#18 Building Cryptography | Part 2: Quantum Algorithms & Cryptography

Welcome to 'Quantum Algorithms & Cryptography' course ! This lecture focuses on building cryptographic systems, starting with a discussion of the one-time pad, the simplest construction for a symmetric key encryption scheme. This lecture also discusses the limitations of the one-time pad, primarily the requirement for the key to be as long as the message, making it impractical for many applications. The lecture explores ways to achieve weaker but practical security by using a shorter key to generate a longer pseudorandom keystream. The lecture briefly introduces the concepts of one-way functions and pseudorandom generators, suggesting their role in constructing more practical symmetric key encryption schemes. The lecture then transitions to the concept of public-key encryption, highlighting the scalability issues of symmetric-key encryption where each pair of users needs a shared secret key. Public-key encryption addresses this issue by using separate public and private keys, enabling secure communication without needing to pre-share secret keys. The lecture discusses two approaches to building public-key encryption schemes, one based on computationally hard problems in lattices and the other on number-theoretic problems. Finally, the lecture defines the power of the adversary in public-key encryption and introduces the concept of negligible probability, a key concept in proving security. NPTEL Courses permit certifications that can be used for Course Credits in Indian Universities as per the UGC and AICTE notifications. To understand various certification options for this course, please visit https://nptel.ac.in/courses/106106241 #Cryptography #SymmetricKeyEncryption #OneTimePad #PseudorandomGenerators #PublicKeyEncryption