OS ppt Modified.pptx
- 1. 1
- 2. SECURIT Y The term operating system (OS) security refers to practices and measures that can ensure the confidentiality, integrity, and availability (CIA) of operating systems.
- 3. GROUP MEMBERS 3 Group E Muhammad Abdullah Hashmi 20021519- 016 Muhammad Yaseen 20021519- 051 Eman Mir 20021519-099 Sheharyar Tariq Butt 20021519-108
- 4. CRYPTOGRAPHY AS A SECURITY TOOL • Broadest security tool available • Source and destination of messages cannot be trusted without cryptography • Means to constrain potential senders (sources) and / or receivers (destinations) of messages • Based on secrets (keys) 4
- 6. ENCRY PTION Encryption algorithm consists of --> Set of K keys --> Set of M Messages --> Set of C ciphertexts (encrypted messages) --> A function E : K → (M→C). That is, for each k K, E(k) is a function for generating ciphertexts from messages. --> Both E and E(k) for any k should be efficiently computable functions. --> A function D : K → (C → M). That is, for each k K, D(k) is a function for generating messages from ciphertexts. --> Both D and D(k) for any k should be efficiently computable functions. 6 An encryption algorithm must provide this essential property: Given a ciphertext c C, a computer can compute m such that E(k)(m) = c only if it possesses D(k). --> Thus, a computer holding D(k) can decrypt ciphertexts to the plaintexts used to produce them, but a computer not holding D(k) cannot decrypt ciphertexts. --> Since ciphertexts are generally exposed (for example, sent on the network), it is important that it be infeasible to derive D(k) from the ciphertexts
- 7. SYMMETRIC ENCRYPTION • Same key used to encrypt and decrypt • E(k) can be derived from D(k), and vice versa • DES is most commonly used symmetric block-encryption algorithm (created by US Govt) • Encrypts a block of data at a time • Triple-DES considered more secure • Advanced Encryption Standard (AES), twofish up and coming • RC4 is most common symmetric stream cipher, but known to have vulnerabilities • Encrypts/decrypts a strem of bytes (i.e wireless transmission) • Key is a input to psuedo-random-bit generator • Generates an infinite keystream 7
- 8. ASYMMETRIC ENCRYPTION • Public-key encryption based on each user having two keys: • public key – published key used to encrypt data • private key – key known only to individual user used to decrypt data • Must be an encryption scheme that can be made public without making it easy to figure out the decryption scheme • Most common is RSA block cipher • Efficient algorithm for testing whether or not a number is prime • No efficient algorithm is know for finding the prime factors of a number 8
- 9. ASYMMETRIC ENCRYPTION • Formally, it is computationally infeasible to derive D(kd , N) from E(ke , N), and so E(ke , N) need not be kept secret and can be widely disseminated • E(ke , N) (or just ke) is the public key • D(kd , N) (or just kd) is the private key • N is the product of two large, randomly chosen prime numbers p and q (for example, p and q are 512 bits each) • Encryption algorithm is E(ke , N)(m) = mke mod N, where ke satisfies kekd mod (p−1)(q −1) = 1 • The decryption algorithm is then D(kd , N)(c) = ckd mod N 9
- 10. ASYMMETRIC ENCRYPTION EXAMPLE • For example. make p = 7and q = 13 • We then calculate N = 7∗13 = 91 and (p−1)(q−1) = 72 • We next select ke relatively prime to 72 and< 72, yielding 5 • Finally , we calculate kd such that kekd mod 72 = 1, yielding 29 • We how have our keys • Public key, ke, N = 5, 91 • Private key, kd , N = 29, 91 • Encrypting the message 69 with the public key results in the cyphertext 62 • Cyphertext can be decoded with the private key • Public key can be distributed in cleartext to anyone who wants to communicate with holder of public key 10
- 11. ENCRYPTION AND DECRYPTION USING RSA ASYMMETRIC CRYPTOGRAPHY 11
- 12. CRYPTOGRAPHY • Note symmetric cryptography based on transformations, asymmetric based on mathematical functions • Asymmetric much more compute intensive • Typically not used for bulk data encryption 12
- 13. 13