to detect attacks on informationbased systems • often threat & attack used to mean same thing • have a wide range of attacks • can focus of generic types of attacks – passive – active
  6. 6. Passive Attacks
  7. 7. Active Attacks
  8. 8. contd., Cryptography- is a “Greek word” which means “Secret writing”. • We use this term to make secure and immune to attacks.
  9. 9. • Plaintext– the original (or) user message, before being transformed is called plain text. • Ciphertext – After wards the plaintext transformed, it is called ciphertext. An encryption algorithm transforms the plaintext into ciphertext; a decryption algorithm transforms the ciphertext back into plaintext. • The sender uses an encryption algorithm and the receiver uses a decryption algorithm. • Cipher – we refer both encryption and decryption algorithms as cipher. it is also refers to different categories of algorithms in cryptography. • Key – a key is number(or set of numbers) used to make cipher
  10. 10. Contd., • An encryption algorithm, need an encryption key and the plaintext.[as same for decryption]. • Alice, Bob and Eve –in cryptography, normally used three characters in an information exchange. • Alice is a person who needs to send secure data. • Bob- is the recipient of the data. • Eve- is the person who somehow disturb the communication between Alice and bob.
  11. 11. Two categories • The ciphers( cryptography algorithm) into two groups: – Symmetric key(also called secret key) – Asymmetric( Also called Public key)
  12. 12. Symmetric key cryptography • Here, the same key is used by both parties(the key is shared). • The sender uses this key and an encryption algorithm to encrypt data; • The receiver uses the same key and decryption algorithm to decrypt the data.
  13. 13. Asymmetric key cryptography • There are two keys; a private key and a public key. • The private key is kept by the receiver. • The public key is announced to the public.
  14. 14. Contd., • Imagine Alice wants to send a message to Bob. Alice uses the public key to encrypt the message. The Bob use the private key to decrypt the message.
  15. 15. Types of keys • The secret key – is the shared key used in symmetric-key cryptography. • The Public and Private key – used in Asymmetric cryptography.
  16. 16. comparison • Encryption can be thought of as electronic locking; decryption as electronic unlocking. • The sender puts the message in a box and locks the box by using a key; the receiver unlocks the box with a key and takes the message. • In symmetric key cryptography- same key used for both locks and unlocks the box. • In asymmetric key cryptography- one key used for lock the box and another key needed to unlock it.
  17. 17. Symmetric key cryptography • It started thousands of years ago and still used.