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Lecture Seven: Sender Authenticity 1. What is Sender Authenticity? • Sender authenticity ensures that the person or system sending a message is truly who they claim to be. For instance, when you receive an email, sender authenticity guarantees that the email actually came from the person listed as the sender. 2. Digital Signatures: • Digital signatures are used to verify the identity of the sender. They work like handwritten signatures but are applied digitally using encryption. For example, if Alice sends a message to Bob, she uses her private key to create a digital signature, and Bob uses Alice’s public key to verify that the message genuinely came from her. 3. Preventing Spoofing: • Spoofing occurs when someone pretends to be someone else, sending fake messages. Digital signatures help prevent this by ensuring that only the real sender can sign the message. For instance, email services use these methods to prevent phishing emails from pretending to be trusted companies. 4. RSA Cryptosystem (Including Key Generation and Security): • RSA Cryptosystem: RSA is a widely-used asymmetric encryption algorithm that relies on the difficulty of factoring large prime numbers. It provides both encryption and digital signatures, making it essential for secure communication. • Key Generation: In RSA, two large prime numbers are chosen, and their product forms the modulus (part of the public key). A public and private key pair is generated. The public key is used to encrypt data, while the private key is used to decrypt it. • Security: The security of RSA relies on the fact that factoring large numbers (the product of the two prime numbers) is extremely difficult. Without the private key, it’s practically impossible to decrypt the data or forge a digital signature. • Example: RSA is commonly used in HTTPS for secure browsing, where a website uses RSA to encrypt data sent between the server and your browser. 5. Security Analysis (Related to Building a Secured Channel): • Definition: Security analysis involves examining potential vulnerabilities in the cryptographic system and ensuring that data transmitted over a channel remains confidential, authentic, and integral. • Building a Secure Channel: A secure channel needs to ensure confidentiality, integrity, and authentication. RSA, when combined with digital signatures and encryption, helps achieve these goals by making it impossible for attackers to decrypt or alter data without the private key. • Example: In a secure communication system, RSA ensures that only the intended receiver can decrypt the message (confidentiality), while a digital signature verifies that the message hasn’t been altered and came from the right sender (integrity and authenticity).