### 你将学到什么

Cryptography

Entropy (Information Theory)

### 课程概况

This specialization is intended for the learners interested in or already pursuing a career in computer security or other cybersecurity-related fields. Through four courses, the learners will cover the security of information systems, information entropy, classical cryptographic algorithms, symmetric cryptography, asymmetric/public-key cryptography, hash functions, message authentication codes, digital signatures, key management and distribution, and other fundamental cryptographic primitives and protocols.

### 包含课程

课程1**Cryptography and Information Theory**

Welcome to Cryptography and Information Theory! This course combines cryptography (the techniques for protecting information from unauthorized access) and information theory (the study of information coding and transfer). More specifically, the course studies cryptography from the information-theoretical perspectives and discuss the concepts such as entropy and the attacker knowledge capabilities, e.g., Kerckhoff's Principle. It also contrasts information-theoretic security and computational security to highlight the different train of thoughts that drive the cryptographic algorithmic construction and the security analyses.

This course is a part of the Applied Cryptography specialization.

课程2**Symmetric Cryptography**

Welcome to Symmetric Cryptography! Symmetric cryptography relies on shared secret key to ensure message confidentiality, so that the unauthorized attackers cannot retrieve the message. The course describes substitution and transposition techniques, which were the bases for classical cryptography when the message is encoded in natural language such as English. Then, we build on product ciphers (using both substitution and transposition/permutation) to describe modern block ciphers and review the widely used cipher algorithms in DES, 3-DES, and AES. Lastly, we enable the use of block ciphers to support variable data length by introducing different modes of block cipher operations in ECB, CBC, CFB, OFB, and CTR modes.

This course is cross-listed and is a part of the two specializations, the Applied Cryptography specialization and the Introduction to Applied Cryptography specialization.

课程3**Asymmetric Cryptography and Key Management**

Welcome to Asymmetric Cryptography and Key Management! In asymmetric cryptography or public-key cryptography, the sender and the receiver use a pair of public-private keys, as opposed to the same symmetric key, and therefore their cryptographic operations are asymmetric. This course will first review the principles of asymmetric cryptography and describe how the use of the pair of keys can provide different security properties. Then, we will study the popular asymmetric schemes in the RSA cipher algorithm and the Diffie-Hellman Key Exchange protocol and learn how and why they work to secure communications/access. Lastly, we will discuss the key distribution and management for both symmetric keys and public keys and describe the important concepts in public-key distribution such as public-key authority, digital certificate, and public-key infrastructure. This course also describes some mathematical concepts, e.g., prime factorization and discrete logarithm, which become the bases for the security of asymmetric primitives, and working knowledge of discrete mathematics will be helpful for taking this course; the Symmetric Cryptography course (recommended to be taken before this course) also discusses modulo arithmetic.

This course is cross-listed and is a part of the two specializations, the Applied Cryptography specialization and the Introduction to Applied Cryptography specialization.

课程4**Cryptographic Hash and Integrity Protection**

Welcome to Cryptographic Hash and Integrity Protection! This course reviews cryptographic hash functions in general and their use in the forms of hash chain and hash tree (Merkle tree). Building on hash functions, the course describes message authentication focusing on message authentication code (MAC) based on symmetric keys. We then discuss digital signatures based on asymmetric cryptography, providing security properties such as non-repudiation which were unavailable in symmetric-cryptography-based message authentication.

This course is a part of the Applied Cryptography specialization.

### 课程项目

Learners will build the logic and the pseudo-code for the widely used cryptographic primitives and algorithms (as opposed to merely knowing how to use them as black boxes), which will enable them to implement the cryptographic primitives in any platforms/language they choose.

### 预备知识

The learners are recommended to have background in engineering and have a working knowledge of discrete mathematics and probability.