Crypto Fundamentals Dr. Mohammed Shafiul Alam Khan Assistant - PowerPoint PPT Presentation

Crypto Fundamentals Dr. Mohammed Shafiul Alam Khan Assistant Professor Institute of Information Technology (IIT), University of Dhaka (DU) shafiul@du.ac.bd December 10, 2017 M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 1 / 31

Outline Fundamental Security Properties 1 Quick View on Different Ciphers 2 Diffie-Hellman Key Exchange 3 Public Key Infrastructure (PKI) 4 Hash Functions 5 Conclusion 6 M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 2 / 31

Fundamental Security Properties Outline Fundamental Security Properties 1 Quick View on Different Ciphers 2 Diffie-Hellman Key Exchange 3 Public Key Infrastructure (PKI) 4 Hash Functions 5 Conclusion 6 M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 3 / 31

Fundamental Security Properties Fundamental Security Properties Properties Confidentiality Integrity Availability OR Authentication protecting the information from disclosure to unauthorized parties protecting information from being modified by unauthorized parties ensuring that authorized parties are able to access the information when needed The CIA triad is a very fundamental concept in security. However, it has been suggested that the CIA triad is not enough. M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 4 / 31

Fundamental Security Properties How Crypto Comes in the Scene It is insufficient to protect ourselves with laws; we need to protect ourselves with mathematics. — Bruce Schneier Security/Cryptographic Tools Encryption Hash / Message Authentication Code Encryption ensures confidentiality property Hash / Message Authentication Code ensures integrity property M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 5 / 31

Quick View on Different Ciphers Outline Fundamental Security Properties 1 Quick View on Different Ciphers 2 Diffie-Hellman Key Exchange 3 Public Key Infrastructure (PKI) 4 Hash Functions 5 Conclusion 6 M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 6 / 31

Quick View on Different Ciphers What is a Cipher OR Encryption Examples When we use Google search or In general when we use https in web browsing Different applications, for example, voice and data communication in telecommunication network M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 7 / 31

Quick View on Different Ciphers How Cipher Works Every cipher should work with an Algorithm (suppose to be public), and a key which is private Mostly the algorithm does a set of Substitution and Transposition based on the secret key. M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 8 / 31

Quick View on Different Ciphers Types of Encryption Symmetric Encryption — use same key for both encryption and decryption Asymmetric Encryption (Public key encryption) — use different keys in encryption and decryption Block ciphers — Encrypt/Decrypt a block of data at a time. Example: AES, RSA Stream ciphers — Encrypt/Decrypt a bit stream. Example: RC4, RC5 M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 9 / 31

Quick View on Different Ciphers Symmetric Encryption Symmetric Encryption Provides only confidentiality service Need to share the key with the receiver If there are n users, then number of keys required are of order n 2 Key distribution is challenging M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 10 / 31

Quick View on Different Ciphers Asymmetric Encryption Asymmetric Encryption Could provides both confidentiality and authentication service If there are n users, then 2n keys are required What could be problem in such encryption? What about key distribution? M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 11 / 31

Quick View on Different Ciphers Asymmetric Encryption Asymmetric Encryption Could provides both confidentiality and authentication service If there are n users, then 2n keys are required What could be problem in such encryption? What about key distribution? CA PKI M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 11 / 31

Quick View on Different Ciphers Key Bit Length and Key Space Cipher algorithms vary in support of different key length. For example, DES uses 56-bit key AES has 128-bit, 192-bit and 256-bit versions RSA keys could be 1024-bit or 2048-bit Bit length impact on the key space M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 12 / 31

Quick View on Different Ciphers Attacks on Encryption Brute force attack — Search for all possible keys in the key space. For example, in DES 2 56 keys need to explore in AES 2 128 , 2 192 or 2 256 keys need to explore in RSA 2 1024 or 2 2048 keys need to explore Cryptanalysis attack — Use probabilistic theories to find the key Known plaintext attack Choosen plaintext attack M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 13 / 31

Quick View on Different Ciphers Attacks on Encryption Dictionary Attack M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 14 / 31

Quick View on Different Ciphers Traditional Ciphers Mono-Alphabetic Cipher Extension could be poly-alphabetic ciphers. Are not suitable in the age of computing (easily breakable using brute force attack) M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 15 / 31

Quick View on Different Ciphers Modern Ciphers AES (Advanced Encryption Standard) — Symmetric crypto-systems RSA (Rivest-Shamir-Adleman) — one of the first practical public-key crypto-systems RSA is based on the difficulties of finding prime factors of a large number. (demo with an url) Other public key crypto-systems are ECC (Elliptic Curve Cryptography), ElGamal crypto-systems RC5 — a symmetric stream cipher In RC5 a key stream is generated based on the secret key and the generated key stream is Xored with the input message. M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 16 / 31

Diffie-Hellman Key Exchange Outline Fundamental Security Properties 1 Quick View on Different Ciphers 2 Diffie-Hellman Key Exchange 3 Public Key Infrastructure (PKI) 4 Hash Functions 5 Conclusion 6 M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 17 / 31

Diffie-Hellman Key Exchange Diffie-Hellman Key Exchange Features Allows two users to exchange a secret key (Addressed the challenge of symmetric ciphers) Requires no prior secrets Real-time over an untrusted network Ensure perfect forward secrecy — a property of secure communication protocols in which compromise of long-term keys does not compromise past session keys M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 18 / 31

Diffie-Hellman Key Exchange How it Works Based on the difficulty of computing discrete logarithms of large numbers M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 19 / 31

Diffie-Hellman Key Exchange Applications and Drawback Applications Secure Sockets Layer (SSL)/Transport Layer Security (TLS) Secure Shell (SSH) Internet Protocol Security (IPSec) Drawbacks Although there is no successful attack on the mathematical aspect of the protocol, however, Man-in-the-Middle attack is possible in the protocol if not carefully designed. Authenticated Diffie-Hellman Key Agreement (1992) could protect such attack M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 20 / 31

Public Key Infrastructure (PKI) Outline Fundamental Security Properties 1 Quick View on Different Ciphers 2 Diffie-Hellman Key Exchange 3 Public Key Infrastructure (PKI) 4 Hash Functions 5 Conclusion 6 M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 21 / 31

Public Key Infrastructure (PKI) Public Key Infrastructure (PKI) Features Provides a set of roles, policies, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates Manage public-key encryption M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 22 / 31

Public Key Infrastructure (PKI) Public Key Infrastructure (PKI) Application In network, PKI allows for the centralization of network authentication Authentication of client systems using SSL (Secure Socket Layer) signatures or encryption in web browser. Other applications include the transmission of authenticated email messages using S/MIME (Secure/Multi-purpose Internet Mail Extensions), OpenPGP (Open Pretty Good Privacy) and other technologies M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 23 / 31

Hash Functions Outline Fundamental Security Properties 1 Quick View on Different Ciphers 2 Diffie-Hellman Key Exchange 3 Public Key Infrastructure (PKI) 4 Hash Functions 5 Conclusion 6 M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 24 / 31

Hash Functions Hash Functions Properties deterministic so the same message always results in the same hash infeasible to find two different messages with the same hash value infeasible to generate a message from its hash value except by trying all possible messages M S A Khan (IIT, DU) Crypto Fundamentals December 10, 2017 25 / 31