Course 17 - Computer Network Security Protocols And Techniques | Episode 4: Asymmetric Cryptography: RSA, Diffie-Hellman

In this lesson, you’ll learn about:What asymmetric (public key) cryptography is and why it is neededHow the RSA algorithm works and where it is used in practiceHow Diffie-Hellman enables secure key exchange over public networksWhy asymmetric cryptography is vulnerable without authenticationIntroduction This lesson provides an in-depth explanation of asymmetric key cryptography, focusing on RSA and Diffie-Hellman. These algorithms solve a fundamental problem in network security: how to communicate securely over an insecure channel, such as the internet, without sharing secrets in advance. Asymmetric Cryptography Overview Asymmetric cryptography uses two mathematically related keys:Public key: Shared with everyonePrivate key: Kept secret by the ownerWhat is encrypted with one key can only be decrypted with the other. This model enables secure communication, authentication, and key exchange at scale. 1. RSA (Rivest–Shamir–Adleman) RSA is a general-purpose asymmetric encryption algorithm based on the computational difficulty of factoring very large numbers. Key GenerationTwo large prime numbers are selected: P and QThese are multiplied to produce n = P × QA public key is created: (n, e)A private key is created: (n, d)Knowing n does not make it feasible to derive d without factoring nEncryption and DecryptionThe sender converts the message into a number MEncryption is performed using the public key:C = M^e mod nThe receiver decrypts using the private key:M = C^d mod nOnly the private key holder can reverse the operation. Practical Use of RSARSA operations are slow and computationally expensiveIt is not used to encrypt large dataInstead, RSA is commonly used to:Securely exchange a symmetric session keyAuthenticate servers and usersThe exchanged symmetric key is then used with fast algorithms like AES2. Diffie-Hellman Key Exchange Diffie-Hellman is not an encryption algorithm; it is a key exchange protocol. PurposeAllows two parties to generate a shared symmetric keyNo prior secret is requiredThe shared key is never transmitted over the networkHow It WorksTwo public values are agreed upon:A large prime number PA generator GEach party chooses a private value:Alice chooses XBob chooses YPublic values are exchanged:Alice sends G^X mod PBob sends G^Y mod PBoth compute the same shared secret:G^(XY) mod PEven though all exchanged values are public, the shared secret remains secure. Key PropertiesSecure against passive eavesdroppingEnables perfect forward secrecy when used correctlyWidely used in secure protocols such as TLS3. Man-in-the-Middle (MITM) Vulnerability Both RSA and Diffie-Hellman are mathematically secure, but they are vulnerable at the protocol level if identities are not verified. The AttackAn attacker intercepts the key exchangeEstablishes one secret key with AliceEstablishes a different secret key with BobRelays messages between both sides while decrypting and re-encrypting themBoth parties believe they are communicating securely, but the attacker sees everything. The SolutionAuthentication is mandatoryIdentity verification must occur before or during key exchangeCommon solutions include:Digital certificatesTrusted certificate authoritiesSigned public keysWithout authentication, encryption alone does not guarantee security. Key TakeawaysAsymmetric cryptography solves the secure key distribution problemRSA relies on the difficulty of factoring large numbersRSA is mainly used for key exchange and authentication, not bulk data encryptionDiffie-Hellman enables secure key exchange without sharing secretsBoth systems are vulnerable to MITM attacks without authenticationSecure systems always combine encryption + authenticationYou can listen and download our episodes for free on more than 10 different platforms:https://linktr.ee/cybercode_academy