Foundations of Cryptography: Symmetric, Public-Key, Hashing and Signatures by NPTEL

About this course

Modern security depends on cryptography, yet many developers and IT professionals use it as a black box. This course helps you build a clear, practical foundation so you can reason about security guarantees, understand what attackers can and cannot do, and choose the right primitives for real systems. Instead of relying on folklore, you will learn the mindset and vocabulary used to define security goals and evaluate whether a construction actually meets them.

You begin with symmetric-key encryption and the core idea of building a secure channel: confidentiality and integrity under well-specified adversary capabilities. From classical ciphers and perfect secrecy, you see why one-time pads are special and why key reuse breaks security. The course then moves to computational security, introducing the kinds of assumptions and efficiency constraints that make cryptography useful in practice, and the definitions that capture what it means for an adversary to learn nothing meaningful from ciphertext.

From there, you connect theory to building blocks that appear everywhere in software: pseudorandom generators and stream ciphers, pseudorandom functions, and block-cipher modes of operation. You will learn how subtle choices like IV handling, randomness, and composition determine whether an encryption scheme withstands realistic attacks. As you progress, the focus expands from passive eavesdroppers to active attackers, leading to message authentication codes, integrity for long messages, and the goal of authenticated encryption where secrecy and tamper resistance work together.

The course also develops a solid understanding of hash functions and how they are modeled, what generic attacks imply about security margins, and why design patterns such as Hash-and-MAC matter in engineering. Moving into public-key cryptography, you will study key exchange and cyclic-group hardness assumptions, then see how those ideas power public-key encryption, hybrid encryption, and the leap from CPA to CCA security.

Finally, you explore digital signatures, certificates and PKI, plus foundational number theory concepts that make the algorithms tick. Along the way, exercises reinforce the definitions and threat models so you can spot dangerous reuse, insecure compositions, and misleading security claims. By the end, you will be able to read cryptographic APIs and protocol descriptions with far more confidence, and make better security decisions in cyber security and software engineering projects.