Network Security and Cryptography
- 1. NETWORK SECURITY NAME OF THE STAFF : Mrs. M. FLORANCE DYANA NAME OF THE STUDENT : S.MAREESWARI, J.GAYATHRI DEVI, R.KAVITHA. REGISTER NUMBER : CB17S 250393 CB17S 250370 CB17S 250383 SUBJECT CODE : P8MCA27 CLASS : III BCA-A BATCH : 2017-2020 YEAR : 2019-2020
- 3. Introduction Symmetric vs asymmetric ciphers Stream ciphers The life cycle and management of keys Classical encryption standards Basic terminology Symmetric cipher model Unconditional& computational security steganography
- 4. Introduction symmetric key algorithm(aka ciphers) are commonly used to product the confidentiality of data, both at rest(e.g in storage devise) and in transit (e. g over networks). The term symmetric comes from the fact that the same key is used both for encryption and decryption.
- 5. Symmetric vs Asymmetric encryption The main advantage of symmetric encryption over asymmetric encryption is that it is fast and efficient for large amount of data. The disadvantage is the need to keep the key secret this can be especially challenging where encryption and decryption take place in different location, requiring the key to be moved safely between locations.
- 6. Stream ciphers Stream ciphers such as RC4 encrypt the plain text one bit at a time and require a key in the form of a pseudo _random bit stream(PRBS) this must be the same for encryption and decryption, hence the need for a secret key to seed the PRBS. Stream ciphers are less commonly used then block ciphers, as the latter offer certain security benefits- specifically they feature high diffusion (i.e. information from one plain text symbol is diffused in to several ciphertext symbols) and immunity to tampering (i.e. it is difficult to insert symbols in to the ciphertext without detection).
- 7. The lifecycle and management of keys As can be seen from the foregoing, keys are a critical component of modern cryptography. Without keys cryptography depends on the algorithm itself being secret, whereas using keys meaning that the algorithm can the fully known to an attacker , as long as keys(i.e. symmetric keys or asymmetric private keys) are kept secret. Thus, strong algorithm can be developed and used by everyone.
- 8. Classical encryption techniques To basic component in classical ciphers: - substitution ciphers: letters replaced by other letters -Transposition ciphers: same letters, but arranged in different order. These ciphers may be: -monoalphabetic : only one substitution/transposition is use. -polyalphabetic: where several substitution /transposition are used several such ciphers may be concatenated together to form a product cipher.
- 9. Basic terminology Plaintext: original message to be encrypted Ciphertext: the encrypted message Enciphering or encryption: the process of converting plaintext into ciphertext Encryption algorithm: performs encryption -two inputs: a plaintext and a secret key
- 11. Symmetric cipher: same key used for encryption and decryption Block cipher: encrypts a block of plaintext at a time (typically 64 or 128 bits) Stream cipher: encrypts data one bit or one byte at a time Asymmetric cipher: different keys used for encryption and decryption
- 12. Unconditional & Computational Security A cipher is unconditionally secure if it is secure no matter how much resources (time, space) the attacker has. A cipher is computationally secure if the best algorithm for breaking it will require so much resources (e.g., 1000 years) that practically the cryptosystem is secure. All the ciphers we have examined are not unconditionally secure.
- 13. Steganography Hide a message in another message. E.g., hide your plaintext in a graphic image Each pixel has 3 bytes specifying the RGB color The least significant bits of pixels can be changed w/o greatly affecting the image quality So can hide messages in these LSBs Advantage: hiding existence of messages Drawback: high overhead